[Federal Register Volume 88, Number 15 (Tuesday, January 24, 2023)]
[Rules and Regulations]
[Pages 4296-4718]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-27957]



[[Page 4295]]

Vol. 88

Tuesday,

No. 15

January 24, 2023

Part II





Environmental Protection Agency





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40 CFR Parts 2, 59, 60, et al.





Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and 
Vehicle Standards; Final Rule

Federal Register / Vol. 88 , No. 15 / Tuesday, January 24, 2023 / 
Rules and Regulations

[[Page 4296]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 2, 59, 60, 80, 85, 86, 600, 1027, 1030, 1031, 1033, 
1036, 1037, 1039, 1042, 1043, 1045, 1048, 1051, 1054, 1060, 1065, 
1066, 1068, and 1090

[EPA-HQ-OAR-2019-0055; FRL-7165-02-OAR]
RIN 2060-AU41


Control of Air Pollution From New Motor Vehicles: Heavy-Duty 
Engine and Vehicle Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is finalizing a 
program to further reduce air pollution, including ozone and 
particulate matter (PM), from heavy-duty engines and vehicles across 
the United States. The final program includes new emission standards 
that are significantly more stringent and that cover a wider range of 
heavy-duty engine operating conditions compared to today's standards; 
further, the final program requires these more stringent emissions 
standards to be met for a longer period of when these engines operate 
on the road. Heavy-duty vehicles and engines are important contributors 
to concentrations of ozone and particulate matter and their resulting 
threat to public health, which includes premature death, respiratory 
illness (including childhood asthma), cardiovascular problems, and 
other adverse health impacts. The final rulemaking promulgates new 
numeric standards and changes key provisions of the existing heavy-duty 
emission control program, including the test procedures, regulatory 
useful life, emission-related warranty, and other requirements. 
Together, the provisions in the final rule will further reduce the air 
quality impacts of heavy-duty engines across a range of operating 
conditions and over a longer period of the operational life of heavy-
duty engines. The requirements in the final rule will lower emissions 
of NOX and other air pollutants (PM, hydrocarbons (HC), 
carbon monoxide (CO), and air toxics) beginning no later than model 
year 2027. We are also finalizing limited amendments to the regulations 
that implement our air pollutant emission standards for other sectors 
(e.g., light-duty vehicles, marine diesel engines, locomotives, and 
various other types of nonroad engines, vehicles, and equipment).

DATES: This final rule is effective on March 27, 2023. The 
incorporation by reference of certain material listed in this rule is 
approved by the Director of the Federal Register as of March 27, 2023.

ADDRESSES: Docket: EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OAR-2019-0055. Publicly available docket materials 
are available either electronically at www.regulations.gov or in hard 
copy at Air and Radiation Docket and Information Center, EPA Docket 
Center, EPA/DC, EPA WJC West Building, 1301 Constitution Ave., NW, Room 
3334, Washington, DC. Out of an abundance of caution for members of the 
public and our staff, the EPA Docket Center and Reading Room are open 
to the public by appointment only to reduce the risk of transmitting 
COVID-19. Our Docket Center staff also continues to provide remote 
customer service via email, phone, and webform. Hand deliveries and 
couriers may be received by scheduled appointment only. For further 
information on EPA Docket Center services and the current status, 
please visit us online at www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Brian Nelson, Assessment and Standards 
Division, Office of Transportation and Air Quality, Environmental 
Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105; 
telephone number: (734) 214-4278; email address: [email protected].

SUPPLEMENTARY INFORMATION: 

Does this action apply to me?

    This action relates to companies that manufacture, sell, or import 
into the United States new heavy-duty highway engines. Additional 
amendments apply for gasoline refueling facilities and for 
manufacturers of all sizes and types of motor vehicles, stationary 
engines, aircraft and aircraft engines, and various types of nonroad 
engines, vehicles, and equipment. Regulated categories and entities 
include the following:

------------------------------------------------------------------------
           NAICS codes \a\                        NAICS title
------------------------------------------------------------------------
326199..............................  All Other Plastics Product
                                       Manufacturing.
332431..............................  Metal Can Manufacturing.
333618..............................  Manufacturers of new marine diesel
                                       engines.
335312..............................  Motor and Generator Manufacturing.
336111..............................  Automobile Manufacturing.
336112..............................  Light Truck and Utility Vehicle
                                       Manufacturing.
336120..............................  Heavy Duty Truck Manufacturing.
336211..............................  Motor Vehicle Body Manufacturing.
336213..............................  Motor Home Manufacturing.
336411..............................  Manufacturers of new aircraft.
336412..............................  Manufacturers of new aircraft
                                       engines.
333618..............................  Other Engine Equipment
                                       Manufacturing.
336999..............................  All Other Transportation Equipment
                                       Manufacturing.
423110..............................  Automotive and Other Motor Vehicle
                                       Merchant Wholesalers.
447110..............................  Gasoline Stations with Convenience
                                       Stores.
447190..............................  Other Gasoline Stations.
454310..............................  Fuel dealers.
811111..............................  General Automotive Repair.
811112..............................  Automotive Exhaust System Repair.
811198..............................  All Other Automotive Repair and
                                       Maintenance.
------------------------------------------------------------------------
\a\ NAICS Association. NAICS & SIC Identification Tools. Available
  online: https://www.naics.com/search.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be regulated by this 
action. This table lists the types of entities that EPA is now aware 
could potentially be regulated by this action. Other types of entities 
not listed in the table could also be regulated. To determine whether 
your entity is regulated by this action, you should carefully examine 
the applicability criteria found in Sections XI and XII of this 
preamble. If you have questions regarding the applicability of this 
action to a particular entity, consult the person listed in the FOR 
FURTHER INFORMATION CONTACT section.
    Public participation: Docket: All documents in the docket are 
listed on the www.regulations.gov website. Although listed in the 
index, some information is not publicly available, e.g., CBI or other 
information whose disclosure is restricted by statute. Certain other 
material, such as copyrighted material, is not placed on the internet 
and will be publicly available only in hard copy form through the EPA 
Docket Center at the location listed in the ADDRESSES section of this 
document.

What action is the agency taking?

    The Environmental Protection Agency (EPA) is adopting a rule to 
reduce air pollution from highway heavy-duty vehicles and engines. The 
final rulemaking will promulgate new numeric standards and change key 
provisions of the existing heavy-duty emission control program, 
including the

[[Page 4297]]

test procedures, regulatory useful life, emission-related warranty, and 
other requirements. Together, the provisions in the final rule will 
further reduce the air quality impacts of heavy-duty engines across a 
range of operating conditions and over a longer period of the 
operational life of heavy-duty engines. Heavy-duty vehicles and engines 
are important contributors to concentrations of ozone and particulate 
matter and their resulting threat to public health, which includes 
premature death, respiratory illness (including childhood asthma), 
cardiovascular problems, and other adverse health impacts. This final 
rule will reduce emissions of nitrogen oxides and other pollutants.

What is the agency's authority for taking this action?

    Clean Air Act section 202(a)(1) requires that EPA set emission 
standards for air pollutants from new motor vehicles or new motor 
vehicle engines that the Administrator has found cause or contribute to 
air pollution that may endanger public health or welfare. See Sections 
I.D and XIII of this preamble for more information on the agency's 
authority for this action.

What are the incremental costs and benefits of this action?

    Our analysis of the final standards shows that annual total costs 
for the final program relative to the baseline (or no action scenario) 
range from $3.9 billion in 2027 to $4.7 billion in 2045 (2017 dollars, 
undiscounted, see Table V-16). The present value of program costs for 
the final rule, and additional details are presented in Section V. 
Section VIII presents our analysis of the human health benefits 
associated with the final standards. We estimate that in 2045, the 
final rule will result in total annual monetized ozone- and 
PM2.5-related benefits of $12 and $33 billion at a 3 percent 
discount rate, and $10 and $30 billion at a 7 percent discount rate 
(2017 dollars, discount rate applied to account for mortality cessation 
lag, see Table VIII-3).\1\ These benefits only reflect those associated 
with reductions in NOX emissions (a precursor to both ozone 
and secondarily-formed PM2.5) and directly-emitted 
PM2.5 from highway heavy-duty engines. The agency was unable 
to quantify or monetize all the benefits of the final program, 
therefore the monetized benefit values are underestimates. There are 
additional human health and environmental benefits associated with 
reductions in exposure to ambient concentrations of PM2.5, 
ozone, and NO2 that data, resource, or methodological 
limitations have prevented EPA from quantifying. There will also be 
benefits associated with reductions in air toxic pollutant emissions 
that result from the final program, but we did not attempt to monetize 
those impacts because of methodological limitations. More detailed 
information about the benefits analysis conducted for the final rule, 
including the present value of program benefits, is included in Section 
VIII and RIA Chapter 8. We compare total monetized health benefits to 
total costs associated with the final rule in Section IX. Our results 
show that annual benefits of the final rule will be larger than the 
annual costs in 2045, with annual net benefits of $6.9 and $29 billion 
assuming a 3 percent discount rate, and net benefits of $5.8 and $25 
billion assuming a 7 percent discount rate.\2\ The benefits of the 
final rule also outweigh the costs when expressed in present value 
terms and as equalized annual values (see Section IX for these values). 
See Section VIII for more details on the net benefit estimates
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    \1\ 2045 is a snapshot year chosen to approximate the annual 
health benefits that occur when the final program will be fully 
implemented and when most of the regulated fleet will have turned 
over.
    \2\ The range of benefits and net benefits reflects a 
combination of assumed PM2.5 and ozone mortality risk 
estimates and selected discount rate.
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Did EPA conduct a peer review before issuing this action?

    This regulatory action was supported by influential scientific 
information. EPA therefore conducted peer review in accordance with 
OMB's Final Information Quality Bulletin for Peer Review. Specifically, 
we conducted peer review on five analyses: (1) Analysis of Heavy-Duty 
Vehicle Sales Impacts Due to New Regulation (Sales Impacts), (2) 
Exhaust Emission Rates for Heavy-Duty Onroad Vehicles in MOVES_CTI NPRM 
(Emission Rates), (3) Population and Activity of Onroad Vehicles in 
MOVES_CTI NPRM (Population and Activity), (4) Cost teardowns of Heavy-
Duty Valvetrain (Valvetrain costs), and (5) Cost teardown of Emission 
Aftertreatment Systems (Aftertreatment Costs). All peer review was in 
the form of letter reviews conducted by a contractor. The peer review 
reports for each analysis are in the docket for this action and at 
EPA's Science Inventory (https://cfpub.epa.gov/si/).

Table of Contents

I. Executive Summary
    A. Introduction
    B. Overview of the Final Regulatory Action
    C. Impacts of the Standards
    D. EPA Statutory Authority for This Action
II. Need for Additional Emissions Control
    A. Background on Pollutants Impacted by This Proposal
    B. Health Effects Associated With Exposure to Pollutants 
Impacted by This Rule
    C. Environmental Effects Associated With Exposure to Pollutants 
Impacted by This Rule
    D. Environmental Justice
III. Test Procedures and Standards
    A. Overview
    B. Summary of Compression-Ignition Exhaust Emission Standards 
and Duty Cycle Test Procedures
    C. Summary of Compression-Ignition Off-Cycle Standards and Off-
Cycle Test Procedures
    D. Summary of Spark-Ignition HDE Exhaust Emission Standards and 
Test Procedures
    E. Summary of Spark-Ignition HDV Refueling Emission Standards 
and Test Procedures
IV. Compliance Provisions and Flexibilities
    A. Regulatory Useful Life
    B. Ensuring Long-Term In-Use Emissions Performance
    C. Onboard Diagnostics
    D. Inducements
    E. Fuel Quality
    F. Durability Testing
    G. Averaging, Banking, and Trading
V. Program Costs
    A. Technology Package Costs
    B. Operating Costs
    C. Program Costs
VI. Estimated Emissions Reductions From the Final Program
    A. Emission Inventory Methodology
    B. Estimated Emission Reductions From the Final Program
    C. Estimated Emission Reductions by Engine Operations and 
Processes
VII. Air Quality Impacts of the Final Rule
    A. Ozone
    B. Particulate Matter
    C. Nitrogen Dioxide
    D. Carbon Monoxide
    E. Air Toxics
    F. Visibility
    G. Nitrogen Deposition
    H. Demographic Analysis of Air Quality
VIII. Benefits of the Heavy-Duty Engine and Vehicle Standards
IX. Comparison of Benefits and Costs
    A. Methods
    B. Results
X. Economic Impact Analysis
    A. Impact on Vehicle Sales, Mode Shift, and Fleet Turnover
    B. Employment Impacts
XI. Other Amendments
    A. General Compliance Provisions (40 CFR Part 1068) and Other 
Cross-Sector Issues
    B. Heavy-Duty Highway Engine and Vehicle Emission Standards (40 
CFR Parts 1036 and 1037)
    C. Fuel Dispensing Rates for Heavy-Duty Vehicles (40 CFR Parts 
80 and 1090)
    D. Refueling Interface for Motor Vehicles (40 CFR Parts 80 and 
1090)
    E. Light-Duty Motor Vehicles (40 CFR Parts 85, 86, and 600)
    F. Large Nonroad Spark-Ignition Engines (40 CFR Part 1048)

[[Page 4298]]

    G. Small Nonroad Spark-Ignition Engines (40 CFR Part 1054)
    H. Recreational Vehicles and Nonroad Evaporative Emissions (40 
CFR Parts 1051 and 1060)
    I. Marine Diesel Engines (40 CFR Parts 1042 and 1043)
    J. Locomotives (40 CFR Part 1033)
    K. Stationary Compression-Ignition Engines (40 CFR Part 60, 
subpart IIII)
    L. Nonroad Compression-Ignition Engines (40 CFR Part 1039)
XII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act (NTTAA) and 
1 CFR Part 51
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act
    L. Judicial Review
XIII. Statutory Provisions and Legal Authority

I. Executive Summary

A. Introduction

1. Summary of the Final Criteria Pollutant Program
    In this action, the EPA is finalizing a program to further reduce 
air pollution, including pollutants that create ozone and particulate 
matter (PM), from heavy-duty engines and vehicles across the United 
States. The final program includes new, more stringent emissions 
standards that cover a wider range of heavy-duty engine operating 
conditions compared to today's standards, and it requires these more 
stringent emissions standards to be met for a longer period of time of 
when these engines operate on the road.
    This final rule is part of a comprehensive strategy, the ``Clean 
Trucks Plan,'' which lays out a series of clean air and climate 
regulations that the agency is developing to reduce pollution from 
large commercial heavy-duty trucks and buses, as well as to advance the 
transition to a zero-emissions transportation future. Consistent with 
President Biden's Executive Order (E.O.) 14037, this final rule is the 
first step in the Clean Trucks Plan.\3\ We expect the next two steps of 
the Clean Trucks Plan will take into consideration recent Congressional 
action, including the recent Inflation Reduction Act of 2022, that we 
anticipate will spur significant change in the heavy-duty sector.\4\ We 
are not taking final action at this time on the proposed targeted 
updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 
program (HD GHG Phase 2); rather, we intend to consider potential 
changes to certain HD GHG Phase 2 standards as part of a subsequent 
rulemaking.
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    \3\ President Joseph Biden. Executive Order on Strengthening 
American Leadership in Clean Cars and Trucks. 86 FR 43583, August 
10, 2021.
    \4\ For example, both the 2021 Infrastructure Investment and 
Jobs Act (commonly referred to as the ``Bipartisan Infrastructure 
Law'' or BIL) and the Inflation Reduction Act of 2022 (``Inflation 
Reduction Act'' or IRA) include many incentives for the development, 
production, and sale of zero emissions vehicles (ZEVs) and charging 
infrastructure. Infrastructure Investment and Jobs Act, Public Law 
117-58, 135 Stat. 429 (2021) (``Bipartisan Infrastructure Law'' or 
``BIL''), available at https://www.congress.gov/117/plaws/publ58/PLAW-117publ58.pdf; Inflation Reduction Act of 2022, Public Law 117-
169, 136 Stat. 1818 (2022) (``Inflation Reduction Act'' or ``IRA''), 
available at https://www.congress.gov/117/bills/hr5376/BILLS-117hr5376enr.pdf.
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    Across the United States, heavy-duty engines emit oxides of 
nitrogen (NOX) and other pollutants that are significant 
contributors to concentrations of ozone and PM2.5 and their 
resulting adverse health effects, which include death, respiratory 
illness (including childhood asthma), and cardiovascular 
problems.5 6 7 Without this final rule, heavy-duty engines 
would continue to be one of the largest contributors to mobile source 
NOX emissions nationwide in the future, representing 32 
percent of the mobile source NOX emissions in calendar year 
2045.\8\ Furthermore, we estimate that without this final rule, heavy-
duty engines would represent 90 percent of the onroad NOX 
inventory in calendar year 2045.\9\ Reducing NOX emissions 
is a critical part of many areas' strategies to attain and maintain the 
National Ambient Air Quality Standards (NAAQS) for ozone and PM; many 
state and local agencies anticipate challenges in attaining the NAAQS, 
maintaining the NAAQS in the future, and/or preventing 
nonattainment.\10\ Some nonattainment areas have already been ``bumped 
up'' to higher classifications because of challenges in attaining the 
NAAQS.\11\
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    \5\ Oxides of nitrogen (NOX) refers to nitric oxide 
(NO) and nitrogen dioxide (NOX).
    \6\ Zawacki et al, 2018. Mobile source contributions to ambient 
ozone and particulate matter in 2025. Atmospheric Environment, Vol 
188, pg 129-141. Available online: https://doi.org/10.1016/j.atmosenv.2018.04.057.
    \7\ Davidson et al, 2020. The recent and future health burden of 
the U.S. mobile sector apportioned by source. Environmental Research 
Letters. Available online: https://doi.org/10.1088/1748-9326/ab83a8.
    \8\ Sectors other than onroad and nonroad were projected from 
2016v1 Emissions Modeling Platform. https://www.epa.gov/air-emissions-modeling/2016v1-platform.
    \9\ U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3. 
https://www.epa.gov/moves.
    \10\ See Section II for additional detail.
    \11\ For example, in September 2019 several 2008 ozone 
nonattainment areas were reclassified from moderate to serious, 
including Dallas, Chicago, Connecticut, New York/New Jersey and 
Houston, and in January 2020, Denver. Also, on September 15, 2022, 
EPA finalized reclassification of 5 areas in nonattainment of the 
2008 ozone NAAQS from serious to severe and 22 areas in 
nonattainment of the 2015 ozone NAAQS from marginal to moderate. The 
2008 NAAQS for ozone is an 8-hour standard with a level of 0.075 
ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.
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    In addition, emissions from heavy-duty engines can result in higher 
pollutant levels for people living near truck freight routes. Based on 
a study EPA conducted of people living near truck routes, an estimated 
72 million people live within 200 meters of a truck freight route.\12\ 
Relative to the rest of the population, people of color and those with 
lower incomes are more likely to live near truck routes.\13\ This 
population includes children; childcare facilities and schools can also 
be in close proximity to freight routes.\14\
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    \12\ See discussion in Section II.B.7.
    \13\ See Section VII.H for additional discussion on our analysis 
of environmental justice impacts of this final rule.
    \14\ Kingsley, S., Eliot, M., Carlson, L. et al. Proximity of 
U.S. schools to major roadways: a nationwide assessment. J Expo Sci 
Environ Epidemiol 24, 253-259 (2014). https://doi.org/10.1038/jes.2014.5.
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    The final rulemaking will promulgate new numeric standards and 
change key provisions of the existing heavy-duty emission control 
program, including the test procedures, regulatory useful life, 
emission-related warranty, and other requirements. Together, the 
provisions in the final rule will further reduce the air quality 
impacts of heavy-duty engines across a range of operating conditions 
and over a longer portion of the operational life of heavy-duty 
engines.\15\ The requirements in the final

[[Page 4299]]

rule will lower emissions of NOX and other air pollutants 
(PM, hydrocarbons (HC), carbon monoxide (CO), and air toxics) beginning 
no later than model year (MY) 2027. The emission reductions from the 
final rule will increase over time as more new, cleaner vehicles enter 
the fleet.
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    \15\ Note that the terms useful life and operational life are 
different, though they are related. As required by Clean Air Act 
(CAA) section 202(a), the useful life period is when manufacturers 
are required to meet the emissions standards in the final rule; 
whereas, operational life is the term we use to describe the 
duration over which an engine is operating on roadways. We are 
finalizing useful life periods that cover a greater portion of the 
operational life. We consider operational life to be the average 
mileage at rebuild for compression-ignition engines and the average 
mileage at replacement for spark-ignition engines (see preamble 
Section IV.A for details).
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    We estimate that the final rule will reduce NOX 
emissions from heavy-duty vehicles in 2040 by more than 40 percent; by 
2045, a year by which most of the regulated fleet will have turned 
over, heavy-duty NOX emissions will be almost 50 percent 
lower than they would have been without this action. These emission 
reductions will result in widespread decreases in ambient 
concentrations of pollutants such as ozone and PM2.5. We 
estimate that in 2045, the final rule will result in total annual 
monetized ozone- and PM2.5-related benefits of $12 and $33 
billion at a 3 percent discount rate, and $10 and $30 billion at a 7 
percent discount rate. These widespread air quality improvements will 
play an important role in addressing concerns raised by state, local, 
and Tribal governments, as well as communities, about the contributions 
of heavy-duty engines to air quality challenges they face such as 
meeting their obligations to attain or continue to meet NAAQS, and to 
reduce other human health and environmental impacts of air pollution. 
This rule's emission reductions will reduce air pollution in close 
proximity to major roadways, where concentrations of many air 
pollutants are elevated and where people of color and people with low 
income are disproportionately exposed.
    In EPA's judgment, our analyses in this final rule show that the 
final standards will result in the greatest degree of emission 
reduction achievable starting in model year 2027, giving appropriate 
consideration to costs and other factors, which is consistent with 
EPA's statutory authority under Clean Air Act (CAA) section 
202(a)(3)(A).\16\
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    \16\ CAA section 202(a)(3)(A) requires standards for emissions 
of NOX, PM, HC, and CO emissions from heavy-duty vehicles 
and engines to ``reflect the greatest degree of emission reduction 
achievable through the application of technology which the 
Administrator determines will be available for the model year to 
which such standards apply, giving appropriate consideration to 
cost, energy, and safety factors associated with the application of 
such technology.'' Throughout this notice we use terms like 
``maximum feasible emissions reductions'' to refer to this statutory 
requirement to set standards that ``reflect the greatest degree of 
emission reduction achievable . . .'.
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    CAA section 202(a)(1) requires the EPA to ``by regulation prescribe 
(and from time to time revise) . . . standards applicable to the 
emission of any air pollutant from any class or classes of new motor 
vehicles or new motor vehicle engines . . . , which in his judgment 
cause, or contribute to, air pollution which may reasonably be 
anticipated to endanger public health or welfare.'' CAA section 
202(a)(3)(C) requires that NOX, PM, HC, and CO (hereafter 
referred to as ``criteria pollutants'') standards for certain heavy-
duty vehicles and engines apply for no less than 3 model years and 
apply no earlier than 4 years after promulgation.\17\
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    \17\ See Sections I.D and XIII for additional discussion on 
EPA's statutory authority for this action, including our authority 
under CAA sections 202(d) and 207.
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    Although heavy-duty engines have become much cleaner over the last 
decade, catalysts and other technologies have evolved such that harmful 
air pollutants can be reduced even further. The final standards are 
based on technology improvements that have become available over the 20 
years since the last major rule was promulgated to address emissions of 
criteria pollutants and toxic pollutants from heavy-duty engines, as 
well as projections of continued technology improvements that build on 
these existing technologies. The criteria pollutant provisions we are 
adopting in this final rule apply for all heavy-duty engine (HDE) 
classes: Spark-ignition (SI) HDE, as well as compression-ignition (CI) 
Light HDE, CI Medium HDE, and CI Heavy HDE.\18\
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    \18\ This final rule includes new criteria pollutant standards 
for engine-certified Class 2b through 8 heavy-duty engines and 
vehicles. Class 2b and 3 vehicles with a Gross Vehicle Weight Rating 
(GVWR) between 8,500 and 14,000 pounds are primarily commercial 
pickup trucks and vans and are sometimes referred to as ``medium-
duty vehicles.'' The majority of Class 2b and 3 vehicles are 
chassis-certified vehicles, and EPA intends to include them in a 
future combined light-duty and medium-duty rulemaking action, 
consistent with E.O, 14037, Section 2a. SI HDE are typically fueled 
by gasoline, whereas CI HDE are typically fueled by diesel; note 
that the Heavy HDE class, which is largely CI engines, does include 
certain SI engines that are generally natural gas-fueled engines 
intended for use in Class 8 vehicles. See 40 CFR 1036.140 for 
additional description of the primary intended service classes for 
heavy-duty engines. Heavy-duty engines and vehicles are also used in 
nonroad applications, such as construction equipment; nonroad heavy-
duty engines and vehicles are not the focus of this final rule. As 
outlined in I.B of this Executive Summary and detailed in Section 
XI, this final rule also includes limited amendments to regulations 
that implement our air pollutant emission standards for other 
industry sectors, including light-duty vehicles, light-duty trucks, 
marine diesel engines, locomotives, and various types of nonroad 
engines, vehicles, and equipment. See 40 CFR 1036.140 for a 
description of the primary intended service classes for heavy-duty 
engines.
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    As described in Section III, the final standards will reduce 
emissions during a broader range of operating conditions compared to 
the current standards, such that nearly all in-use operation will be 
covered. Available data indicate that emission levels demonstrated for 
certification are not currently achieved under the broad range of real-
world operating conditions.19 20 21 22 In fact, less than 
ten percent of the data collected during a typical test while the 
vehicle is operated on the road is subject to EPA's current on-the-road 
emission standards.\23\ These testing data further show that 
NOX emissions from heavy-duty CI engines are high during 
many periods of vehicle operation that are not subject to current on-
the-road emission standards. For example, ``low-load'' engine 
conditions occur when a vehicle operates in stop-and-go traffic or is 
idling; these low-load conditions can result in exhaust temperature 
decreases that then lead to the diesel engine's selective catalytic 
reduction (SCR)-based emission control system becoming less effective 
or ceasing to function. Test data collected as part of EPA's 
manufacturer-run in-use testing program indicate that this low-load 
operation could account for more than half of the NOX 
emissions from a vehicle during a typical workday.\24\ Similarly, 
heavy-duty SI engines also operate in conditions where their catalyst 
technology becomes less effective, resulting in higher levels of air 
pollutants; however, unlike CI engines, it is sustained medium-to-high 
load operation where emission levels are less certain. To address these 
concerns, as part of our comprehensive approach, the final standards 
include both revisions to our existing test procedures and new test 
procedures to reduce emissions

[[Page 4300]]

from heavy-duty engines under a broader range of operating conditions, 
including low-load conditions.
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    \19\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of 
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel 
Engines Using Portable Emissions Measurement System (PEMS).'' 29th 
CRC Real World Emissions Workshop, March 10-13, 2019.
    \20\ Sandhu, Gurdas, et al. ``Identifying Areas of High 
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
    \21\ Sandhu, Gurdas, et al. ``In-Use Emission Rates for MY 2010+ 
Heavy-Duty Diesel Vehicles''. 27th CRC Real-World Emissions 
Workshop, March 26-29, 2017.
    \22\ As noted in Section I.B and discussed in Section III, 
testing engines and vehicles while they are operating without a 
defined duty cycle is referred to as ``off-cycle'' testing; as 
detailed in Section III, we are finalizing new off-cycle test 
procedures and standards as part of this rulemaking.
    \23\ Heavy-duty CI engines are currently subject to off-cycle 
standards that are not limited to specific test cycles; throughout 
this notice we use the terms ``on-the-road'', ``over the road'', or 
``real world'' interchangeably to refer to off-cycle standards.
    \24\ Sandhu, Gurdas, et al. ``Identifying Areas of High 
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
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    Data also show that tampering and mal-maintenance of the engine's 
emission control system after the useful life period is projected to 
result in NOX emissions that would represent a substantial 
part of the HD emissions inventory in 2045.\25\ To address this 
problem, as part of our comprehensive approach, the final rule includes 
longer regulatory useful life and emission-related warranty 
requirements to ensure the final emissions standards will be met 
through more of the operational life of heavy-duty 
vehicles.26 27 Further, the final rule includes requirements 
for manufacturers to better ensure that operators keep in-use engines 
and emission control systems working properly in the real world. We 
expect these final provisions to improve maintenance and serviceability 
will reduce incentives to tamper with the emission control systems on 
MY 2027 and later engines, which would avoid large increases in 
emissions that would impact the reductions projected from the final 
rule. For example, we estimate NOX emissions will increase 
more than 3000 percent due to malfunction of the NOX 
emissions aftertreatment on a MY 2027 and later heavy heavy-duty 
vehicle. To address this, the final rule requires manufacturers to meet 
emission standards with less frequent scheduled maintenance for 
emission-related parts and systems, and to provide more information on 
how to diagnose and repair emission control systems. In addition, the 
final rule requires manufacturers to demonstrate that they design their 
engines to limit access to electronic controls to prevent operators 
from reprogramming the engine to bypass or disable emission controls. 
The final rule also specifies a balanced approach for manufacturers to 
design their engines with features to ensure that operators perform 
ongoing maintenance to keep SCR emission control systems working 
properly, without creating a level of burden and corresponding 
frustration for operators that could increase the risk of operators 
completely disabling emission control systems. These provisions 
combined with the longer useful life and warranty periods will provide 
a comprehensive approach to ensure that the new, much more stringent 
emissions standards are met during in use operations.
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    \25\ See Section VI for more information on projected inventory 
contributions from each operating mode or process, as well as 
discussion on the emissions impacts of tampering and mal-
maintenance.
    \26\ Emission standards set under CAA section 202(a) apply to 
vehicles and engines ``for their useful life.'' CAA section 202(d) 
directs EPA to prescribe regulations under which the useful life of 
vehicles and engines shall be determined, and for heavy-duty 
vehicles and engines establishes minimum values of 10 years or 
100,000 miles, whichever occurs first, unless EPA determines that 
greater values are appropriate. CAA section 207(a) further requires 
manufacturers to provide emission-related warranty, and EPA set the 
current emission-related warranty periods for heavy-duty engines in 
1983 (48 FR 52170, November 16, 1983). See Section I.D for more 
discussion on the statutory authority for the final rule.
    \27\ See Section IV for more discussion on the final useful life 
and warranty requirements.
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    The final standards and requirements are based on further 
consideration of the data included in the proposed rule, as well as 
additional supporting data from our own test programs, and 
consideration of the extensive public input EPA received in response to 
the proposed rule. The proposal was posted on the EPA website on March 
7, 2022, and published in the Federal Register on March 28, 2022 (87 FR 
17414, March 28, 2022). EPA held three virtual public hearings in April 
2022. We received more than 260,000 public comments.\28\ A broad range 
of stakeholders provided comments, including state and local 
governments, heavy-duty engine manufacturers, emissions control 
suppliers and others in the heavy-duty industry, environmental 
organizations, environmental justice organizations, state, local, and 
Tribal organizations, consumer groups, labor groups, private citizens, 
and others. Some of the issues raised in comments included the need for 
new, more stringent NOX standards, particularly in 
communities already overburdened by pollution; the feasibility and 
costs of more stringent NOX standards combined with much 
longer useful life periods; the longer emissions-related warranty 
periods; a single- vs. two-step program; and various details on the 
flexibilities and other program design features of the proposed 
program. We briefly discuss several of these key issues in Section I.B, 
with more detail in later sections in this preamble and in the Response 
to Comments document that is available in the public docket for this 
rule.\29\
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    \28\ Of these comments, 1,860 were unique letters, many of which 
provided data and other detailed information for EPA to consider; 
the remaining comments were mass mailers sponsored by 30 different 
organizations, nearly all of which urged EPA to take action to 
reduce emissions from trucks or to adopt more stringent limits.
    \29\ U.S. EPA, ``Control of Air Pollution from New Motor 
Vehicles: Heavy-Duty Engine and Vehicle Standards--Response to 
Comments'', Docket EPA-HQ-OAR-2019-0055.
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    This Section I provides an overview of the final program, the 
impacts of the final program, and how the final program is consistent 
with EPA's statutory requirements. The need for additional emissions 
control from heavy-duty engines is described in Section II. We describe 
the final standards and compliance flexibilities in detail in Sections 
III and IV. We discuss our analyses of estimated emission reductions, 
air quality improvements, costs, and monetized benefits of the final 
program in Sections V through X. Section XI describes limited 
amendments to the regulations that implement our air pollutant emission 
standards for other sectors (e.g., light-duty vehicles, marine diesel 
engines, locomotives, and various types of nonroad engines, vehicles, 
and equipment).
2. EPA Will Address HD GHG Emissions in a Subsequent Rulemaking
    Although we proposed targeted revisions to the MY2027 GHG Phase 2 
standards as part of the same proposal in which we laid out more 
stringent NOX standards, in this final rule we are not 
taking final action on updates to the GHG standards. Instead, we intend 
to consider potential changes to certain HD GHG Phase 2 standards as 
part of a subsequent rulemaking.

B. Overview of the Final Regulatory Action

    We are finalizing a program that will begin in MY 2027, which is 
the earliest year that these new criteria pollutant standards can begin 
to apply under CAA section 202(a)(3)(C).\30\ The final NOX 
standards are a single-step program that reflect the greatest degree of 
emission reduction achievable starting in MY2027, giving appropriate 
consideration to costs and other factors. The final rule establishes 
not only new, much more stringent NOX standards compared to 
today's standards, but also requires lower NOX emissions 
over a much wider range of testing conditions both in the laboratory 
and when engines are operating on the road. Further, the final 
standards include longer useful life periods, as well as significant 
increases in the emissions-related warranty periods. The longer useful 
life and emissions warranty periods are particularly important for 
ensuring continued emissions control when the engines are operating on 
the road. These final standards will result in significant reductions 
in emissions of NOX, PM2.5, and other air 
pollutants across the country, which we project will meaningfully 
decrease ozone

[[Page 4301]]

concentrations across the country. We expect the largest improvements 
in both ozone and PM2.5 to occur in areas with the worst 
baseline air quality. In a supplemental demographic analysis, we also 
found that larger numbers of people of color are projected to reside in 
these areas with the worst baseline air quality.
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    \30\ Section 202(a)(3)(C) requires that standards under 
202(a)(3)(A), such as the standards in this final rule, apply no 
earlier than 4 years after promulgation, and apply for no less than 
3 model years. See Section I.D for additional discussion on the 
statutory authority for this action.
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    The final standards and requirements are based on further 
consideration of the data included in the proposed rule, as well as 
additional supporting data from our own test programs, and 
consideration of the extensive public input EPA received in response to 
the proposed rule. As required by CAA section 202(a)(3), the final new 
numeric NOX standards will result in the greatest degree of 
emission reduction achievable for a national program starting in MY 
2027 through the application of technology that the Administrator has 
determined will be available starting in MY 2027, after giving 
appropriate consideration to cost, energy, and safety factors 
associated with the application of such technology. The EPA proposal 
included two options for the NOX program. Proposed Option 1 
was the more stringent option, and it included new standards and other 
program elements starting in MY 2027, which were further strengthened 
in MY 2031. Proposed Option 2 was the less stringent option, with new 
standards and requirements implemented fully in MY 2027. The final 
numeric NOX standards and testing requirements are largely 
consistent with the proposed Option 1 in MY 2027. The final numeric 
standards and regulatory useful life values will reduce NOX 
emissions not only when trucks are new, but throughout a longer period 
of their operational life under real-world conditions. For the smaller 
engine service-class categories, we are finalizing the longest 
regulatory useful life and emissions warranty periods proposed, and for 
the largest engines we are finalizing requirements for useful life and 
emissions aftertreatment durability demonstration that are 
significantly longer than required today.
    As previously noted in this Section I, we received a large number 
and wide range of comments on the proposed rule. Several comments 
raised particularly significant issues related to some fundamental 
components of the proposed program, including the level of the numeric 
standards and feasibility of lower numeric standards combined with 
longer useful life periods. We briefly discuss these key issues in this 
Section I.B, with more detail in later sections in this preamble. The 
Response to Comments document provides our responses to the comments we 
received; it is located in the docket for this rulemaking.
1. Key Changes From the Proposal
i. Feasibility of More Stringent NOX Standards Combined With 
Much Longer Useful Life Periods
    Many stakeholders commented on the proposed numeric NOX 
standards, and the feasibility of maintaining those numeric standards 
over the proposed useful life periods. Environmental organizations and 
other commenters, including suppliers to the heavy-duty industry, 
generally urged EPA to adopt the most stringent standards proposed, or 
to finalize even more stringent standards by fully aligning with the 
California Air Resources Board (CARB) Low NOX Omnibus 
program.\31\ In contrast, most engine manufacturers, truck dealers, 
fleets, and other members of the heavy-duty industry stated that even 
the less stringent proposed numeric standards and useful life periods 
would be extremely challenging to meet, particularly for the largest 
heavy-duty engines. Some of these commenters provided data that they 
stated showed the potential for large impacts on the purchase price of 
a new truck if EPA were to finalize the most stringent proposed numeric 
standards and useful life periods for the largest heavy-duty engines.
---------------------------------------------------------------------------

    \31\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule. For more information on the 
California Air Resources Board Omnibus rule see, ``Heavy-Duty Engine 
and Vehicle Omnibus Regulation and Associated Amendments,'' December 
22, 2021. https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox. 
Last accessed September 21, 2022. See also ``California State Motor 
Vehicle Pollution Control Standards and Nonroad Engine Pollution 
Control Standards; The ``Omnibus'' Low NOX Regulation; 
Request for Waivers of Preemption; Opportunity for Public Hearing 
and Public Comment'' at 87 FR 35765 (June 13, 2022).
---------------------------------------------------------------------------

    As summarized in I.B.2 and detailed in preamble Section III, we are 
finalizing numeric NOX standards and useful life periods 
that are largely consistent with the most stringent proposed option for 
MY 2027. For all heavy-duty engine classes, the final numeric 
NOX standards for medium- and high-load engine operations 
match the most stringent standards proposed for MY 2027; for low-load 
operations we are finalizing the most stringent standard proposed for 
any model year (see I.B.1.ii for discussion).\32\ For smaller heavy-
duty engines (i.e., light and medium heavy-duty engines CI and SI 
heavy-duty engines), the numeric standards are combined with the 
longest useful life periods we proposed. The final numeric 
NOX emissions standards and useful life periods for smaller 
heavy-duty engines are based on further consideration of data included 
in the proposal from our engine demonstration programs that show the 
final NOX emissions standards are feasible at the final 
useful life periods applicable to these smaller heavy-duty engines. Our 
assessment of the data available at the time of proposal is further 
supported by our evaluation of additional information and public 
comments stating that the proposed standards are feasible for these 
smaller engine categories. For the largest heavy-duty engines (i.e., 
heavy heavy-duty engines), the final numeric standards are combined 
with the longest useful life mileage that we proposed for MY 2027. The 
final useful life periods for the largest heavy-duty engines are 50 
percent longer than today's useful life periods, which will play an 
important role in ensuring continued emissions control while the 
engines operate on the road.
---------------------------------------------------------------------------

    \32\ As proposed, we are finalizing a new test procedure for 
heavy-duty CI engines to demonstrate emission control when the 
engine is operating under low-load and idle conditions; this new 
test procedure does not apply to heavy-duty SI engines (see Sections 
I.B.2 and III for additional discussion).
---------------------------------------------------------------------------

    After further consideration of the data included in the proposal, 
as well as information submitted by commenters and additional data we 
collected since the time of proposal, we are finalizing two updates 
from our proposed testing requirements in order to ensure the greatest 
degree of emission reduction achievable are met throughout the final 
useful life periods; these updates are tailored to the larger engine 
classes (medium and heavy heavy-duty engines), which have longer useful 
life periods and more rigorous duty-cycles compared to the smaller 
engine classes. First, we are finalizing a requirement for 
manufacturers to demonstrate before heavy heavy-duty engines are in-use 
that the emissions control technology is durable through a period of 
time longer than the final useful life mileage.\33\ For these largest 
engines with the longest useful life mileages, the extended laboratory 
durability demonstration will better ensure the final standards will be 
met throughout the regulatory useful life

[[Page 4302]]

under real-world operations where conditions are more variable. Second, 
we are finalizing an interim compliance allowance that applies when EPA 
evaluates whether the heavy or medium heavy-duty engines are meeting 
the final standards after these engines are in use in the real world. 
When combined with the final useful life values, we believe the interim 
compliance allowance will address concerns raised in comments from 
manufacturers that the more stringent proposed MY 2027 standards would 
not be feasible to meet over the very long useful life periods of heavy 
heavy-duty engines, or under the challenging duty-cycles of medium 
heavy-duty engines. This interim, in-use compliance allowance is 
generally consistent with our past practice (for example, see 66 FR 
5114, January 18, 2001); also consistent with past practice, the 
interim compliance allowance is included as an interim provision that 
we may reassess in the future through rulemaking based on the 
performance of emissions controls over the final useful life periods 
for medium and heavy heavy-duty engines. To set standards that result 
in the greatest emission reductions achievable for medium and heavy 
heavy-duty engines, we considered additional data that we and others 
collected since the time of the proposal; these data show the 
significant technical challenge of maintaining very low NOX 
emissions throughout very long useful life periods for heavy heavy-duty 
engines, and greater amounts of certain aging mechanisms over the long 
useful life periods of medium heavy-duty engines. In addition to these 
data, in setting these standards, we gave appropriate consideration to 
costs associated with the application of technology to achieve maximum 
emissions reductions in MY 2027 (i.e., cost of compliance for 
manufacturers associated with the standards) and other factors. We 
determined that for heavy heavy-duty engines the combination of: (1) 
The most stringent MY 2027 standards proposed, (2) longer useful life 
periods compared to today's useful life periods, (3) targeted, interim 
compliance allowance approach to in-use compliance testing, and (4) the 
extended durability demonstration for emissions control technologies is 
appropriate, feasible, and consistent with our authority under the CAA 
to set technology-forcing NOX pollutant standards for heavy-
duty engines for their useful life.\34\ Similarly, for medium heavy-
duty engines we determined that the combination of the first three 
elements (i.e., most stringent MY 2027 standards proposed, increase in 
useful life periods, and interim compliance allowance for in-use 
testing) is appropriate, feasible, and consistent with our CAA 
authority to set technology-forcing NOX pollutant standards 
for heavy-duty engines for their useful life.
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    \33\ Manufacturers of any size heavy-duty engine must 
demonstrate that the emission control technology is durable through 
a period equivalent to the useful life period of the engine, and may 
be subject to recall if EPA subsequently determines that properly 
maintained and used engines do not conform to our regulations over 
the useful life period (as specified in our regulations and 
consistent with CAA section 207). As outlined here, the extended 
laboratory durability demonstration in the final program will 
require manufacturers of the largest heavy-duty engines to 
demonstrate emission control durability for a longer period to 
better ensure that in-use engines will meet emission standards 
throughout the long regulatory useful life of these engines.
    \34\ CAA section 202(a)(3)(A) is a technology-forcing provision 
and reflects Congress' intent that standards be based on projections 
of future advances in pollution control capability, considering 
costs and other statutory factors. See National Petrochemical & 
Refiners Association v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002) 
(explaining that EPA is authorized to adopt ``technology-forcing'' 
regulations under CAA section 202(a)(3)); NRDC v. Thomas, 805 F.2d 
410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory 
language that ``seek[s] to promote technological advances while also 
accounting for cost does not detract from their categorization as 
technology-forcing standards''); see also Husqvarna AB v. EPA, 254 
F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213 
have similar language and are technology-forcing standards). In this 
context, the term ``technology-forcing'' has a specific legal 
meaning and is used to distinguish standards that may require 
manufacturers to develop new technologies (or significantly improve 
existing technologies) from standards that can be met using existing 
off-the-shelf technology alone. Technology-forcing standards such as 
those in this final rule do not require manufacturers to use 
specific technologies.
---------------------------------------------------------------------------

ii. Test Procedures To Control Emissions Under a Broader Range of 
Engine Operations
    Many commenters supported our proposal to update our test 
procedures to more accurately account for and control emissions across 
a broader range of engine operation, including in urban driving 
conditions and other operations that could impact communities already 
overburdened with pollution. Consistent with our proposal, we are 
finalizing several provisions to reduce emissions from a broader range 
of engine operating conditions. First, we are finalizing new standards 
for our existing test procedures to reduce emissions under medium- and 
high-load operations (e.g., when trucks are traveling on the highway). 
Second, we are finalizing new standards and a corresponding new test 
procedure to measure emissions during low-load operations (i.e., the 
low-load cycle, LLC). Third, we are finalizing new standards and 
updates to an existing test procedure to measure emissions over the 
broader range of operations that occur when heavy-duty engines are 
operating on the road (i.e., off-cycle). \35\
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    \35\ Duty-cycle test procedures measure emissions while the 
engine is operating over precisely defined duty cycles in an 
emissions testing laboratory and provide very repeatable emission 
measurements. ``Off-cycle'' test procedures measure emissions while 
the engine is not operating on a specified duty cycle; this testing 
can be conducted while the engine is being driven on the road (e.g., 
on a package delivery route), or in an emission testing laboratory. 
Both duty-cycle and off-cycle testing are conducted pre-production 
(e.g., for certification) or post-production to verify that the 
engine meets applicable duty-cycle or off-cycle emission standards 
throughout useful life (see Section III for more discussion).
---------------------------------------------------------------------------

    The new, more stringent numeric standards for the existing 
laboratory-based test procedures that measure emissions during medium- 
and high-load operations will ensure significant emissions reductions 
from heavy-duty engines. Without this final rule, these medium- and 
high-load operations are projected to contribute the most to heavy-duty 
NOX emissions in 2045.
    We are finalizing as proposed a new LLC test procedure, which will 
ensure demonstration of emission control under sustained low-load 
operations. After further consideration of data included in the 
proposal, as well as additional information from the comments 
summarized in this section, we are finalizing the most stringent 
numeric LLC standard proposed for any model year. As discussed in our 
proposal, data from our CI engine demonstration program showed that the 
lowest numeric NOX standard proposed would be feasible for 
the LLC throughout a useful life period similar to the useful life 
period we are finalizing for the largest heavy-duty engines. After 
further consideration of this data, and additional support from data 
collected since the time of proposal, we are finalizing the most 
stringent standard proposed for any model year.
    We are finalizing new numeric standards and revisions to the 
proposed off-cycle test procedure. We proposed updates to the current 
off-cycle test procedure that included binning emissions measurements 
based on the type of operation the engine is performing when the 
measurement data is being collected. Specifically, we proposed that 
emissions data would be grouped into three bins, based on whether the 
engine was operating in idle (Bin 1), low-load (Bin 2), or medium-to-
high load (Bin 3). Given the different operational profiles of each of 
the three bins, we proposed a separate standard for each bin. Based on 
further consideration of data included in the proposal, as well as 
additional support from our consideration of data provided by 
commenters, we are finalizing off-cycle standards for two bins, rather 
than three bins; correspondingly, we are finalizing a two-bin approach 
for grouping emissions data collected during off-cycle test procedures. 
Our evaluation of available information shows that two bins better 
represent the

[[Page 4303]]

differences in engine operations that influence emissions (e.g., 
exhaust temperature, catalyst efficiency) and ensure sufficient data is 
collected in each bin to allow for an accurate analysis of the data to 
determine if emissions comply with the standard for each bin. Preamble 
Section 0 further discusses the final off-cycle standards with 
additional detail in preamble Section III.
iii. Lengthening Emissions-Related Warranty
    EPA received general support from many commenters for the proposal 
to lengthen the emissions-related warranty beyond existing 
requirements. Some commenters expressed support for one of the proposed 
options, and one organization suggested a warranty period even longer 
than either proposed option. Several stakeholders also commented on the 
costs of lengthened warranty periods and potential economic impacts. 
For instance, one state commenter supported EPA's cost estimates and 
agreed that the higher initial cost will be offset by lower repair 
costs; further, the commenter expects the resale value of lengthened 
warranty will be maintained for subsequent owners. In contrast, 
stakeholders in the heavy-duty engine and truck industry (e.g., engine 
and vehicle manufacturers, truck dealers, suppliers of emissions 
control technologies) commented that the proposed warranty periods 
would add costs to vehicles, and raised concerns about these cost 
impacts on first purchasers. Many commenters indicated that purchase 
price increases due to the longer warranty periods may delay emission 
reductions, stating that high costs could incentivize pre-buy and 
reduce fleet turnover from old technology.
    After further consideration of data included in the proposal, and 
consideration of additional supporting information from the comments 
summarized in this Section I.B.1.iii, we are finalizing a single-step 
increase for new, longer warranty periods to begin in MY 2027. Several 
commenters recommended we pull ahead the longest proposed warranty 
periods to start in MY 2027. We agree with that approach for the 
smaller heavy-duty engine classes, and our final warranty mileages 
match the longest proposed warranty periods for these smaller engines 
(i.e., Spark-ignition HDE, Light HDE, and Medium HDE). However, we are 
finalizing a different approach for the largest heavy-duty engines 
(i.e., Heavy HDE). We are finalizing a warranty mileage that matches 
the MY 2027 step of the most stringent proposed option to maximize the 
emission control assurance and to cover a percentage of the final 
useful life that is more consistent with the warranty periods of the 
smaller engine classes. The final emissions warranty periods are 
approximately two to four times longer than today's emissions warranty 
periods. The durations of the final emissions warranty periods balance 
two factors: First, the expected improvements in engine emission 
performance from longer emissions warranty periods due to increases in 
maintenance and lower rates of tampering with emissions controls (see 
preamble Section IV.B for more discussion); and second, the potential, 
particularly for the largest heavy-duty engines, for very large 
increases in purchase price due to much longer warranty periods to slow 
fleet turnover through increases in pre- and low-buy, and subsequently 
result in fewer emissions reductions. We are finalizing emissions 
warranty periods that in our evaluation will provide a significant 
increase in the emissions warranty coverage while avoiding large 
increases in the purchase price of a new truck.
iv. Model Year 2027 Single-Step Program
    Many stakeholders expressed support for a single-step program to 
implement new emissions standards and program requirements beginning in 
model year 2027, which is consistent with one of the proposed options. 
Stakeholders in the heavy-duty engine and truck industry, including 
suppliers of emissions controls technologies, truck dealers, and engine 
manufacturers, generally stated that a single-step program avoids 
technology disruptions and allows industry to focus on research and 
development for zero-emissions vehicle technologies for model years 
beyond 2027. Some of these commenters further noted that a two-step 
approach would result in gaps in available technology for some vehicle 
types and could exacerbate slower fleet turnover from pre- and low-buy 
associated with new standards. The trade association for truck dealers 
noted that a two-step approach would significantly compromise expected 
vehicle performance characteristics, including fuel economy. Other 
commenters also generally supported a single-step approach in order for 
the most stringent standards to begin as soon as possible, which would 
lead to larger emissions reductions earlier than a two-step approach. 
Several of these stakeholders noted the importance of early emissions 
reductions in communities already overburdened with pollution.
    The final NOX standards are a single-step program that 
reflect the greatest emission reductions achievable starting in MY 
2027, giving appropriate consideration to costs and other factors. In 
this final rule, we are focused on achieving the greatest emission 
reductions achievable in the MY 2027 timeframe, and have applied our 
judgment in determining the appropriate standards for MY 2027 under our 
CAA authority for a national program. As the heavy-duty industry 
continues to transition to zero-emission technologies, EPA could 
consider additional criteria pollutant standards for model years beyond 
2027 in future rules.
v. Averaging, Banking, and Trading of NOX Emissions
    The majority of stakeholders supported the proposed program to 
allow averaging, banking, and trading (ABT) of NOX 
emissions, although several suggested adjustments for EPA to consider 
in the final rule. Stakeholders provided additional input on several 
specific aspects of the proposed ABT program, including the proposed 
family emissions limit (FEL) caps, the proposed Early Adoption 
Incentives, and the proposed allowance for manufacturers to generate 
NOX emissions credits from Zero Emissions Vehicles (ZEVs). 
In this Section we briefly discuss stakeholder perspectives on these 
specific aspects of the proposed ABT program, as well as our approach 
for each in the final rule.
a. Family Emissions Limit Caps
    A wide range of stakeholders urged EPA to finalize a lower FEL cap 
than proposed; there was broad agreement that the FEL cap in the final 
rule should be 100 mg/hp-hr or lower, with commenters citing various 
considerations, such as the magnitude of reduction between the current 
and proposed standards, as well as the desire to prevent competitive 
disruption.
    After further consideration, including consideration of public 
comments, we are finalizing lower FEL caps than proposed. The FEL caps 
in the final rule are 65 mg/hp-hr for MY 2027 through 2030, and 50 mg/
hp-hr for MY 2031 and later. Our rationale for the final FEL caps 
includes two main factors. First, we agree with commenters that the 
difference between the current standard (approximately 200 mg/hp-hr) 
and the standards we are finalizing for MY 2027 and later suggests that 
FEL caps lower than the current standard are

[[Page 4304]]

appropriate to ensure that available emissions control technologies are 
adopted. This is consistent with our past practice when issuing rules 
for heavy-duty onroad engines or nonroad engines in which there was a 
substantial (e.g., greater than 50 percent) difference between the 
numeric levels of the existing and new standards (69 FR 38997, June 29, 
2004; 66 FR 5111, January 18, 2001). Specifically, by finalizing FEL 
caps below the current standards, we are ensuring that the vast 
majority of new engines introduced into commerce include updated 
emissions control technologies compared to the emissions control 
technologies manufacturers use to meet the current standards.\36\
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    \36\ As discussed in Section IV.G.9, we are finalizing an 
allowance for manufacturers to continue to produce a small number (5 
percent of production volume) of engines that meet the current 
standards for a few model years (i.e., through MY 2030); thus, the 
vast majority of, but not all, new engines will need to include 
updated emissions control technologies compared to those used to 
meet today's standards until MY 2031, when all engines will need 
updated emissions control technologies to comply with the final 
standards or use credits up to the FEL cap. See Section IV.G.9 for 
details on our approach and rationale for including this allowance 
in the final rule.
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    Second, finalizing FEL caps below the current standard is 
consistent with comments from manufacturers stating that a FEL cap of 
100 mg/hp-hr or between 50 and 100 mg/hp-hr would help to prevent 
competitive disruptions (i.e., require all manufacturers to make 
improvements in their emissions control technologies).
    The FEL caps for the final rule have been set at a level to ensure 
sizeable emission reductions from the current 2010 standards, while 
providing manufacturers with flexibility in meeting the final 
standards. When combined with the other restrictions in the final ABT 
program (i.e., credit life, averaging sets, expiration of existing 
credit balances), we determined the final FEL caps of 65 mg/hp-hr in 
MYs 2027 through 2030, and 50 mg/hp-hr in MY 2031 and later avoid 
potential adverse effects on the emissions reductions expected from the 
final program.
b. Encouraging Early Adoption of New Emissions Controls Technologies
    Several stakeholders provided general comments on the proposed 
Early Adoption Incentive program, which included emissions credit 
multipliers of 1.5 or 2.0 for meeting all proposed requirements prior 
to the applicable model year. Although many of the stakeholders in the 
heavy-duty engine industry generally supported incentives such as 
emissions credit multipliers to encourage early investments in 
emissions reductions technology; other industry stakeholders were 
concerned that the multipliers would incentivize some technologies 
(e.g., hybrid powertrains, natural gas engines) over others (e.g., 
battery-electric vehicles). Environmental organizations and other 
commenters were concerned that the emissions credit multipliers would 
result in an excess of credits that would undermine some of the 
benefits of the rule.
    After consideration of public comments, EPA is not finalizing the 
proposed Early Adoption Incentives program, and in turn we are not 
including emissions credit multipliers in the final program. Rather, we 
are finalizing an updated version of the proposed transitional credit 
program under the ABT program. As described in preamble Section IV.G.7, 
the transitional credit program that we are finalizing provides four 
pathways to generate straight NOX emissions credits (i.e., 
no credit multipliers) in order to encourage the early introduction 
engines with NOX-reducing technology.
c. Heavy-Duty Zero Emissions Vehicles and NOX Emissions 
Credits
    Numerous stakeholders provided feedback on EPA's proposal to allow 
manufacturers to generate NOX emissions credits from ZEVs. 
Environmental organizations and other commenters, as well as suppliers 
of heavy-duty engine and vehicle components, broadly oppose allowing 
manufacturers to generate NOX emissions credits from ZEVs. 
These stakeholders present several lines of argument, including the 
potential for: (1) Substantial impacts on the emissions reductions 
expected from the proposed rule, which could also result in 
disproportionate impacts in disadvantaged communities already 
overburdened with pollution; and (2) higher emissions from internal 
combustion engines, rather than further incentives for additional ZEVs 
(further noting that other State and Federal actions are providing more 
meaningful and less environmentally costly HD ZEV incentives). In 
contrast, heavy-duty engine and vehicle manufacturers generally support 
allowing manufacturers to generate these credits. These stakeholders 
also provided several lines of argument, including: (1) The potential 
for ZEVs to help meet emissions reductions and air quality goals; (2) 
an assertion that ZEV NOX credits are essential to the 
achievability of the standards for some manufacturers; and (3) ZEV 
NOX credits allow manufacturers to manage investments across 
different products that may ultimately result in increased ZEV 
deployment.
    After further consideration, including consideration of public 
comments, we are not finalizing the allowance for manufacturers to 
generate NOX emissions credits from heavy-duty ZEVs. Our 
decision is based on two primary considerations. First, the standards 
in the final rule are technology-forcing, yet achievable for MY 2027 
and later internal combustion engines without this flexibility. Second, 
because the final standards are not based on projected utilization of 
ZEV technology, and because we believe there will be increased 
penetration of ZEVs in the heavy-duty fleet by MY 2027 and later,\37\ 
we are concerned that allowing ZEVs to generate NOX 
emissions credits would result in fewer emissions reductions than 
intended from this rule. For example, by allowing manufacturers to 
generate ZEV NOX credits, EPA would be allowing higher 
emissions (through internal combustion engines using credits to emit up 
to the FEL cap) in MY 2027 and later, without requiring commensurate 
emissions reductions (through additional ZEVs beyond those already 
entering the market without this rule). This erosion of emissions 
benefits could have particularly adverse impacts in communities already 
overburdened by pollution. In addition, we continue to believe that 
testing requirements to ensure continued battery and fuel cell 
performance over the useful life of a ZEV may be important to ensure 
the zero-emissions tailpipe performance for which they are generating 
NOX credits; however, after further consideration, including 
consideration of public comments, we believe it is appropriate to take 
additional time to work with industry and other stakeholders on any 
test procedures and other specifications for ZEV battery and fuel cell 
performance over the useful life period of the ZEV.
---------------------------------------------------------------------------

    \37\ For example, the recently passed Inflation Reduction Act 
(IRA) has many incentives for promoting zero-emission vehicles, see 
Sections 13403 (Qualified Clean Vehicles), 13404 (Alternative Fuel 
Refueling Property Credit), 60101 (Clean Heavy-Duty Vehicles), 60102 
(Grants to Reduce Air Pollution at Ports), and 70002 (United States 
Postal Service Clean Fleets) of H. R. 5376.
---------------------------------------------------------------------------

2. Summary of the Key Provisions in the Regulatory Action
i. Controlling Criteria Pollutant Emissions Under a Broader Range of 
Operating Conditions
    The final rule provisions will reduce emissions from heavy-duty 
engines

[[Page 4305]]

under a range of operating conditions through revisions to our 
emissions standards and test procedures. These revisions will apply to 
both laboratory-based standards and test procedures for both heavy-duty 
CI and SI engines, as well as the off-cycle standards and test 
procedures for heavy-duty CI engines. These final provisions are 
outlined immediately below and detailed in Section III.
a. Final Laboratory Standards and Test Procedures
    For heavy-duty CI engines, we are finalizing new standards for 
laboratory-based tests using the current duty cycles, the transient 
Federal Test Procedure (FTP) and the steady-state Supplemental Emission 
Test (SET) procedure. These existing test procedures require CI engine 
manufacturers to demonstrate the effectiveness of emission controls 
when the engine is transitioning from low-to-high loads or operating 
under sustained high load, but do not include demonstration of emission 
control under sustained low-load operations. As proposed, we are 
finalizing a new, laboratory-based LLC test procedure for heavy-duty CI 
engines to demonstrate emission control when the engine is operating 
under low-load and idle conditions. The addition of the LLC will help 
ensure lower NOX emissions in urban areas and other 
locations where heavy-duty vehicles operate in stop-and-go traffic or 
other low-load conditions. As stated in Section I.B.1, we are 
finalizing the most stringent standard proposed for any model year for 
low-load operations based on further evaluation of data included in the 
proposal, and supported by information received during the comment 
period. We are also finalizing as proposed the option for manufacturers 
to test hybrid engines and powertrains together using the final 
powertrain test procedure.
    For heavy-duty SI engines, we are finalizing new standards for 
laboratory-based testing using the current FTP duty cycle, as well as 
updates to the current engine mapping procedure to ensure the engines 
achieve the highest torque level possible during testing. We are also 
finalizing the proposed addition of the SET duty-cycle test procedure 
to the heavy-duty SI laboratory demonstrations; it is currently only 
required for heavy-duty CI engines. Heavy-duty SI engines are 
increasingly used in larger heavy-duty vehicles, which makes it more 
likely for these engines to be used in higher-load operations covered 
by the SET.
    Our final NOX emission standards for all defined duty 
cycles for heavy-duty CI and SI engines are detailed in Table I-1. As 
shown, the final NOX standards will be implemented with a 
single step in MY 2027 and reflect the greatest emission reductions 
achievable starting in MY 2027, giving appropriate consideration to 
costs and other factors. As discussed in I.B.1.i, for the largest 
heavy-duty engines we are finalizing two updates to our testing 
requirements to ensure the greatest emissions reductions technically 
achievable are met throughout the final useful life periods of the 
largest heavy-duty engines: (1) A requirement for manufacturers to 
demonstrate before heavy heavy-duty engines are in-use that the 
emissions control technology are durable through a period of time 
longer than the final useful mileage, and (2) a compliance allowance 
that applies when EPA evaluates whether medium or heavy heavy-duty 
engines are meeting the final standards after these engines are in-use 
in the real world. We requested comment on an interim compliance 
allowance, and it is consistent with our past practice (for example, 
see 66 FR 5114, January 18, 2001); the interim compliance allowance is 
shown in the final column of Table I-1. See Section III for more 
discussion on feasibility of the final standards. Consistent with our 
existing, MY 2010 standards for criteria pollutants, the final 
standards, presented in Table 1, are numerically identical for SI and 
CI engines.\38\
---------------------------------------------------------------------------

    \38\ See Section III for our final PM, HC, and CO standards.

        Table I-1--Final NOX Emission Standards for Heavy-Duty CI and SI Engines on Specific Duty Cycles
                                     [milligrams/horsepower-hour (mg/hp-hr)]
----------------------------------------------------------------------------------------------------------------
                                                                      Current       Model years 2027 and later
                                                                 -----------------------------------------------
                                                                                  Spark ignition    Medium and
                                                                                    HDE, light    heavy HDE with
                                                                  All HD engines    HDE, medium   interim in-use
                                                                                  HDE, and heavy    compliance
                                                                                        HDE          allowance
----------------------------------------------------------------------------------------------------------------
Federal Test Procedure (transient mid/high load conditions).....             200              35              50
Supplemental Emission Test (steady-state conditions)............             200              35              50
Low Load Cycle (low-load conditions)............................             N/A              50              65
----------------------------------------------------------------------------------------------------------------

b. Final On-the-Road Standards and Test Procedures
    In addition to demonstrating emission control over defined duty 
cycles tested in a laboratory, heavy-duty CI engines must be able to 
demonstrate emission control over operations experienced while engines 
are in use on the road in the real world (i.e., ``off-cycle'' 
testing).\39\ We are finalizing with revisions the proposed updates to 
the procedure for off-cycle testing, such that data collected during a 
wider range of operating conditions will be valid, and therefore 
subject to emission standards.
---------------------------------------------------------------------------

    \39\ As discussed in Section III, ``off-cycle'' testing measures 
emissions while the engine is not operating on a specified duty 
cycle; this testing can be conducted while the engine is being 
driven on the road (e.g., on a package delivery route), or in an 
emission testing laboratory.
---------------------------------------------------------------------------

    Similar to the current approach, emission measurements collected 
during off-cycle testing will be collected on a second-by-second basis. 
As proposed, we are finalizing that the emissions data will be grouped 
into 300-second windows of operation. Each 300-second window will then 
be binned based on the type of operation that the engine performs 
during that 300-second period. Specifically, the average power of the 
engine during each 300-second window will determine whether the 
emissions during that window are binned as idle (Bin 1), or non-idle 
(Bin 2).\40\
---------------------------------------------------------------------------

    \40\ Due to the challenges of measuring engine power directly on 
in-use vehicles, we are finalizing as proposed the use of the 
CO2 emission rate (grams per second) as a surrogate for 
engine power; further, we are finalizing as proposed to normalize 
CO2 emission rates relative to the nominal maximum 
CO2 rate of the engine (e.g., when an engine with a 
maximum CO2 emission rate of 50 g/sec emits at a rate of 
10 g/sec, its normalized CO2 emission rate is 20 
percent).

---------------------------------------------------------------------------

[[Page 4306]]

    Our final, two-bin approach covers a wide range of operations that 
occur in the real world--significantly more in-use operation than 
today's requirements. Bin 1 includes extended idle and other very low-
load operations, where engine exhaust temperatures may drop below the 
optimal temperature where SCR-based aftertreatment works best. Bin 2 
includes a large fraction of urban driving conditions, during which 
engine exhaust temperatures are generally moderate, as well as higher-
power operations, such as on-highway driving, that typically results in 
higher exhaust temperatures and high catalyst efficiencies.\41\ Given 
the different operational profiles of each of these two bins, we are 
finalizing, as proposed, a separate standard for each bin. As proposed, 
the final structure follows that of our current not-to-exceed (NTE) 
off-cycle standards where testing is conducted while the engine 
operates on the road conducting its normal driving patterns, however, 
the final standards apply over a much broader range of engine 
operation.
---------------------------------------------------------------------------

    \41\ Because the final approach considers time-averaged power, 
either of the bins could include some idle operation and any of the 
bins could include some high-power operation.
---------------------------------------------------------------------------

    Table I-2 presents our final off-cycle standards for NOX 
emissions from heavy-duty CI engines. As discussed in I.B.1.i, for the 
medium and heavy heavy-duty engines we are also finalizing an interim 
compliance allowance that applies to non-idle (Bin 2) off-cycle 
standard after the engines are in-use. This interim compliance 
allowance is consistent with our past practice (for example, see 66 FR 
5114, January 18, 2001) and is shown in the final column of Table I-2. 
See Section III for details on the final off-cycle standards for other 
pollutants.

 Table I-2--Final Off-Cycle NOX Standards for Heavy-Duty CI Engines \a\
------------------------------------------------------------------------
                                            Model years 2027 and later
                                         -------------------------------
                                                          Medium HDE and
                                            Light HDE,    heavy HDE with
                                            medium HDE,       in-use
                                             heavy HDE      compliance
                                                             allowance
------------------------------------------------------------------------
Bin 1: Idle (g/hr)......................            10.0        \b\ 10.0
Bin 2: Low/medium/high load (mg/hp-hr)..              58              73
------------------------------------------------------------------------
\a\ The standards reflected in Table I-2 are applicable at 25 [deg]C and
  above; at lower temperatures the numerical off-cycle Bin 1 and Bin 2
  standards for NOX adjust as a function of ambient air temperature (see
  preamble Section III.C for details).
\b\ The interim compliance allowance we are finalizing for medium and
  heavy heavy-duty engines does not apply to the Bin 1 (Idle) off-cycle
  standard (see preamble Section III for details).

    In addition to the final standards for the defined duty cycle and 
off-cycle test procedures, the final standards include several other 
provisions for controlling emissions from specific operations in CI or 
SI engines. First, we are finalizing, as proposed, to allow CI engine 
manufacturers to voluntarily certify to idle standards using a new idle 
test procedure that is based on an existing California Air Resources 
Board (CARB) procedure.\42\
---------------------------------------------------------------------------

    \42\ 13 CCR 1956.8 (a)(6)(C)--Optional NOX idling 
emission standard.
---------------------------------------------------------------------------

    We are also finalizing two options for manufacturers to control 
engine crankcase emissions. Specifically, manufacturers will be 
required to either: (1) As proposed, close the crankcase, or (2) 
measure and account for crankcase emissions using an updated version of 
the current requirements for an open crankcase. We believe that either 
will ensure that the total emissions are accounted for during 
certification testing and throughout the engine operation during useful 
life. See Section III.B for more discussion on both the final idle and 
crankcase provisions.
    For heavy-duty SI, we are finalizing as proposed a new refueling 
emission standard for incomplete vehicles above 14,000 lb GVWR starting 
in MY 2027.\43\ The final refueling standard is based on the current 
refueling standard that applies to complete heavy-duty gasoline-fueled 
vehicles. Consistent with the current evaporative emission standards 
that apply for these same vehicles, we are finalizing a requirement 
that manufacturers can use an engineering analysis to demonstrate that 
they meet our final refueling standard. We are also adopting an 
optional alternative phase-in compliance pathway that manufacturers can 
opt into in lieu of being subject to this implementation date for all 
incomplete heavy-duty vehicles above 14,000 pounds GVWR (see Section 
III.E for details).
---------------------------------------------------------------------------

    \43\ Some vehicle manufactures sell their engines or 
``incomplete vehicles'' (i.e., chassis that include their engines, 
the frame, and a transmission) to body builders who design and 
assemble the final vehicle.
---------------------------------------------------------------------------

ii. Ensuring Standards Are Met Over a Greater Portion of an Engine's 
Operational Life
    In addition to reducing emissions under a broad range of engine 
operating conditions, the final program also includes provisions to 
ensure emissions standards are met over a greater portion of an 
engine's operational life. These final provisions include: (1) 
Lengthened regulatory useful life periods for heavy-duty engines, (2) 
revised requirement for the largest heavy-duty engines to demonstrate 
that the emissions control technology is durable through a period of 
time longer than the final useful life mileage, (3) updated methods to 
more accurately and efficiently demonstrate the durability of emissions 
controls, (4) lengthened emission warranty periods, and (5) increased 
assurance that emission controls will be maintained properly through 
more of the service life of heavy-duty engines. Each of these final 
provisions is outlined immediately below and detailed in Section IV.
a. Final Useful Life Periods
    Consistent with the proposal, the final useful life periods will 
cover a significant portion of the engine's operational life.\44\ The 
longer useful life periods, in combination with the durability 
demonstration requirements we are finalizing in this rule, are expected 
to lead manufacturers to further improve the durability of their

[[Page 4307]]

emission-related components. After additional consideration of data 
included in the proposal, as well as additional data provided in public 
comments, we are modifying our proposed useful life periods to account 
for the combined effect of useful life and the final numeric standards 
on the overall stringency and emissions reductions of the program (see 
Section IV.A for additional details).
---------------------------------------------------------------------------

    \44\ We consider operational life to be the average mileage at 
rebuild for CI engines and the average mileage at replacement for SI 
engines (see preamble Section IV.A for details).
---------------------------------------------------------------------------

    For smaller heavy-duty engines (i.e., Spark-ignition HDE, Light 
HDE, and Medium HDE) we are finalizing the longest useful life periods 
proposed (i.e., MY 2031 step of proposed option 1), to apply starting 
in MY 2027. The final useful life mileage for Heavy HDE, which has a 
distinctly longer operational life than the smaller engine classes, is 
approximately 50 percent longer than today's useful life mileage for 
these engines and matches the longest useful life we proposed for MY 
2027. Our final useful life periods for all heavy-duty engine classes 
are presented in Table I-3. We are also increasing the years-based 
useful life from the current 10 years to values that vary by engine 
class and match the respective proposed options. After considering 
comments, we are also adding hours-based useful life values to all 
engine categories based on a 20 mile per hour speed threshold and the 
corresponding final mileage values.\45\
---------------------------------------------------------------------------

    \45\ As noted in this I.B.2, we are finalizing, as proposed, 
refueling standards for certain HD SI engines that apply for a 
useful life of 15 years or 150,000 miles. See 40 CFR 1037.103(f) and 
preamble Section IV.A for more details.

                Table I-3--Current and Final Useful Life Periods for Heavy-Duty CI and SI Engines
----------------------------------------------------------------------------------------------------------------
                                                   Current                           MY 2027 and later
  Primary intended service class   -----------------------------------------------------------------------------
                                       Miles        Years        Hours        Miles        Years        Hours
----------------------------------------------------------------------------------------------------------------
Spark-ignition HDE \a\............      110,000           10  ...........      200,000           15       10,000
Light HDE \a\.....................      110,000           10  ...........      270,000           15       13,000
Medium HDE........................      185,000           10  ...........      350,000           12       17,000
Heavy HDE \b\.....................      435,000           10       22,000      650,000           11       32,000
----------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Spark-ignition HDE and Light HDE for GHG emission standards is 15 years or
  150,000 miles; we are not revising these useful life periods in this final rule. See 40 CFR 1036.108(d).
\b\ As discussed in Section I.B.2.ii.c, we are finalizing a requirement for manufacturers to demonstrate at the
  time of certification that the emissions controls on these largest heavy-duty engines are durable through the
  equivalent of 750,000 miles.

b. Extended Laboratory Demonstration of Emissions Control Durability 
for the Largest Heavy-Duty Engines
    As discussed in Section I.B.1.i, for the largest heavy-duty engines 
we are finalizing two updates to our proposed testing requirements in 
order to ensure the greatest emissions reductions technically 
achievable are met throughout the final useful life periods of these 
engines. One of the approaches (an in-use interim compliance allowance 
for medium and heavy heavy-duty engines) was noted in Section I.B.2.i; 
here we focus on the requirement for manufacturers to demonstrate 
before the largest heavy-duty engines are in use that the emissions 
control technology is durable through a period of time longer than the 
final useful mileage. Specifically, we are finalizing a requirement for 
manufacturers to demonstrate before the largest heavy-duty engines are 
in use that the emissions controls on these engines are durable (e.g., 
capable of controlling NOX emissions over the FTP duty-cycle 
at a level of 35 mg/hp-hr) through the equivalent of 750,000 miles. The 
extended durability demonstration in a laboratory environment will 
better ensure the final standards will be met throughout the longer 
final regulatory useful life mileage of 650,000 miles when these 
engines are operating in the real world where conditions are more 
variable.\46\ As discussed immediately below in Section I.B.2.ii.c, we 
are also finalizing provisions to improve the accuracy and efficiency 
of emissions control durability demonstrations for all heavy-duty 
engine classes.
---------------------------------------------------------------------------

    \46\ Once these engines are in use, EPA can require 
manufacturers to submit test data, or can conduct our own testing, 
to verify that the emissions control technologies continue to 
control emissions through the 650,000 mile useful life period (or 
the equivalent hours or years requirements as applicable).
---------------------------------------------------------------------------

c. Final Durability Demonstration
    EPA regulations require manufacturers to include durability 
demonstration data as part of an application for certification of an 
engine family. Manufacturers typically complete this demonstration by 
following regulatory procedures to calculate a deterioration factor 
(DF). The final useful life periods outlined in Table I-4 will require 
manufacturers to extend their durability demonstrations to show that 
the engines will meet applicable emission standards throughout the 
lengthened useful life.
    To address the need for accurate and efficient emission durability 
demonstration methods, EPA worked with manufacturers and CARB to 
address this concern through guidance for MY 2020 and later 
engines.\47\ Consistent with the recent guidance, we proposed three 
methods for determining DFs. We are finalizing two of the three 
proposed methods; we are not finalizing the option to perform a fuel-
based accelerated DF determination, noting that it has been shown to 
underestimate emission control system deterioration. The two methods we 
are finalizing include: (1) Allowing manufacturers to continue the 
current practice of determining DFs based on engine dynamometer-based 
aging of the complete engine and aftertreatment system out to 
regulatory useful life, and (2) a new option to bench-age the 
aftertreatment system at an accelerated rate to limit the burden of 
generating a DF over the final lengthened useful life periods. If 
manufacturers choose the second option (accelerated bench-aging of the 
aftertreatment system), then they may also choose to use an accelerated 
aging test procedure that we are codifying in this final rule; the test 
procedure is, based on a test program that we introduced in the 
proposal to evaluate a rapid-aging protocol for diesel catalysts. We 
are also finalizing with revisions two of the three proposed DF 
verification options to confirm the accuracy of the DF values submitted 
by manufacturers for certification. After further consideration of data 
included in the proposal, as well as supported by

[[Page 4308]]

information provided in public comments, we are finalizing that, upon 
EPA request, manufacturers would be required to provide confirmation of 
the DF accuracy through one of two options.
---------------------------------------------------------------------------

    \47\ U.S. EPA. ``Guidance on Deterioration Factor Validation 
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel 
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad). 
November 17, 2020.
---------------------------------------------------------------------------

d. Final Emission-Related Warranty Periods
    We are updating and significantly strengthening the emission-
related warranty periods, for model year 2027 and later heavy-duty 
engines.\48\ We are finalizing most of the emission-related warranty 
provisions of 40 CFR 1036.120 as proposed. Following our approach for 
useful life, we are revising the proposed warranty periods for each 
primary intended service class to reflect the difference in average 
operational life of each class and in consideration of the information 
provided by commenters (see preamble Section IV and the Response to 
Comments document for details).
---------------------------------------------------------------------------

    \48\ Components installed to control only criteria pollutant 
emissions or both greenhouse gas (i.e., CO2, 
N2O, and CH4) and criteria pollutant emissions 
would be subject to the final warranty periods of 40 CFR 1036.120. 
See 40 CFR 1036.150(w).
---------------------------------------------------------------------------

    EPA's current emissions-related warranty periods for heavy-duty 
engines range from 22 percent to 54 percent of the current regulatory 
useful life. Notably, these percent values have decreased over time 
given that the warranty periods have not changed since 1983 even as the 
useful life periods were lengthened.\49\ The revised warranty periods 
are expected to result in better maintenance, including maintenance of 
emission-related components, and less tampering, which would help to 
ensure the benefits of the emission controls in-use. In addition, 
longer regulatory warranty periods may lead engine manufacturers to 
simplify repair processes and make them more aware of system defects 
that need to be tracked and reported to EPA.
---------------------------------------------------------------------------

    \49\ The useful life for heavy heavy-duty engines was increased 
from 290,000 miles to 435,000 miles for 2004 and later model years 
(62 FR 54694, October 21, 1997).
---------------------------------------------------------------------------

    Our final emission-related warranty periods for heavy-duty engines 
are presented in Table I-4. The final warranty mileages that apply 
starting in MY 2027 for Spark-ignition HDE, Light HDE, and Medium HDE 
match the longest warranty mileages proposed (i.e., MY 2031 step of 
proposed Option 1) for these primary intended service classes. For 
Heavy HDE, which has a distinctly longer operational life, the final 
warranty mileage matches the longest warranty mileage proposed to apply 
in MY 2027 (i.e., MY 2027 step of proposed Option 1), and is more than 
four times longer than today's warranty mileage for these engines. We 
are also increasing the years-based warranty from the current 5 years 
to 10 years for all engine classes. After considering comments, we are 
also adding hours-based warranty values to all primary intended service 
classes based on a 20 mile per hour speed threshold and the 
corresponding final mileage values. Consistent with current warranty 
provisions, the warranty period would be whichever warranty value 
(i.e., mileage, hours, or years) occurs first.

    Table I-4--Current and Final Emission-Related Warranty Periods for Heavy-Duty CI and SI Engines Criteria
                                               Pollutant Standards
----------------------------------------------------------------------------------------------------------------
                                                   Current                       Model year 2027 and later
  Primary intended service class   -----------------------------------------------------------------------------
                                      Mileage       Years        Hours       Mileage       Years        Hours
----------------------------------------------------------------------------------------------------------------
Spark-Ignition HDE................       50,000            5  ...........      160,000           10        8,000
Light HDE.........................       50,000            5  ...........      210,000           10       10,000
Medium HDE........................      100,000            5  ...........      280,000           10       14,000
Heavy HDE.........................      100,000            5  ...........      450,000           10       22,000
----------------------------------------------------------------------------------------------------------------

e. Provisions To Ensure Long-Term Emissions Performance
    We proposed several approaches for an enhanced, comprehensive 
strategy to increase the likelihood that emission controls will be 
maintained properly through more of the operational life of heavy-duty 
engines, including beyond their useful life periods. These approaches 
include updated maintenance provisions, revised requirements for the 
owner's manual and emissions label, codified engine derates or 
``inducements'' regulations, and updated onboard diagnostics (OBD) 
regulations.
    Our final updates to maintenance provisions include defining the 
type of maintenance manufacturers may choose to recommend to owners in 
maintenance instructions, updating minimum maintenance intervals for 
certain critical emission-related components, and outlining specific 
requirements for maintenance instructions provided in the owner's 
manual.
    We are finalizing changes to the owner's manual and emissions label 
requirements to ensure access to certain maintenance information and 
improve serviceability. We expect this additional maintenance 
information to improve factors that contribute to mal-maintenance, 
which would result in better service experiences for independent repair 
technicians, specialized repair technicians, owners who repair their 
own equipment, and possibly vehicle inspection and maintenance 
technicians. We also believe improving owner experiences with operating 
and maintaining heavy-duty engines can reduce the likelihood of 
tampering.
    In addition, we are adopting inducement regulations that are an 
update to and replace existing guidance regarding recommended methods 
for manufacturers to reduce engine performance to induce operators to 
maintain appropriate levels of high-quality diesel emission fluid (DEF) 
in their SCR-based aftertreatment systems and discourage tampering with 
such systems. See Section IV.D for details on the principles we 
followed to develop multi-step derate schedules that are tailored to 
different operating characteristics, as well as changes in the final 
rule inducement regulations from the proposal.
    We are also finalizing updated OBD regulations both to better 
address newer diagnostic methods and available technologies, and to 
streamline provisions where possible. We are incorporating by reference 
the current CARB OBD regulations, updated in 2019, as proposed.\50\ 
Specifically, manufacturers must comply with OBD requirements as 
referenced in the CARB

[[Page 4309]]

OBD regulations starting in model year 2027, with optional compliance 
based on the CARB OBD regulations for earlier model years. After 
considering comments, many of which included specific technical 
information and requests for clarification, we are finalizing certain 
provisions with revisions from proposal and postponing others for 
consideration in a future rulemaking (see Section IV.C for details).
---------------------------------------------------------------------------

    \50\ CARB's 2019 Heavy-duty OBD Final Regulation Order was 
approved and became effective October 3, 2019. Title 13, California 
Code of Regulations sections 1968.2, 1968.5, 1971.1, and 1971.5, 
available at https://ww2.arb.ca.gov/rulemaking/2018/heavy-duty-board-diagnostic-system-requirements-2018.
---------------------------------------------------------------------------

iii. Averaging, Banking, and Trading of NOX Emissions 
Credits
    In addition the key program provisions, EPA is finalizing an 
averaging, banking, and trading (ABT) program for heavy-duty engines 
that provides manufacturers with flexibility in their product planning 
while encouraging the early introduction of emissions control 
technologies and maintaining the expected emissions reductions from the 
program. Several core aspects of the final ABT program are consistent 
with the proposal, but the final ABT program also includes several 
updates after consideration of public comments. In particular, EPA 
requested comment on and agrees with commenters that a lower family 
emission limit (FEL) cap than proposed is appropriate for the final 
rule. Further, after consideration of public comments, EPA is choosing 
not to finalize at this time the proposed Early Adoption Incentives 
program, and in turn we are not including emissions credit multipliers 
in the final program. Rather, we are finalizing an updated version of 
the proposed transitional credit program under the ABT program. The 
revised transitional credit program that we are finalizing provides 
four pathways to generate NOX emissions credits in MYs 2022 
through 2026 that are valued based on the extent to which the engines 
generating credits comply with the requirements we are finalizing for 
MY 2027 and later (e.g., credits discounted at a rate of 40 percent for 
engines meeting a lower numeric standard but none of the other MY 2027 
and later requirements). Specifically, the four transitional credit 
pathways in the final rule are: (1) In MY 2026, for heavy heavy-duty or 
medium heavy-duty engine service classes, certify all engines in the 
manufacturer's respective service class to a FEL of 50 mg/hp-hr or less 
and meet all other EPA requirements for MYs 2027 and later to generate 
undiscounted credits that have additional flexibilities for use in MYs 
2027 and later (2026 Service Class Pull Ahead Credits); (2) starting in 
MY 2024, certify one or more engine family(ies) to a FEL below the 
current MY 2010 emissions standards and meet all other EPA requirements 
for MYs 2027 and later to generate undiscounted credits based on the 
longer UL periods included in the 2027 and later program (Full 
Credits); (3) starting in MY 2024, certify one or more engine 
family(ies) to a FEL below the current MY 2010 emissions standards and 
several of the key requirements for MYs 2027 and later, while meeting 
the current useful life and warranty requirements to generate 
undiscounted credits based on the shorter UL period (Partial Credits); 
(4) starting in MY 2022, certify one or more engine family(ies) to a 
FEL below the current MY 2010 emissions standards, while complying with 
all other MY2010 requirements, to generate discounted credits 
(Discounted Credits). We note that the transitional credit and main ABT 
program we are finalizing does not allow engines certified to state 
standards that are different than the Federal EPA standards to generate 
Federal EPA credits.
    In addition, we are finalizing an optional production volume 
allowance for MYs 2027 through 2029 that is consistent with our request 
for comment in the proposal but different in several key aspects, 
including a requirement for manufacturers to use NOX 
emissions credits to certify heavy heavy-duty engines compliant with MY 
2010 requirements in MYs 2027 through 2029. Finally, we have decided 
not to finalize an allowance for manufacturers to generate 
NOX emissions credits from heavy-duty ZEVs (see Section IV.G 
for details on the final ABT program).
iv. Migration From 40 CFR Part 86, Subpart A
    Heavy-duty criteria pollutant regulations were originally codified 
into 40 CFR part 86, subpart A, in the 1980s. As discussed in the 
proposal, this rulemaking provides an opportunity to clarify and 
improve the wording of our existing heavy-duty criteria pollutant 
regulations in plain language and migrate them to 40 CFR part 1036.\51\ 
Part 1036, which was created for the Phase 1 GHG program, provides a 
consistent, updated format for our heavy-duty regulations, with 
improved organization. In general, this migration is not intended to 
change the compliance program specified in part 86, except as 
specifically stated in this final rulemaking. See our summary of the 
migration in Section III.A. The final provisions of part 1036 will 
generally apply for model years 2027 and later, unless noted, and 
manufacturers will continue to use part 86 in the interim.
---------------------------------------------------------------------------

    \51\ We are also adding and amending some provisions in parts 
1065 and 1068 as part of the migration from part 86 for heavy-duty 
highway engines; these provisions in part 1065 and 1068 will apply 
to other sectors that are already subject to part 1065 and 1068. 
Additionally, some current vehicle provisions in part 1037 refer to 
part 86 and, as proposed, the final rule updates those references in 
part 1037 as needed.
---------------------------------------------------------------------------

v. Technical Amendments to Regulatory Provisions for Mobile Source 
Sectors
    EPA has promulgated emission standards for highway and nonroad 
engines, vehicles, and equipment. Section XI of this final rule 
describes several amendments to correct, clarify, and streamline a wide 
range of regulatory provisions for many of those different types of 
engines, vehicles, and equipment. Section XI.A includes technical 
amendments to compliance provisions that apply broadly across EPA's 
emission control programs to multiple industry sectors, including 
light-duty vehicles, light-duty trucks, marine diesel engines, 
locomotives, and various other types of nonroad engines, vehicles, and 
equipment. Some of those amendments are for broadly applicable testing 
and compliance provisions in 40 CFR parts 1065, 1066, and 1068. Other 
cross-sector issues involve making the same or similar changes in 
multiple standard-setting parts for individual industry sectors. The 
rest of Section XI describes amendments we are finalizing that apply 
uniquely for individual industry sectors. Except as specifically 
identified in this rulemaking, EPA did not reopen any of the underlying 
provisions across these standard setting parts.
    We are finalizing amendments in two areas of note for the general 
compliance provisions in 40 CFR part 1068. First, we are finalizing, 
with updates from proposal, a comprehensive approach for making 
confidentiality determinations related to compliance information that 
companies submit to or is collected by EPA. These provisions apply for 
highway, nonroad, and stationary engine, vehicle, and equipment 
programs, as well as aircraft and portable fuel containers.
    Second, we are finalizing, with updates from proposal, provisions 
that include clarifying text to establish what qualifies as an 
adjustable parameter and to identify the practically adjustable range 
for those adjustable parameters. The adjustable-parameter provisions in 
the final rule also include specific provisions related to electronic 
controls that aim to deter tampering.

[[Page 4310]]

C. Impacts of the Standards

1. Projected Emission Reductions and Air Quality Improvements
    Our analysis of the estimated emission reductions, air quality 
improvements, costs, and monetized benefits of the final rule is 
outlined in this section and detailed in Sections V through X. The 
final standards, which are described in detail in Sections III and IV, 
are expected to reduce emissions from highway heavy-duty engines in 
several ways. We project the final emission standards for heavy-duty CI 
engines will reduce tailpipe emissions of NOX; the 
combination of the final low-load test cycle and off-cycle test 
procedure for CI engines will help to ensure that the reductions in 
tailpipe emissions are achieved in-use, not only under high-speed, on-
highway conditions, but also under low-load and idle conditions. We 
also project reduced tailpipe emissions of NOX from the 
final emission standards for heavy-duty SI engines, as well as 
reductions of CO, PM, VOCs, and associated air toxics, particularly 
under cold-start and high-load operating conditions. The final 
emissions warranty and regulatory useful life requirements for heavy-
duty CI and SI engines will also help maintain emissions controls of 
all pollutants beyond the existing useful life periods, which will 
result in additional emissions reductions of all pollutants from both 
CI and SI engines, including primary exhaust PM2.5. The 
onboard refueling vapor recovery requirements for heavy-duty SI engines 
will reduce VOCs and associated air toxics. Table I-5 summarizes the 
projected reductions in heavy-duty emissions from the final standards 
in 2045 and shows the significant reductions in NOX 
emissions. Section VI and Regulatory Impact Analysis (RIA) Chapter 5 
provide more information on our projected emission reductions for the 
final rule.

  Table I-5--Projected Heavy-Duty Emission Reductions in 2045 From the
                             Final Standards
------------------------------------------------------------------------
                                                              Percent
                                                           reduction in
                        Pollutant                         highway heavy-
                                                          duty emissions
                                                             (percent)
------------------------------------------------------------------------
NOX.....................................................              48
Primary PM2.5...........................................               8
VOC.....................................................              23
CO......................................................              18
------------------------------------------------------------------------

    The final standards will also reduce emissions of other pollutants. 
For instance, the final rule will result in a 28 percent reduction in 
benzene from highway heavy-duty engines in 2045. Leading up to 2045, 
emission reductions are expected to increase over time as the fleet 
turns over to new, compliant engines.
    We expect this rule will decrease ambient concentrations of air 
pollutants, including significant improvements in ozone concentrations 
in 2045, as demonstrated in the air quality modeling analysis. We also 
expect reductions in ambient PM2.5, NO2 and CO 
due to this rule. The emission reductions provided by the final 
standards will be important in helping areas attain and maintain the 
NAAQS and prevent future nonattainment. This rule's emission reductions 
will also reduce air pollution in close proximity to major roadways, 
reduce nitrogen deposition and improve visibility.
    Our consideration of environmental justice literature indicates 
that people of color and people with low income are disproportionately 
exposed to elevated concentrations of many pollutants in close 
proximity to major roadways. We also used our air quality data from the 
proposal to conduct a demographic analysis of human exposure to future 
air quality in scenarios with and without the rule in place. Although 
the spatial resolution of the air quality modeling is not sufficient to 
capture very local heterogeneity of human exposures, particularly the 
pollution concentration gradients near roads, the analysis does allow 
estimates of demographic trends at a national scale. To compare 
demographic trends, we sorted 2045 baseline air quality concentrations 
from highest to lowest concentration and created two groups: Areas 
within the contiguous United States with the worst air quality and the 
rest of the country. We found that in the 2045 baseline, the number of 
people of color living within areas with the worst air quality is 
nearly double that of non-Hispanic Whites. We also found that the 
largest predicted improvements in both ozone and PM2.5 are 
estimated to occur in areas with the worst baseline air quality, where 
larger numbers of people of color are projected to reside. An expanded 
analysis of the air quality impacts experienced by specific race and 
ethnic groups found that non-Hispanic Blacks will receive the greatest 
improvement in PM2.5 and ozone concentrations as a result of 
the standards. More details on our air quality modeling and demographic 
analyses are included in Section VII and RIA Chapter 6.
2. Summary of Costs and Benefits
    Our estimates of reductions in heavy-duty engine emissions and the 
associated air quality impacts are based on manufacturers adding 
emissions-reduction technologies and making emission control components 
more durable in response to the final standards and longer regulatory 
useful life periods; our estimates of emissions reductions also account 
for improved repair of emissions controls by owners in response to the 
longer emissions-related warranty periods and other provisions in the 
final rule.
    Our program cost analysis includes both the total technology costs 
(i.e., manufacturers' costs to add or update emissions control 
technologies) and the operating costs (i.e., owners' costs to maintain 
and operate MY 2027 and later vehicles) (see Section V and RIA Chapter 
7). Our evaluation of total technology costs of the final rule includes 
direct costs (i.e., cost of materials, labor costs) and indirect 
manufacturing costs (e.g., warranty, research and development). The 
direct manufacturing costs include individual technology costs for 
emission-related engine components and for exhaust aftertreatment 
systems. Importantly, our analysis of direct manufacturing costs 
includes the costs of the existing emission control technologies, 
because we expect the emissions warranty and regulatory useful life 
provisions in the final standards to have some impact on not only the 
new technology added to comply with the standards, but also on any 
existing emission control components. The cost estimates thus account 
for existing engine hardware and aftertreatment systems for which new 
costs will be incurred due to the new warranty and useful life 
provisions, even absent any changes in the level of emission standards. 
The indirect manufacturing costs in our analysis include the additional 
costs--research and development, marketing, administrative costs, 
etc.--incurred by manufacturers in running the company.
    As part of our evaluation of operating costs, we estimate costs 
truck owners incur to repair emission control system components. Our 
repair cost estimates are based on industry data showing the amount 
spent annually by truck owners on different types of repairs, and our 
estimate of the percentage of those repairs that are related to 
emission control components. Our analysis of this data shows that 
extending the useful life and emission warranty periods will lower 
emission repair costs during several years of operation for several 
vehicle types. More discussion on our

[[Page 4311]]

emission repair costs estimates is included in Section V, with 
additional details presented in RIA Chapter 7.
    We combined our estimates of emission repair costs with other 
operating costs (i.e., urea/DEF, fuel consumption) and technology costs 
to calculate total program costs. Our analysis of the final standards 
shows that total costs for the final program relative to the baseline 
(or no action scenario) range from $3.9 billion in 2027 to $4.7 billion 
in 2045 (2017 dollars, undiscounted, see Table V-16). The present value 
of program costs for the final rule, and additional details are 
presented in Section V.
    Section VIII presents our analysis of the human health benefits 
associated with the final standards. We estimate that in 2045, the 
final rule will result in total annual monetized ozone- and 
PM2.5-related benefits of $12 and $33 billion at a 3 percent 
discount rate, and $10 and $30 billion at a 7 percent discount 
rate.\52\ These benefits only reflect those associated with reductions 
in NOX emissions (a precursor to both ozone and secondarily-
formed PM2.5) and directly-emitted PM2.5 from 
highway heavy-duty engines.
---------------------------------------------------------------------------

    \52\ 2045 is a snapshot year chosen to approximate the annual 
health benefits that occur when the final program will be fully 
implemented and when most of the regulated fleet will have turned 
over.
---------------------------------------------------------------------------

    There are additional human health and environmental benefits 
associated with reductions in exposure to ambient concentrations of 
PM2.5, ozone, and NO2 that EPA has not quantified 
due to data, resource, or methodological limitations. There will also 
be health benefits associated with reductions in air toxic pollutant 
emissions that result from the final program, but we did not attempt to 
quantify or monetize those impacts due to methodological limitations. 
Because we were unable to quantify and monetize all of the benefits 
associated with the final program, the monetized benefits presented in 
this analysis are an underestimate of the program's total benefits. 
More detailed information about the benefits analysis conducted for the 
final rule, including the present value of program benefits, is 
included in Section VIII and RIA Chapter 8.
    We compare total monetized health benefits to total costs 
associated with the final rule in Section IX. Table I-6 shows that 
annual benefits of the final rule will be larger than the annual costs 
in 2045, with annual net benefits of $6.9 and $29 billion assuming a 3 
percent discount rate, and net benefits of $5.8 and $25 billion 
assuming a 7 percent discount rate.\53\ The benefits of the final rule 
also outweigh the costs when expressed in present value terms and as 
equalized annual values (see Section IX for these values).\54\
---------------------------------------------------------------------------

    \53\ The range of benefits and net benefits reflects a 
combination of assumed PM2.5 and ozone mortality risk 
estimates and selected discount rate.
    \54\ EPA's analysis of costs and benefits does not include 
California's Omnibus rule or actions by other states to adopt it. 
EPA is reviewing a waiver request under CAA section 209(b) from 
California for the Omnibus rule; until EPA grants the waiver, the HD 
Omnibus program is not enforceable. EPA's analysis also does not 
include the recent IRA of 2022, which we anticipate will accelerate 
zero emissions technology in the heavy-duty sector.

        Table I-6--Final Costs, Benefits and Net Benefits in 2045
                            [billions, 2017$]
------------------------------------------------------------------------
                                            3% Discount     7% Discount
------------------------------------------------------------------------
Benefits................................         $12-$33         $10-$30
Costs...................................            $4.7            $4.7
Net Benefits............................        $6.9-$29        $5.8-$25
------------------------------------------------------------------------

3. Summary of Economic Impacts
    Section X examines the potential impacts of the final rule on 
heavy-duty vehicles (sales, mode shift, fleet turnover) and employment 
in the heavy-duty industry. The final rule may impact vehicle sales due 
to both changes in purchase price and longer emission warranty mileage 
requirements. The final rule may impact vehicle sales by increasing 
purchases of new vehicles before the final standards come into effect, 
in anticipation of higher prices after the standards (``pre-buy''). The 
final rule may also reduce sales after the final standards are in place 
(``low-buy''). In this final rule, we outline an approach to quantify 
potential impacts on vehicle sales due to new emission standards. Our 
illustrative analysis for this final rule, discussed in RIA Chapter 
10.1, suggest pre- and low-buy for Class 8 trucks may range from zero 
to approximately 2 percent increase in sales over a period of up to 8 
months before the 2027 standards begin (pre-buy), and a decrease in 
sales from zero to approximately 3 percent over a period of up to 12 
months after the 2027 standards begin (low-buy). We expect little mode 
shift due to the final rule because of the large difference in cost of 
moving goods via trucks versus other modes of transport (e.g., planes 
or barges).
    Employment impacts of the final rule depend on the effects of the 
rule on sales, the share of labor in the costs of the rule, and changes 
in labor intensity due to the rule. We quantify the effects of costs on 
employment, and we discuss the effects due to sales and labor intensity 
qualitatively. In response to comments, we have added a discussion in 
Chapter 10 of the RIA describing a method that could be used to 
quantitatively estimate a demand effect on employment, as well as an 
illustrative application of that method. The partial quantification of 
employment impacts due to increases in the costs of vehicles and parts, 
holding labor intensity constant, shows an increase in employment by 
1,000 to 5,300 job-years in 2027.\55\ See Section X for further detail 
on limitations and assumptions of this analysis.
---------------------------------------------------------------------------

    \55\ A job-year is, for example, one year of full-time work for 
one person, or one year of half-time work for two people.
---------------------------------------------------------------------------

D. EPA Statutory Authority for This Action

    This section briefly summarizes the statutory authority for the 
final rule. Title II of the Clean Air Act provides for comprehensive 
regulation of mobile sources, authorizing EPA to regulate emissions of 
air pollutants from all mobile source categories. Specific Title II 
authorities for this final rule include: CAA sections 202, 203, 206, 
207, 208, 213, 216, and 301 (42 U.S.C. 7521, 7522, 7525, 7541, 7542, 
7547, 7550, and 7601). We discuss some key aspects of these sections in 
relation to this final action immediately below (see also Section XIII 
of this preamble), as well as in each of the relevant sections later in 
this preamble. As noted in Section I.B.2.v, the final rule includes 
confidentiality determinations for much of the information collected by 
EPA for certification and compliance under Title II; see Section XI.A. 
for discussion of

[[Page 4312]]

relevant statutory authority for these final rule provisions.
    Statutory authority for the final NOX, PM, HC, and CO 
emission standards in this action comes from CAA section 202(a), which 
states that ``the Administrator shall by regulation prescribe (and from 
time to time revise) . . . standards applicable to the emission of any 
air pollutant from any class or classes of new . . . motor vehicle 
engines, which in his judgment cause, or contribute to, air pollution 
which may reasonably be anticipated to endanger public health or 
welfare.'' Standards under CAA section 202(a) take effect after such 
period as the Administrator finds necessary to permit the development 
and application of the requisite technology, giving appropriate 
consideration to the cost of compliance within such period.''
    Section 202(a)(3) further addresses EPA authority to establish 
standards for emissions of NOX, PM, HC, and CO from heavy-
duty engines and vehicles. Section 202(a)(3)(A) requires that such 
standards ``reflect the greatest degree of emission reduction 
achievable through the application of technology which the 
Administrator determines will be available for the model year to which 
such standards apply, giving appropriate consideration to cost, energy, 
and safety factors associated with the application of such 
technology.'' Section 202(a)(3)(B) allows EPA to take into account air 
quality information in revising such standards. Section 202(a)(3)(C) 
provides that standards shall apply for a period of no less than three 
model years beginning no earlier than the model year commencing four 
years after promulgation. CAA section 202(a)(3)(A) is a technology-
forcing provision and reflects Congress' intent that standards be based 
on projections of future advances in pollution control capability, 
considering costs and other statutory factors.56 57 CAA 
section 202(a)(3) neither requires that EPA consider all the statutory 
factors equally nor mandates a specific method of cost-analysis; rather 
EPA has discretion in determining the appropriate consideration to give 
such factors.\58\
---------------------------------------------------------------------------

    \56\ See National Petrochemical & Refiners Association v. EPA, 
287 F.3d 1130, 1136 (D.C. Cir. 2002) (explaining that EPA is 
authorized to adopt ``technology-forcing'' regulations under CAA 
section 202(a)(3)); NRDC v. Thomas, 805 F.2d 410, 428 n.30 (D.C. 
Cir. 1986) (explaining that such statutory language that ``seek[s] 
to promote technological advances while also accounting for cost 
does not detract from their categorization as technology-forcing 
standards''); see also Husqvarna AB v. EPA, 254 F.3d 195 (D.C. Cir. 
2001) (explaining that CAA sections 202 and 213 have similar 
language and are technology-forcing standards).
    \57\ In this context, the term ``technology-forcing'' has a 
specific legal meaning and is used to distinguish standards that may 
require manufacturers to develop new technologies (or significantly 
improve existing technologies) from standards that can be met using 
off-the-shelf technology alone. Technology-forcing standards such as 
those in this final rule do not require manufacturers to use 
specific technologies.
    \58\ See, e.g., Sierra Club v. EPA, 325 F.3d 374, 378 (D.C. Cir. 
2003) (explaining that similar technology-forcing language in CAA 
section 202(l)(2) ``does not resolve how the Administrator should 
weigh all [the statutory] factors in the process of finding the 
`greatest emission reduction achievable' ''); Husqvarna AB v. EPA, 
254 F.3d 195, 200 (D.C. Cir. 2001) (explaining that under CAA 
section 213's similar technology-forcing authority that ``EPA did 
not deviate from its statutory mandate or frustrate congressional 
will by placing primary significance on the `greatest degree of 
emission reduction achievable' '' or by considering cost and other 
statutory factors as important but secondary).
---------------------------------------------------------------------------

    CAA section 202(d) directs EPA to prescribe regulations under which 
the useful life of vehicles and engines are determined and establishes 
minimum values of 10 years or 100,000 miles, whichever occurs first, 
unless EPA determines that a period of greater duration or mileage is 
appropriate. EPA may apply adjustment factors to assure compliance with 
requirements in use throughout useful life (CAA section 206(a)). CAA 
section 207(a) requires manufacturers to provide emissions-related 
warranty, which EPA last updated in its regulations for heavy-duty 
engines in 1983 (see 40 CFR 86.085-2).\59\
---------------------------------------------------------------------------

    \59\ 48 FR 52170, November 16, 1983.
---------------------------------------------------------------------------

    EPA is promulgating the final emission standards pursuant to its 
authority under CAA section 202(a), including 202(a)(3)(A). Section II 
and Chapter 4 of the RIA describe EPA's analysis of information 
regarding heavy-duty engines' contribution to air pollution and how 
that pollution adversely impacts public health and welfare. Sections 
III and IV discuss our feasibility analysis of the emission standards 
and useful life periods in the final rule, with more detail in Chapter 
3 of the RIA. Our analysis shows that the final emission standards and 
useful life periods are feasible and will result in the greatest 
emission reductions achievable for the model years to which they will 
apply, pursuant to CAA section 202(a)(3), giving appropriate 
consideration to costs, lead time, and other factors. Our analysis of 
the final standards includes providing manufacturers with sufficient 
time to ensure that emission control components are durable enough for 
the longer useful life periods in the final program. In setting the 
final emission standards, EPA appropriately assessed the statutory 
factors specified in CAA section 202(a)(3)(A), including giving 
appropriate consideration to the cost associated with the application 
of technology EPA determined will be available for the model year the 
final standards apply (i.e., cost of compliance for the manufacturer 
associated with the application of such technology). EPA's assessment 
of the relevant statutory factors in CAA section 202(a)(3)(A) justify 
the final emission standards. We also evaluated additional factors, 
including factors to comply with E.O. 12866; our assessment of these 
factors lend further support to the final rule.
    As proposed, we are finalizing new emission standards along with 
new and revised test procedures for both laboratory-based duty-cycles 
and off-cycle testing. Manufacturers demonstrate compliance over 
specified duty-cycle test procedures during pre-production testing, as 
well as confirmatory testing during production, which is conducted by 
EPA or the manufacturer. Test data and other information submitted by 
the manufacturer as part of their certification application are the 
basis on which EPA issues certificates of conformity pursuant to CAA 
section 206. Under CAA section 203, sales of new vehicles are 
prohibited unless the vehicle is covered by a certificate of 
conformity. Compliance with engine emission standards is required 
throughout the regulatory useful life of the engine, not only at 
certification but throughout the regulatory useful life in-use in the 
real word. In-use engines can be tested for compliance with duty-cycle 
and off-cycle standards, with testing over corresponding specific duty-
cycle test procedures and off-cycle test procedures, either on the road 
or in the laboratory (see Section III for more discussion on for 
testing at various stages in the life of an engine).
    Also as proposed, we are finalizing lengthened regulatory useful 
life and emission warranty periods to better reflect the mileages and 
time periods over which heavy-duty engines are driven today. These and 
other provisions in the final rule are further discussed in the 
preamble sections that follow. The proposed rule (87 FR 17414, March 
28, 2022) includes additional information relevant to the development 
of this rule, including: History of Emissions Standards for Heavy-duty 
Engines and Vehicles; Petitions to EPA for Additional NOX 
control; the California Heavy-Duty Highway Low NOX Program 
Development; and the Advance Notice of Proposed Rulemaking.

[[Page 4313]]

II. Need for Additional Emissions Control

    This final rule will reduce emissions from heavy-duty engines that 
contribute to ambient levels of ozone, PM, NOX and CO, which 
are all pollutants for which EPA has established health-based NAAQS. 
These pollutants are linked to premature death, respiratory illness 
(including childhood asthma), cardiovascular problems, and other 
adverse health impacts. Many groups are at greater risk than healthy 
people from these pollutants, including people with heart or lung 
disease, outdoor workers, older adults and children. These pollutants 
also reduce visibility and negatively impact ecosystems. This final 
rule will also reduce emissions of air toxics from heavy-duty engines. 
A more detailed discussion of the health and environmental effects 
associated with the pollutants affected by this rule is included in 
Sections II.B and II.C and Chapter 4 of the RIA.
    Populations who live, work, or go to school near high-traffic 
roadways experience higher rates of numerous adverse health effects, 
compared to populations far away from major roads. We note that there 
is substantial evidence that people who live or attend school near 
major roadways are more likely to be people of color, Hispanic 
ethnicity, and/or low socioeconomic status.
    Across the United States, NOX emissions from heavy-duty 
engines are important contributors to concentrations of ozone and 
PM2.5 and their resulting threat to public 
health.60 61 The emissions modeling done for the final rule 
(see Chapter 5 of the RIA) indicates that without these standards, 
heavy-duty engines will continue to be one of the largest contributors 
to mobile source NOX emissions nationwide in the future, 
representing 32 percent of the mobile source NOX in calendar 
year 2045.\62\ Furthermore, it is estimated that heavy-duty engines 
would represent 90 percent of the onroad NOX inventory in 
calendar year 2045.\63\ The emission reductions that will occur from 
the final rule are projected to reduce air pollution that is (and is 
projected to continue to be) at levels that endanger public health and 
welfare. For the reasons discussed in this Section II, EPA concludes 
that new standards are warranted to address the emissions of these 
pollutants and their contribution to national air pollution. We note 
that in the summer of 2016 more than 20 organizations, including state 
and local air agencies from across the country, petitioned EPA to 
develop more stringent NOX emission standards for on-road 
heavy-duty engines.64 65 Among the reasons stated by the 
petitioners for such an EPA rulemaking was the need for NOX 
emission reductions to reduce adverse health and welfare impacts and to 
help areas attain the NAAQS. EPA responded to the petitions on December 
20, 2016, noting that an opportunity exists to develop a new national 
NOX reduction strategy for heavy-duty highway engines.\66\ 
We subsequently initiated this rulemaking and issued an Advanced Notice 
of Proposed Rulemaking in January 2020.\67\ This final rule culminates 
the rulemaking proceeding and is responsive to those petitions.
---------------------------------------------------------------------------

    \60\ Zawacki et al., 2018. Mobile source contributions to 
ambient ozone and particulate matter in 2025. Atmospheric 
Environment, Vol 188, pg 129-141. Available online: https://doi.org/10.1016/j.atmosenv.2018.04.057.
    \61\ Davidson et al., 2020. The recent and future health burden 
of the U.S. mobile sector apportioned by source. Environmental 
Research Letters. Available online: https://doi.org/10.1088/1748-9326/ab83a8.
    \62\ Sectors other than onroad and nonroad were projected from 
2016v1 Emissions Modeling Platform. https://www.epa.gov/air-emissions-modeling/2016v1-platform.
    \63\ U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3. 
https://www.epa.gov/moves.
    \64\ Brakora, Jessica. ``Petitions to EPA for Revised 
NOX Standards for Heavy-Duty Engines'' Memorandum to 
Docket EPA-HQ-OAR-2019-0055. December 4, 2019.
    \65\ 87 FR 17414, March 28, 2022.
    \66\ U.S. EPA. 2016. Memorandum in Response to Petition for 
Rulemaking to Adopt Ultra-Low NOX Standards for On-
Highway Heavy-Duty Trucks and Engines. Available at https://19january2017snapshot.epa.gov/sites/production/files/2016-12/documents/nox-memorandum-nox-petition-response-2016-12-20.pdf.
    \67\ The Agency published an ANPR on January 21, 2020 to present 
EPA's early thinking on this rulemaking and solicit feedback from 
stakeholders to inform this proposal (85 FR 3306).
---------------------------------------------------------------------------

    Many state and local agencies across the country commented on the 
NPRM and have asked the EPA to reduce NOX emissions, 
specifically from heavy-duty engines, because such reductions will be a 
critical part of many areas' strategies to attain and maintain the 
ozone and PM NAAQS. These state and local agencies anticipate 
challenges in attaining the NAAQS, maintaining the NAAQS in the future, 
and/or preventing nonattainment. Some nonattainment areas have already 
been ``bumped up'' to higher classifications because of challenges in 
attaining the NAAQS; others say they are struggling to avoid 
nonattainment.\68\ Others note that the ozone and PM NAAQS are being 
reconsidered so they could be made more stringent in the 
future.69 70 Many state and local agencies commented on the 
NPRM that heavy-duty vehicles are one of their largest sources of 
NOX emissions. They commented that without action to reduce 
emissions from heavy-duty vehicles, they will have to adopt other 
potentially more burdensome and costly measures to reduce emissions 
from other sources under their state or local authority, such as local 
businesses. More information on the projected emission reductions and 
air quality impacts that will result from this rule is provided in 
Sections VI and VII.
---------------------------------------------------------------------------

    \68\ For example, in September 2019 several 2008 ozone 
nonattainment areas were reclassified from moderate to serious, 
including Dallas, Chicago, Connecticut, New York/New Jersey and 
Houston, and in January 2020, Denver. Also, on September 15, 2022, 
EPA finalized reclassification, bumping up 5 areas in nonattainment 
of the 2008 ozone NAAQS from serious to severe and 22 areas in 
nonattainment of the 2015 ozone NAAQS from marginal to moderate. The 
2008 NAAQS for ozone is an 8-hour standard with a level of 0.075 
ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.
    \69\ https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone.
    \70\ https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm.
---------------------------------------------------------------------------

    In their comments on the NPRM, many nonprofit groups, citizen 
groups, individuals, and state, local, and Tribal organizations 
emphasized the role that emissions from trucks have in harming 
communities and that communities living near truck routes are 
disproportionately people of color and those with lower incomes. They 
supported additional NOX reductions from heavy-duty vehicles 
to address concerns about environmental justice and ensuring that all 
communities benefit from improvements in air quality. In addition, many 
groups and commenters noted the link between emissions from heavy duty 
trucks and harmful health effects, in particular asthma in children. 
Commenters also supported additional NOX reductions from 
heavy-duty vehicles to address concerns about regional haze, and damage 
to terrestrial and aquatic ecosystems. They mentioned the impacts of 
NOX emissions on numerous locations, such as the Chesapeake 
Bay, Long Island Sound, the Rocky Mountains, Sierra Nevada Mountains, 
Appalachian Mountains, Southwestern Desert ecosystems, and other areas. 
For further detail regarding these comments and EPA's responses, see 
Section 2 of the Response to Comments document for this rulemaking.

A. Background on Pollutants Impacted by This Proposal

1. Ozone
    Ground-level ozone pollution forms in areas with high 
concentrations of ambient nitrogen oxides (NOX) and

[[Page 4314]]

volatile organic compounds (VOCs) when solar radiation is strong. Major 
U.S. sources of NOX are highway and nonroad motor vehicles, 
engines, power plants and other industrial sources, with natural 
sources, such as soil, vegetation, and lightning, serving as smaller 
sources. Vegetation is the dominant source of VOCs in the United 
States. Volatile consumer and commercial products, such as propellants 
and solvents, highway and nonroad vehicles, engines, fires, and 
industrial sources also contribute to the atmospheric burden of VOCs at 
ground-level.
    The processes underlying ozone formation, transport, and 
accumulation are complex. Ground-level ozone is produced and destroyed 
by an interwoven network of free radical reactions involving the 
hydroxyl radical (OH), NO, NO2, and complex reaction 
intermediates derived from VOCs. Many of these reactions are sensitive 
to temperature and available sunlight. High ozone events most often 
occur when ambient temperatures and sunlight intensities remain high 
for several days under stagnant conditions. Ozone and its precursors 
can also be transported hundreds of miles downwind, which can lead to 
elevated ozone levels in areas with otherwise low VOC or NOX 
emissions. As an air mass moves and is exposed to changing ambient 
concentrations of NOX and VOCs, the ozone photochemical 
regime (relative sensitivity of ozone formation to NOX and 
VOC emissions) can change.
    When ambient VOC concentrations are high, comparatively small 
amounts of NOX catalyze rapid ozone formation. Without 
available NOX, ground-level ozone production is severely 
limited, and VOC reductions would have little impact on ozone 
concentrations. Photochemistry under these conditions is said to be 
``NOX-limited.'' When NOX levels are sufficiently 
high, faster NO2 oxidation consumes more radicals, dampening 
ozone production. Under these ``VOC-limited'' conditions (also referred 
to as ``NOX-saturated'' conditions), VOC reductions are 
effective in reducing ozone, and NOX can react directly with 
ozone, resulting in suppressed ozone concentrations near NOX 
emission sources. Under these NOX-saturated conditions, 
NOX reductions can actually increase local ozone under 
certain circumstances, but overall ozone production (considering 
downwind formation) decreases. Even in VOC-limited areas, 
NOX reductions are not expected to increase ozone levels if 
the NOX reductions are sufficiently large--large enough to 
become NOX-limited.
    The primary NAAQS for ozone, established in 2015 and retained in 
2020, is an 8-hour standard with a level of 0.07 ppm.\71\ EPA announced 
that it will reconsider the decision to retain the ozone NAAQS.\72\ The 
EPA is also implementing the previous 8-hour ozone primary standard, 
set in 2008, at a level of 0.075 ppm. As of August 31, 2022, there were 
34 ozone nonattainment areas for the 2008 ozone NAAQS, composed of 141 
full or partial counties, with a population of more than 90 million, 
and 49 ozone nonattainment areas for the 2015 ozone NAAQS, composed of 
212 full or partial counties, with a population of more than 125 
million. In total, there are currently, as of August 31, 2022, 57 ozone 
nonattainment areas with a population of more than 130 million 
people.\73\
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    \71\ https://www.epa.gov/ground-level-ozone-pollution/ozone-national-ambient-air-quality-standards-naaqs.
    \72\ https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone.
    \73\ The population total is calculated by summing, without 
double counting, the 2008 and 2015 ozone nonattainment populations 
contained in the Criteria Pollutant Nonattainment Summary report 
(https://www.epa.gov/green-book/green-book-data-download).
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    States with ozone nonattainment areas are required to take action 
to bring those areas into attainment. The attainment date assigned to 
an ozone nonattainment area is based on the area's classification. The 
attainment dates for areas designated nonattainment for the 2008 8-hour 
ozone NAAQS are in the 2015 to 2032 timeframe, depending on the 
severity of the problem in each area. Attainment dates for areas 
designated nonattainment for the 2015 ozone NAAQS are in the 2021 to 
2038 timeframe, again depending on the severity of the problem in each 
area.\74\ The final NOX standards will take effect starting 
in MY 2027 and will assist areas with attaining the NAAQS and may 
relieve areas with already stringent local regulations from some of the 
burden associated with adopting additional local controls.\75\ The rule 
will also provide assistance to counties with ambient concentrations 
near the level of the NAAQS who are working to ensure long-term 
attainment or maintenance of the NAAQS.
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    \74\ https://www.epa.gov/ground-level-ozone-pollution/ozone-naaqs-timelines.
    \75\ While not quantified in the air quality modeling analysis 
for this rule, elements of the Averaging, Banking, and Trading (ABT) 
program could encourage manufacturers to introduce new emission 
control technologies prior to the 2027 model year, which may help to 
accelerate some emission reductions of the final rule (See Preamble 
Section IV.G for more details on the ABT program in the final rule). 
In RIA Chapter 5.5 we also include a sensitivity analysis that shows 
allowing manufacturers to generate NOX emissions credits 
by meeting requirements of the final rule one model year before 
required would lead to meaningful, additional reductions in 
NOX emissions in the early years of the program compared 
to the emissions reductions expected from the final rule (see 
preamble Section IV.G.7 and RIA Chapter 5.5 for additional details).
---------------------------------------------------------------------------

2. Particulate Matter
    Particulate matter (PM) is a complex mixture of solid particles and 
liquid droplets distributed among numerous atmospheric gases which 
interact with solid and liquid phases. Particles in the atmosphere 
range in size from less than 0.01 to more than 10 micrometers ([mu]m) 
in diameter.\76\ Atmospheric particles can be grouped into several 
classes according to their aerodynamic diameter and physical sizes. 
Generally, the three broad classes of particles include ultrafine 
particles (UFPs, generally considered as particles with a diameter less 
than or equal to 0.1 [mu]m [typically based on physical size, thermal 
diffusivity or electrical mobility]), ``fine'' particles 
(PM2.5; particles with a nominal mean aerodynamic diameter 
less than or equal to 2.5 [mu]m), and ``thoracic'' particles 
(PM10; particles with a nominal mean aerodynamic diameter 
less than or equal to 10 [mu]m). Particles that fall within the size 
range between PM2.5 and PM10, are referred to as 
``thoracic coarse particles'' (PM10-2.5, 
particles with a nominal mean aerodynamic diameter greater than 2.5 
[mu]m and less than or equal to 10 [mu]m). EPA currently has NAAQS for 
PM2.5 and PM10.\77\
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    \76\ U.S. EPA. Policy Assessment (PA) for the Review of the 
National Ambient Air Quality Standards for Particulate Matter (Final 
Report, 2020). U.S. Environmental Protection Agency, Washington, DC, 
EPA/452/R-20/002, 2020.
    \77\ Regulatory definitions of PM size fractions, and 
information on reference and equivalent methods for measuring PM in 
ambient air, are provided in 40 CFR parts 50, 53, and 58. With 
regard to NAAQS which provide protection against health and welfare 
effects, the 24-hour PM10 standard provides protection 
against effects associated with short-term exposure to thoracic 
coarse particles (i.e., PM10-2.5).
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    Most particles are found in the lower troposphere, where they can 
have residence times ranging from a few hours to weeks. Particles are 
removed from the atmosphere by wet deposition, such as when they are 
carried by rain or snow, or by dry deposition, when particles settle 
out of suspension due to gravity. Atmospheric lifetimes are generally 
longest for PM2.5, which often remains in the atmosphere for 
days to weeks before being removed by wet or dry deposition.\78\ In 
contrast,

[[Page 4315]]

atmospheric lifetimes for UFP and PM10-2.5 are 
shorter. Within hours, UFP can undergo coagulation and condensation 
that lead to formation of larger particles, or can be removed from the 
atmosphere by evaporation, deposition, or reactions with other 
atmospheric components. PM10-2.5 are also 
generally removed from the atmosphere within hours, through wet or dry 
deposition.\79\
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    \78\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
    \79\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
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    Particulate matter consists of both primary and secondary 
particles. Primary particles are emitted directly from sources, such as 
combustion-related activities (e.g., industrial activities, motor 
vehicle operation, biomass burning), while secondary particles are 
formed through atmospheric chemical reactions of gaseous precursors 
(e.g., sulfur oxides (SOX), NOX, and VOCs).
    There are two primary NAAQS for PM2.5: An annual 
standard (12.0 micrograms per cubic meter ([mu]g/m\3\)) and a 24-hour 
standard (35 [mu]g/m\3\), and there are two secondary NAAQS for 
PM2.5: An annual standard (15.0 [mu]g/m\3\) and a 24-hour 
standard (35 [mu]g/m\3\). The initial PM2.5 standards were 
set in 1997 and revisions to the standards were finalized in 2006 and 
in December 2012 and then retained in 2020. On June 10, 2021, EPA 
announced that it will reconsider the decision to retain the PM 
NAAQS.\80\
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    \80\ https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm.
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    There are many areas of the country that are currently in 
nonattainment for the annual and 24-hour primary PM2.5 
NAAQS. As of August 31, 2022, more than 19 million people lived in the 
4 areas that are designated as nonattainment for the 1997 
PM2.5 NAAQS. Also, as of August 31, 2022, more than 31 
million people lived in the 14 areas that are designated as 
nonattainment for the 2006 PM2.5 NAAQS and more than 20 
million people lived in the 5 areas designated as nonattainment for the 
2012 PM2.5 NAAQS. In total, there are currently 15 
PM2.5 nonattainment areas with a population of more than 32 
million people.\81\ The final NOX standards will take effect 
in MY 2027 and will assist areas with attaining the NAAQS and may 
relieve areas with already stringent local regulations from some of the 
burden associated with adopting additional local controls.\82\ The rule 
will also assist counties with ambient concentrations near the level of 
the NAAQS who are working to ensure long-term attainment or maintenance 
of the PM2.5 NAAQS.
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    \81\ The population total is calculated by summing, without 
double counting, the 1997, 2006 and 2012 PM2.5 
nonattainment populations contained in the Criteria Pollutant 
Nonattainment Summary report (https://www.epa.gov/green-book/green-book-data-download).
    \82\ While not quantified in the air quality modeling analysis 
for this rule, elements of the Averaging, Banking, and Trading (ABT) 
program could encourage manufacturers to introduce new emission 
control technologies prior to the 2027 model year, which may help to 
accelerate some emission reductions of the final rule (See Preamble 
Section IV.G for more details on the ABT program in the final rule).
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3. Nitrogen Oxides
    Oxides of nitrogen (NOX) refers to nitric oxide (NO) and 
nitrogen dioxide (NO2). Most NO2 is formed in the 
air through the oxidation of NO emitted when fuel is burned at a high 
temperature. NO2 is a criteria pollutant, regulated for its 
adverse effects on public health and the environment, and highway 
vehicles are an important contributor to NO2 emissions. 
NOX, along with VOCs, are the two major precursors of ozone 
and NOX is also a major contributor to secondary 
PM2.5 formation. There are two primary NAAQS for 
NO2: An annual standard (53 ppb) and a 1-hour standard (100 
ppb).\83\ In 2010, EPA established requirements for monitoring 
NO2 near roadways expected to have the highest 
concentrations within large cities. Monitoring within this near-roadway 
network began in 2014, with additional sites deployed in the following 
years. At present, there are no nonattainment areas for NO2.
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    \83\ The statistical form of the 1-hour NAAQS for NO2 
is the 3-year average of the yearly distribution of 1-hour daily 
maximum concentrations.
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4. Carbon Monoxide
    Carbon monoxide (CO) is a colorless, odorless gas emitted from 
combustion processes. Nationally, particularly in urban areas, the 
majority of CO emissions to ambient air come from mobile sources.\84\ 
There are two primary NAAQS for CO: An 8-hour standard (9 ppm) and a 1-
hour standard (35 ppm). There are currently no CO nonattainment areas; 
as of September 27, 2010, all CO nonattainment areas have been 
redesignated to attainment. The past designations were based on the 
existing community-wide monitoring network. EPA made an addition to the 
ambient air monitoring requirements for CO during the 2011 NAAQS 
review. Those new requirements called for CO monitors to be operated 
near roads in Core Based Statistical Areas (CBSAs) of 1 million or more 
persons, in addition to the existing community-based network (76 FR 
54294, August 31, 2011).
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    \84\ U.S. EPA, (2010). Integrated Science Assessment for Carbon 
Monoxide (Final Report). U.S. Environmental Protection Agency, 
Washington, DC, EPA/600/R-09/019F, 2010. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686. See Section 2.1.
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5. Diesel Exhaust
    Diesel exhaust is a complex mixture composed of particulate matter, 
carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide, 
nitrogen compounds, sulfur compounds and numerous low-molecular-weight 
hydrocarbons. A number of these gaseous hydrocarbon components are 
individually known to be toxic, including aldehydes, benzene and 1,3-
butadiene. The diesel particulate matter present in diesel exhaust 
consists mostly of fine particles (<2.5 [mu]m), of which a significant 
fraction is ultrafine particles (<0.1 [mu]m). These particles have a 
large surface area which makes them an excellent medium for adsorbing 
organics and their small size makes them highly respirable. Many of the 
organic compounds present in the gases and on the particles, such as 
polycyclic organic matter, are individually known to have mutagenic and 
carcinogenic properties.
    Diesel exhaust varies significantly in chemical composition and 
particle sizes between different engine types (heavy-duty, light-duty), 
engine operating conditions (idle, acceleration, deceleration), and 
fuel formulations (high/low sulfur fuel). Also, there are emissions 
differences between on-road and nonroad engines because the nonroad 
engines are generally of older technology. After being emitted in the 
engine exhaust, diesel exhaust undergoes dilution as well as chemical 
and physical changes in the atmosphere. The lifetime of the components 
present in diesel exhaust ranges from seconds to days.
    Because diesel particulate matter (DPM) is part of overall ambient 
PM, varies considerably in composition, and lacks distinct chemical 
markers that enable it to be easily distinguished from overall primary 
PM, we do not have direct measurements of DPM in the ambient air.\85\ 
DPM concentrations are

[[Page 4316]]

estimated using ambient air quality modeling based on DPM emission 
inventories. DPM emission inventories are computed as the exhaust PM 
emissions from mobile sources combusting diesel or residual oil fuel. 
DPM concentrations were estimated as part of the 2018 national Air 
Toxics Screening Assessment (AirToxScreen).\86\ Areas with high 
concentrations are clustered in the Northeast and Great Lake States, 
with a smaller number of higher concentration locations in Western 
states. The highest impacts occur in major urban cores, and are also 
distributed throughout the rest of the United States near high truck 
traffic, coasts with marine diesel activity, construction sites, and 
rail facilities. Approximately half of the average ambient DPM 
concentration in the United States can be attributed to heavy-duty 
diesel engines, with the remainder attributable to nonroad engines.
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    \85\ DPM in exhaust from a high-load, high-speed engine (e.g., 
heavy-duty truck engines) without aftertreatment such as a diesel 
particle filter (DPM) is mostly made of ``soot,'' consisting of 
elemental/black carbon (EC/BC), some organic material, and trace 
elements. At low loads, DPM in high-speed engine exhaust is mostly 
made of organic carbon (OC), with considerably less EC/BC. Low-speed 
diesel engines' (e.g., large marine engines) exhaust PM is comprised 
of more sulfate and less EC/BC, with OC contributing as well.
    \86\ U.S. EPA (2022) Technical Support Document EPA Air Toxics 
Screening Assessment. 2018AirToxScreen TSD. https://www.epa.gov/AirToxScreen/airtoxscreen-technical-support-document.
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6. Air Toxics
    The most recent available data indicate that millions of Americans 
live in areas where air toxics pose potential health concerns.\87\ The 
levels of air toxics to which people are exposed vary depending on 
where people live and work and the kinds of activities in which they 
engage, as discussed in detail in EPA's 2007 Mobile Source Air Toxics 
Rule.\88\ According to EPA's Air Toxics Screening Assessment 
(AirToxScreen) for 2018, mobile sources were responsible for 40 percent 
of outdoor anthropogenic toxic emissions and were the largest 
contributor to national average cancer and noncancer risk from directly 
emitted pollutants.89 90 Mobile sources are also significant 
contributors to precursor emissions which react to form air toxics.\91\ 
Formaldehyde is the largest contributor to cancer risk of all 71 
pollutants quantitatively assessed in the 2018 AirToxScreen. Mobile 
sources were responsible for 26 percent of primary anthropogenic 
emissions of this pollutant in 2018 and are significant contributors to 
formaldehyde precursor emissions. Benzene is also a large contributor 
to cancer risk, and mobile sources account for about 60 percent of 
average exposure to ambient concentrations.
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    \87\ U.S. EPA (2022) Technical Support Document EPA Air Toxics 
Screening Assessment. 2017AirToxScreen TSD. https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf.
    \88\ U.S. Environmental Protection Agency (2007). Control of 
Hazardous Air Pollutants from Mobile Sources; Final Rule. 72 FR 
8434, February 26, 2007.
    \89\ U.S. EPA. (2022) Air Toxics Screening Assessment. https://www.epa.gov/AirToxScreen/2018-airtoxscreen-assessment-results.
    \90\ AirToxScreen also includes estimates of risk attributable 
to background concentrations, which includes contributions from 
long-range transport, persistent air toxics, and natural sources; as 
well as secondary concentrations, where toxics are formed via 
secondary formation. Mobile sources substantially contribute to 
long-range transport and secondarily formed air toxics.
    \91\ Rich Cook, Sharon Phillips, Madeleine Strum, Alison Eyth & 
James Thurman (2020): Contribution of mobile sources to secondary 
formation of carbonyl compounds, Journal of the Air & Waste 
Management Association, DOI: 10.1080/10962247.2020.1813839.
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B. Health Effects Associated With Exposure to Pollutants Impacted by 
This Rule

    Heavy-duty engines emit pollutants that contribute to ambient 
concentrations of ozone, PM, NO2, CO, and air toxics. This 
section of the preamble discusses the health effects associated with 
exposure to these pollutants.
    Additionally, because children have increased vulnerability and 
susceptibility for adverse health effects related to air pollution 
exposures, EPA's findings regarding adverse effects for children 
related to exposure to pollutants that are impacted by this rule are 
noted in this section. The increased vulnerability and susceptibility 
of children to air pollution exposures may arise because infants and 
children generally breathe more relative to their size than adults do, 
and consequently may be exposed to relatively higher amounts of air 
pollution.\92\ Children also tend to breathe through their mouths more 
than adults and their nasal passages are less effective at removing 
pollutants, which leads to greater lung deposition of some pollutants, 
such as PM.93 94 Furthermore, air pollutants may pose health 
risks specific to children because children's bodies are still 
developing.\95\ For example, during periods of rapid growth such as 
fetal development, infancy, and puberty, their developing systems and 
organs may be more easily harmed.96 97 EPA's America's 
Children and the Environment is a tool which presents national trends 
on air pollutants and other contaminants and environmental health of 
children.\98\
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    \92\ EPA (2009) Metabolically-derived ventilation rates: A 
revised approach based upon oxygen consumption rates. Washington, 
DC: Office of Research and Development. EPA/600/R-06/129F. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=202543.
    \93\ U.S. EPA Integrated Science Assessment for Particulate 
Matter (Final Report, 2019). U.S. Environmental Protection Agency, 
Washington, DC, EPA/600/R-19/188, 2019. Chapter 4 ``Overall 
Conclusions'' p. 4-1.
    \94\ Foos, B.; Marty, M.; Schwartz, J.; Bennet, W.; Moya, J.; 
Jarabek, A.M.; Salmon, A.G. (2008) Focusing on children's inhalation 
dosimetry and health effects for risk assessment: An introduction. J 
Toxicol Environ Health 71A: 149-165.
    \95\ Children's environmental health includes conception, 
infancy, early childhood and through adolescence until 21 years of 
age as described in the EPA Memorandum: Issuance of EPA's 2021 
Policy on Children's Health. October 5, 2021. Available at https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf.
    \96\ EPA (2006) A Framework for Assessing Health Risks of 
Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-
05/093F, 2006.
    \97\ U.S. Environmental Protection Agency. (2005). Supplemental 
guidance for assessing susceptibility from early-life exposure to 
carcinogens. Washington, DC: Risk Assessment Forum. EPA/630/R-03/
003F. https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf.
    \98\ U.S. EPA. America's Children and the Environment. Available 
at: https://www.epa.gov/americaschildrenenvironment.
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    Information on environmental effects associated with exposure to 
these pollutants is included in Section II.C, and information on 
environmental justice is included in Section VII.H. Information on 
emission reductions and air quality impacts from this rule are included 
in Section VI and VII.
1. Ozone
    This section provides a summary of the health effects associated 
with exposure to ambient concentrations of ozone.\99\ The information 
in this section is based on the information and conclusions in the 
April 2020 Integrated Science Assessment for Ozone (Ozone ISA).\100\ 
The Ozone ISA concludes that human exposures to ambient concentrations 
of ozone are associated with a number of adverse health effects and 
characterizes the weight of evidence for these health effects.\101\ The 
following discussion highlights the Ozone ISA's

[[Page 4317]]

conclusions pertaining to health effects associated with both short-
term and long-term periods of exposure to ozone.
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    \99\ Human exposure to ozone varies over time due to changes in 
ambient ozone concentration and because people move between 
locations which have notably different ozone concentrations. Also, 
the amount of ozone delivered to the lung is influenced not only by 
the ambient concentrations but also by the breathing route and rate.
    \100\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone 
and Related Photochemical Oxidants (Final Report). U.S. 
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012, 
2020.
    \101\ The ISA evaluates evidence and draws conclusions on the 
causal relationship between relevant pollutant exposures and health 
effects, assigning one of five ``weight of evidence'' 
determinations: causal relationship, likely to be a causal 
relationship, suggestive of a causal relationship, inadequate to 
infer a causal relationship, and not likely to be a causal 
relationship. For more information on these levels of evidence, 
please refer to Table II in the Preamble of the ISA.
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    For short-term exposure to ozone, the Ozone ISA concludes that 
respiratory effects, including lung function decrements, pulmonary 
inflammation, exacerbation of asthma, respiratory-related hospital 
admissions, and mortality, are causally associated with ozone exposure. 
It also concludes that metabolic effects, including metabolic syndrome 
(i.e., changes in insulin or glucose levels, cholesterol levels, 
obesity, and blood pressure) and complications due to diabetes are 
likely to be causally associated with short-term exposure to ozone. The 
evidence is also suggestive of a causal relationship between short-term 
exposure to ozone and cardiovascular effects, central nervous system 
effects, and total mortality.
    For long-term exposure to ozone, the Ozone ISA concludes that 
respiratory effects, including new onset asthma, pulmonary 
inflammation, and injury, are likely to be causally related with ozone 
exposure. The Ozone ISA characterizes the evidence as suggestive of a 
causal relationship for associations between long-term ozone exposure 
and cardiovascular effects, metabolic effects, reproductive and 
developmental effects, central nervous system effects, and total 
mortality. The evidence is inadequate to infer a causal relationship 
between chronic ozone exposure and increased risk of cancer.
    Finally, interindividual variation in human responses to ozone 
exposure can result in some groups being at increased risk for 
detrimental effects in response to exposure. In addition, some groups 
are at increased risk of exposure due to their activities, such as 
outdoor workers and children. The Ozone ISA identified several groups 
that are at increased risk for ozone-related health effects. These 
groups are people with asthma, children and older adults, individuals 
with reduced intake of certain nutrients (i.e., Vitamins C and E), 
outdoor workers, and individuals having certain genetic variants 
related to oxidative metabolism or inflammation. Ozone exposure during 
childhood can have lasting effects through adulthood. Such effects 
include altered function of the respiratory and immune systems. 
Children absorb higher doses (normalized to lung surface area) of 
ambient ozone, compared to adults, due to their increased time spent 
outdoors, higher ventilation rates relative to body size, and a 
tendency to breathe a greater fraction of air through the mouth. 
Children also have a higher asthma prevalence compared to adults. 
Recent epidemiologic studies provide generally consistent evidence that 
long-term ozone exposure is associated with the development of asthma 
in children. Studies comparing age groups reported higher magnitude 
associations for short-term ozone exposure and respiratory hospital 
admissions and emergency room visits among children than among adults. 
Panel studies also provide support for experimental studies with 
consistent associations between short-term ozone exposure and lung 
function and pulmonary inflammation in healthy children. Additional 
children's vulnerability and susceptibility factors are listed in 
Section XII of this preamble.
2. Particulate Matter
    Scientific evidence spanning animal toxicological, controlled human 
exposure, and epidemiologic studies shows that exposure to ambient PM 
is associated with a broad range of health effects. These health 
effects are discussed in detail in the Integrated Science Assessment 
for Particulate Matter, which was finalized in December 2019 (PM ISA). 
In addition, there is a more targeted evaluation of studies published 
since the literature cutoff date of the 2019 p.m. ISA in the Supplement 
to the Integrated Science Assessment for PM 
(Supplement).102 103 The PM ISA characterizes the causal 
nature of relationships between PM exposure and broad health categories 
(e.g., cardiovascular effects, respiratory effects, etc.) using a 
weight-of-evidence approach.\104\ Within this characterization, the PM 
ISA summarizes the health effects evidence for short-term (i.e., hours 
up to one month) and long-term (i.e., one month to years) exposures to 
PM2.5, PM10-2.5, and 
ultrafine particles, and concludes that exposures to ambient 
PM2.5 are associated with a number of adverse health 
effects. The following discussion highlights the PM ISA's conclusions, 
and summarizes additional information from the Supplement where 
appropriate, pertaining to the health effects evidence for both short- 
and long-term PM exposures. Further discussion of PM-related health 
effects can also be found in the 2022 Policy Assessment for the review 
of the PM NAAQS.\105\
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    \102\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \103\ U.S. EPA. Supplement to the 2019 Integrated Science 
Assessment for Particulate Matter (Final Report, 2022). U.S. 
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028, 
2022.
    \104\ The causal framework draws upon the assessment and 
integration of evidence from across scientific disciplines, spanning 
atmospheric chemistry, exposure, dosimetry and health effects 
studies (i.e., epidemiologic, controlled human exposure, and animal 
toxicological studies), and assess the related uncertainties and 
limitations that ultimately influence our understanding of the 
evidence. This framework employs a five-level hierarchy that 
classifies the overall weight-of-evidence with respect to the causal 
nature of relationships between criteria pollutant exposures and 
health and welfare effects using the following categorizations: 
causal relationship; likely to be causal relationship; suggestive 
of, but not sufficient to infer, a causal relationship; inadequate 
to infer the presence or absence of a causal relationship; and not 
likely to be a causal relationship (U.S. EPA. (2019). Integrated 
Science Assessment for Particulate Matter (Final Report). U.S. 
Environmental Protection Agency, Washington, DC, EPA/600/R-19/188, 
Section P. 3.2.3).
    \105\ U.S. EPA. Policy Assessment (PA) for the Reconsideration 
of the National Ambient Air Quality Standards for Particulate Matter 
(Final Report, 2022). U.S. Environmental Protection Agency, 
Washington, DC, EPA-452/R-22-004, 2022.
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    EPA has concluded that recent evidence in combination with evidence 
evaluated in the 2009 p.m. ISA supports a ``causal relationship'' 
between both long- and short-term exposures to PM2.5 and 
premature mortality and cardiovascular effects and a ``likely to be 
causal relationship'' between long- and short-term PM2.5 
exposures and respiratory effects.\106\ Additionally, recent 
experimental and epidemiologic studies provide evidence supporting a 
``likely to be causal relationship'' between long-term PM2.5 
exposure and nervous system effects, and long-term PM2.5 
exposure and cancer. Because of remaining uncertainties and limitations 
in the evidence base, EPA determined a ``suggestive of, but not 
sufficient to infer, a causal relationship'' for long-term 
PM2.5 exposure and reproductive and developmental effects 
(i.e., male/female reproduction and fertility; pregnancy and birth 
outcomes), long- and short-term exposures and metabolic effects, and 
short-term exposure and nervous system effects.
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    \106\ U.S. EPA. (2009). Integrated Science Assessment for 
Particulate Matter (Final Report). U.S. Environmental Protection 
Agency, Washington, DC, EPA/600/R-08/139F.
---------------------------------------------------------------------------

    As discussed extensively in the 2019 p.m. ISA and the Supplement, 
recent studies continue to support a ``causal relationship'' between 
short- and long-term PM2.5 exposures and 
mortality.107 108 For short-term PM2.5 exposure, 
multi-city studies, in combination with single- and multi-city studies 
evaluated in the 2009 p.m. ISA,

[[Page 4318]]

provide evidence of consistent, positive associations across studies 
conducted in different geographic locations, populations with different 
demographic characteristics, and studies using different exposure 
assignment techniques. Additionally, the consistent and coherent 
evidence across scientific disciplines for cardiovascular morbidity, 
particularly ischemic events and heart failure, and to a lesser degree 
for respiratory morbidity, including exacerbations of chronic 
obstructive pulmonary disease (COPD) and asthma, provide biological 
plausibility for cause-specific mortality and ultimately total 
mortality. Recent epidemiologic studies evaluated in the Supplement, 
including studies that employed alternative methods for confounder 
control, provide additional support to the evidence base that 
contributed to the 2019 p.m. ISA conclusion for short-term 
PM2.5 exposure and mortality.
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    \107\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \108\ U.S. EPA. Supplement to the 2019 Integrated Science 
Assessment for Particulate Matter (Final Report, 2022). U.S. 
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028, 
2022.
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    The 2019 p.m. ISA concluded a ``causal relationship'' between long-
term PM2.5 exposure and mortality. In addition to reanalyses 
and extensions of the American Cancer Society (ACS) and Harvard Six 
Cities (HSC) cohorts, multiple new cohort studies conducted in the 
United States and Canada consisting of people employed in a specific 
job (e.g., teacher, nurse), and that apply different exposure 
assignment techniques, provide evidence of positive associations 
between long-term PM2.5 exposure and mortality. Biological 
plausibility for mortality due to long-term PM2.5 exposure 
is provided by the coherence of effects across scientific disciplines 
for cardiovascular morbidity, particularly for coronary heart disease, 
stroke, and atherosclerosis, and for respiratory morbidity, 
particularly for the development of COPD. Additionally, recent studies 
provide evidence indicating that as long-term PM2.5 
concentrations decrease there is an increase in life expectancy. Recent 
cohort studies evaluated in the Supplement, as well as epidemiologic 
studies that conducted accountability analyses or employed alternative 
methods for confounder controls, support and extend the evidence base 
that contributed to the 2019 p.m. ISA conclusion for long-term 
PM2.5 exposure and mortality.
    A large body of studies examining both short- and long-term 
PM2.5 exposure and cardiovascular effects builds on the 
evidence base evaluated in the 2009 p.m. ISA. The strongest evidence 
for cardiovascular effects in response to short-term PM2.5 
exposures is for ischemic heart disease and heart failure. The evidence 
for short-term PM2.5 exposure and cardiovascular effects is 
coherent across scientific disciplines and supports a continuum of 
effects ranging from subtle changes in indicators of cardiovascular 
health to serious clinical events, such as increased emergency 
department visits and hospital admissions due to cardiovascular disease 
and cardiovascular mortality. For long-term PM2.5 exposure, 
there is strong and consistent epidemiologic evidence of a relationship 
with cardiovascular mortality. This evidence is supported by 
epidemiologic and animal toxicological studies demonstrating a range of 
cardiovascular effects including coronary heart disease, stroke, 
impaired heart function, and subclinical markers (e.g., coronary artery 
calcification, atherosclerotic plaque progression), which collectively 
provide coherence and biological plausibility. Recent epidemiologic 
studies evaluated in the Supplement, as well as studies that conducted 
accountability analyses or employed alternative methods for confounder 
control, support and extend the evidence base that contributed to the 
2019 p.m. ISA conclusion for both short- and long-term PM2.5 
exposure and cardiovascular effects.
    Studies evaluated in the 2019 p.m. ISA continue to provide evidence 
of a ``likely to be causal relationship'' between both short- and long-
term PM2.5 exposure and respiratory effects. Epidemiologic 
studies provide consistent evidence of a relationship between short-
term PM2.5 exposure and asthma exacerbation in children and 
COPD exacerbation in adults, as indicated by increases in emergency 
department visits and hospital admissions, which is supported by animal 
toxicological studies indicating worsening allergic airways disease and 
subclinical effects related to COPD. Epidemiologic studies also provide 
evidence of a relationship between short-term PM2.5 exposure 
and respiratory mortality. However, there is inconsistent evidence of 
respiratory effects, specifically lung function declines and pulmonary 
inflammation, in controlled human exposure studies. With respect to 
long term PM2.5 exposure, epidemiologic studies conducted in 
the United States and abroad provide evidence of a relationship with 
respiratory effects, including consistent changes in lung function and 
lung function growth rate, increased asthma incidence, asthma 
prevalence, and wheeze in children; acceleration of lung function 
decline in adults; and respiratory mortality. The epidemiologic 
evidence is supported by animal toxicological studies, which provide 
coherence and biological plausibility for a range of effects including 
impaired lung development, decrements in lung function growth, and 
asthma development.
    Since the 2009 p.m. ISA, a growing body of scientific evidence 
examined the relationship between long-term PM2.5 exposure 
and nervous system effects, resulting for the first time in a causality 
determination for this health effects category of a ``likely to be 
causal relationship.'' The strongest evidence for effects on the 
nervous system come from epidemiologic studies that consistently report 
cognitive decrements and reductions in brain volume in adults. The 
effects observed in epidemiologic studies in adults are supported by 
animal toxicological studies demonstrating effects on the brain of 
adult animals including inflammation, morphologic changes, and 
neurodegeneration of specific regions of the brain. There is more 
limited evidence for neurodevelopmental effects in children, with some 
studies reporting positive associations with autism spectrum disorder 
and others providing limited evidence of an association with cognitive 
function. While there is some evidence from animal toxicological 
studies indicating effects on the brain (i.e., inflammatory and 
morphological changes) to support a biologically plausible pathway for 
neurodevelopmental effects, epidemiologic studies are limited due to 
their lack of control for potential confounding by copollutants, the 
small number of studies conducted, and uncertainty regarding critical 
exposure windows.
    Building off the decades of research demonstrating mutagenicity, 
DNA damage, and other endpoints related to genotoxicity due to whole PM 
exposures, recent experimental and epidemiologic studies focusing 
specifically on PM2.5 provide evidence of a relationship 
between long-term PM2.5 exposure and cancer. Epidemiologic 
studies examining long-term PM2.5 exposure and lung cancer 
incidence and mortality provide evidence of generally positive 
associations in cohort studies spanning different populations, 
locations, and exposure assignment techniques. Additionally, there is 
evidence of positive associations with lung cancer incidence and 
mortality in analyses limited to never smokers. In addition, 
experimental and epidemiologic studies of genotoxicity, epigenetic 
effects, carcinogenic potential, and that PM2.5 exhibits 
several characteristics of

[[Page 4319]]

carcinogens provide biological plausibility for cancer development. 
This collective body of evidence contributed to the conclusion of a 
``likely to be causal relationship.''
    For the additional health effects categories evaluated for 
PM2.5 in the 2019 p.m. ISA, experimental and epidemiologic 
studies provide limited and/or inconsistent evidence of a relationship 
with PM2.5 exposure. As a result, the 2019 p.m. ISA 
concluded that the evidence is ``suggestive of, but not sufficient to 
infer a causal relationship'' for short-term PM2.5 exposure 
and metabolic effects and nervous system effects, and long-term 
PM2.5 exposures and metabolic effects as well as 
reproductive and developmental effects.
    In addition to evaluating the health effects attributed to short- 
and long-term exposure to PM2.5, the 2019 p.m. ISA also 
conducted an extensive evaluation as to whether specific components or 
sources of PM2.5 are more strongly related with health 
effects than PM2.5 mass. An evaluation of those studies 
resulted in the 2019 p.m. ISA concluding that ``many PM2.5 
components and sources are associated with many health effects, and the 
evidence does not indicate that any one source or component is 
consistently more strongly related to health effects than 
PM2.5 mass.'' \109\
---------------------------------------------------------------------------

    \109\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
---------------------------------------------------------------------------

    For both PM10-2.5 and UFPs, for all health effects 
categories evaluated, the 2019 p.m. ISA concluded that the evidence was 
``suggestive of, but not sufficient to infer, a causal relationship'' 
or ``inadequate to determine the presence or absence of a causal 
relationship.'' For PM10-2.5, although a Federal Reference 
Method (FRM) was instituted in 2011 to measure PM10-2.5 
concentrations nationally, the causality determinations reflect that 
the same uncertainty identified in the 2009 p.m. ISA persists with 
respect to the method used to estimate PM10-2.5 
concentrations in epidemiologic studies. Specifically, across 
epidemiologic studies, different approaches are used to estimate 
PM10-2.5 concentrations (e.g., direct measurement of 
PM10-2.5, difference between PM10 and 
PM2.5 concentrations), and it remains unclear how well 
correlated PM10-2.5 concentrations are both spatially and 
temporally across the different methods used.
    For UFPs, which have often been defined as particles <0.1 [micro]m, 
the uncertainty in the evidence for the health effect categories 
evaluated across experimental and epidemiologic studies reflects the 
inconsistency in the exposure metric used (i.e., particle number 
concentration, surface area concentration, mass concentration) as well 
as the size fractions examined. In epidemiologic studies the size 
fraction examined can vary depending on the monitor used and exposure 
metric, with some studies examining number count over the entire 
particle size range, while experimental studies that use a particle 
concentrator often examine particles up to 0.3 [micro]m. Additionally, 
due to the lack of a monitoring network, there is limited information 
on the spatial and temporal variability of UFPs within the United 
States, as well as population exposures to UFPs, which adds uncertainty 
to epidemiologic study results.
    The 2019 p.m. ISA cites extensive evidence indicating that ``both 
the general population as well as specific populations and life stages 
are at risk for PM2.5-related health effects.'' \110\ For 
example, in support of its ``causal'' and ``likely to be causal'' 
determinations, the ISA cites substantial evidence for (1) PM-related 
mortality and cardiovascular effects in older adults; (2) PM-related 
cardiovascular effects in people with pre-existing cardiovascular 
disease; (3) PM-related respiratory effects in people with pre-existing 
respiratory disease, particularly asthma exacerbations in children; and 
(4) PM-related impairments in lung function growth and asthma 
development in children. The ISA additionally notes that stratified 
analyses (i.e., analyses that directly compare PM-related health 
effects across groups) provide strong evidence for racial and ethnic 
differences in PM2.5 exposures and in the risk of 
PM2.5-related health effects, specifically within Hispanic 
and non-Hispanic Black populations, with some evidence of increased 
risk for populations of low socioeconomic status. Recent studies 
evaluated in the Supplement support the conclusion of the 2019 p.m. ISA 
with respect to disparities in both PM2.5 exposure and 
health risk by race and ethnicity and provide additional support for 
disparities for populations of lower socioeconomic status.\111\ 
Additionally, evidence spanning epidemiologic studies that conducted 
stratified analyses, experimental studies focusing on animal models of 
disease or individuals with pre-existing disease, dosimetry studies, as 
well as studies focusing on differential exposure suggest that 
populations with pre-existing cardiovascular or respiratory disease, 
populations that are overweight or obese, populations that have 
particular genetic variants, and current/former smokers could be at 
increased risk for adverse PM2.5-related health effects. The 
2022 Policy Assessment for the review of the PM NAAQS also highlights 
that factors that may contribute to increased risk of PM2.5-
related health effects include lifestage (children and older adults), 
pre-existing diseases (cardiovascular disease and respiratory disease), 
race/ethnicity, and socioeconomic status.\112\
---------------------------------------------------------------------------

    \110\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \111\ U.S. EPA. Supplement to the 2019 Integrated Science 
Assessment for Particulate Matter (Final Report, 2022). U.S. 
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028, 
2022.
    \112\ U.S. EPA. Policy Assessment (PA) for the Reconsideration 
of the National Ambient Air Quality Standards for Particulate Matter 
(Final Report, 2022). U.S. Environmental Protection Agency, 
Washington, DC, EPA-452/R-22-004, 2022, p. 3-53.
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3. Nitrogen Oxides
    The most recent review of the health effects of oxides of nitrogen 
completed by EPA can be found in the 2016 Integrated Science Assessment 
for Oxides of Nitrogen--Health Criteria (ISA for Oxides of 
Nitrogen).\113\ The primary source of NO2 is motor vehicle 
emissions, and ambient NO2 concentrations tend to be highly 
correlated with other traffic-related pollutants. Thus, a key issue in 
characterizing the causality of NO2-health effect 
relationships consists of evaluating the extent to which studies 
supported an effect of NO2 that is independent of other 
traffic-related pollutants. EPA concluded that the findings for asthma 
exacerbation integrated from epidemiologic and controlled human 
exposure studies provided evidence that is sufficient to infer a causal 
relationship between respiratory effects and short-term NO2 
exposure. The strongest evidence supporting an independent effect of 
NO2 exposure comes from controlled human exposure studies 
demonstrating increased airway responsiveness in individuals with 
asthma following ambient-relevant NO2 exposures. The 
coherence of this evidence with epidemiologic findings for asthma 
hospital admissions and emergency department visits as well as lung 
function decrements and increased pulmonary inflammation in children 
with asthma describe a plausible pathway by which NO2 
exposure can

[[Page 4320]]

cause an asthma exacerbation. The 2016 ISA for Oxides of Nitrogen also 
concluded that there is likely to be a causal relationship between 
long-term NO2 exposure and respiratory effects. This 
conclusion is based on new epidemiologic evidence for associations of 
NO2 with asthma development in children combined with 
biological plausibility from experimental studies.
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    \113\ U.S. EPA. Integrated Science Assessment for Oxides of 
Nitrogen--Health Criteria (2016 Final Report). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-15/068, 2016.
---------------------------------------------------------------------------

    In evaluating a broader range of health effects, the 2016 ISA for 
Oxides of Nitrogen concluded that evidence is ``suggestive of, but not 
sufficient to infer, a causal relationship'' between short-term 
NO2 exposure and cardiovascular effects and mortality and 
between long-term NO2 exposure and cardiovascular effects 
and diabetes, birth outcomes, and cancer. In addition, the scientific 
evidence is inadequate (insufficient consistency of epidemiologic and 
toxicological evidence) to infer a causal relationship for long-term 
NO2 exposure with fertility, reproduction, and pregnancy, as 
well as with postnatal development. A key uncertainty in understanding 
the relationship between these non-respiratory health effects and 
short- or long-term exposure to NO2 is copollutant 
confounding, particularly by other roadway pollutants. The available 
evidence for non-respiratory health effects does not adequately address 
whether NO2 has an independent effect or whether it 
primarily represents effects related to other or a mixture of traffic-
related pollutants.
    The 2016 ISA for Oxides of Nitrogen concluded that people with 
asthma, children, and older adults are at increased risk for 
NO2-related health effects. In these groups and lifestages, 
NO2 is consistently related to larger effects on outcomes 
related to asthma exacerbation, for which there is confidence in the 
relationship with NO2 exposure.
4. Carbon Monoxide
    Information on the health effects of CO can be found in the January 
2010 Integrated Science Assessment for Carbon Monoxide (CO ISA).\114\ 
The CO ISA presents conclusions regarding the presence of causal 
relationships between CO exposure and categories of adverse health 
effects.\115\ This section provides a summary of the health effects 
associated with exposure to ambient concentrations of CO, along with 
the CO ISA conclusions.\116\
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    \114\ U.S. EPA, (2010). Integrated Science Assessment for Carbon 
Monoxide (Final Report). U.S. Environmental Protection Agency, 
Washington, DC, EPA/600/R-09/019F, 2010. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686.
    \115\ The ISA evaluates the health evidence associated with 
different health effects, assigning one of five ``weight of 
evidence'' determinations: causal relationship, likely to be a 
causal relationship, suggestive of a causal relationship, inadequate 
to infer a causal relationship, and not likely to be a causal 
relationship. For definitions of these levels of evidence, please 
refer to Section 1.6 of the ISA.
    \116\ Personal exposure includes contributions from many 
sources, and in many different environments. Total personal exposure 
to CO includes both ambient and non-ambient components; and both 
components may contribute to adverse health effects.
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    Controlled human exposure studies of subjects with coronary artery 
disease show a decrease in the time to onset of exercise-induced angina 
(chest pain) and electrocardiogram changes following CO exposure. In 
addition, epidemiologic studies observed associations between short-
term CO exposure and cardiovascular morbidity, particularly increased 
emergency room visits and hospital admissions for coronary heart 
disease (including ischemic heart disease, myocardial infarction, and 
angina). Some epidemiologic evidence is also available for increased 
hospital admissions and emergency room visits for congestive heart 
failure and cardiovascular disease as a whole. The CO ISA concludes 
that a causal relationship is likely to exist between short-term 
exposures to CO and cardiovascular morbidity. It also concludes that 
available data are inadequate to conclude that a causal relationship 
exists between long-term exposures to CO and cardiovascular morbidity.
    Animal studies show various neurological effects with in-utero CO 
exposure. Controlled human exposure studies report central nervous 
system and behavioral effects following low-level CO exposures, 
although the findings have not been consistent across all studies. The 
CO ISA concludes that the evidence is suggestive of a causal 
relationship with both short- and long-term exposure to CO and central 
nervous system effects.
    A number of studies cited in the CO ISA have evaluated the role of 
CO exposure in birth outcomes such as preterm birth or cardiac birth 
defects. There is limited epidemiologic evidence of a CO-induced effect 
on preterm births and birth defects, with weak evidence for a decrease 
in birth weight. Animal toxicological studies have found perinatal CO 
exposure to affect birth weight, as well as other developmental 
outcomes. The CO ISA concludes that the evidence is suggestive of a 
causal relationship between long-term exposures to CO and developmental 
effects and birth outcomes.
    Epidemiologic studies provide evidence of associations between 
short-term CO concentrations and respiratory morbidity such as changes 
in pulmonary function, respiratory symptoms, and hospital admissions. A 
limited number of epidemiologic studies considered copollutants such as 
ozone, SO2, and PM in two-pollutant models and found that CO 
risk estimates were generally robust, although this limited evidence 
makes it difficult to disentangle effects attributed to CO itself from 
those of the larger complex air pollution mixture. Controlled human 
exposure studies have not extensively evaluated the effect of CO on 
respiratory morbidity. Animal studies at levels of 50-100 ppm CO show 
preliminary evidence of altered pulmonary vascular remodeling and 
oxidative injury. The CO ISA concludes that the evidence is suggestive 
of a causal relationship between short-term CO exposure and respiratory 
morbidity, and inadequate to conclude that a causal relationship exists 
between long-term exposure and respiratory morbidity.
    Finally, the CO ISA concludes that the epidemiologic evidence is 
suggestive of a causal relationship between short-term concentrations 
of CO and mortality. Epidemiologic evidence suggests an association 
exists between short-term exposure to CO and mortality, but limited 
evidence is available to evaluate cause-specific mortality outcomes 
associated with CO exposure. In addition, the attenuation of CO risk 
estimates that was often observed in copollutant models contributes to 
the uncertainty as to whether CO is acting alone or as an indicator for 
other combustion-related pollutants. The CO ISA also concludes that 
there is not likely to be a causal relationship between relevant long-
term exposures to CO and mortality.
5. Diesel Exhaust
    In EPA's 2002 Diesel Health Assessment Document (Diesel HAD), 
exposure to diesel exhaust was classified as likely to be carcinogenic 
to humans by inhalation from environmental exposures, in accordance 
with the revised draft 1996/1999 EPA cancer 
guidelines.117 118 A number of

[[Page 4321]]

other agencies (National Institute for Occupational Safety and Health, 
the International Agency for Research on Cancer, the World Health 
Organization, California EPA, and the U.S. Department of Health and 
Human Services) made similar hazard classifications prior to 2002. EPA 
also concluded in the 2002 Diesel HAD that it was not possible to 
calculate a cancer unit risk for diesel exhaust due to limitations in 
the exposure data for the occupational groups or the absence of a dose-
response relationship.
---------------------------------------------------------------------------

    \117\ U.S. EPA. (1999). Guidelines for Carcinogen Risk 
Assessment. Review Draft. NCEA-F-0644, July. Washington, DC: U.S. 
EPA. Retrieved on March 19, 2009 from http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=54932.
    \118\ U.S. EPA (2002). Health Assessment Document for Diesel 
Engine Exhaust. EPA/600/8-90/057F Office of research and 
Development, Washington, DC. Retrieved on March 17, 2009 from http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=29060. pp. 1-1 1-2.
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    In the absence of a cancer unit risk, the Diesel HAD sought to 
provide additional insight into the significance of the diesel exhaust 
cancer hazard by estimating possible ranges of risk that might be 
present in the population. An exploratory analysis was used to 
characterize a range of possible lung cancer risk. The outcome was that 
environmental risks of cancer from long-term diesel exhaust exposures 
could plausibly range from as low as 10-5 to as 
high as 10-3. Because of uncertainties, the 
analysis acknowledged that the risks could be lower than 
10-5, and a zero risk from diesel exhaust 
exposure could not be ruled out.
    Noncancer health effects of acute and chronic exposure to diesel 
exhaust emissions are also of concern to EPA. EPA derived a diesel 
exhaust reference concentration (RfC) from consideration of four well-
conducted chronic rat inhalation studies showing adverse pulmonary 
effects. The RfC is 5 [micro]g/m3 for diesel exhaust 
measured as diesel particulate matter. This RfC does not consider 
allergenic effects such as those associated with asthma or immunologic 
or the potential for cardiac effects. There was emerging evidence in 
2002, discussed in the Diesel HAD, that exposure to diesel exhaust can 
exacerbate these effects, but the exposure-response data were lacking 
at that time to derive an RfC based on these then-emerging 
considerations. The Diesel HAD states, ``With [diesel particulate 
matter] being a ubiquitous component of ambient PM, there is an 
uncertainty about the adequacy of the existing [diesel exhaust] 
noncancer database to identify all the pertinent [diesel exhaust]-
caused noncancer health hazards.'' The Diesel HAD also notes ``that 
acute exposure to [diesel exhaust] has been associated with irritation 
of the eye, nose, and throat, respiratory symptoms (cough and phlegm), 
and neurophysiological symptoms such as headache, lightheadedness, 
nausea, vomiting, and numbness or tingling of the extremities.'' The 
Diesel HAD notes that the cancer and noncancer hazard conclusions 
applied to the general use of diesel engines then on the market and as 
cleaner engines replace a substantial number of existing ones, the 
applicability of the conclusions would need to be reevaluated.
    It is important to note that the Diesel HAD also briefly summarizes 
health effects associated with ambient PM and discusses EPA's then-
annual PM2.5 NAAQS of 15 [micro]g/m3.\119\ There 
is a large and extensive body of human data showing a wide spectrum of 
adverse health effects associated with exposure to ambient PM, of which 
diesel exhaust is an important component. The PM2.5 NAAQS is 
designed to provide protection from the noncancer health effects and 
premature mortality attributed to exposure to PM2.5. The 
contribution of diesel PM to total ambient PM varies in different 
regions of the country and also, within a region, from one area to 
another. The contribution can be high in near-roadway environments, for 
example, or in other locations where diesel engine use is concentrated.
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    \119\ See Section II.A.2 for discussion of the current 
PM2.5 NAAQS standard.
---------------------------------------------------------------------------

    Since 2002, several new studies have been published which continue 
to report increased lung cancer risk associated with occupational 
exposure to diesel exhaust from older engines. Of particular note since 
2011 are three new epidemiology studies that have examined lung cancer 
in occupational populations, for example, truck drivers, underground 
nonmetal miners, and other diesel motor-related occupations. These 
studies reported increased risk of lung cancer with exposure to diesel 
exhaust with evidence of positive exposure-response relationships to 
varying degrees.120 121 122 These newer studies (along with 
others that have appeared in the scientific literature) add to the 
evidence EPA evaluated in the 2002 Diesel HAD and further reinforce the 
concern that diesel exhaust exposure likely poses a lung cancer hazard. 
The findings from these newer studies do not necessarily apply to newer 
technology diesel engines (i.e., heavy-duty highway engines from 2007 
and later model years) since the newer engines have large reductions in 
the emission constituents compared to older technology diesel engines.
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    \120\ Garshick, Eric, Francine Laden, Jaime E. Hart, Mary E. 
Davis, Ellen A. Eisen, and Thomas J. Smith. 2012. Lung cancer and 
elemental carbon exposure in trucking industry workers. 
Environmental Health Perspectives 120(9): 1301-1306.
    \121\ Silverman, D.T., Samanic, C.M., Lubin, J.H., Blair, A.E., 
Stewart, P.A., Vermeulen, R., & Attfield, M.D. (2012). The diesel 
exhaust in miners study: a nested case-control study of lung cancer 
and diesel exhaust. Journal of the National Cancer Institute.
    \122\ Olsson, Ann C., et al. ``Exposure to diesel motor exhaust 
and lung cancer risk in a pooled analysis from case-control studies 
in Europe and Canada.'' American Journal of Respiratory and Critical 
Care Medicine 183.7 (2011): 941-948.
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    In light of the growing body of scientific literature evaluating 
the health effects of exposure to diesel exhaust, in June 2012 the 
World Health Organization's International Agency for Research on Cancer 
(IARC), a recognized international authority on the carcinogenic 
potential of chemicals and other agents, evaluated the full range of 
cancer-related health effects data for diesel engine exhaust. IARC 
concluded that diesel exhaust should be regarded as ``carcinogenic to 
humans.'' \123\ This designation was an update from its 1988 evaluation 
that considered the evidence to be indicative of a ``probable human 
carcinogen.''
---------------------------------------------------------------------------

    \123\ IARC [International Agency for Research on Cancer]. 
(2013). Diesel and gasoline engine exhausts and some nitroarenes. 
IARC Monographs Volume 105. [Online at http://monographs.iarc.fr/ENG/Monographs/vol105/index.php].
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6. Air Toxics
    Heavy-duty engine emissions contribute to ambient levels of air 
toxics that are known or suspected human or animal carcinogens, or that 
have noncancer health effects. These compounds include, but are not 
limited to, benzene, formaldehyde, acetaldehyde, and naphthalene. These 
compounds were identified as national or regional cancer risk drivers 
or contributors in the 2018 AirToxScreen Assessment and have 
significant inventory contributions from mobile 
sources.124 125 Chapter 4 of the RIA includes additional 
information on the health effects associated with exposure to each of 
these pollutants.
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    \124\ U.S. EPA (2022) Technical Support Document EPA Air Toxics 
Screening Assessment. 2017AirToxScreen TSD. https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf.
    \125\ U.S. EPA (2022) 2018 AirToxScreen Risk Drivers. https://www.epa.gov/AirToxScreen/airtoxscreen-risk-drivers.
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7. Exposure and Health Effects Associated With Traffic
    Locations in close proximity to major roadways generally have 
elevated concentrations of many air pollutants emitted from motor 
vehicles. Hundreds of studies have been published in peer-reviewed 
journals, concluding that concentrations of CO, CO2, NO, 
NO2, benzene, aldehydes, PM, black carbon, and many other 
compounds are elevated in ambient air within approximately

[[Page 4322]]

300-600 meters (about 1,000-2,000 feet) of major roadways. The highest 
concentrations of most pollutants emitted directly by motor vehicles 
are found at locations within 50 meters (about 165 feet) of the edge of 
a roadway's traffic lanes.
    A large-scale review of air quality measurements in the vicinity of 
major roadways between 1978 and 2008 concluded that the pollutants with 
the steepest concentration gradients in vicinities of roadways were CO, 
UFPs, metals, elemental carbon (EC), NO, NOX, and several 
VOCs.\126\ These pollutants showed a large reduction in concentrations 
within 100 meters downwind of the roadway. Pollutants that showed more 
gradual reductions with distance from roadways included benzene, 
NO2, PM2.5, and PM10. In reviewing the 
literature, Karner et al., (2010) reported that results varied based on 
the method of statistical analysis used to determine the gradient in 
pollutant concentration. More recent studies continue to show 
significant concentration gradients of traffic-related air pollution 
around major 
roads.127 128 129 130 131 132 133 134 135 136 
There is evidence that EPA's regulations for vehicles have lowered the 
near-road concentrations and gradients.\137\ Starting in 2010, EPA 
required through the NAAQS process that air quality monitors be placed 
near high-traffic roadways for determining concentrations of CO, 
NO2, and PM2.5 (in addition to those existing 
monitors located in neighborhoods and other locations farther away from 
pollution sources). The monitoring data for NO2 indicate 
that in urban areas, monitors near roadways often report the highest 
concentrations of NO2.\138\ More recent studies of traffic-
related air pollutants continue to report sharp gradients around 
roadways, particularly within several hundred meters.139 140
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    \126\ Karner, A.A.; Eisinger, D.S.; Niemeier, D.A. (2010). Near-
roadway air quality: synthesizing the findings from real-world data. 
Environ Sci Technol 44: 5334-5344.
    \127\ McDonald, B.C.; McBride, Z.C.; Martin, E.W.; Harley, R.A. 
(2014) High-resolution mapping of motor vehicle carbon dioxide 
emissions. J. Geophys. Res. Atmos.,119, 5283-5298, doi:10.1002/
2013JD021219.
    \128\ Kimbrough, S.; Baldauf, R.W.; Hagler, G.S.W.; Shores, 
R.C.; Mitchell, W.; Whitaker, D.A.; Croghan, C.W.; Vallero, D.A. 
(2013) Long-term continuous measurement of near-road air pollution 
in Las Vegas: seasonal variability in traffic emissions impact on 
air quality. Air Qual Atmos Health 6: 295-305. DOI 10.1007/s11869-
012-0171-x.
    \129\ Kimbrough, S.; Palma, T.; Baldauf, R.W. (2014) Analysis of 
mobile source air toxics (MSATs)--Near-road VOC and carbonyl 
concentrations. Journal of the Air & Waste Management Association, 
64:3, 349-359, DOI: 10.1080/10962247.2013.863814.
    \130\ Kimbrough, S.; Owen, R.C.; Snyder, M.; Richmond-Bryant, J. 
(2017) NO to NO2 Conversion Rate Analysis and 
Implications for Dispersion Model Chemistry Methods using Las Vegas, 
Nevada Near-Road Field Measurements. Atmos Environ 165: 23-24.
    \131\ Hilker, N.; Wang, J.W.; Jong, C-H.; Healy, R.M.; Sofowote, 
U.; Debosz, J.; Su, Y.; Noble, M.; Munoz, A.; Doerkson, G.; White, 
L.; Audette, C.; Herod, D.; Brook, J.R.; Evans, G.J. (2019) Traffic-
related air pollution near roadways: discerning local impacts from 
background. Atmos. Meas. Tech., 12, 5247-5261. https://doi.org/10.5194/amt-12-5247-2019.
    \132\ Grivas, G.; Stavroulas, I.; Liakakou, E.; Kaskaoutis, 
D.G.; Bougiatioti, A.; Paraskevopoulou, D.; Gerasopoulos, E.; 
Mihalopoulos, N. (2019) Measuring the spatial variability of black 
carbon in Athens during wintertime. Air Quality, Atmosphere & Health 
(2019) 12:1405-1417. https://doi.org/10.1007/s11869-019-00756-y.
    \133\ Apte, J.S.; Messier, K.P.; Gani, S.; Brauer, M.; 
Kirchstetter, T.W.; Lunden, M.M.; Marshall, J.D.; Portier, C.J.; 
Vermeulen, R.C.H.; Hamburg, S.P. (2017) High-Resolution Air 
Pollution Mapping with Google Street View Cars: Exploiting Big Data. 
Environ Sci Technol 51: 6999-7008. https://doi.org/10.1021/acs.est.7b00891.
    \134\ Dabek-Zlotorzynska, E.; Celo, V.; Ding, L.; Herod, D.; 
Jeong, C-H.; Evans, G.; Hilker, N. (2019) Characteristics and 
sources of PM2.5 and reactive gases near roadways in two 
metropolitan areas in Canada. Atmos Environ 218: 116980. https://doi.org/10.1016/j.atmosenv.2019.116980.
    \135\ Apte, J.S.; Messier, K.R.; Gani, S.; et al. (2017) High-
resolution air pollution mapping with Google Street View cars: 
exploiting big data. Environ Sci Technol 51: 6999-7018, [Online at 
https://doi.org/10.1021/acs.est.7b00891].
    \136\ Gu, P.; Li, H.Z.; Ye, Q.; et al. (2018) Intercity 
variability of particulate matter is driven by carbonaceous sources 
and correlated with land-use variables. Environ Sci Technol 52: 52: 
11545-11554. [Online at http://dx.doi.org/10.1021/acs.est.8b03833].
    \137\ Sarnat, J.A.; Russell, A.; Liang, D.; Moutinho, J.L.; 
Golan, R.; Weber, R.; Gao, D.; Sarnat, S.; Chang, H.H.; Greenwald, 
R.; Yu, T. (2018) Developing Multipollutant Exposure Indicators of 
Traffic Pollution: The Dorm Room Inhalation to Vehicle Emissions 
(DRIVE) Study. Health Effects Institute Research Report Number 196. 
[Online at: https://www.healtheffects.org/publication/developing-multipollutant-exposure-indicators-traffic-pollution-dorm-room-inhalation].
    \138\ Gantt, B; Owen, R.C.; Watkins, N. (2021) Characterizing 
nitrogen oxides and fine particulate matter near major highways in 
the United States using the National Near-road Monitoring Network. 
Environ Sci Technol 55: 2831-2838. [Online at https://doi.org/10.1021/acs.est.0c05851].
    \139\ Apte, J.S.; Messier, K.R.; Gani, S.; et al. (2017) High-
resolution air pollution mapping with Google Street View cars: 
exploiting big data. Environ Sci Technol 51: 6999-7018, [Online at 
https://doi.org/10.1021/acs.est.7b00891].
    \140\ Gu, P.; Li, H.Z.; Ye, Q.; et al. (2018) Intercity 
variability of particulate matter is driven by carbonaceous sources 
and correlated with land-use variables. Environ Sci Technol 52: 52: 
11545-11554. [Online at http://dx.doi.org/10.1021/acs.est.8b03833].
---------------------------------------------------------------------------

    For pollutants with relatively high background concentrations 
relative to near-road concentrations, detecting concentration gradients 
can be difficult. For example, many carbonyls have high background 
concentrations as a result of photochemical breakdown of precursors 
from many different organic compounds. However, several studies have 
measured carbonyls in multiple weather conditions and found higher 
concentrations of many carbonyls downwind of 
roadways.141 142 These findings suggest a substantial 
roadway source of these carbonyls.
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    \141\ Liu, W.; Zhang, J.; Kwon, J.l.; et l. (2006). 
Concentrations and source characteristics of airborne carbonyl 
compounds measured outside urban residences. J Air Waste Manage 
Assoc 56: 1196-1204.
    \142\ Cahill, T.M.; Charles, M.J.; Seaman, V.Y. (2010). 
Development and application of a sensitive method to determine 
concentrations of acrolein and other carbonyls in ambient air. 
Health Effects Institute Research Report 149. Available at https://www.healtheffects.org/system/files/Cahill149.pdf.
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    In the past 30 years, many studies have been published with results 
reporting that populations who live, work, or go to school near high-
traffic roadways experience higher rates of numerous adverse health 
effects, compared to populations far away from major roads.\143\ In 
addition, numerous studies have found adverse health effects associated 
with spending time in traffic, such as commuting or walking along high-
traffic roadways, including studies among 
children.144 145 146 147 The health outcomes with the 
strongest evidence linking them with traffic-associated air pollutants 
are respiratory effects, particularly in asthmatic children, and 
cardiovascular effects. Commenters on the NPRM stressed the importance 
of consideration of the impacts of traffic-related air pollution, 
especially NOX, on children's health.
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    \143\ In the widely-used PubMed database of health publications, 
between January 1, 1990 and December 31, 2021, 1,979 publications 
contained the keywords ``traffic, pollution, epidemiology,'' with 
approximately half the studies published after 2015.
    \144\ Laden, F.; Hart, J.E.; Smith, T.J.; Davis, M.E.; Garshick, 
E. (2007) Cause-specific mortality in the unionized U.S. trucking 
industry. Environmental Health Perspect 115:1192-1196.
    \145\ Peters, A.; von Klot, S.; Heier, M.; Trentinaglia, I.; 
H[ouml]rmann, A.; Wichmann, H.E.; L[ouml]wel, H. (2004) Exposure to 
traffic and the onset of myocardial infarction. New England J Med 
351: 1721-1730.
    \146\ Zanobetti, A.; Stone, P.H.; Spelzer, F.E.; Schwartz, J.D.; 
Coull, B.A.; Suh, H.H.; Nearling, B.D.; Mittleman, M.A.; Verrier, 
R.L.; Gold, D.R. (2009) T-wave alternans, air pollution and traffic 
in high-risk subjects. Am J Cardiol 104: 665-670.
    \147\ Adar, S.; Adamkiewicz, G.; Gold, D.R.; Schwartz, J.; 
Coull, B.A.; Suh, H. (2007) Ambient and microenvironmental particles 
and exhaled nitric oxide before and after a group bus trip. Environ 
Health Perspect 115: 507-512.
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    Numerous reviews of this body of health literature have been 
published. In a 2022 final report, an expert panel of the Health 
Effects Institute (HEI) employed a systematic review focusing on 
selected health endpoints related to exposure to traffic-related air 
pollution.\148\ The HEI panel concluded

[[Page 4323]]

that there was a high level of confidence in evidence between long-term 
exposure to traffic-related air pollution and health effects in adults, 
including all-cause, circulatory, and ischemic heart disease 
mortality.\149\ The panel also found that there is a moderate-to-high 
level of confidence in evidence of associations with asthma onset and 
acute respiratory infections in children and lung cancer and asthma 
onset in adults. This report follows on an earlier expert review 
published by HEI in 2010, where it found strongest evidence for asthma-
related traffic impacts. Other literature reviews have been published 
with conclusions generally similar to the HEI 
panels'.150 151 152 153 Additionally, in 2014, researchers 
from the U.S. Centers for Disease Control and Prevention (CDC) 
published a systematic review and meta-analysis of studies evaluating 
the risk of childhood leukemia associated with traffic exposure and 
reported positive associations between ``postnatal'' proximity to 
traffic and leukemia risks, but no such association for ``prenatal'' 
exposures.\154\ The U.S. Department of Health and Human Services' 
National Toxicology Program (NTP) published a monograph including a 
systematic review of traffic-related air pollution and its impacts on 
hypertensive disorders of pregnancy. The NTP concluded that exposure to 
traffic-related air pollution is ``presumed to be a hazard to pregnant 
women'' for developing hypertensive disorders of pregnancy.\155\
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    \148\ HEI Panel on the Health Effects of Long-Term Exposure to 
Traffic-Related Air Pollution (2022) Systematic review and meta-
analysis of selected health effects of long-term exposure to 
traffic-related air pollution. Health Effects Institute Special 
Report 23. [Online at https://www.healtheffects.org/system/files/hei-special-report-23_1.pdf.] This more recent review focused on 
health outcomes related to birth effects, respiratory effects, 
cardiometabolic effects, and mortality.
    \149\ Boogaard, H.; Patton. A.P.; Atkinson, R.W.; Brook, J.R.; 
Chang, H.H.; Crouse, D.L.; Fussell, J.C.; Hoek, G.; Hoffman, B.; 
Kappeler, R.; Kutlar Joss, M.; Ondras, M.; Sagiv, S.K.; Somoli, E.; 
Shaikh, R.; Szpiro, A.A.; Van Vliet E.D.S.; Vinneau, D.; Weuve, J.; 
Lurmann, F.W.; Forastiere, F. (2022) Long-term exposure to traffic-
related air pollution and selected health outcomes: a systematic 
review and meta-analysis. Environ Intl 164: 107262. [Online at 
https://doi.org/10.1016/j.envint.2022.107262].
    \150\ Boothe, V.L.; Shendell, D.G. (2008). Potential health 
effects associated with residential proximity to freeways and 
primary roads: review of scientific literature, 1999-2006. J Environ 
Health 70: 33-41.
    \151\ Salam, M.T.; Islam, T.; Gilliland, F.D. (2008). Recent 
evidence for adverse effects of residential proximity to traffic 
sources on asthma. Curr Opin Pulm Med 14: 3-8.
    \152\ Sun, X.; Zhang, S.; Ma, X. (2014) No association between 
traffic density and risk of childhood leukemia: a meta-analysis. 
Asia Pac J Cancer Prev 15: 5229-5232.
    \153\ Raaschou-Nielsen, O.; Reynolds, P. (2006). Air pollution 
and childhood cancer: a review of the epidemiological literature. 
Int J Cancer 118: 2920-9.
    \154\ Boothe, V.L.; Boehmer, T.K.; Wendel, A.M.; Yip, F.Y. 
(2014) Residential traffic exposure and childhood leukemia: a 
systematic review and meta-analysis. Am J Prev Med 46: 413-422.
    \155\ National Toxicology Program (2019) NTP Monograph on the 
Systematic Review of Traffic-related Air Pollution and Hypertensive 
Disorders of Pregnancy. NTP Monograph 7. https://ntp.niehs.nih.gov/ntp/ohat/trap/mgraph/trap_final_508.pdf.
---------------------------------------------------------------------------

    Health outcomes with few publications suggest the possibility of 
other effects still lacking sufficient evidence to draw definitive 
conclusions. Among these outcomes with a small number of positive 
studies are neurological impacts (e.g., autism and reduced cognitive 
function) and reproductive outcomes (e.g., preterm birth, low birth 
weight).156 157 158 159 160
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    \156\ Volk, H.E.; Hertz-Picciotto, I.; Delwiche, L.; et al. 
(2011). Residential proximity to freeways and autism in the CHARGE 
study. Environ Health Perspect 119: 873-877.
    \157\ Franco-Suglia, S.; Gryparis, A.; Wright, R.O.; et al. 
(2007). Association of black carbon with cognition among children in 
a prospective birth cohort study. Am J Epidemiol. doi: 10.1093/aje/
kwm308. [Online at http://dx.doi.org].
    \158\ Power, M.C.; Weisskopf, M.G.; Alexeef, S.E.; et al. 
(2011). Traffic-related air pollution and cognitive function in a 
cohort of older men. Environ Health Perspect 2011: 682-687.
    \159\ Wu, J.; Wilhelm, M.; Chung, J.; et al. (2011). Comparing 
exposure assessment methods for traffic-related air pollution in and 
adverse pregnancy outcome study. Environ Res 111: 685-6692.
    \160\ Stenson, C.; Wheeler, A.J.; Carver, A.; et al. (2021) The 
impact of traffic-related air pollution on child and adolescent 
academic performance: a systematic review. Environ Intl 155: 106696 
[Online at https://doi.org/10.1016/j.envint.2021.106696].
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    In addition to health outcomes, particularly cardiopulmonary 
effects, conclusions of numerous studies suggest mechanisms by which 
traffic-related air pollution affects health. For example, numerous 
studies indicate that near-roadway exposures may increase systemic 
inflammation, affecting organ systems, including blood vessels and 
lungs.161 162 163 164 Additionally, long-term exposures in 
near-road environments have been associated with inflammation-
associated conditions, such as atherosclerosis and 
asthma.165 166 167
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    \161\ Riediker, M. (2007). Cardiovascular effects of fine 
particulate matter components in highway patrol officers. Inhal 
Toxicol 19: 99-105. doi: 10.1080/08958370701495238.
    \162\ Alexeef, S.E.; Coull, B.A.; Gryparis, A.; et al. (2011). 
Medium-term exposure to traffic-related air pollution and markers of 
inflammation and endothelial function. Environ Health Perspect 119: 
481-486. doi:10.1289/ehp.1002560.
    \163\ Eckel. S.P.; Berhane, K.; Salam, M.T.; et al. (2011). 
Residential Traffic-related pollution exposure and exhaled nitric 
oxide in the Children's Health Study. Environ Health Perspect. 
doi:10.1289/ehp.1103516.
    \164\ Zhang, J.; McCreanor, J.E.; Cullinan, P.; et al. (2009). 
Health effects of real-world exposure diesel exhaust in persons with 
asthma. Res Rep Health Effects Inst 138. [Online at http://www.healtheffects.org].
    \165\ Adar, S.D.; Klein, R.; Klein, E.K.; et al. (2010). Air 
pollution and the microvasculature: a cross-sectional assessment of 
in vivo retinal images in the population-based Multi-Ethnic Study of 
Atherosclerosis. PLoS Med 7(11): E1000372. doi:10.1371/
journal.pmed.1000372. Available at http://dx.doi.org.
    \166\ Kan, H.; Heiss, G.; Rose, K.M.; et al. (2008). Prospective 
analysis of traffic exposure as a risk factor for incident coronary 
heart disease: The Atherosclerosis Risk in Communities (ARIC) study. 
Environ Health Perspect 116: 1463-1468. doi:10.1289/ehp.11290. 
Available at http://dx.doi.org.
    \167\ McConnell, R.; Islam, T.; Shankardass, K.; et al. (2010). 
Childhood incident asthma and traffic-related air pollution at home 
and school. Environ Health Perspect 1021-1026.
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    Several studies suggest that some factors may increase 
susceptibility to the effects of traffic-associated air pollution. 
Several studies have found stronger adverse health associations in 
children experiencing chronic social stress, such as in violent 
neighborhoods or in homes with low incomes or high family 
stress.168 169 170 171
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    \168\ Islam, T.; Urban, R.; Gauderman, W.J.; et al. (2011). 
Parental stress increases the detrimental effect of traffic exposure 
on children's lung function. Am J Respir Crit Care Med.
    \169\ Clougherty, J.E.; Levy, J.I.; Kubzansky, L.D.; et al. 
(2007). Synergistic effects of traffic-related air pollution and 
exposure to violence on urban asthma etiology. Environ Health 
Perspect 115: 1140-1146.
    \170\ Chen, E.; Schrier, H.M.; Strunk, R.C.; et al. (2008). 
Chronic traffic-related air pollution and stress interact to predict 
biologic and clinical outcomes in asthma. Environ Health Perspect 
116: 970-5.
    \171\ Long, D.; Lewis, D.; Langpap, C. (2021) Negative traffic 
externalities and infant health: the role of income heterogeneity 
and residential sorting. Environ and Resource Econ 80: 637-674. 
[Online at https://doi.org/10.1007/s10640-021-00601-w].
---------------------------------------------------------------------------

    The risks associated with residence, workplace, or schools near 
major roads are of potentially high public health significance due to 
the large population in such locations. The 2013 U.S. Census Bureau's 
American Housing Survey (AHS) was the last AHS that included whether 
housing units were within 300 feet of an ``airport, railroad, or 
highway with four or more lanes.'' \172\ The 2013 survey reports that 
17.3 million housing units, or 13 percent of all housing units in the 
United States, were in such areas. Assuming that populations and 
housing units are in the same locations, this corresponds to a 
population of more than 41 million U.S. residents in close proximity to 
high-traffic roadways or other transportation sources. According to the 
Central Intelligence Agency's World Factbook, based on data collected 
between 2012-2014, the United States had 6,586,610 km of roadways, 
293,564 km of railways, and 13,513 airports. As such, highways 
represent the overwhelming majority of transportation facilities 
described by this factor in the AHS.
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    \172\ The variable was known as ``ETRANS'' in the questions 
about the neighborhood.

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[[Page 4324]]

    EPA also conducted a study to estimate the number of people living 
near truck freight routes in the United States.\173\ Based on a 
population analysis using the U.S. Department of Transportation's 
(USDOT) Freight Analysis Framework 4 (FAF4) and population data from 
the 2010 decennial census, an estimated 72 million people live within 
200 meters of these freight routes.174 175 In addition, 
relative to the rest of the population, people of color and those with 
lower incomes are more likely to live near FAF4 truck routes. They are 
also more likely to live in metropolitan areas. The EPA's Exposure 
Factor Handbook also indicates that, on average, Americans spend more 
than an hour traveling each day, bringing nearly all residents into a 
high-exposure microenvironment for part of the day.\176\
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    \173\ U.S. EPA (2021). Estimation of Population Size and 
Demographic Characteristics among People Living Near Truck Routes in 
the Conterminous United States. Memorandum to the Docket.
    \174\ FAF4 is a model from the USDOT's Bureau of Transportation 
Statistics (BTS) and Federal Highway Administration (FHWA), which 
provides data associated with freight movement in the U.S. It 
includes data from the 2012 Commodity Flow Survey (CFS), the Census 
Bureau on international trade, as well as data associated with 
construction, agriculture, utilities, warehouses, and other 
industries. FAF4 estimates the modal choices for moving goods by 
trucks, trains, boats, and other types of freight modes. It includes 
traffic assignments, including truck flows on a network of truck 
routes. https://ops.fhwa.dot.gov/freight/freight_analysis/faf/.
    \175\ The same analysis estimated the population living within 
100 meters of a FAF4 truck route is 41 million.
    \176\ EPA. (2011) Exposure Factors Handbook: 2011 Edition. 
Chapter 16. Online at https://www.epa.gov/sites/production/files/2015-09/documents/efh-Chapter16.pdf.
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    As described in Section VII.H.1, we estimate that about 10 million 
students attend schools within 200 meters of major roads.\177\ Research 
into the impact of traffic-related air pollution on school performance 
is tentative. A review of this literature found some evidence that 
children exposed to higher levels of traffic-related air pollution show 
poorer academic performance than those exposed to lower levels of 
traffic-related air pollution.\178\ However, this evidence was judged 
to be weak due to limitations in the assessment methods.
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    \177\ Pedde, M.; Bailey, C. (2011) Identification of Schools 
within 200 Meters of U.S. Primary and Secondary Roads. Memorandum to 
the docket.
    \178\ Stenson, C.; Wheeler, A.J.; Carver, A.; et al. (2021) The 
impact of traffic-related air pollution on child and adolescent 
academic performance: a systematic review. Environ Intl 155: 106696. 
[Online at https://doi.org/10.1016/j.envint.2021.106696].
---------------------------------------------------------------------------

    While near-roadway studies focus on residents near roads or others 
spending considerable time near major roads, the duration of commuting 
results in another important contributor to overall exposure to 
traffic-related air pollution. Studies of health that address time 
spent in transit have found evidence of elevated risk of cardiac 
impacts.179 180 181 Studies have also found that school bus 
emissions can increase student exposures to diesel-related air 
pollutants, and that programs that reduce school bus emissions may 
improve health and reduce school absenteeism.182 183 184 185
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    \179\ Riediker, M.; Cascio, W.E.; Griggs, T.R.; et al. (2004) 
Particulate matter exposure in cars is associated with 
cardiovascular effects in healthy young men. Am J Respir Crit Care 
Med 169. [Online at https://doi.org/10.1164/rccm.200310-1463OC].
    \180\ Peters, A.; von Klot, S.; Heier, M.; et al. (2004) 
Exposure to traffic and the onset of myocardial infarction. New Engl 
J Med 1721-1730. [Online at https://doi.org/10.1056/NEJMoa040203].
    \181\ Adar, S.D.; Gold, D.R.; Coull, B.A.; (2007) Focused 
exposure to airborne traffic particles and heart rate variability in 
the elderly. Epidemiology 18: 95-103 [Online at: https://doi.org/10.1097/01.ede.0000249409.81050.46].
    \182\ Sabin, L.; Behrentz, E.; Winer, A.M.; et al. 
Characterizing the range of children's air pollutant exposure during 
school bus commutes. J Expo Anal Environ Epidemiol 15: 377-387. 
[Online at https://doi.org/10.1038/sj.jea.7500414].
    \183\ Li, C.; N, Q.; Ryan, P.H.; School bus pollution and 
changes in the air quality at schools: a case study. J Environ Monit 
11: 1037-1042. [https://doi.org/10.1039/b819458k].
    \184\ Austin, W.; Heutel, G.; Kreisman, D. (2019) School bus 
emissions, student health and academic performance. Econ Edu Rev 70: 
108-12.
    \185\ Adar, S.D.; D. Souza, J.; Sheppard, L.; Adopting clean 
fuels and technologies on school buses. Pollution and health impacts 
in children. Am J Respir Crit Care Med 191. [Online at http://doi.org/10.1164/rccm.201410-1924OC].
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C. Environmental Effects Associated With Exposure to Pollutants 
Impacted by This Rule

    This section discusses the environmental effects associated with 
pollutants affected by this rule, specifically PM, ozone, 
NOX and air toxics.
1. Visibility
    Visibility can be defined as the degree to which the atmosphere is 
transparent to visible light.\186\ Visibility impairment is caused by 
light scattering and absorption by suspended particles and gases. It is 
dominated by contributions from suspended particles except under 
pristine conditions. Visibility is important because it has direct 
significance to people's enjoyment of daily activities in all parts of 
the country. Individuals value good visibility for the well-being it 
provides them directly, where they live and work, and in places where 
they enjoy recreational opportunities. Visibility is also highly valued 
in significant natural areas, such as national parks and wilderness 
areas, and special emphasis is given to protecting visibility in these 
areas. For more information on visibility see the final 2019 p.m. 
ISA.\187\
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    \186\ National Research Council, (1993). Protecting Visibility 
in National Parks and Wilderness Areas. National Academy of Sciences 
Committee on Haze in National Parks and Wilderness Areas. National 
Academy Press, Washington, DC. This book can be viewed on the 
National Academy Press website at https://www.nap.edu/catalog/2097/protecting-visibility-in-national-parks-and-wilderness-areas.
    \187\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
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    EPA is working to address visibility impairment. Reductions in air 
pollution from implementation of various programs associated with the 
Clean Air Act Amendments of 1990 provisions have resulted in 
substantial improvements in visibility and will continue to do so in 
the future. Nationally, because trends in haze are closely associated 
with trends in particulate sulfate and nitrate due to the relationship 
between their concentration and light extinction, visibility trends 
have improved as emissions of SO2 and NOX have 
decreased over time due to air pollution regulations such as the Acid 
Rain Program.\188\ However between 1990 and 2018, in the western part 
of the country, changes in total light extinction were smaller, and the 
contribution of particulate organic matter to atmospheric light 
extinction was increasing due to increasing wildfire emissions.\189\
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    \188\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \189\ Hand, J.L.; Prenni, A.J.; Copeland, S.; Schichtel, B.A.; 
Malm, W.C. (2020). Thirty years of the Clean Air Act Amendments: 
Impacts on haze in remote regions of the United States (1990-2018). 
Atmos Environ 243: 117865.
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    In the Clean Air Act Amendments of 1977, Congress recognized 
visibility's value to society by establishing a national goal to 
protect national parks and wilderness areas from visibility impairment 
caused by manmade pollution.\190\ In 1999, EPA finalized the regional 
haze program to protect the visibility in Mandatory Class I Federal 
areas.\191\ There are 156 national parks, forests and wilderness areas 
categorized as Mandatory Class I Federal areas.\192\ These areas are 
defined in CAA section 162 as those national parks exceeding 6,000 
acres, wilderness areas, and memorial parks exceeding 5,000 acres, and 
all international parks which were in existence on August 7, 1977.
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    \190\ See CAA section 169(a).
    \191\ 64 FR 35714, July 1, 1999.
    \192\ 62 FR 38680-38681, July 18, 1997.

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[[Page 4325]]

    EPA has also concluded that PM2.5 causes adverse effects 
on visibility in other areas that are not targeted by the Regional Haze 
Rule, such as urban areas, depending on PM2.5 concentrations 
and other factors such as dry chemical composition and relative 
humidity (i.e., an indicator of the water composition of the 
particles). The secondary (welfare-based) PM NAAQS provide protection 
against visibility effects. In recent PM NAAQS reviews, EPA evaluated a 
target level of protection for visibility impairment that is expected 
to be met through attainment of the existing secondary PM standards.
2. Plant and Ecosystem Effects of Ozone
    The welfare effects of ozone include effects on ecosystems, which 
can be observed across a variety of scales, i.e., subcellular, 
cellular, leaf, whole plant, population and ecosystem. When ozone 
effects that begin at small spatial scales, such as the leaf of an 
individual plant, occur at sufficient magnitudes (or to a sufficient 
degree), they can result in effects being propagated along a continuum 
to higher and higher levels of biological organization. For example, 
effects at the individual plant level, such as altered rates of leaf 
gas exchange, growth and reproduction, can, when widespread, result in 
broad changes in ecosystems, such as productivity, carbon storage, 
water cycling, nutrient cycling, and community composition.
    Ozone can produce both acute and chronic injury in sensitive plant 
species depending on the concentration level and the duration of the 
exposure.\193\ In those sensitive species,\194\ effects from repeated 
exposure to ozone throughout the growing season of the plant can tend 
to accumulate, so even relatively low concentrations experienced for a 
longer duration have the potential to create chronic stress on 
vegetation.195 196 Ozone damage to sensitive plant species 
includes impaired photosynthesis and visible injury to leaves. The 
impairment of photosynthesis, the process by which the plant makes 
carbohydrates (its source of energy and food), can lead to reduced crop 
yields, timber production, and plant productivity and growth. Impaired 
photosynthesis can also lead to a reduction in root growth and 
carbohydrate storage below ground, resulting in other, more subtle 
plant and ecosystems impacts.\197\ These latter impacts include 
increased susceptibility of plants to insect attack, disease, harsh 
weather, interspecies competition, and overall decreased plant vigor. 
The adverse effects of ozone on areas with sensitive species could 
potentially lead to species shifts and loss from the affected 
ecosystems,\198\ resulting in a loss or reduction in associated 
ecosystem goods and services. Additionally, visible ozone injury to 
leaves can result in a loss of aesthetic value in areas of special 
scenic significance like national parks and wilderness areas and 
reduced use of sensitive ornamentals in landscaping.\199\ In addition 
to ozone effects on vegetation, newer evidence suggests that ozone 
affects interactions between plants and insects by altering chemical 
signals (e.g., floral scents) that plants use to communicate to other 
community members, such as attraction of pollinators.
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    \193\ 73 FR 16486, March 27, 2008.
    \194\ 73 FR 16491, March 27, 2008. Only a small percentage of 
all the plant species growing within the U.S. (over 43,000 species 
have been catalogued in the USDA PLANTS database) have been studied 
with respect to ozone sensitivity.
    \195\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone 
and Related Photochemical Oxidants (Final Report). U.S. 
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012, 
2020.
    \196\ The concentration at which ozone levels overwhelm a 
plant's ability to detoxify or compensate for oxidant exposure 
varies. Thus, whether a plant is classified as sensitive or tolerant 
depends in part on the exposure levels being considered.
    \197\ 73 FR 16492, March 27, 2008.
    \198\ 73 FR 16493-16494, March 27, 2008. Ozone impacts could be 
occurring in areas where plant species sensitive to ozone have not 
yet been studied or identified.
    \199\ 73 FR 16490-16497, March 27, 2008.
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    The Ozone ISA presents more detailed information on how ozone 
affects vegetation and ecosystems.200 201 The Ozone ISA 
reports causal and likely causal relationships between ozone exposure 
and a number of welfare effects and characterizes the weight of 
evidence for different effects associated with ozone.\202\ The Ozone 
ISA concludes that visible foliar injury effects on vegetation, reduced 
vegetation growth, reduced plant reproduction, reduced productivity in 
terrestrial ecosystems, reduced yield and quality of agricultural 
crops, alteration of below-ground biogeochemical cycles, and altered 
terrestrial community composition are causally associated with exposure 
to ozone. It also concludes that increased tree mortality, altered 
herbivore growth and reproduction, altered plant-insect signaling, 
reduced carbon sequestration in terrestrial ecosystems, and alteration 
of terrestrial ecosystem water cycling are likely to be causally 
associated with exposure to ozone.
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    \200\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone 
and Related Photochemical Oxidants (Final Report). U.S. 
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012, 
2020.
    \201\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone 
and Related Photochemical Oxidants (Final Report). U.S. 
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012, 
2020.
    \202\ The Ozone ISA evaluates the evidence associated with 
different ozone related health and welfare effects, assigning one of 
five ``weight of evidence'' determinations: causal relationship, 
likely to be a causal relationship, suggestive of a causal 
relationship, inadequate to infer a causal relationship, and not 
likely to be a causal relationship. For more information on these 
levels of evidence, please refer to Table II of the ISA.
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3. Atmospheric Deposition
    The Integrated Science Assessment for Oxides of Nitrogen, Oxides of 
Sulfur, and Particulate Matter--Ecological Criteria documents the 
ecological effects of the deposition of these criteria air 
pollutants.\203\ It is clear from the body of evidence that 
NOX, oxides of sulfur (SOX), and PM contribute to 
total nitrogen (N) and sulfur (S) deposition. In turn, N and S 
deposition cause either nutrient enrichment or acidification depending 
on the sensitivity of the landscape or the species in question. Both 
enrichment and acidification are characterized by an alteration of the 
biogeochemistry and the physiology of organisms, resulting in harmful 
declines in biodiversity in terrestrial, freshwater, wetland, and 
estuarine ecosystems in the United States. Decreases in biodiversity 
mean that some species become relatively less abundant and may be 
locally extirpated. In addition to the loss of unique living species, 
the decline in total biodiversity can be harmful because biodiversity 
is an important determinant of the stability of ecosystems and their 
ability to provide socially valuable ecosystem services.
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    \203\ U.S. EPA. Integrated Science Assessment (ISA) for Oxides 
of Nitrogen, Oxides of Sulfur and Particulate Matter Ecological 
Criteria (Final Report). U.S. Environmental Protection Agency, 
Washington, DC, EPA/600/R-20/278, 2020.
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    Terrestrial, wetland, freshwater, and estuarine ecosystems in the 
United States are affected by N enrichment/eutrophication caused by N 
deposition. These effects have been consistently documented across the 
United States for hundreds of species. In aquatic systems increased N 
can alter species assemblages and cause eutrophication. In terrestrial 
systems N loading can lead to loss of nitrogen-sensitive lichen 
species, decreased biodiversity of grasslands, meadows and other 
sensitive habitats, and increased potential for invasive species. For a 
broader explanation of the topics treated here, refer to the 
description in Chapter 4 of the RIA.
    The sensitivity of terrestrial and aquatic ecosystems to 
acidification from N and S deposition is predominantly governed by 
geology. Prolonged exposure to excess nitrogen and sulfur

[[Page 4326]]

deposition in sensitive areas acidifies lakes, rivers, and soils. 
Increased acidity in surface waters creates inhospitable conditions for 
biota and affects the abundance and biodiversity of fishes, 
zooplankton, and macroinvertebrates and ecosystem function. Over time, 
acidifying deposition also removes essential nutrients from forest 
soils, depleting the capacity of soils to neutralize future acid 
loadings and negatively affecting forest sustainability. Major effects 
in forests include a decline in sensitive tree species, such as red 
spruce (Picea rubens) and sugar maple (Acer saccharum).
    Building materials including metals, stones, cements, and paints 
undergo natural weathering processes from exposure to environmental 
elements (e.g., wind, moisture, temperature fluctuations, sunlight, 
etc.). Pollution can worsen and accelerate these effects. Deposition of 
PM is associated with both physical damage (materials damage effects) 
and impaired aesthetic qualities (soiling effects). Wet and dry 
deposition of PM can physically affect materials, adding to the effects 
of natural weathering processes, by potentially promoting or 
accelerating the corrosion of metals, by degrading paints, and by 
deteriorating building materials such as stone, concrete, and 
marble.\204\ The effects of PM are exacerbated by the presence of 
acidic gases and can be additive or synergistic due to the complex 
mixture of pollutants in the air and surface characteristics of the 
material. Acidic deposition has been shown to have an effect on 
materials including zinc/galvanized steel and other metal, carbonate 
stone (such as monuments and building facings), and surface coatings 
(paints).\205\ The effects on historic buildings and outdoor works of 
art are of particular concern because of the uniqueness and 
irreplaceability of many of these objects. In addition to aesthetic and 
functional effects on metals, stone, and glass, altered energy 
efficiency of photovoltaic panels by PM deposition is also becoming an 
important consideration for impacts of air pollutants on materials.
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    \204\ U.S. EPA. Integrated Science Assessment (ISA) for 
Particulate Matter (Final Report, 2019). U.S. Environmental 
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \205\ Irving, P.M., e.d. 1991. Acid Deposition: State of Science 
and Technology, Volume III, Terrestrial, Materials, Health, and 
Visibility Effects, The U.S. National Acid Precipitation Assessment 
Program, Chapter 24, page 24-76.
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4. Environmental Effects of Air Toxics
    Emissions from producing, transporting, and combusting fuel 
contribute to ambient levels of pollutants that contribute to adverse 
effects on vegetation. VOCs, some of which are considered air toxics, 
have long been suspected to play a role in vegetation damage.\206\ In 
laboratory experiments, a wide range of tolerance to VOCs has been 
observed.\207\ Decreases in harvested seed pod weight have been 
reported for the more sensitive plants, and some studies have reported 
effects on seed germination, flowering, and fruit ripening. Effects of 
individual VOCs or their role in conjunction with other stressors 
(e.g., acidification, drought, temperature extremes) have not been well 
studied. In a recent study of a mixture of VOCs including ethanol and 
toluene on herbaceous plants, significant effects on seed production, 
leaf water content, and photosynthetic efficiency were reported for 
some plant species.\208\
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    \206\ U.S. EPA. (1991). Effects of organic chemicals in the 
atmosphere on terrestrial plants. EPA/600/3-91/001.
    \207\ Cape J.N., I.D. Leith, J. Binnie, J. Content, M. Donkin, 
M. Skewes, D.N. Price, A.R. Brown, A.D. Sharpe. (2003). Effects of 
VOCs on herbaceous plants in an open-top chamber experiment. 
Environ. Pollut. 124:341-343.
    \208\ Cape J.N., I.D. Leith, J. Binnie, J. Content, M. Donkin, 
M. Skewes, D.N. Price, A.R. Brown, A.D. Sharpe. (2003). Effects of 
VOCs on herbaceous plants in an open-top chamber experiment. 
Environ. Pollut. 124:341-343.
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    Research suggests an adverse impact of vehicle exhaust on plants, 
which has in some cases been attributed to aromatic compounds and in 
other cases to NOX.209 210 211 The impacts of 
VOCs on plant reproduction may have long-term implications for 
biodiversity and survival of native species near major roadways. Most 
of the studies of the impacts of VOCs on vegetation have focused on 
short-term exposure and few studies have focused on long-term effects 
of VOCs on vegetation and the potential for metabolites of these 
compounds to affect herbivores or insects.
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    \209\ Viskari E-L. (2000). Epicuticular wax of Norway spruce 
needles as indicator of traffic pollutant deposition. Water, Air, 
and Soil Pollut. 121:327-337.
    \210\ Ugrekhelidze D., F. Korte, G. Kvesitadze. (1997). Uptake 
and transformation of benzene and toluene by plant leaves. Ecotox. 
Environ. Safety 37:24-29.
    \211\ Kammerbauer H., H. Selinger, R. Rommelt, A. Ziegler-Jons, 
D. Knoppik, B. Hock. (1987). Toxic components of motor vehicle 
emissions for the spruce Picea abies. Environ. Pollut. 48:235-243.
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III. Test Procedures and Standards

    In applying heavy-duty criteria pollutant emission standards, EPA 
divides engines primarily into two types: Compression ignition (CI) 
(primarily diesel-fueled engines) and spark-ignition (SI) (primarily 
gasoline-fueled engines). The CI standards and requirements also apply 
to the largest natural gas engines. Battery-electric and fuel-cell 
vehicles are also subject to criteria pollutant standards and 
requirements. Criteria pollutant exhaust emission standards apply for 
four criteria pollutants: Oxides of nitrogen (NOX), 
particulate matter (PM), hydrocarbons (HC), and carbon monoxide 
(CO).\212\ In this Section III we describe new emission standards that 
will apply for these pollutants starting in MY 2027. We also describe 
new and updated test procedures we are finalizing in this rule.
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    \212\ Reference to hydrocarbon (HC) standards includes 
nonmethane hydrocarbon (NMHC), nonmethane-nonethane hydrocarbon 
(NMNEHC) and nonmethane hydrocarbon equivalent (NMHCE). See 40 CFR 
86.007-11.
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    Section III.A provides an overview of provisions that broadly apply 
for this final rule. Section III.B and Section III.D include the new 
laboratory-based standards and final updates to test procedures for 
heavy-duty compression-ignition and spark-ignition engines, 
respectively. Section III.C introduces the final off-cycle standards 
and test procedures that apply for compression-ignition engines and 
extend beyond the laboratory to on-the-road, real-world conditions. 
Section III.E describes the new refueling standards we are finalizing 
for certain heavy-duty spark-ignition engines. Each of these sections 
describe the final new standards and their basis, as well as describe 
the new test procedures and any updates to current test procedures, and 
describe our rationale for the final program, including feasibility 
demonstrations, available data, and comments received.

A. Overview

1. Migration and Clarifications of Regulatory Text
    As noted in Section I of this preamble, we are migrating our 
criteria pollutant regulations for model year 2027 and later heavy-duty 
highway engines from their current location in 40 CFR Part 86, subpart 
A, to 40 CFR Part 1036.\213\ Consistent with this migration, the 
compliance provisions discussed in this preamble refer to the 
regulations in their new location in part 1036. In general, this 
migration is not intended to change the compliance program specified in 
part 86, except as specifically finalized in this rulemaking. EPA 
submitted a memorandum to the docket describing how we proposed to 
migrate

[[Page 4327]]

certification and compliance provisions into 40 CFR part 1036.\214\
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    \213\ As noted in the following sections, we are proposing some 
updates to 40 CFR parts 1037, 1065, and 1068 to apply to other 
sectors in addition to heavy-duty highway engines.
    \214\ Stout, Alan; Brakora, Jessica. Memorandum to docket EPA-
HQ-OAR-2019-0055. ``Technical Issues Related to Migrating Heavy-Duty 
Highway Engine Certification Requirements from 40 CFR part 86, 
subpart A, to 40 CFR part 1036''. March 2022.
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i. Compression- and Spark-Ignition Engines Regulatory Text
    For many years, the regulations of 40 CFR part 86 have referred to 
``diesel heavy-duty engines'' and ``Otto-cycle heavy-duty engines''; 
however, as we migrate the heavy-duty provisions of 40 CFR part 86, 
subpart A, to 40 CFR part 1036 in this rule, we proposed to refer to 
these engines as ``compression-ignition'' (CI) and ``spark-ignition'' 
(SI), respectively, which are more comprehensive terms and consistent 
with existing language in 40 CFR part 1037 for heavy-duty motor vehicle 
regulations. We also proposed to update the terminology for the primary 
intended service classes in 40 CFR 1036.140 to replace Heavy heavy-duty 
engine with Heavy HDE, Medium heavy-duty engine with Medium HDE, Light 
heavy-duty engine with Light HDE, and Spark-ignition heavy-duty engine 
with Spark-ignition HDE.\215\ We received no adverse comment and are 
finalizing these terminology changes, as proposed. This final rule 
revises 40 CFR parts 1036 and 1037 to reflect this updated terminology. 
Throughout this preamble, reference to diesel and Otto-cycle engines 
and the previous service class nomenclature is generally limited to 
discussions relating to current test procedures and specific 
terminology used in 40 CFR part 86. Heavy-duty engines not meeting the 
definition of compression-ignition or spark-ignition are deemed to be 
compression-ignition engines for purposes of part 1036, per 40 CFR 
1036.1(c) and are subject to standards in 40 CFR 1036.104.
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    \215\ This new terminology for engines is also consistent with 
the ``HDV'' terminology used for vehicle classifications in 40 CFR 
1037.140.
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ii. Heavy-Duty Hybrid Regulatory Text
    Similar to our updates to more comprehensive and consistent 
terminology for CI and SI engines, as part of this rule we are also 
finalizing three main updates and clarifications to regulatory language 
for hybrid engines and hybrid powertrains. First, as proposed, we are 
finalizing an updated definition of ``engine configuration'' in 40 CFR 
1036.801; the updated definition clarifies that an engine configuration 
includes hybrid components if it is certified as a hybrid engine or 
hybrid powertrain. Second, we are finalizing, as proposed, a 
clarification in 40 CFR 1036.101(b) that regulatory references in part 
1036 to engines generally apply to hybrid engines and hybrid 
powertrains. Third, we are finalizing as proposed that manufacturers 
may optionally test the hybrid engine and powertrain together, rather 
than testing the engine alone. The option to test hybrid engine and 
powertrain together allows manufacturers to demonstrate emission 
performance of the hybrid technology that are not apparent when testing 
the engine alone. If the emissions results of testing the hybrid engine 
and powertrain together show NOX emissions lower than the 
final standards, then EPA anticipates that manufacturers may choose to 
participate in the NOX ABT program in the final rule (see 
preamble Section IV.G for details on the final ABT program).
    We requested comment on our proposed clarification in 40 CFR 
1036.101(b) that manufacturers may optionally test the hybrid engine 
and powertrain together, rather than testing the engine alone, and 
specifically, whether EPA should require all hybrid engines and 
powertrains to be certified together, rather than making it optional. 
For additional details on our proposed updates and clarifications to 
regulatory language for hybrid engines and hybrid powertrains, as well 
as our specific requests for comment on these changes, see the proposed 
rule preamble (87 FR 17457, March 28, 2022).
    Several commenters support the proposal to allow manufacturers to 
certify hybrid powertrains with a powertrain test procedure, but urge 
EPA to continue to allow manufacturers to certify hybrid systems using 
engine dynamometer testing procedures. These commenters stated that the 
powertrain dynamometer test procedures produce emission results that 
are more representative of hybrid engine or powertrain on-road 
operation than engine-only testing, however, commenters also stated the 
proposed test cycles are not reflective of real-world applications 
where hybrid technology works well and urged EPA to finalize different 
duty-cycles. In contrast, one commenter pointed to data collected from 
light-duty hybrid electric vehicles in Europe that the commenter stated 
shows hybrid-electric vehicles (HEVs) emit at higher levels than 
demonstrated in current certification test procedures; based on those 
data the commenter stated that EPA should not allow HEVs to generate 
NOX emissions credits. Separately, some commenters also 
stated that requiring powertrain testing for hybrid engines or hybrid 
powertrains certification would add regulatory costs or other 
logistical challenges.
    After considering these comments, EPA has determined that 
powertrain testing for hybrid systems should remain an option in this 
final rule. This option allows manufacturers to demonstrate emission 
performance of the hybrid technology, without requiring added test 
burden or logistical constraints. We are therefore finalizing as 
proposed the allowance for manufacturers to test the hybrid engine and 
powertrain together. If testing the hybrid engine and hybrid powertrain 
together results in NOX emissions that are below the final 
standards, then manufacturers can choose to certify to a FEL below the 
standard, and then generate NOX emissions credits as 
provided under the final ABT program (see Section IV.G). We disagree 
with one commenter who asserted that manufacturers should not be 
allowed to generate NOX emissions credits from HEVs based on 
data showing higher emissions from HEVs operating in the real-world 
compared to certification test data in Europe. Rather, we expect the 
powertrain test procedures we are finalizing will accurately reflect 
NOX emissions from HEVs due to the specifications we are 
including in the final test procedures, which differ from the 
certification test procedures to which the commenter referred.\216\ See 
preamble Section III.B.2.v for more details on the powertrain test 
procedures that we are finalizing.
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    \216\ We note that the data provided by the commenter was 
specific to light-duty vehicles and evaluated CO2 
emissions, not criteria pollutant emissions. EPA proposed and is 
finalizing changes to the light-duty test procedures for HEVs; in 
this Section III we focus on heavy-duty test procedures. See 
preamble Section XI and RTC Section 32 for details on the light-duty 
test procedures for HEVs.
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    Similarly, we disagree with those commenters urging EPA to finalize 
different duty-cycle tests to reflect hybrid real-world operations. 
While the duty-cycles suggested by commenters would represent some 
hybrid operations, they would not represent the duty-cycles of other 
hybrid vehicle types. See Section 3 of the Response to Comments 
document for additional details on our responses to comments on 
different duty-cycles for hybrid vehicles, and responses to other 
comments on hybrid engines and hybrid powertrains.
    In addition to our three main proposed updates and clarifications 
to regulatory language for hybrid engines and hybrid powertrain, we 
also proposed that manufacturers would certify a hybrid engine or 
hybrid powertrain to criteria pollutant

[[Page 4328]]

standards by declaring a primary intended service class of the engine 
configuration using the proposed, updated 40 CFR 1036.140.\217\ Our 
proposal included certifying to the same useful life requirements of 
the primary intended service class, which would provide truck owners 
and operators with similar assurance of durability regardless of the 
powertrain configuration they choose. Finally, we proposed an update to 
40 CFR 1036.230(e) such that engine configurations certified as a 
hybrid engine or hybrid powertrain may not be included in an engine 
family with conventional engines, which is consistent with the current 
provisions. We received no adverse comment and are finalizing as 
proposed these updates to 40 CFR 1036.140 and 1036.230(e).
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    \217\ The current provisions of 40 CFR 1036.140 distinguish 
classes based on engine characteristics and characteristics of the 
vehicles for which manufacturers intend to design and market their 
engines.
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iii. Heavy-Duty Zero Emissions Vehicles Regulatory Text
    As part of this final rule we are also updating and consolidating 
regulatory language for battery-electric vehicles and fuel cell 
electric vehicles (BEVs and FCEVs), collectively referred to as zero 
emissions vehicles (ZEVs). For ZEVs, we are finalizing as proposed a 
consolidation and update to our regulations as part of a migration of 
heavy-duty vehicle regulations from 40 CFR part 86 to 40 CFR part 1037. 
In the HD GHG Phase 1 rulemaking, EPA revised the heavy-duty vehicle 
and engine regulations to make them consistent with our regulatory 
approach to electric vehicles (EVs) under the light-duty vehicle 
program. Specifically, we applied standards for all regulated criteria 
pollutants and GHGs to all heavy-duty vehicle types, including 
EVs.\218\ Starting in MY 2016, criteria pollutant standards and 
requirements applicable to heavy-duty vehicles at or below 14,000 
pounds gross vehicle weight rating (GVWR) in 40 CFR part 86, subpart S, 
applied to heavy-duty EVs above 14,000 pounds GVWR through the use of 
good engineering judgment (see current 40 CFR 86.016-1(d)(4)). Under 
the current 40 CFR 86.016-1(d)(4), heavy-duty vehicles powered solely 
by electricity are deemed to have zero emissions of regulated 
pollutants; this provision also provides that heavy-duty EVs may not 
generate NOX or PM emission credits.
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    \218\ 76 FR 57106, September 15, 2011.
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    As proposed, this final rule consolidates certification 
requirements for ZEVs over 14,000 pounds GVWR in 40 CFR part 1037 such 
that manufacturers of ZEVs over 14,000 pounds GVWR will certify to 
meeting the emission standards and requirements of 40 CFR part 1037. 
There are no criterial pollutant emission standards in 40 CFR part 
1037, so we state in a new 40 CFR 1037.102, with revisions from the 
proposed rule, that heavy-duty vehicles without propulsion engines are 
subject to the same criteria pollutant emission standards that apply 
for engines under 40 CFR part 86, subpart A, and 40 CFR part 1036. We 
further specify in the final 40 CFR 1037.102 that ZEVs are deemed to 
have zero tailpipe emissions of criteria pollutants. As discussed in 
Section IV.G, we are choosing not to finalize our proposal to allow 
manufacturers to generate NOX emission credits from ZEVs if 
the vehicle met certain proposed requirements. We are accordingly 
carrying forward in the final 40 CFR 1037.102 a provisions stating that 
manufacturers may not generate emission credits from ZEVs. We are 
choosing not to finalize the proposed durability requirements for ZEVs, 
but we may choose in a future action to reexamine this issue. We are 
finalizing as proposed to continue to not allow heavy-duty ZEVs to 
generate PM emission credits since we are finalizing as proposed not to 
allow any manufacturer to generate PM emission credits for use in MY 
2027 and later under the final ABT program presented in Section IV.G.
    The provisions in existing and final 40 CFR 1037.5 defer to 40 CFR 
86.1801-12 to clarify how certification requirements apply for heavy-
duty vehicles at or below 14,000 pounds GVWR. Emission standards and 
certification requirements in 40 CFR part 86, subpart S, generally 
apply for complete heavy-duty vehicles at or below 14,000 pounds GVWR. 
We proposed to also apply emission standards and certification 
requirements under 40 CFR part 86, subpart S, for all incomplete 
vehicles at or below 14,000 pounds GVWR. We decided not to adopt this 
requirement and are instead continuing to allow manufacturers to choose 
whether to certify incomplete vehicles at or below 14,000 pounds GVWR 
to the emission standards and certification requirements in either 40 
CFR part 86, subpart S, or 40 CFR part 1037.
2. Numeric Standards and Test Procedures for Compression-Ignition and 
Spark-Ignition Engines
    As summarized in preamble Section I.B and detailed in this preamble 
Section III, we are finalizing numeric NOX standards and 
useful life periods that are largely consistent with the most stringent 
proposed option for MY 2027. The specific standards are summarized in 
Section III.B, Section 0, Section III.D, and Section III.E. As required 
by CAA section 202(a)(3), EPA is finalizing new NOX, PM, HC, 
and CO emission standards for heavy-duty engines that reflect the 
greatest degree of emission reduction achievable through the 
application of technology that we have determined would be available 
for MY 2027, and in doing so have given appropriate consideration to 
additional factors, namely lead time, cost, energy, and safety. For all 
heavy-duty engine classes, the final numeric NOX standards 
for medium- and high-load engine operations match the most stringent 
standards proposed for MY 2027; for low-load operations we are 
finalizing the most stringent standard proposed for any model year (see 
III.B.2.iii for discussion).\219\ For smaller heavy-duty engine service 
classes (i.e., light and medium heavy-duty engines CI and SI heavy-duty 
engines), the numeric standards are combined with the longest useful 
life periods we proposed. For the largest heavy-duty engines (i.e., 
heavy heavy-duty engines), the final numeric standards are combined 
with the longest useful life mileage that we proposed for MY 2027. The 
final useful life periods for the largest heavy-duty engines are 50 
percent longer than today's useful life periods, which will play an 
important role in ensuring continued emissions control while the 
engines operate on the road. The final numeric emissions standards and 
useful life periods for all heavy-duty engines are based on further 
consideration of data included in the proposal from our engine 
demonstration programs that show the final emissions standards are 
feasible at the final useful life periods applicable to these each 
heavy-duty engine service class. Our assessment of the data available 
at the time of proposal is further supported by our evaluation of 
additional information and public comments stating that the proposed 
standards are feasible. Our technical assessments are primarily based 
on results from testing several diesel engine and aftertreatment 
systems at Southwest Research Institute and at EPA's National Vehicle 
and Fuel Emissions Laboratory (NVFEL), as well as heavy-duty gasoline 
engine testing conducted at NVFEL; we also

[[Page 4329]]

considered heavy-duty engine certification data submitted to EPA by 
manufacturers, ANPR and NPRM comments, and other data submitted by 
industry stakeholders or studies conducted by EPA, as more specifically 
identified in the sections that follow.
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    \219\ As proposed, we are finalizing a new test procedure for 
heavy-duty CI engines to demonstrate emission control when the 
engine is operating under low-load and idle conditions; this new 
test procedure does not apply to heavy-duty SI engines (see Section 
III.B.2.iii for additional discussion).
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    After further consideration of the data included in the proposal, 
as well as information submitted by commenters and additional data we 
collected since the time of proposal, we are finalizing two updates 
from our proposed testing requirements in order to ensure the greatest 
emissions reductions technically achievable are met throughout the 
final useful life periods; these updates are tailored to the larger 
engine classes (medium and heavy heavy-duty engines). First, we are 
finalizing a requirement for manufacturers to demonstrate before heavy 
heavy-duty engines are in-use that the emissions control technology is 
durable through a period of time longer than the final useful life 
mileage. For these largest engines with the longest useful life 
mileages, the extended laboratory durability demonstration will better 
ensure the final standards will be met throughout the regulatory useful 
life under real-world operations where conditions are more variable. 
Second, we are finalizing an interim in-use compliance allowance that 
applies when EPA evaluates whether heavy or medium heavy-duty engines 
are meeting the final standards after these engines are in use in the 
real-world. When combined with the final useful life values, we believe 
the interim in-use compliance allowance will address concerns raised in 
comments from manufacturers that the more stringent proposed MY 2027 
standards would not be feasible to meet over the very long useful life 
periods of heavy heavy-duty engines, or under the challenging duty-
cycles of medium heavy-duty engines. This interim, in-use compliance 
allowance is generally consistent with our past practice (for example, 
see 66 FR 5114, January 18, 2001); also consistent with past practice, 
the compliance allowance is included as an interim provision that we 
may reassess in the future through rulemaking based on the performance 
of emissions controls over the final useful life periods for medium and 
heavy heavy-duty engines.\220\ To set standards that result in the 
greatest emission reductions achievable for medium and heavy heavy-duty 
engines, we considered additional data that we and others collected 
since the time of the proposal; these data show the significant 
technical challenge of maintaining very low NOX emissions 
throughout very long useful life periods for heavy heavy-duty engines, 
and greater amounts of certain aging mechanisms over the long useful 
life periods of medium heavy-duty engines. In addition to these data, 
in setting the standards we gave appropriate consideration to costs 
associated with the application of technology to achieve the greatest 
emissions reductions in MY 2027 (i.e., cost of compliance for 
manufacturers associated with the standards \221\) and other statutory 
factors, including energy and safety. We determined that for heavy 
heavy-duty engines the combination of: (1) The most stringent MY 2027 
standards proposed, (2) longer useful life periods compared to today's 
useful life periods, (3) targeted, interim compliance allowance 
approach to in-use compliance testing, and (4) the extended durability 
demonstration for emissions control technologies is appropriate, 
feasible, and consistent with our authority under the CAA to set 
technology-forcing criteria pollutant standards for heavy-duty engines 
for their useful life.\222\ Similarly, for medium heavy-duty engines we 
determined that the combination of the first three elements (i.e., most 
stringent MY 2027 standards proposed, increase in useful life periods, 
and interim compliance allowance for in-use testing) is appropriate, 
feasible, and consistent with our CAA authority to set technology-
forcing criteria pollutant standards for heavy-duty engines for their 
useful life.
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    \220\ We plan to closely monitor the in-use emissions 
performance of model year 2027 and later engines to determine the 
long-term need for the interim compliance allowance. For example, we 
intend to analyze the data from the manufacturer run in-use testing 
program to compare how engines age in the field compared to how they 
age in the laboratory.
    \221\ More specifically, for this rule in setting the final 
standards and consistent with CAA section 202(a)(3)(A), the cost of 
compliance for manufacturers associated with the standards that EPA 
gave appropriate consideration to includes the direct manufacturing 
costs and indirect costs incurred by manufacturers associated with 
meeting the final standards over the corresponding final useful life 
values, given that this rule sets new more stringent standards 
through both the numeric level of the standard and the length of the 
useful life period.
    \222\ CAA section 202(a)(3)(A) is a technology-forcing provision 
and reflects Congress' intent that standards be based on projections 
of future advances in pollution control capability, considering 
costs and other statutory factors. See National Petrochemical & 
Refiners Association v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002) 
(explaining that EPA is authorized to adopt ``technology-forcing'' 
regulations under CAA section 202(a)(3)); NRDC v. Thomas, 805 F.2d 
410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory 
language that ``seek[s] to promote technological advances while also 
accounting for cost does not detract from their categorization as 
technology-forcing standards''); see also Husqvarna AB v. EPA, 254 
F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213 
have similar language and are technology-forcing standards). In this 
context, the term ``technology-forcing'' has a specific legal 
meaning and is used to distinguish standards that may require 
manufacturers to develop new technologies (or significantly improve 
existing technologies) from standards that can be met using existing 
off-the-shelf technology alone. Technology-forcing standards such as 
those in this final rule do not require manufacturers to use 
specific technologies.
---------------------------------------------------------------------------

    In addition to the final standards for the defined duty cycle and 
off-cycle test procedures, the final standards include several other 
provisions for controlling emissions from specific operations in CI or 
SI engines. First, we are finalizing, as proposed, to allow CI engine 
manufacturers to voluntarily certify to idle standards using a new idle 
test procedure that is based on an existing California Air Resources 
Board (CARB) procedure.\223\
---------------------------------------------------------------------------

    \223\ 13 CCR 1956.8 (a)(6)(C)--Optional NOX idling 
emission standard.
---------------------------------------------------------------------------

    We are also finalizing two options for manufacturers to control 
engine crankcase emissions. Specifically, manufacturers will be 
required to either: (1) As proposed, close the crankcase, or (2) 
measure and account for crankcase emissions using an updated version of 
the current requirements for an open crankcase. We believe that either 
will ensure that the total emissions are accounted for during 
certification testing and throughout the engine operation during useful 
life. See Section III.B for more discussion on both the final idle and 
crankcase provisions.
    For heavy-duty SI, we are finalizing as proposed a new refueling 
emission standard for incomplete vehicles above 14,000 lb GVWR starting 
in MY 2027.\224\ The final refueling standard is based on the current 
refueling standard that applies to complete heavy-duty gasoline-fueled 
vehicles. Consistent with the current evaporative emission standards 
that apply for these same vehicles, we are finalizing a requirement 
that manufacturers can use an engineering analysis to demonstrate that 
they meet our final refueling standard. We are also adopting an 
optional alternative phase-in compliance pathway that manufacturers can 
opt into in lieu of being subject to this implementation date for all 
incomplete heavy-duty vehicles above 14,000 pounds GVWR (see Section 
III.E for details).
---------------------------------------------------------------------------

    \224\ Some vehicle manufactures sell their engines or 
``incomplete vehicles'' (i.e., chassis that include their engines, 
the frame, and a transmission) to body builders who design and 
assemble the final vehicle.
---------------------------------------------------------------------------

    Consistent with our proposal, we are also finalizing several 
provisions to

[[Page 4330]]

reduce emissions from a broader range of engine operating conditions. 
First, we are finalizing new standards for our existing test procedures 
to reduce emissions under medium- and high-load operations (e.g., when 
trucks are traveling on the highway). Second, we are finalizing new 
standards and a corresponding new test procedure to measure emissions 
during low-load operations (i.e., the low-load cycle, LLC). Third, we 
are finalizing new standards and updates to an existing test procedure 
to measure emissions over the broader range of operations that occur 
when heavy-duty engines are operating on the road (i.e., off-
cycle).\225\
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    \225\ Duty-cycle test procedures measure emissions while the 
engine is operating over precisely defined duty cycles in an 
emissions testing laboratory and provide very repeatable emission 
measurements. ``Off-cycle'' test procedures measure emissions while 
the engine is not operating on a specified duty cycle; this testing 
can be conducted while the engine is being driven on the road (e.g., 
on a package delivery route), or in an emission testing laboratory. 
Both duty-cycle and off-cycle testing are conducted pre-production 
(e.g., for certification) or post-production to verify that the 
engine meets applicable duty-cycle or off-cycle emission standards 
throughout useful life (see Section III for more discussion).
---------------------------------------------------------------------------

    The new, more stringent numeric standards for the existing 
laboratory-based test procedures that measure emissions during medium- 
and high-load operations will ensure significant emissions reductions 
from heavy-duty engines. Without this final rule, these medium- and 
high-load operations are projected to contribute the most to heavy-duty 
NOX emissions in 2045.
    We are finalizing as proposed a new LLC test procedure, which will 
ensure demonstration of emission control under sustained low-load 
operations. After further consideration of data included in the 
proposal, as well as additional information from the comments 
summarized in this section, we are finalizing the most stringent 
numeric standard for the LLC that we proposed for any model year. As 
discussed in our proposal, data from our CI engine demonstration 
program showed that the lowest numeric NOX standard proposed 
would be feasible for the LLC throughout a useful life period similar 
to the useful life we are finalizing for the largest heavy-duty 
engines. After further consideration of this data, and additional 
support from data collected since the time of proposal, we are 
finalizing the most stringent standard proposed for any model year.
    We are finalizing new numeric standards and revisions to the 
proposed off-cycle test procedure. We proposed updates to the current 
off-cycle test procedure that included binning emissions measurements 
based on the type of operation the engine is performing when the 
measurement data is being collected. Specifically, we proposed that 
emissions data would be grouped into three bins, based on if the engine 
was operating in idle (Bin 1), low-load (Bin 2), or medium-to-high load 
(Bin 3) operation. Given the different operational profiles of each of 
the three bins, we proposed a separate standard for each bin. Based on 
further consideration of data included in the proposal, as well as 
additional support from our consideration of data provided by 
commenters, we are finalizing off-cycle standards for two bins, rather 
than three bins; correspondingly, we are finalizing a two-bin approach 
for grouping emissions data collected during off-cycle test procedures. 
Our evaluation of available information shows that two bins better 
represent the differences in engine operations that influence emissions 
(e.g., exhaust temperature, catalyst efficiency) and ensure sufficient 
data is collected in each bin to allow for an accurate analysis of the 
data to determine if emissions comply with the standard for each bin. 
Preamble Section III.C further discusses the final off-cycle standards.
3. Implementation of the Final Program
    As discussed in this section, we have evaluated the final standards 
in terms of technological feasibility, lead time, and stability, and 
given appropriate consideration to cost, energy, and safety, consistent 
with the requirements in CAA section 202(a)(3). The final standards are 
based on data from our CI and SI engine feasibility demonstration 
programs that was included in the proposal, and further supported by 
information submitted by commenters and additional data we collected 
since the time of proposal. Our evaluation of available data shows that 
the final standards and useful life periods are feasible and will 
result in the greatest emission reductions achievable for MY 2027, 
pursuant to CAA section 202(a)(3), giving appropriate consideration to 
cost, lead time, and other factors. We note that CAA section 202(a)(3) 
neither requires that EPA consider all the statutory factors equally 
nor mandates a specific method of cost analysis; rather EPA has 
discretion in determining the appropriate consideration to give such 
factors.\226\ As discussed in the Chapter 3 of the RIA, the final 
standards are achievable without increasing the overall fuel 
consumption and CO2 emissions of the engine (1) for each of 
the duty cycles (SET, FTP, and LLC), and (2) for the fuel mapping test 
procedures defined in 40 CFR 1036.535 and 1036.540.\227\ Finally, the 
final standards will have no negative impact on safety, based on the 
existing use of these technologies in light-duty and heavy-duty engines 
on the road today (see section 3 of the Response to Comments document 
for additional discussion on our assessment that the final standards 
will have no negative impact on safety). This includes the safety of 
closed crankcase systems, which we received comment on. As discussed in 
Section 3 of the RTC, one commenter stated that requiring closed 
crankcases could increase the chance of engine run away caused by 
combustion of engine oil that could enter the intake from the closed-
crankcase system. We disagree with the commenter since closed crankcase 
systems are used on engines today with no adverse effect on safety; 
however, we are providing flexibility for manufactures to meet the 
final standards regarding crankcase emissions (see preamble Section 
III.B.2.vi for details).
---------------------------------------------------------------------------

    \226\ See, e.g., Sierra Club v. EPA, 325 F.3d 374, 378 (D.C. 
Cir. 2003) (explaining that similar technology forcing language in 
CAA section 202(l)(2) ``does not resolve how the Administrator 
should weigh all [the statutory] factors in the process of finding 
the `greatest emission reduction achievable' ''); Husqvarna AB v. 
EPA, 254 F.3d 195, 200 (D.C. Cir. 2001) (explaining that under CAA 
section 213's similar technology-forcing authority that ``EPA did 
not deviate from its statutory mandate or frustrate congressional 
will by placing primary significance on the `greatest degree of 
emission reduction achievable' '' or by considering cost and other 
statutory factors as important but secondary).
    \227\ The final ORVR requirements discussed in Section III.E 
will reduce fuel consumed from gasoline fuel engines, but these fuel 
savings will not be measured on the duty cycles since the test 
procedures for these tests measure tailpipe emissions and do not 
measure emissions from refueling. We describe our estimate of the 
fuel savings in Chapter 7 of the RIA.
---------------------------------------------------------------------------

    While we have referenced a technology pathway for complying with 
our standards (Chapter 3 of the RIA) that is consistent with CAA 
section 202(a)(3), there are other technology pathways that 
manufacturers may choose in order to comply with the performance-based 
final standards. We did not rely on alternative technology pathways in 
our assessment of the feasibility of the final standards, however, 
manufacturers may choose from any number of technology pathways to 
comply with the final standards (e.g., alternative fuels, including 
biodiesel, renewable diesel, renewable natural gas, renewable propane, 
or hydrogen in combination with relevant emissions aftertreatment 
technologies, and electrification, including plug-in hybrid electric 
vehicles, battery-electric or fuel cell

[[Page 4331]]

electric vehicles). As noted in Section I, we are finalizing a program 
that will begin in MY 2027, which is the earliest year that standards 
can begin to apply under CAA section 202(a)(3)(C).\228\ The final 
NOX standards are a single-step program that reflect the 
greatest emission reductions achievable starting in MY 2027, giving 
appropriate consideration to costs and other factors. In this final 
rule, we are focused on achieving the greatest emission reductions 
achievable in the MY 2027 timeframe, and have applied our judgment in 
determining the appropriate standards for MY 2027 under this authority 
for a national program. As the heavy-duty industry continues to 
transition to zero-emission technologies, EPA could consider additional 
criteria pollutant standards for model years beyond 2027 in future 
rules.
---------------------------------------------------------------------------

    \228\ Section 202(a)(3)(C) requires that standards under 
202(a)(3)(A) apply no earlier than 4 years after promulgation, and 
apply for no less than 3 model years.
---------------------------------------------------------------------------

    In the event that manufacturers start production of some engine 
families sooner than four years from our final rule, we are finalizing 
a provision for manufacturers to split the 2027 model year, with an 
option for manufacturers to comply with the final MY 2027 standards for 
all engines produced for that engine family in MY 2027. Specifically, 
we are finalizing as proposed that a MY 2027 engine family that starts 
production within four years of the final rule could comply with the 
final MY 2027 standards for all engines produced for that engine family 
in MY2027, or could split the engine family by production date in MY 
2027 such that engines in the family produced prior to four years after 
the date that the final rule is promulgated would continue to be 
subject to the existing standards.229 230 The split model 
year provision for MY 2027 provides assurance that all manufacturers, 
regardless of when they start production of their engine families, will 
have four years of lead time to the MY 2027 standards under this final 
rule, while also maximizing emission reductions, which is consistent 
with our CAA authority. This final rule is promulgated upon the date of 
signature, upon which date EPA also provided this signed final rule to 
manufacturers and other stakeholders by email and posted it on EPA's 
public website.\231\
---------------------------------------------------------------------------

    \229\ See 40 CFR 86.007-11.
    \230\ 40 CFR 1036.150(t).
    \231\ This final rule will also be published in the Federal 
Register, and the effective date runs from the date of publication 
as specified in the DATES section. Note, non-substantive edits from 
the Office of the Federal Register may appear in the published 
version of the final rule.
---------------------------------------------------------------------------

4. Severability
    This final rule includes new and revised requirements for numerous 
provisions under various aspects of the highway heavy-duty emission 
control program, including numeric standards, test procedures, 
regulatory useful life, emission-related warranty, and other 
requirements. Further, as explained in Sections I and XI, it modernizes 
and amends numerous other CFR parts for other standard-setting parts 
for various specific reasons. Therefore, this final rule is a 
multifaceted rule that addresses many separate things for independent 
reasons, as detailed in each respective section of this preamble. We 
intended each portion of this rule to be severable from each other, 
though we took the approach of including all the parts in one 
rulemaking rather than promulgating multiple rules to modernize each 
part of the program.
    For example, the following portions of this rulemaking are mutually 
severable from each other, as numbered: (1) The emission standards in 
section III; (2) warranty in Section IV.B.1; (3) OBD requirements in 
Section IV.C; (4) inducements requirements in Section IV.D; (5) ABT 
program in Section IV.G; (6) the migration and clarification of 
regulatory text in Section III.A; and (7) other regulatory amendments 
discussed in Section XI. Each emission standard in Section III is also 
severable from each other emission standard, including for each duty-
cycle, off-cycle, and refueling standard; each pollutant; and each 
primary intended service class. For example, the NOX 
standard for the FTP duty-cycle for Heavy HDE is severable from all 
other emission standards. Each of the migration and clarification 
regulatory amendments in Section III.A is also severable from all the 
other regulatory amendments in that Section, and each of the regulatory 
amendments in Section XI is also severable from all the other 
regulatory amendments in that Section. If any of the above portions is 
set aside by a reviewing court, then we intend the remainder of this 
action to remain effective, and the remaining portions will be able to 
function absent any of the identified portions that have been set 
aside. Moreover, this list is not intended to be exhaustive, and should 
not be viewed as an intention by EPA to consider other parts of the 
rule not explicitly listed here as not severable from other parts of 
the rule.

B. Summary of Compression-Ignition Exhaust Emission Standards and Duty 
Cycle Test Procedures

    EPA is finalizing new NOX, PM, HC, and CO emission 
standards for heavy-duty compression-ignition engines that will be 
certified under 40 CFR part 1036.232 233 We are finalizing 
new emission standards for our existing laboratory test cycles (i.e., 
SET and FTP) and finalizing new NOX, PM, HC and CO emission 
standards based on a new LLC, as described in this section.\234\ The 
standards for NOX, PM, and HC are in units of milligrams/
horsepower-hour instead of the grams/horsepower-hour used for existing 
standards because using units of milligrams better reflects the 
precision of the new standards, rather than adding multiple zeros after 
the decimal place. Making this change will require updates to how 
manufacturers report data to the EPA in the certification application, 
but it does not require changes to the test procedures that define how 
to determine emission values.
---------------------------------------------------------------------------

    \232\ See 40 CFR 1036.104.
    \233\ See 40 CFR 1036.605 and Section XI.B of this preamble for 
a discussion of engines installed in specialty vehicles.
    \234\ See 40 CFR 1036.104.
---------------------------------------------------------------------------

    The final duty cycle emission standards in 40 CFR 1037.104 apply 
starting in model year 2027. This final rule includes new standards 
over the SET and FTP duty cycles currently used for certification, as 
well as new standards over a new LLC duty cycle to ensure manufacturers 
of compression-ignition engines are designing their engines to address 
emissions in during lower load operation that is not covered by the SET 
and FTP. The new standards are shown in Table III-1.

            Table III-1--Final Duty Cycle Emission Standards for Light HDE, Medium HDE, and Heavy HDE
----------------------------------------------------------------------------------------------------------------
                                                                     Model year 2027 and later
                                                 ---------------------------------------------------------------
                   Duty cycle                     NOX \a\ mg/hp-
                                                        hr          HC mg/hp-hr     PM mg/hp-hr     CO g/hp-hr
----------------------------------------------------------------------------------------------------------------
SET and FTP.....................................              35              60               5             6.0

[[Page 4332]]

 
LLC.............................................              50             140               5             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.

    This Section III.B describes the duty cycle emission standards and 
test procedures we are finalizing for compression-ignition engines. We 
describe compression-ignition engine technology packages that 
demonstrate the feasibility of achieving these standards in Section 
III.B.3.ii. The proposed rule provided an extensive discussion of the 
rationale and information supporting the proposed duty cycle standards 
(87 FR 17460, March 28, 2022). Chapters 1, 2, and 3 of the RIA include 
additional information related to the range of technologies to control 
criteria emissions, background on applicable test procedures, and the 
full feasibility analysis for compression-ignition engines. See also 
section 3 of the Response to Comments for a detailed discussion of the 
comments and how they have informed this final rule.
    As part of this rulemaking, we are finalizing an increase in the 
useful life for each engine class as described in Section IV.A. The 
emission standards outlined in this section will apply for the longer 
useful life periods and manufacturers will be responsible for 
demonstrating that their engines will meet these standards as part of 
the revisions to durability requirements described in Section IV.F. In 
Section IV.G, we discuss the updates to the ABT program, including 
updates to account for the three laboratory cycles (SET, FTP, and LLC) 
with unique standards.
1. Background on Existing Duty Cycle Test Procedures and Standards
    We begin by providing background information on the existing duty 
cycle test procedures and standards as relevant to this final rule, 
including the SET and FTP standards and test procedures, powertrain and 
hybrid powertrain test procedures, test procedure adjustments to 
account for production and measurement variability, and crankcase 
emissions. Current criteria pollutant standards must be met by 
compression-ignition engines over both the SET and FTP duty cycles. The 
FTP duty cycles, which date back to the 1970s, are composites of a 
cold-start and a hot-start transient duty cycle designed to represent 
urban driving. There are separate FTP duty cycles for both SI and CI 
engines. The cold-start emissions are weighted by one-seventh and the 
hot-start emissions are weighted by six-sevenths.\235\ The SET is a 
more recent duty cycle for diesel engines that is a continuous cycle 
with ramped transitions between the thirteen steady-state modes.\236\ 
The SET does not include engine starting and is intended to represent 
fully warmed-up operating modes not emphasized in the FTP, such as more 
sustained high speeds and loads.
---------------------------------------------------------------------------

    \235\ See 40 CFR 86.007-11 and 40 CFR 86.008-10.
    \236\ See 40 CFR 86.1362.
---------------------------------------------------------------------------

    Emission standards for criteria pollutants are currently set to the 
same numeric value for SET and FTP test cycles, as shown in Table III-
2. Manufacturers of compression-ignition engines have the option under 
the existing regulations to participate in our ABT program for 
NOX and PM, as discussed in the background of Section 
IV.G.\237\ These pollutants are subject to FEL caps under the existing 
regulations of 0.50 g/hp-hr for NOX and 0.02 g/hp-hr for 
PM.\238\
---------------------------------------------------------------------------

    \237\ See 40 CFR 86.007-15.
    \238\ See 40 CFR 86.007-11.

          Table III-2--Existing Part 86 Diesel-Cycle Engine Standards Over the SET and FTP Duty Cycles
----------------------------------------------------------------------------------------------------------------
                                                                   PM \b\ (g/hp-
                        NOX \a\ (g/hp-hr)                               hr)        HC (g/hp-hr)    CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
0.20............................................................            0.01            0.14            15.5
----------------------------------------------------------------------------------------------------------------
\a\ Engine families participating in the existing ABT program are subject to a FEL cap of 0.50 g/hp-hr for NOX.
\b\ Engine families participating in the existing ABT program are subject to a FEL cap of 0.02 g/hp-hr for PM.

    EPA developed powertrain and hybrid powertrain test procedures for 
the HD GHG Phase 2 Heavy-Duty Greenhouse Gas rulemaking (81 FR 73478, 
October 25, 2016) with updates in the HD Technical Amendments final 
rule (86 FR 34321, June 29, 2021).\239\ The powertrain and hybrid 
powertrain tests allow manufacturers to directly measure the 
effectiveness of the engine, the transmission, the axle and the 
integration of these components as an input to the Greenhouse gas 
Emission Model (GEM) for compliance with the greenhouse gas standards. 
As part of the technical amendments, EPA updated the powertrain test 
procedure to allow use of test cycles beyond the current GEM vehicle 
drive cycles, to include the SET and FTP engine-based test cycles and 
to facilitate hybrid powertrain testing (40 CFR 1036.510, 1036.512, and 
1037.550).
---------------------------------------------------------------------------

    \239\ See 40 CFR 1037.550.
---------------------------------------------------------------------------

    These heavy-duty diesel-cycle engine standards are applicable for a 
useful life period based on the primary intended service class of the 
engine.\240\ For certification, manufacturers must demonstrate that 
their engines will meet these standards throughout the useful life by 
performing a durability test and applying a deterioration factor (DF) 
to their certification value.\241\ Additionally, manufacturers must 
adjust emission rates for engines with exhaust aftertreatment to 
account for infrequent

[[Page 4333]]

regeneration events accordingly.\242\ To account for variability in 
these measurements, as well as production variability, manufacturers 
typically add margin between the DF plus infrequent regeneration 
adjustment factor (IRAF) adjusted test result and the FEL. A summary of 
the margins manufacturers have added for MY 2019 and newer engines is 
summarized in Chapter 3.1.2 of the RIA.
---------------------------------------------------------------------------

    \240\ 40 CFR 86.004-2.
    \241\ See 40 CFR 86.004-26(c) and (d) and 86.004-28(c) and (d).
    \242\ See 40 CFR 1036.501(d).
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    Current regulations restrict the discharge of crankcase emissions 
directly into the ambient air. Blowby gases from gasoline engine 
crankcases have been controlled for many years by sealing the crankcase 
and routing the gases into the intake air through a positive crankcase 
ventilation (PCV) valve. However, in the past there have been concerns 
about applying a similar technology for diesel engines. For example, 
high PM emissions venting into the intake system could foul 
turbocharger compressors. As a result of this concern, diesel-fueled 
and other compression-ignition engines equipped with turbochargers (or 
other equipment) were not required to have sealed crankcases (see 40 
CFR 86.007-11(c)). For these engines, manufacturers are allowed to vent 
the crankcase emissions to ambient air as long as they are measured and 
added to the exhaust emissions during all emission testing to ensure 
compliance with the emission standards. Because all new highway heavy-
duty diesel engines on the market today are equipped with 
turbochargers, they are not required to have closed crankcases under 
the current regulations. Chapter 1.1.4 of the RIA describes EPA's 
recent test program to evaluate the emissions from open crankcase 
systems on two modern heavy-duty diesel engines. Results suggest HC and 
CO emitted from the crankcase can be a notable fraction of overall 
tailpipe emissions. By closing the crankcase, those emissions would be 
rerouted to the engine or aftertreatment system to ensure emission 
control.
2. Test Procedures and Standards
    As described in Section III.B.3.ii, we have determined that the 
technology packages evaluated for this final action can achieve the new 
duty-cycle standards. We are finalizing a single set of standards that 
take effect starting in MY 2027, including not only new numerical 
standards for new and existing duty-cycles but also other new numerical 
standards for revised off-cycles test procedures and compliance 
provisions, longer useful life periods, and other requirements.
    The final standards were derived to achieve the maximum feasible 
emissions reductions from heavy-duty diesel engines for MY 2027, 
considering lead time, stability, cost, energy, and safety. To 
accomplish this, we evaluated what operation made up the greatest part 
of the inventory, as discussed in Section VI.B, and what technologies 
can be used to reduce emissions in these areas. As discussed in Section 
I, we project that emissions from operation at low power, medium-to-
high power, and mileages beyond the current regulatory useful life of 
the engine will account for the majority of heavy-duty highway 
emissions in 2045. To achieve reductions in these three areas, we 
identified options for cycle-specific standards to ensure that the 
maximum achievable reductions are seen across the operating range of 
the engine. As described in Section IV, we are finalizing an increase 
in the regulatory useful life periods for each heavy-duty engine class 
to ensure these new standards are met for a greater portion of the 
engine's operational life. Also as described in Section IV, we are 
separately lengthening the warranty periods for each heavy-duty engine 
class, which is expected to help to maintain the benefits of the 
emission controls for a greater portion of the engine's operational 
life.
    To achieve the goal of reducing emissions across the operating 
range of the engine, we are finalizing standards for three duty cycles 
(SET, FTP, and LLC). In finalizing these standards, we assessed the 
performance of the best available aftertreatment systems under various 
operating conditions. For example, we observed that these systems are 
more effective at reducing NOX emissions at the higher 
exhaust temperatures that occur at high engine power than they are at 
reducing NOX emissions at low exhaust temperatures that 
occur at low engine power. To achieve the maximum NOX 
reductions from the engine at maximum power, the aftertreatment system 
was designed to ensure that the downstream selective catalytic 
reduction (SCR) catalyst was properly sized, diesel exhaust fluid (DEF) 
was fully mixed with the exhaust gas ahead of the SCR catalyst and the 
diesel oxidation catalyst (DOC) was designed to provide a molar ratio 
of NO to NO2 of near one. The final standards for the FTP 
and LLC are 80 to 90 percent, or more, lower as compared to current 
standards, which will contribute to reductions in emissions under low 
power operation and under cold-start conditions. The standards are 
achievable by utilizing cylinder deactivation (CDA), dual-SCR 
aftertreatment configuration, closed crankcase, and heated diesel 
exhaust fluid (DEF) dosing. To reduce emissions under medium to high 
power, the final standards for the SET are greater than 80 percent 
lower as compared to current standards. The SET standards are 
achievable by utilizing improvements to the SCR formulation, SCR 
catalyst sizing, and improved mixing of DEF with the exhaust. Further 
information about these technologies can be found in Chapters 1 and 3 
of the RIA.
    The final PM standards are set at a level that requires heavy-duty 
engines to maintain the emissions performance of current diesel 
engines. The final standards for HC and CO are set at levels that are 
equivalent to the maximum emissions reductions achievable by spark-
ignition engines over the FTP, with the general intent of making the 
final standards fuel neutral.243 244 Compared to current 
standards, the final standards for the SET and FTP duty cycles are 50 
percent lower for PM, 57 percent lower for HC, and 61 percent lower for 
CO. Each of these standards are discussed in more detail in the 
following sections.
---------------------------------------------------------------------------

    \243\ See Section III.D for a discussion of these standards as 
they relate to Spark-ignition HDE.
    \244\ See 65 FR 6728 (February 10, 2000) and 79 FR 23454 (April 
28, 2014) for more discussion on the principle of fuel neutrality 
applied in recent rulemakings for light-duty vehicle criteria 
pollutant standards.
---------------------------------------------------------------------------

    For Heavy HDE, we are finalizing NOX standards to a 
useful life of 650,000 miles with a durability demonstration out to 
750,000 miles, as discussed later in Section III.B.2. We recognize the 
greater demonstration burden of a useful life of 650,000 miles for 
these engines, and after careful analysis are updating our DF 
demonstration provisions to include two options for an accelerated 
aging demonstration. However, we also are taking into account that 
extending a durability demonstration, given that it is conducted in the 
controlled laboratory environment, will better ensure the final 
standards will be met throughout the longer final regulatory useful 
life mileage of 650,000 miles when these engines are operating in the 
real-world where conditions are more variable. We are thus requiring 
the durability demonstration to show that the emission control system 
hardware is designed to comply with the NOX standards out to 
750,000 miles. As discussed further in Section III.B, the aging 
demonstration out to 750,000 miles in a controlled laboratory 
environment ensures that manufacturers are designing Heavy HDE to meet 
the

[[Page 4334]]

final standards out to the regulatory useful life of 650,000 miles once 
the engine is in the real-world, while reducing the risk of greater 
real world uncertainties impacting emissions at the longest useful life 
mileages in the proposed rule. This approach both sets standards that 
result in the maximum emission reductions achievable in MY 2027 while 
addressing the technical issues raised by manufacturers regarding 
various uncertainties in variability and the degradation of system 
performance over time due to contamination of the aftertreatment from, 
for example, fuel contamination (the latter of which is out of the 
manufacturer's control).
    As discussed in Section III.B.3, we have assessed the feasibility 
of the standards for compression-ignition engines by testing a Heavy 
HDE equipped with cylinder CDA technology, closed crankcase, and dual-
SCR aftertreatment configuration with heated DEF dosing. The 
demonstration work consisted of two phases. The first phase of the 
demonstration was led by CARB and is referred to as CARB Stage 3. In 
this demonstration the aftertreatment was chemically- and 
hydrothermally-aged to the equivalent of 435,000 miles. During this 
aging the emissions performance of the engine was assessed after the 
aftertreatment was degreened \245\, at the equivalent of 145,000 miles, 
290,000 miles and 435,000 miles. The second phase of the demonstration 
was led by EPA and is referred to as the EPA Stage 3 engine. In this 
phase, improvements were made to the aftertreatment by replacing the 
zone-coated catalyzed soot filter with a separate DOC and diesel 
particulate filter (DPF) that were chemically- and hydrothermally-aged 
to the equivalent of 800,000 miles and improving the mixing of the DEF 
with exhaust prior to the downstream SCR catalyst. The EPA Stage 3 
engine was tested at an age equivalent to 435,000, 600,000, and 800,000 
miles. We also tested two additional aftertreatment systems, referred 
to as ``System A'' and ``System B,'' which are each also a dual-SCR 
aftertreatment configuration with heated DEF dosing. However, they each 
have unique catalyst washcoat formulation and the ``System A'' 
aftertreatment has greater SCR catalyst volume. The details of these 
aftertreatment systems, along with the test results, can be found in 
RIA Chapter 3.
---------------------------------------------------------------------------

    \245\ Degreening is a process by which the catalyst is broken in 
and is critical in order to obtain a stable catalyst prior to 
assessing the catalyst's performance characteristics.
---------------------------------------------------------------------------

i. FTP
    We are finalizing new emission standards for testing over the FTP 
duty cycle, as shown in Table III-3.\246\ These brake-specific FTP 
standards apply across the Heavy HDE, Medium HDE, and Light HDE primary 
intended service classes over the useful life periods shown in Table 
III-4.\247\ The numeric levels of the NOX FTP standards at 
the time of certification are consistent with the most stringent 
proposed for MY 2027; as summarized in Section III.A.2 and detailed in 
this Section III.B we are also finalizing an interim, in-use compliance 
allowance for Medium and Heavy HDEs. The numeric level of the PM and CO 
FTP standards are the same as proposed, and the numeric level of the HC 
FTP standard is consistent with the proposed Option 1 standard starting 
in MY 2027. These standards have been shown to be feasible for 
compression-ignition engines based on testing of the CARB Stage 3 and 
EPA Stage 3 engine with a chemically- and hydrothermally-aged 
aftertreatment system.\248\ The EPA Stage 3 engine, was aged to and 
tested at the equivalent of 800,000 miles.\249\ EPA's System A 
demonstration engine, was aged to and tested at the equivalent of 
650,000 miles.\250\ The System B demonstration engine was not aged and 
was only tested after it was degreened. A summary of the data used for 
EPA's feasibility analysis can be found in Section III.B.3. See Section 
III.B.3 for details on how we addressed compliance margin when setting 
the standards, including discussion of the interim in-use testing 
allowance for Medium and Heavy HDE for determining the interim in-use 
testing standards for these primary intended service classes.
---------------------------------------------------------------------------

    \246\ See 40 CFR 1036.510 for the FTP duty-cycle test procedure.
    \247\ The same FTP duty-cycle standards apply for Spark-ignition 
HDE as discussed in Section III.D.
    \248\ See Section III.B.2 for a description of the engine.
    \249\ For the EPA Stage 3 engine, the data at the equivalent of 
435,000 and 600,000 miles were included in the preamble of the NPRM 
and the data at the equivalent of 800,000 miles was added to the 
docket on May 5th, 2022.
    \250\ Due to the timing of when the data from the System A 
system were available, the data were added to the public docket 
prior to the signing of the final rule.

            Table III-3--Final Compression-Ignition Engine Standards Over the SET and FTP Duty Cycles
----------------------------------------------------------------------------------------------------------------
                                                  NOX (mg/hp-hr)
                   Model year                                      HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
2027 and later..................................          \a\ 35              60               5             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.


      Table III-4--Useful Life Periods for Heavy-Duty Compression-Ignition Primary Intended Service Classes
----------------------------------------------------------------------------------------------------------------
                                            Current (Pre-MY 2027)                 Final MY 2027 and later
  Primary intended service class   -----------------------------------------------------------------------------
                                       Miles        Years        Hours        Miles        Years        Hours
----------------------------------------------------------------------------------------------------------------
Light HDE \a\.....................      110,000           10  ...........      270,000           15       13,000
Medium HDE........................      185,000           10  ...........      350,000           12       17,000
Heavy HDE.........................      435,000           10       22,000      650,000           11       32,000
----------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Light HDE for GHG emission standards is 15 years or 150,000 miles; we are not
  revising GHG useful life periods in this final rule. See 40 CFR 1036.108(d).


[[Page 4335]]

    As further discussed in Section III.B.3, taking into account 
measurement variability of the PM measurement test procedure and the 
low numeric level of the new PM standards, we believe PM emissions from 
current diesel engines are at the lowest feasible level for standards 
starting in MY 2027. As summarized in Section III.B.3.ii.b, 
manufacturers are submitting certification data to the agency for 
current production engines well below the existing PM standards over 
the FTP duty cycle. Setting the new PM FTP standards lower than the 
existing FTP PM standards, at 5 mg/hp-hr (0.005 g/hp-hr), ensures that 
future engines will maintain the low level of PM emissions of the 
current engines and not increase PM emissions. We received comment 
stating that a 5 mg/hp-hr standard did not provide enough margin for 
some engine designs and that a 7.5 mg/hp-hr would be a more appropriate 
standard to maintain current PM emissions levels while providing enough 
margin to account for the measurement variability of the PM measurement 
test procedure. The reason submitted in comment to justify the 7.5 mg/
hp-hr standard was that data from the Stage 3 testing at Southwest 
Research Institute (SwRI) shows that in some conditions PM values 
exceed the 5 mg/hp-hr emission standard. EPA took a further look at 
this data and determined that the higher PM emission data points occur 
immediately following DPF ash cleaning, and that the PM level returns 
to a level well below the 5 mg/hp-hr standards shortly after return to 
service once a soot cake layer reestablishes itself in the DPF. EPA 
concluded from this assessment that these very short-term elevations in 
PM that occur after required maintenance of the DPF should not be the 
basis for the stringency of the PM standards and that the standards are 
feasible.
    As noted earlier in this section, we are finalizing HC and CO FTP 
standards based on the feasibility demonstration for SI engines. As 
summarized in Section III.B.3.ii.b, manufacturers are submitting data 
to the agency that show emissions performance for current production CI 
engines that are well below the current standards. Keeping FTP 
standards at the same value for all fuels is consistent with the 
agency's approach to previous criteria pollutant standards. See Section 
III.D for more information on how the numeric values of the HC and CO 
standards were determined.
    In the NPRM, we did not propose any changes to the weighting 
factors for the FTP cycle for heavy-duty engines. The current FTP 
weighting of cold-start and hot-start emissions was promulgated in 1980 
(45 FR 4136, January 21, 1980). It reflects the overall ratio of cold 
and hot operation for heavy-duty engines generally and does not 
distinguish by engine size or intended use. We received comment to 
change the weighting factors to reduce the effect of the cold start 
portion of the FTP on the composite FTP emission results or to add 300 
seconds of idle before the first acceleration in the cold start FTP to 
reduce the emissions impact of the cold start on the first 
acceleration. Duty-cycles are an approximation of the expected real-
world operation of the engine and no duty cycle captures all aspects of 
the real-world operation. Changing the cold/hot weighting factors would 
not fully capture all aspects of what really occurs in-use, and there 
is precedent in experience and historical approach with the current \1/
7\ cold and \6/7\ hot weighting factors. Adding 300 seconds of idle to 
the beginning of the FTP would simply reduce the stringency of the 
standard by reducing the impact of cold start emissions, as the 300 
seconds of idle would allow the aftertreatment to light off prior to 
the first major acceleration in the FTP. Although the case can be made 
that many vehicles idle for some amount of time after start up, any 
attempt to add idle time before the first acceleration is simply an 
approximation and this ``one size fits all'' approach doesn't afford an 
improvement over the current FTP duty-cycle, nor does it allow 
determination of cold start emissions where the vehicle is underway 
shortly after start up. After considering these comments we are also 
not including any changes to the weighting factors for the FTP duty-
cycle in this final rule.
    For Heavy HDE, we are finalizing test procedures for the 
determination of deterioration factors in 40 CFR 1036.245 that require 
these engines to be aged to an equivalent of 750,000 miles, which is 15 
percent longer than the regulatory useful life of those engines. As 
explained earlier in this section, we are finalizing this requirement 
for Heavy HDE to ensure the final NOX standard will be met 
through the lengthy regulatory useful life of 650,000 miles. See 
preamble Section IV.A for details on how we set the regulatory useful 
life for Heavy HDE.
ii. SET
    We are finalizing new emissions standards for testing over the SET 
duty-cycle as shown in Table III-3. These brake-specific SET standards 
apply across the Heavy HDE, Medium HDE, and Light HDE primary intended 
service classes, as well as the SI HDE primary intended service class 
as discussed in Section III.D, over the same useful life periods shown 
in Table III-4. The numeric levels of the NOX SET standards 
at the time of certification are consistent with the most stringent 
standard proposed for MY 2027.\251\ The numeric level of the CO SET 
standard is consistent with the most stringent standard proposed for MY 
2027 for all CI engine classes.\252\ The numeric level of the PM SET 
standard is the same as proposed, and the numeric level of the HC SET 
standard is consistent with the proposed Option 1 standard starting in 
MY 2027. Consistent with our current standards, we are finalizing the 
same numeric values for the standards over the SET and FTP duty cycles 
for the CI engine classes. As with the FTP cycle, the standards have 
been shown to be feasible for compression-ignition engines based on 
testing of the CARB Stage 3 and EPA Stage 3 engines with a chemically- 
and hydrothermally-aged aftertreatment system. The EPA Stage 3 engine 
was aged to and tested at the equivalent of 800,000 miles.\253\ EPA's 
Team A demonstration engine was aged to and tested at the equivalent of 
650,000 miles.\254\ See Section III.B.3 for details on how we addressed 
compliance margin when setting the standards, including discussion of 
the interim in-use testing allowance for Medium and Heavy HDEs for 
determining the interim in-use testing standards for these primary 
intended service classes. A summary of the data used for EPA's 
feasibility analysis can be found in Section III.B.3.
---------------------------------------------------------------------------

    \251\ As discussed in Section III.B.3, we are finalizing an 
interim, in-use compliance allowance that applies when Medium and 
Heavy HDE are tested in-use.
    \252\ As explained in Section III.D.1.ii, the final Spark-
ignition HDE CO standard for the SET duty-cycle is 14.4 g/hp-hr.
    \253\ For the EPA Stage 3 engine, the data at the equivalent of 
435,000 and 600,000 miles were included in the preamble of the NPRM 
and the data at the equivalent of 800,000 miles was added to the 
docket on May 5th, 2022.
    \254\ Due to the timing of when the data from the System A 
system were available, the data were added to the public docket 
prior to the signing of the final rule.
---------------------------------------------------------------------------

    As with the PM standards for the FTP (see Section III.B.2.i), and 
as further discussed in Section III.B.3, taking into account 
measurement variability of the PM measurement test procedure and the 
low numeric level of the new PM standards, we believe PM emissions from 
current diesel engines are at the lowest feasible level for standards 
starting in MY 2027. Thus, the PM standard for the SET duty-cycle is 
intended to ensure that there is not an increase in PM emissions from 
future engines. We are finalizing new PM SET

[[Page 4336]]

standards of 5 mg/hp-hr for the same reasons outlined for the FTP in 
Section III.B.2.i. Also similar to the FTP (see Section III.B.2.i), we 
are finalizing HC and CO SET standards based on the feasibility 
demonstration for SI engines (see Section III.D).
    We have also observed an industry trend toward engine down-
speeding--that is, designing engines to do more of their work at lower 
engine speeds where frictional losses are lower. To better reflect this 
trend in our duty cycle testing, in the HD GHG Phase 2 final rule we 
promulgated new SET weighting factors for measuring CO2 
emissions (81 FR 73550, October 25, 2016). Since we believe these new 
weighting factors better reflect in-use operation of current and future 
heavy-duty engines, we are finalizing application of these new 
weighting factors to criteria pollutant measurement, as show in Table 
III-5, for NOX and other criteria pollutants as well. To 
assess the impact of the new test cycle on criteria pollutant 
emissions, we analyzed data from the EPA Stage 3 engine that was tested 
on both versions of the SET. The data summarized in Section 
III.B.3.ii.a show that the NOX emissions from the EPA Stage 
3 engine at an equivalent of 435,000 miles are slightly lower using the 
SET weighting factors in 40 CFR 1036.510 versus the current SET 
procedure in 40 CFR 86.1362. The lower emissions using the SET cycle 
weighting factors in 40 CFR 1036.510 are reflected in the stringency of 
the final SET standards.

               Table III-5--Weighting Factors for the SET
------------------------------------------------------------------------
                                                             Weighting
                      Speed/% load                          factor (%)
------------------------------------------------------------------------
Idle....................................................              12
A, 100..................................................               9
B, 50...................................................              10
B, 75...................................................              10
A, 50...................................................              12
A, 75...................................................              12
A, 25...................................................              12
B, 100..................................................               9
B, 25...................................................               9
C, 100..................................................               2
C, 25...................................................               1
C, 75...................................................               1
C, 50...................................................               1
                                                         ---------------
    Total...............................................             100
Idle Speed..............................................              12
Total A Speed...........................................              45
Total B Speed...........................................              38
Total C Speed...........................................               5
------------------------------------------------------------------------

iii. LLC
    EPA is finalizing the addition of new standards for testing over 
the new low-load duty-cycle, that will require CI engine manufacturers 
to demonstrate that the emission control system maintains functionality 
during low-load operation where the catalyst temperatures have 
historically been found to be below the catalyst's operational 
temperature (see Chapter 2.2.2 of the RIA). We believe the addition of 
this LLC will complement the expanded operational coverage of our new 
off-cycle testing requirements (see Section III.C).
    During ``Stage 2'' of the CARB Low NOX Demonstration 
program, SwRI and NREL developed several candidate cycles with average 
power and duration characteristics intended to test current diesel 
engine emission controls under three low-load operating conditions: 
Transition from high- to low-load, sustained low-load, and transition 
from low- to high-load.\255\ In September 2019, CARB selected the 92-
minute ``LLC Candidate #7'' as the low load cycle they adopted for 
their Low NOX Demonstration program and subsequent Omnibus 
regulation.256 257
---------------------------------------------------------------------------

    \255\ California Air Resources Board. ``Heavy-Duty Low 
NOx Program Public Workshop: Low Load Cycle 
Development''. Sacramento, CA. January 23, 2019. Available online: 
https://ww3.arb.ca.gov/msprog/hdlownox/files/workgroup_20190123/02-llc_ws01232019-1.pdf.
    \256\ California Air Resources Board. Heavy-Duty Omnibus 
Regulation. Available online: https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox.
    \257\ California Air Resources Board. ``Heavy-Duty Low 
NOx Program: Low Load Cycle'' Public Workshop. Diamond 
Bar, CA. September 26, 2019. Available online: https://ww3.arb.ca.gov/msprog/hdlownox/files/workgroup_20190926/staff/03_llc.pdf.
---------------------------------------------------------------------------

    We are adopting CARB's Omnibus LLC as a new duty-cycle, the LLC. 
This cycle is described in Chapter 2 of the RIA for this rulemaking and 
the test procedures are specified in 40 CFR 1036.514. The LLC includes 
applying the accessory loads defined in the HD GHG Phase 2 rule, that 
were based on data submitted to EPA as part of the development of the 
HD GHG Phase 2. These accessory loads are 1.5, 2.5 and 3.5 kW for Light 
HDE, Medium HDE, and Heavy HDE engines, respectively. As detailed 
further in section 3 of the Response to Comments, we received comments 
that EPA should revise the accessory loads. One commenter provided 
specific recommendations for engines installed in tractors but in all 
cases commenters didn't provide data to support their comments; after 
consideration of these comments and further consideration of the basis 
of the proposal, we are finalizing the accessory loads for the LLC as 
proposed. To allow vehicle level technologies to be recognized on this 
cycle, we are including a powertrain test procedure option for the LLC. 
More information on the powertrain test procedure can be found in 
Section III.B.2.v. IRAF determination for the LLC follows the test 
procedures defined in 40 CFR 1036.580, which are the same test 
procedures used for the SET and FTP. The IRAF test procedures that 
apply to the SET and FTP in 40 CFR 1065.680 are appropriate for the LLC 
as the procedures in 40 CFR 1065.680 were developed to work with any 
engine-based duty-cycle. We are finalizing as proposed that, while the 
IRAF procedures in 40 CFR 1036.580 and 1065.680 require that 
manufacturers determine an IRAF for the SET, FTP, and LLC duty cycles, 
manufacturers may omit the adjustment factor for a given duty cycle if 
they determine that infrequent regeneration does not occur over the 
types of engine operation contained in the duty cycle as described in 
40 CFR 1036.580(c).
    The final emission standards for the LLC are presented in Table 
III-6, over the useful life periods shown in Table III-4. The numeric 
levels of the NOX LLC standards at the time of certification 
are the most stringent proposed for any model year.\258\ The numeric 
level of the PM and CO LLC standards are the same as proposed, and the 
numeric level of the HC LLC standard is consistent with the proposed 
Option 1 standard starting in MY 2027. As with the FTP cycle, these 
standards have been shown to be feasible for compression-ignition 
engines based on testing of the EPA Stage 3 demonstration engine with 
chemically- and hydrothermally-aged aftertreatment system, and for the 
LLC the data shows that the standards are feasible for all engine 
service classes with available margins between the data and the 
standards. The summary of this data along with how we addressed 
compliance margin can be found in Section III.B.3, including discussion 
of the interim in-use compliance allowance for Medium and Heavy HDEs 
for determining the interim in-use

[[Page 4337]]

standards for these primary intended service classes.
---------------------------------------------------------------------------

    \258\ As summarized in Section III.A.2 and detailed in this 
Section III.B we are also finalizing an interim, in-use compliance 
allowance for medium and heavy heavy-duty engines.

                   Table III-6--Compression-Ignition Engine Standards Over the LLC Duty Cycle
----------------------------------------------------------------------------------------------------------------
                                                  NOX (mg/hp-hr)
                   Model year                                      PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
2027 and later..................................          \a\ 50               5             140             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.

    We are finalizing an LLC PM standard of 5 mg/hp-hr for the same 
reasons outlined for the FTP in Section III.B.2.i. We are finalizing HC 
and CO standards based on data from the CARB and EPA Stage 3 engine 
discussed in Section III.B.3. We are finalizing the same numeric 
standard for CO on the LLC as we have for the SET and FTP cycles 
because the demonstration data from the EPA Stage 3 engine shows that 
CO emissions on the LLC are similar to CO emissions from the SET and 
FTP. We are finalizing HC standards that are different than the 
standards of the SET and FTP cycles, to reflect our assessment of the 
performance of the EPA Stage 3 engine on the LLC. The data discussed in 
Section III.B.3 of this preamble shows that the PM, HC, and CO 
standards are feasible for both current and future new engines.
iv. Idle
    CARB currently has an optional idle test procedure and accompanying 
standard of 30 g/hr of NOX for diesel engines to be ``Clean 
Idle Certified.''.\259\ In the CARB Omnibus rule, the CARB lowered the 
optional NOX standard to 10 g/hr for MY 2024 to MY 2026 
engines and 5 g/hr for MY 2027 and beyond. In the NPRM, we proposed 
optional NOX idle standards with a corresponding idle test 
procedure, with potentially different numeric levels of the 
NOX idle standards for MY 2023, MY 2024 to MY 2026 engines, 
and for MY 2027 and beyond, that would allow compression ignition 
engine manufacturers to voluntarily choose to certify (i.e., it would 
be optional for a manufacturer to include the idle standard in an EPA 
certification but once included the idle standard would become 
mandatory and full compliance would be required). We proposed to 
require that the brake-specific HC, CO, and PM emissions during the 
Clean Idle test may not exceed measured emission rates from the idle 
mode in the SET or the idle segments of the FTP, in addition to meeting 
the applicable idle NOX standard. We requested comment on 
whether EPA should make the idle standards mandatory instead of 
voluntary for MY 2027 and beyond, as well as whether EPA should set 
clean idle standards for HC, CO, and PM emissions (in g/hr) rather than 
capping the idle emissions for those pollutants based on the measured 
emission levels during the idle mode in the SET or the idle segments of 
the FTP. We also requested comment on the need for EPA to define a 
label that would be put on the vehicles that are certified to the 
optional idle standard.
---------------------------------------------------------------------------

    \259\ 13 CCR 1956.8(a)(6)(C)--Optional NOX idling 
emission standard.
---------------------------------------------------------------------------

    We received comments on the EPA's proposal to adopt California's 
Clean Idle NOX standard as a voluntary emission standard for 
Federal certification.\260\ All commenters provided general support for 
EPA's proposal to set idle standards for heavy duty engines, with some 
qualifications. Some commentors supported making idle standards 
mandatory, while others commented that the idle standards should be 
optional. With regard to the level of the idle standard, there was 
support from many commenters that the standards should be set at the 
Proposed Option 1 levels or lower, while several manufactures stated 
that 10 g/hr for certification and 15 g/hr in-use would be the lowest 
feasible standards for NOX. One manufacturer commented that 
EPA must set standards that do not increase CO2 emissions. 
EPA has considered these comments, along with the available data 
including the data from the EPA Stage 3 engine,\261\ and we are 
finalizing optional idle standards in 40 CFR 1036.104(b) and a new idle 
test procedure in 40 CFR 1036.525. The standards are based on CARB's 
test procedure with revisions to not require the measurement of PM, HC 
and CO,\262\ to allow compression-ignition engine manufacturers to 
voluntarily certify to an idle NOX standard of 30.0 g/hr for 
MY 2024 to MY 2026, which is consistent with proposed Option 1 for MY 
2023. For MY 2027 and beyond, the final NOX idle standard is 
10.0 g/hr, which is the same as proposed Option 2 for those MYs. 
Manufacturers certifying to the optional idle standard must comply with 
the standard and related requirements as if they were mandatory.
---------------------------------------------------------------------------

    \260\ See RTC section 3.
    \261\ See RIA Chapter 3 for a summary of the data collected with 
the EPA Stage 3 engine run on the Clean Idle test in three 
configurations. These data show that the MY 2027 and beyond, final 
NOX idle standard of 10 g/hr is feasible through useful 
life with margin, and show that an additional 5 g/hr in-use margin 
is not justified.
    \262\ 86.1360-2007.B.4, California Exhaust Emission Standards 
and Test Procedures for 2004 and Subsequent Model Heavy-Duty Diesel 
Engines and Vehicles, April 18, 2019.
---------------------------------------------------------------------------

    We received comments stating that the proposed PM, HC, and CO 
standards are unworkable since the standards are set at the level the 
engine emits at during idle over the engine SET and FTP duty cycles and 
that variability in the emissions between the different tests could 
cause the engine to fail the idle PM, HC, and CO standards. EPA 
recognized this issue in the proposal and requested comment on if EPA 
should instead set PM, HC, and CO standards that are fixed and not 
based on the emissions from the engine during the SET and FTP. EPA has 
considered these comments and we are not finalizing the proposed 
requirement to measure brake-specific HC, CO, and PM emissions during 
the Clean Idle test for comparison to emission rates from the idle 
modes in the SET or the idle segments of the FTP.\263\ The measurement 
of these additional pollutants would create unnecessary test burden for 
the manufacturers at this time, especially with respect to measuring PM 
during idle segments of the SET or FTP as it would require running 
duplicate tests or adding a PM sampler. Further, setting the PM, HC and 
CO standards right at the idle emissions level of the engine on the SET 
and FTP could cause false failures due to test-to-test variability from 
either the SET or FTP, or the Clean Idle test itself.

[[Page 4338]]

Idle operation is included as part of off-cycle testing and the SET, 
FTP, and LLC duty cycles; standards for off-cycle and duty-cycle 
testing ensure that emissions of HC, CO, and PM are well controlled as 
aftertreatment temperatures are not as critical to controlling these 
pollutants over extended idle periods as they are for NOX. 
We are therefore not requiring the measurement of these other 
pollutants to meet EPA voluntary clean idle standards.
---------------------------------------------------------------------------

    \263\ See 40 CFR 1036.104(b).
---------------------------------------------------------------------------

    We are finalizing a provision in new 40 CFR 1036.136 requiring 
engine manufacturers that certify to the Federal Clean Idle 
NOX standard to create stickers to identify their engines as 
meeting the Federal Clean Idle NOX standard. The regulatory 
provisions require that the stickers meet the same basic requirements 
that apply for stickers showing that engines meet CARB's Clean Idle 
NOX standard. For example, stickers must be durable and 
readable throughout each vehicle's operating life, and the preferred 
placement for Clean Idle stickers is on the driver's side of the hood. 
Engine manufacturers must provide exactly the right number of these 
stickers to vehicle manufacturers so they can apply the stickers to 
vehicles with the engines that the engine manufacturer has certified to 
meet the Federal Clean Idle NOX standard. If engine 
manufacturers install engines in their own vehicles, they must apply 
the stickers themselves to the appropriate vehicles. Engine 
manufacturers must keep the following records for at least five years: 
(1) Written documentation of the vehicle manufacturer's request for a 
certain number of stickers, and (2) tracking information for stickers 
the engine manufacturer sends and the date they sent them. 40 CFR 
1036.136 also clarifies that the provisions in 40 CFR 1068.101 apply 
for the Clean Idle sticker in the same way that those provisions apply 
for emission control information labels. For example, manufacturing, 
selling, and applying false labels are all prohibited actions subject 
to civil penalties.
v. Powertrain
    EPA recently finalized a separate rulemaking that included an 
option for manufacturers to certify a hybrid powertrain to the SET and 
FTP greenhouse gas engine standards by using a powertrain test 
procedure (86 FR 34321, June 29, 2021).\264\ In this rulemaking, we are 
similarly finalizing as proposed that manufacturers may certify hybrid 
powertrains to criteria pollutant emissions standards by using the 
powertrain test procedure. In this section we describe how 
manufacturers would apply the powertrain test procedure to certify 
hybrid powertrains.
---------------------------------------------------------------------------

    \264\ The powertrain test procedure was established in the GHG 
Phase 1 rulemaking but the recent rulemaking included adjustments to 
apply the test procedure to the engine test cycles.
---------------------------------------------------------------------------

a. Development of Powertrain Test Procedures
    Powertrain testing allows manufacturers to demonstrate emission 
benefits that cannot be captured by testing an engine alone on a 
dynamometer. For hybrid engines and powertrains, powertrain testing 
captures when the engine operates less or at lower power levels due to 
the use of the hybrid powertrain function. However, powertrain testing 
requires the translation of an engine test procedure to a powertrain 
test procedure. Chapter 2 of the RIA describes how we translated the 
SET, FTP, and LLC engine test cycles to the powertrain test 
cycles.\265\ The two primary goals of this process were to make sure 
that the powertrain version of each test cycle was equivalent to each 
respective engine test cycle in terms of positive power demand versus 
time and that the powertrain test cycle had appropriate levels of 
negative power demand. To achieve this goal, over 40 engine torque 
curves were used to create the powertrain test cycles.
---------------------------------------------------------------------------

    \265\ As discussed in Section III.B.1, as part of the technical 
amendments rulemaking, EPA finalized that manufacturers may use the 
powertrain test procedure for GHG emission standards on the FTP and 
SET engine-based test cycles. In this rulemaking we are extending 
this to allow the powertrain test procedure to be used for criteria 
emission standards on these test cycles and the LLC. As discussed in 
Section 2.ii, we are setting new weighting factors for the engine-
based SET procedure for criteria pollutant emissions, which are 
reflected in the SET powertrain test cycle.
---------------------------------------------------------------------------

b. Testing Hybrid Engines and Hybrid Powertrains
    As noted in the introduction of this Section III, we are finalizing 
clarifications in 40 CFR 1036.101 that manufacturers may optionally 
test the hybrid engine and hybrid powertrain to demonstrate compliance. 
We are finalizing as proposed with one clarification that the 
powertrain test procedures specified in 40 CFR 1036.510 and 1036.512, 
which were previously developed for demonstrating compliance with GHG 
emission standards on the SET and FTP test cycles, are applicable for 
demonstrating compliance with criteria pollutant standards on the SET 
and FTP test cycles. The clarification in 40 CFR 1036.510 provides 
direction that the idle points in the SET should be run as neutral or 
parked idle. In addition, for GHG emission standards we are finalizing 
updates to 40 CFR 1036.510 and 1036.512 to further clarify how to carry 
out the test procedure for plug-in hybrids. We have done additional 
work for this rulemaking to translate the LLC to a powertrain test 
procedure, and we are finalizing that manufacturers can similarly 
certify hybrid engines and hybrid powertrains to criteria pollutant 
emission standards on the LLC using the test procedures defined in 40 
CFR 1036.514.
    We are allowing manufacturers to use the powertrain test procedures 
to certify hybrid engine and powertrain configurations to all MY 2023 
and later criteria pollutant engine standards. Manufacturers can choose 
to use either the SET duty-cycle in 40 CFR 86.1362 or the SET in 40 CFR 
1036.510 in model years prior to 2027, and may use only the SET in 40 
CFR 1036.510 for model year 2027 and beyond.\266\ \267\
---------------------------------------------------------------------------

    \266\ We are allowing either the SET duty-cycle in 40 CFR 
86.1362 or 40 CFR 1036.505 because the duty cycles are similar and, 
as shown in Chapter 3.1.2 of the RIA, the criteria pollutant 
emissions level of current production engines is similar between the 
two cycles.
    \267\ Prior to MY 2027, only manufacturers choosing to 
participate in the 2026 Service Class Pull Ahead Credits, Full 
Credits, or Partial Credits pathways under the Transitional Credits 
Program need to conduct LLC powertrain testing (see Section IV.G for 
details on).
---------------------------------------------------------------------------

    We are allowing the use of these procedures starting in MY 2023 for 
plug-in hybrids and, consistent with the requirements for light-duty 
plug-in hybrids, we are finalizing that the applicable criteria 
pollutant standards must be met under the worst-case conditions, which 
is achieved by testing and evaluating emission under both charge-
depleting and charge-sustaining operation. This is to ensure that under 
all drive cycles the powertrain meets the criteria pollutant standards 
and is not based on an assumed amount of zero emissions range. We 
received comment stating that the charge-depleting and charge-
sustaining operation should be weighted together for criteria 
pollutants as well as GHG pollutants, but consistent with the light-
duty test procedure we want to ensure that criteria pollutant emissions 
are controlled under all conditions, which would include under 
conditions where the vehicle is not charged and is only operated in 
charge sustaining-operation.
    We are finalizing changes to the test procedures defined in 40 CFR 
1036.510 and 1036.512 to clarify how to weight together the charge-
depleting and charge-sustaining greenhouse gas emissions for 
determining the greenhouse gas emissions of plug-in

[[Page 4339]]

hybrids for the SET and FTP duty cycles. This weighting is done using 
an application specific utility factor curve that is approved by EPA. 
We are also finalizing a provision to not apply the cold and hot 
weighting factors for the determination of the FTP composite emission 
result for greenhouse gas pollutants because the charge-depleting and 
sustaining test procedures finalized in 40 CFR 1036.512 include both 
cold and hot start emissions by running repeat FTP cycles back-to-back. 
By running back-to-back FTPs, the finalized test procedure captures 
both cold and hot emissions and their relative contribution to daily 
greenhouse gas emissions per unit work, removing the need for weighting 
the cold and hot emissions.
    We are finalizing the application of the powertrain test procedure 
only for hybrid powertrains, to avoid having two different testing 
pathways (engine only and powertrain) for non-hybrid engines for the 
same standards. That said, we recognize there may be other technologies 
where the emissions performance is not reflected on the engine test 
procedures, so in such cases manufacturers may seek approval from EPA 
to use the powertrain test procedure for non-hybrid engines and 
powertrains consistent with 40 CFR 1065.10(c)(1).
    Finally, for all pollutants, we requested comment on if we should 
remove 40 CFR 1037.551 or limit the use of it to only selective 
enforcement audits (SEAs). 40 CFR 1037.551 was added as part of the HD 
GHG Phase 2 rulemaking to provide flexibility for an SEA or a 
confirmatory test, by allowing just the engine of the powertrain to be 
tested. Allowing just the engine to be tested over the engine speed and 
torque cycle that was recorded during the powertrain test enables the 
testing to be conducted in more widely available engine dynamometer 
test cells, but this flexibility could increase the variability of the 
test results. We didn't receive any comments on this topic and, for the 
reason just stated, we are limiting the use of 40 CFR 1037.551 to SEA 
testing.
vi. Crankcase Emissions
    During combustion, gases can leak past the piston rings sealing the 
cylinder and into the crankcase. These gases are called blowby gases 
and generally include unburned fuel and other combustion products. 
Blowby gases that escape from the crankcase are considered crankcase 
emissions (see 40 CFR 86.402-78). Current regulations restrict the 
discharge of crankcase emissions directly into the ambient air. Blowby 
gases from gasoline engine crankcases have been controlled for many 
years by sealing the crankcase and routing the gases into the intake 
air through a PCV valve. However, in the past there have been concerns 
about applying a similar technology for diesel engines. For example, 
high PM emissions venting into the intake system could foul 
turbocharger compressors. As a result of this concern, diesel-fueled 
and other compression-ignition engines equipped with turbochargers (or 
other equipment) were not required to have sealed crankcases (see 40 
CFR 86.007-11(c)). For these engines, manufacturers were allowed to 
vent the crankcase emissions to ambient air as long as they are 
measured and added to the exhaust emissions during all emission testing 
to ensure compliance with the emission standards.
    Because all new highway heavy-duty diesel engines on the market 
today are equipped with turbochargers, they are not required to have 
closed crankcases under the current regulations. We estimate 
approximately one-third of current highway heavy-duty diesel engines 
have closed crankcases, indicating that some heavy-duty engine 
manufacturers have developed systems for controlling crankcase 
emissions that do not negatively impact the turbocharger. EPA proposed 
provisions in 40 CFR 1036.115(a) to require a closed crankcase 
ventilation system for all highway compression-ignition engines to 
prevent crankcase emissions from being emitted directly to the 
atmosphere starting for MY 2027 engines.\268\ Comments were received 
regarding concerns closing the crankcase that included coking, degraded 
performance and turbo efficiencies leading to increased CO2 
emissions, secondary damage to components, and increased engine-out PM 
(see section 3 of the Response to Comments document for further 
details). After considering these comments, we are finalizing a 
requirement for manufacturers to use one of two options for controlling 
crankcase emissions, either: (1) As proposed, closing the crankcase, or 
(2) an updated version of the current requirements for an open 
crankcase that includes additional requirements for measuring and 
accounting for crankcase emissions. We believe that either approach is 
appropriate, so long as the total emissions are accounted for during 
certification and in-use testing through useful life (including full 
accounting for crankcase emission deterioration).
---------------------------------------------------------------------------

    \268\ We proposed to move the current crankcase emissions 
provisions to a new paragraph (u) in the interim provisions of 40 
CFR 1036.150, which would apply through model year 2026.
---------------------------------------------------------------------------

a. Closed Crankcase Option
    As EPA explained at proposal, the environmental advantages to 
closing the crankcase are twofold. While the exception in the current 
regulations for certain compression-ignition engines requires 
manufacturers to quantify their engines' crankcase emissions during 
certification, they report non-methane hydrocarbons in lieu of total 
hydrocarbons. As a result, methane emissions from the crankcase are not 
quantified. Methane emissions from diesel-fueled engines are generally 
low; however, they are a concern for compression-ignition-certified 
natural gas-fueled heavy-duty engines because the blowby gases from 
these engines have a higher potential to include significant methane 
emissions. We note that in the HD GHG Phase 2 rule we set methane 
standards which required natural gas engines to close the crankcase in 
order to comply with the methane standard. EPA proposed to require that 
all natural gas-fueled engines have closed crankcases in the HD GHG 
Phase 2 rulemaking, but opted to wait to finalize any updates to 
regulations in a future rulemaking, where we could then propose to 
apply these requirements to natural gas-fueled engines and to the 
diesel fueled engines that many of the natural gas-fueled engines are 
based off of (81 FR 73571, October 25, 2016).
    In addition to our concern of unquantified methane emissions, we 
believe another benefit to closed crankcases would be reduced engine 
wear due to improved engine component durability. We know that the 
performance of piston seals reduces as the engine ages, which would 
allow more blowby gases and could increase crankcase emissions. While 
crankcase emissions are currently included in the durability tests that 
estimate an engine's deterioration at useful life, those tests were not 
designed to capture the deterioration of the crankcase. These 
unquantified age impacts continue throughout the operational life of 
the engine. Closing crankcases could be a means to ensure those 
emissions are addressed long-term to the same extent as other exhaust 
emissions.
    After considering all of the manufacturer concerns, we still 
believe, noting that one-third of current highway heavy-duty diesel 
engines have closed crankcases, that improvements in the design of 
engine hardware would allow manufacturers to close the crankcase, with 
the potential for increased maintenance intervals on some

[[Page 4340]]

components. For these reasons, EPA is finalizing provisions in 40 CFR 
1036.115(a) to require a closed crankcase ventilation system as one of 
two options for all highway compression-ignition engines to control 
crankcase emissions for MY 2027 and later engines.
b. Open Crankcase Option
    Given consideration of the concerns from commenters regarding 
engine hardware durability associated with closing the crankcase, we 
have decided to finalize an option that allows the crankcase to remain 
open. This option requires manufacturers of compression ignition 
engines that choose to leave the crankcase open to account for any 
increase in the contribution of crankcase emissions (due to reduction 
in performance of piston seals, etc.) to the total emissions from the 
engine throughout the engine's useful life. Manufacturers that choose 
to perform engine dynamometer-based testing out to useful life will 
provide a deterioration factor that includes deteriorated crankcase 
emissions because the engine components will be aged out to the 
engine's useful life. Manufacturers that choose to use the accelerated 
aging option in 40 CFR 1036.245(b), where the majority of the emission 
control system aging is done, must use good engineering judgment to 
determine the impact of engine deterioration on crankcase emissions and 
adjust the tailpipe emissions at useful life to reflect this 
deterioration. For example, manufacturers may determine deteriorated 
crankcase emissions from the assessment of field-aged engines.
    Manufacturers who choose this option must also account for 
crankcase criteria pollutant emissions during any manufacturer run in-
use testing to determine the overall compliance of the engine as 
described in 40 CFR 1036.415(d)(2). The crankcase emissions must be 
measured separately from the tailpipe emissions or be routed into the 
exhaust system, downstream from the last catalyst in the aftertreatment 
system, to ensure that there is proper mixing of the two streams prior 
to the sample point. In lieu of these two options, manufacturers may 
use the contribution of crankcase emissions over the FTP duty-cycle at 
useful life from the deterioration factor determination testing in 40 
CFR 1036.245, as described in 40 CFR 1036.115(a) and add them to the 
binned emission results determined in 40 CFR 1036.530.
    Chapter 1.1.4 of the RIA describes EPA's recent test program to 
evaluate the emissions from open crankcase systems on two modern heavy-
duty diesel engines. Results suggest HC and CO emitted from the 
crankcase can be a notable fraction of overall tailpipe emissions. By 
closing the crankcase, those emissions would be rerouted to the engine 
or aftertreatment system to ensure control of the crankcase emissions. 
If a manufacturer chooses the option to keep the crankcase open, 
overall emission control will still be achieved, but the manufacturer 
will have to design and optimize the emission control system for lower 
tailpipe emissions to offset the emissions from the crankcase as the 
total emissions are accounted for both in-use and at useful life.
3. Feasibility of the Diesel (Compression-Ignition) Engine Standards
i. Summary of Technologies Considered
    Our finalized standards for compression-ignition engines are based 
on the performance of technology packages described in Chapters 1 and 3 
of the RIA for this rulemaking. Specifically, we are evaluating the 
performance of next-generation catalyst formulations in a dual SCR 
catalyst configuration with a smaller SCR catalyst as the first 
substrate in the aftertreatment system for improved low-temperature 
performance, and a larger SCR catalyst downstream of the diesel 
particulate filter to improve NOX conversion efficiency 
during high power operation and to allow for passive regeneration of 
the particulate filter.\269\ Additionally, the technology package 
includes CDA that reduces the number of active cylinders, resulting in 
increased exhaust temperatures for improved catalyst performance under 
light-load conditions and can be used to reduce fuel consumption and 
CO2 emissions. The technology package also includes the use 
of a heated DEF injector for the upfront SCR catalyst; the heated DEF 
injector allows DEF injection at temperatures as low as approximately 
140[deg]C. The heated DEF injector also improves the mixing of DEF and 
exhaust gas within a shorter distance than with unheated DEF injectors, 
which enables the aftertreatment system to be packaged in a smaller 
space. Finally, the technology package includes hardware needed to 
close the crankcase of diesel engines.
---------------------------------------------------------------------------

    \269\ As described in Chapter 3 of the RIA, we are evaluating 3 
different aftertreatment systems that contain different catalyst 
formulation.
---------------------------------------------------------------------------

ii. Summary of Feasibility Analysis
a. Projected Technology Package Effectiveness and Cost
    Based upon data from EPA's and CARB's Stage 3 Heavy-duty Low 
NOX Research Programs (see Chapter 3.1.1.1 and Chapter 
3.1.3.1 of the RIA), an 80 percent reduction in the Heavy HDE 
NOX standard as compared to the current NOX 
standard is technologically feasible when using CDA or other 
valvetrain-related air control strategies in combination with dual SCR 
systems, and closed crankcase. As noted in the proposal, EPA continued 
to evaluate aftertreatment system durability via accelerated aging of 
advanced emissions control systems as part of EPA's diesel engine 
demonstration program that is described in Chapter 3 of the RIA. In 
assessing the technical feasibility of each of our final standards, we 
have taken into consideration the emissions of the EPA Stage 3 engine 
and other available data, the additional emissions from infrequent 
regenerations, the final longer useful life, test procedure 
variability, emissions performance of other child engines in an engine 
family, production and engine variability, fuel and DEF quality, 
sulfur, soot and ash levels on the aftertreatment, aftertreatment aging 
due to severe-service operation, aftertreatment packaging and lead time 
for manufacturers.
    Manufacturers are required to design engines that meet the duty 
cycle and off-cycle standards throughout the engines' useful life. In 
recognition that emissions performance will degrade over time, 
manufacturers generally design their engines to perform significantly 
better than the standards when first sold to ensure that the emissions 
are below the standard throughout useful life even as the emissions 
controls deteriorate. As discussed in this section and in Chapter 3 of 
the RIA and shown in Table III-12 and Table III-13, some manufactures 
have submitted certification data with zero emissions (with rounding), 
which results in a margin at 100 percent of the FEL, while other 
manufacturers have margin that is less than 25 percent of the FEL.
    To assess the feasibility of the final MY 2027 standards for Light, 
Medium, and Heavy HDE at the corresponding final useful lives, EPA took 
into consideration and evaluated the data from the EPA Stage 3 engine 
as well as other available data and comments received on the proposed 
standards. See section 3 of the Response to Comment document for 
further information on the comments received and EPA's detailed 
response.

[[Page 4341]]

    As discussed in Section III.B.2, the EPA Stage 3 engine includes 
improvements beyond the CARB Stage 3 engine, namely replacing the zone-
coated catalyzed soot filter with a separate DOC and DPF and improving 
the mixing of the DEF with exhaust for the downstream SCR catalyst. 
These improvements lowered the emissions on the SET, FTP, and LLC below 
what was measured with the CARB Stage 3 engine. The emissions for the 
EPA Stage 3 engine on the SET, FTP, and LLC aged to an equivalent of 
435,000, 600,000 and 800,000 miles are shown in Table III-7, Table III-
8, and Table III-9. To account for the IRAF for both particulate matter 
and sulfur on the aftertreatment system, we assessed and determined it 
was appropriate to rely on an analysis by SwRI that is summarized in 
Chapter 3 of the RIA. In this analysis SwRI determined that IRAF 
NOX emissions were at 2 mg/hp-hr for both the SET and FTP 
cycles and 5 mg/hp-hr for the LLC. To account for the crankcase 
emissions, we assessed and determined it was appropriate to rely on an 
analysis by SwRI that is summarized in Chapter 3 of the RIA. In this 
analysis, SwRI determined that the NOX emissions from the 
crankcase were at 6 mg/hp-hr for the LLC, FTP, and SET cycles.
    To determine whether or how to account for the effects of test 
procedure variability, emissions performance of other ratings in an 
engine family, production and engine variability, fuel and DEF quality, 
sulfur, soot and ash levels on the aftertreatment, aftertreatment aging 
due to severe-service operation, and aftertreatment packaging--and 
given the low level of the standards under consideration--EPA further 
assessed two potential approaches after taking into consideration 
comments received. The first approach considered was assigning standard 
deviation and offsets to each of these effects and then combining them 
using a mathematical method similar to what one commenter presented in 
their comments to the NPRM.\270\ The second approach considered was 
defining the margin as a percentage of the standards, similar to 
assertions by two commenters. We considered both of these approaches, 
the comments and supporting information submitted, historical 
approaches by EPA to compliance margin in previous heavy-duty criteria 
pollutant standards rules, and the data collected from the EPA Stage 3 
engine and other available data, to determine the numeric level of each 
standard over the corresponding useful life that is technically 
feasible.
---------------------------------------------------------------------------

    \270\ See RIA Chapter 3 for the details on this analysis.
---------------------------------------------------------------------------

    For the first approach, we determined that a minimum of 15 mg/hp-hr 
of margin between an emission standard and the NOX emissions 
of the EPA Stage 3 engine for each of the duty cycles was 
appropriate.\271\ For the second approach, we first assessed the 
average emissions rates from the EPA Stage 3 engine at the respective 
aged miles. For Light HDEs, we looked at the data at the equivalent of 
435,000 miles. For the Medium and Heavy HDEs standards the interpolated 
emissions performance at 650,000 miles was determined from the tests at 
the equivalent of 600,000 and 800,000 miles, which is shown in Table 
III-10.\272\ Second, the average emissions values were then adjusted to 
account for the IRAF and crankcase emissions from the EPA Stage 3 
engine. Third, we divided the adjusted emissions values by 0.55 to 
calculate an emission standard that would provide 45 percent margin to 
the standard. We determined it would be appropriate to apply a 45 
percent margin in this case after evaluating the margin in engines that 
meet the current standards as outlined in RIA chapter 3 and in CARB's 
comment to the NPRM and considering the level of the standards in this 
final rule. Our determination is based on our analysis that the 
certification data from engines meeting today's standards shows that 
more than 80 percent of engine families are certified with less than 45 
percent compliance margin. For Light HDEs, we took the resulting values 
from the third step of our approach and rounded them. EPA then also 
checked that each of these values for each of the duty cycles 
(resulting from the second approach) provided a minimum of 15 mg/hp-hr 
of margin between those values and the NOX emissions of the 
EPA Stage 3 engine (consistent with the first approach). For Light 
HDEs, we determined those resulting values were appropriate final 
numeric emission standards (as specified in Preamble Section III.B.2). 
The last step of checking that the Light HDE standards provide a 
minimum of 15 mg/hp-hr of NOX margin was to ensure that the 
margin determined from the percent of the standard (the second approach 
to margin) also provided the margin that we determined under the first 
approach to margin. For Light HDEs, given the level of the final 
standards and the length of the final useful life mileages, we 
determined that this approach to margin was appropriate for both 
certification and in-use testing of engines.
---------------------------------------------------------------------------

    \271\ See RIA Chapter 3 for the details on how the margin of 15 
mg/hp-hr was defined.
    \272\ See RIA Chapter 3.1.1.2 for additional information on why 
each aging test point was used for each primary intended service 
class. We note that we received data claimed as confidential 
business information from a manufacturer on August 2, 2022, and 
considered that data as part of this assessment to use the EPA Stage 
3 data at the equivalent of 650,000 miles for setting the Medium HDE 
standards. The data were added to the docket prior to the signing of 
the final rule. See also U.S. EPA. Stakeholder Meeting Log. 
December, 2022.
---------------------------------------------------------------------------

    Given the very long useful life mileages for Heavy HDE and greater 
amounts of certain aging mechanisms over the long useful life periods 
of Medium HDE, we determined that a different application of 
considering these two approaches to margin was appropriate. The in-use 
standards of Medium and Heavy HDEs were determined using the second 
approach for determining margin. The certification standards where then 
determined by subtracting the margin from the first approach (15 mg/hp-
hr) from the in-use standards.
    Separating the standards from the level that applies for in-use 
testing was appropriate because we recognize that laboratory aging of 
the engine doesn't fully capture all the sources of deterioration of 
the aftertreatment that can occur once the engine enters the real-world 
and those uncertainties would be most difficult for these engine 
classes at the level of the final standards and the final useful life 
mileages. Some of these effects are SCR sulfation, fuel quality, DEF 
quality, sensor variability, and field aging from severe duty cycles. 
Thus, the last step in determining the standards for Medium and Heavy 
HDE was to subtract the 15 mg/hp-hr from the rounded value that 
provided 45 percent margin to the Stage 3 data. We determined each of 
the resulting final duty cycle NOX standards for Medium and 
Heavy HDE that must be demonstrated at the time of certification out to 
350,000 and 750,000 miles, respectively, are feasible with enough 
margin to account for test procedure variability. We determined this by 
comparing the EPA Stage 3 emissions results at 800,000 miles (Table 
III-9) after adjusting for IRAF and crankcase emissions to each of the 
NOX standards in Section III.B.2. The EPA Stage 3 
NOX emissions results at 800,000 miles adjusted for IRAF and 
crankcase emissions are 26 mg/hp-hr for the SET, 33 mg/hp-hr for the 
FTP, and 33 mg/hp-hr for the LLC. For any in-use testing of Medium and 
Heavy HDEs, a 15 mg/hp-hr compliance allowance is added to the 
applicable standard, in consideration of the other sources of 
variability and deterioration of the aftertreatment that can occur once 
the engine enters the real world.

[[Page 4342]]

    As explained in the proposal, our technology cost analysis included 
an increased SCR catalyst volume from what was used on the EPA and CARB 
Stage 3 engines. By increasing the SCR catalyst volume, the 
NOX reduction performance of the aftertreatment system 
should deteriorate slower than what was demonstrated with the EPA Stage 
3 engine. The increase in total SCR catalyst volume relative to the EPA 
and CARB Stage 3 SCR was approximately 23.8 percent. We believe this 
further supports our conclusion that the final standards are achievable 
in MY 2027, including for the final useful life of 650,000 miles for 
Heavy HDEs. In addition to NOX, the final HC and CO 
standards are feasible for CI engines on all three cycles. This is 
shown in Table III-10, where the demonstrated HC and CO emission 
results are below the final standards discussed in Section III.B.2. The 
final standard for PM of 5 mg/hp-hr for the SET, FTP, and LLC continue 
to be feasible with the additional technology and control strategies 
needed to meet the final NOX standards, as seen by the PM 
emissions results in Table III-10. As discussed in Section III.B.2, 
taking into account measurement variability of the PM measurement test 
procedure, we believe PM emissions from current diesel engines are at 
the lowest feasible level for standards starting in MY 2027.

             Table III-7--Stage 3 Engine Emissions at 435,000 Mile Equivalent Test Point Without Adjustments for IRAF or Crankcase Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                            NOX (mg/hp-hr)                        NMHC (nonmethane                         CO2 (g/hp-hr)   N2O (g/hp-hr)
                Duty cycle                                   PM (mg/hp-hr)     hydrocarbon) (mg/hp-hr)     CO (g/hp-hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
SET \a\...................................              17               1                             1           0.030             455           0.024
FTP.......................................              20               2                            12           0.141             514           0.076
LLC.......................................              29               3                            35           0.245             617           0.132
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).


   Table III-8--Stage 3 Engine Emissions at 600,000 Mile Equivalent Test Point Without Adjustments for IRAF or
                                               Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         24          1          1      0.015        460      0.030
FTP...........................................         27          1          9      0.144        519      0.058
LLC...........................................         33          4         16      0.153        623      0.064
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).


   Table III-9--Stage 3 Engine Emissions at 800,000 Mile Equivalent Test Point Without Adjustments for IRAF or
                                               Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         30          2          1      0.023        458      0.028
FTP...........................................         37          1         14      0.149        520      0.092
LLC...........................................         34          1         40      0.205        629      0.125
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).


 Table III-10--Stage 3 Engine Emissions at Interpolated at 650,000 Mile Equivalent Without Adjustments for IRAF
                                             or Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         26          1          1      0.017        460      0.030
FTP...........................................         30          1         10      0.145        519      0.067
LLC...........................................         33          3         22      0.166        625      0.079
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).

    In addition to evaluating the feasibility of the new criteria 
pollutant standards, we also evaluated how CO2 was impacted 
on the CARB Stage 3 engine (which is the same engine that was used for 
EPA's Stage 3 engine with modifications to the aftertreatment system 
and engine calibration to lower NOX emissions). We did this 
by evaluating how CO2 emissions changed from the base engine 
over the SET, FTP, and LLC, as well as the fuel mapping test procedures 
defined in 40 CFR 1036.535 and 1036.540. For all three cycles the CARB 
Stage 3 engine emitted CO2 with no measurable difference 
compared to the base 2017 Cummins X15 engine. Specifically, we compared 
the CARB Stage 3 engine including the 0-hour (degreened) aftertreatment 
with the 2017 Cummins X15 engine including degreened aftertreatment and 
found the percent reduction in CO2 was

[[Page 4343]]

0 percent for the SET, 1 percent for the FTP, and 1 percent for the 
LLC.\273\
---------------------------------------------------------------------------

    \273\ See Chapter 3 of the RIA for the CO2 emissions 
of the 2017 Cummins X15 engine and the CARB Stage 3 engine.
---------------------------------------------------------------------------

    We note that while the data from the EPA Stage 3 engine (the same 
engine as the CARB Stage 3 engine but after SwRI made changes to the 
thermal management strategies) at the equivalent age of 435,000 miles 
showed an increase in CO2 emissions for the SET, FTP, and 
LLC of 0.6, 0.7 and 1.3 percent respectively, which resulted in the 
CO2 emissions for the EPA Stage 3 engine being higher than 
the 2017 Cummins X15 engine, this is not directly comparable because 
the baseline 2017 Cummins X15 aftertreatment had not been aged to an 
equivalent of 435,000 miles.\274\ As discussed in Chapter 3 of the RIA, 
aging the EPA Stage 3 engine included exposing the aftertreatment to 
ash, that increased the back pressure on the engine, which contributed 
to the increase in CO2 emissions from the EPA Stage 3 
engine. We would expect the same increase in backpressure and in 
CO2 emissions from the 2017 Cummins X15 engine if the 
aftertreatment of the 2017 Cummins X15 engine was aged to an equivalent 
of 435,000 miles.
---------------------------------------------------------------------------

    \274\ As part of the agency's diesel demonstration program, we 
didn't age the aftertreatment of the base 2017 Cummins X15 engine 
since the focus of this program was to demonstrate emissions 
performance of future technologies and due to resource constraints. 
Thus, there isn't data directly comparable to the baseline engine at 
each aging step.
---------------------------------------------------------------------------

    To evaluate how the technology on the CARB Stage 3 engine compares 
to the 2017 Cummins X15 engine with respect to the HD GHG Phase 2 
vehicle CO2 standards, both engines were tested on the fuel 
mapping test procedures defined in 40 CFR 1036.535 and 1036.540. These 
test procedures define how to collect the fuel consumption data from 
the engine for use in GEM. For these tests the CARB Stage 3 engine was 
tested with the development aged aftertreatment.\275\ The fuel maps 
from these tests were run in GEM and the results from this analysis 
showed that the EPA and CARB Stage 3 engine emitted CO2 at 
the same rate as the 2017 Cummins X15 engine. The details of this 
analysis are described in Chapter 3.1 of the RIA.
---------------------------------------------------------------------------

    \275\ The CARB Stage 3 0-hour (degreened) aftertreatment could 
not be used for these tests, because it had already been aged past 
the 0-hour point when these tests were conducted.
---------------------------------------------------------------------------

    The technologies included in the EPA Stage 3 engine were selected 
to both demonstrate the lowest criteria pollutant emissions and have a 
negligible effect on GHG emissions. Manufactures may choose to use 
other technologies to meet the final standards, but manufacturers will 
still also need to comply with the GHG standards that apply under HD 
GHG Phase 2. We have, therefore, not projected an increase in GHG 
emissions resulting from compliance with the final standards.
---------------------------------------------------------------------------

    \276\ See RIA Chapter 3 for the details of the cost for the 
aftertreatment and CDA, which are the drivers for why the 
incremental direct manufacturing cost is lowest for Medium HDE.
    \277\ See Table III-3 for the final useful life values and 
Section IV.B.1 for the final emissions warranty periods.
---------------------------------------------------------------------------

    Table III-11 summarizes the incremental direct manufacturing costs 
for the final standards, from the baseline costs shown in Table III-15. 
These values include aftertreatment system, closed crankcase, and CDA 
costs. As discussed in Chapter 7 of the RIA, the direct manufacturing 
costs include the technology costs plus some costs to improve the 
durability of the technology through regulatory useful life. The 
details of this analysis can be found in Chapters 3 and 7 of the 
RIA.\276\ The cost of the final standards and useful life periods are 
further accounted for in the indirect costs as discussed in Chapter 7 
of the RIA.\277\

 Table III-11--Incremental Direct Manufacturing Cost of Final Standards
      for the Aftertreatment, Closed Crankcase, and CDA Technology
                                [2017 $]
------------------------------------------------------------------------
                                           Medium
               Light HDE                    HDE     Heavy HDE  Urban bus
------------------------------------------------------------------------
$1,957.................................     $1,817     $2,316     $1,850
------------------------------------------------------------------------

b. Baseline Emissions and Cost
    The basis for our baseline technology assessment is the data 
provided by manufacturers in the heavy-duty in-use testing program. 
This data encompasses in-use operation from nearly 300 Light HDE, 
Medium HDE, and Heavy HDE vehicles. Chapter 5 of the RIA describes how 
the data was used to update the MOVES model emissions rates for HD 
diesel engines. Chapter 3 of the RIA summarizes the in-use emissions 
performance of these engines.
    We also evaluated the certification data submitted to the agency. 
The data includes test results adjusted for IRAF and FEL that includes 
adjustments for deterioration and margin. The certification data, 
summarized in Table III-12 and Table III-13, shows that manufacturers 
vary in their approach to how much margin is built into the FEL. Some 
manufactures have submitted certification data with zero emissions 
(with rounding), which results in a margin at 100 percent of the FEL, 
while other manufacturers have margin that is less than 25 percent of 
the FEL.

                            Table III-12--Summary of Certification Data for FTP Cycle
----------------------------------------------------------------------------------------------------------------
                                                           NOX (g/hp- PM (g/hp-   NMHC (g/  CO (g/hp-  N2O (g/hp-
                                                              hr)        hr)       hp-hr)      hr)        hr)
----------------------------------------------------------------------------------------------------------------
Average..................................................       0.13       0.00       0.01       0.18       0.07
Minimum..................................................       0.05       0.00       0.00       0.00       0.04
Maximum..................................................       0.18       0.00       0.04       1.10       0.11
----------------------------------------------------------------------------------------------------------------


                            Table III-13--Summary of Certification Data for SET Cycle
----------------------------------------------------------------------------------------------------------------
                                                           NOX (g/hp- PM (g/hp-   NMHC (g/  CO (g/hp-  N2O (g/hp-
                                                              hr)        hr)       hp-hr)      hr)        hr)
----------------------------------------------------------------------------------------------------------------
Average..................................................       0.11       0.00       0.01       0.00       0.06
Minimum..................................................       0.00       0.00       0.00       0.00       0.00
Maximum..................................................       0.18       0.00       0.04       0.20       0.11
----------------------------------------------------------------------------------------------------------------


[[Page 4344]]

    In addition to analyzing the on-cycle certification data submitted 
by manufacturers, we tested three modern HD diesel engines on an engine 
dynamometer and analyzed the data. These engines were a 2018 Cummins 
B6.7, 2018 Detroit DD15 and 2018 Navistar A26. These engines were 
tested on cycles that range in power demand from the creep mode of the 
Heavy Heavy-Duty Diesel Truck (HHDDT) schedule to the HD SET cycle 
defined in 40 CFR 1036.510. Table III-14 summarizes the range of 
results from these engines on the SET, FTP, and LLC. As described in 
Chapter 3 of the RIA, the emissions of current production heavy-duty 
engines vary from engine to engine but the largest difference in NOX 
between engines is seen on the LLC.

                   Table III-14--Range of NOX Emissions From MY2018 Heavy-Duty Diesel Engines
----------------------------------------------------------------------------------------------------------------
                                                   SET in 40 CFR   SET in 40 CFR
                  NOX (g/hp-hr)                       86.1333        1036.510      FTP composite        LLC
----------------------------------------------------------------------------------------------------------------
Minimum.........................................            0.01            0.01            0.10            0.35
Maximum.........................................            0.12            0.05            0.15            0.81
Average.........................................            0.06            0.03            0.13            0.59
----------------------------------------------------------------------------------------------------------------

    Table III-15 summarizes the baseline sales-weighted total 
aftertreatment cost of Light HDEs, Medium HDEs, Heavy HDEs and urban 
bus engines. The details of this analysis can be found in Chapters 3 
and 7 of the RIA.

                         Table III-15--Baseline Direct Manufacturing Aftertreatment Cost
                                                    [2017 $]
----------------------------------------------------------------------------------------------------------------
                          Light HDE                               Medium HDE       Heavy HDE        Urban bus
----------------------------------------------------------------------------------------------------------------
$2,585.......................................................          $2,536           $3,761           $2,613
----------------------------------------------------------------------------------------------------------------

C. Summary of Compression-Ignition Off-Cycle Standards and Off-Cycle 
Test Procedures

    In this Section 0, we describe the final off-cycle standards and 
test procedures that will apply for model year 2027 and later heavy-
duty compression-ignition engines. The final off-cycle standards and 
test procedures cover the range of operation included in the duty cycle 
test procedures and operation that is outside of the duty cycle test 
procedures for each regulated pollutant (NOX, HC, CO, and 
PM). As described in Section III.C.1, our current not-to-exceed (NTE) 
test procedures were not designed to capture and control low-load 
operation. In contrast to the current NTE approach that evaluates 
engine operation within the NTE zone and excludes operation out of the 
NTE zone, we are finalizing a moving average window (MAW) approach that 
divides engine operation into two categories (or ``bins'') based on the 
time-weighted average engine power of each MAW of engine data. See 
Section III.C.2 for a discussion of the derivation of the final off-
cycle standards for each bin. For bin 1, the NOX emission 
standard is 10.0 g/hr. The final off-cycle standards for bin 2 are 
shown in Table III-16.

             Table III-16--Final Off-Cycle Bin 2 Standards for Light HDE, Medium HDE, and Heavy HDE
----------------------------------------------------------------------------------------------------------------
                        NOX (mg/hp-hr)                          HC (mg/hp-hr)    PM (mg/hp-hr)     CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
58 \a\.......................................................             120              7.5                9
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle testing, with both field testing and laboratory testing.

    The proposed rule provided an extensive discussion of the rationale 
and information supporting the proposed off-cycle standards (87 FR 
17472, March 28, 2022). Chapters 2 and 3 of the RIA include additional 
information including background on applicable test procedures and the 
full feasibility analysis for compression-ignition engines. See also 
section 11.3 of the Response to Comments for a detailed discussion of 
the comments and how they have informed this final rule.

1. Existing NTE Standards and Need for Changes to Off-Cycle Test 
Procedures

    Heavy-duty CI engines are currently subject to Not-To-Exceed (NTE) 
standards that are not limited to specific test cycles, which means 
they can be evaluated not only in the laboratory but also in-use. NTE 
standards and test procedures are generally referred to as ``off-
cycle'' standards and test procedures. These off-cycle emission 
standards are 1.5 (1.25 for CO) times the laboratory certification 
standard for NOX, HC, PM and CO and can be found in 40 CFR 
86.007-11.\278\ NTE standards have been successful in broadening the 
types of operation for which manufacturers design their emission 
controls to remain effective, including steady cruise operation. 
However, there remains a significant proportion of vehicle operation 
not covered by NTE standards.
---------------------------------------------------------------------------

    \278\ As noted in Section IV.G, manufacturers choosing to 
participate in the existing or final averaging, banking, and trading 
program agree to meet the family emissions limit (FEL) declared 
whenever the engine is tested over the applicable duty- or off-cycle 
test procedure. The FELs serves as the emission standard for 
compliance testing instead of the standards specified in 40 CFR 
86.007-11 or 40 CFR 1036.104(a); thus, the existing off-cycle 
standards are 1.5 (1.25 for CO) times the FEL for manufacturers who 
choose to participate in ABT.

---------------------------------------------------------------------------

[[Page 4345]]

    Compliance with an NTE standard is based on emission test data 
(whether collected in a laboratory or in use) analyzed pursuant to 40 
CFR 86.1370 to identify NTE events, which are intervals of at least 30 
seconds when engine speeds and loads remain in the NTE control area or 
``NTE zone''. The NTE zone excludes engine operation that falls below 
certain torque, power, and speed values.\279\ The NTE procedure also 
excludes engine operation that occurs in certain ambient conditions 
(i.e., high altitudes, high intake manifold humidity), or when 
aftertreatment temperatures are below 250 [deg]C. Collected data is 
considered a valid NTE event if it occurs within the NTE zone, lasts at 
least 30 seconds, and does not occur during any of the exclusion 
conditions (ambient conditions or aftertreatment temperature).
---------------------------------------------------------------------------

    \279\ Specifically, engine operations are excluded if they fall 
below 30 percent of maximum torque, 30 percent of maximum power, or 
15 percent of the European Stationary Cycle speed.
---------------------------------------------------------------------------

    The purpose of the NTE test procedure is to measure emissions 
during engine operation conditions that could reasonably be expected to 
occur during normal vehicle use; however, only data in a valid NTE 
event is then compared to the NTE emission standard. Our analysis of 
existing heavy-duty in-use vehicle test data indicates that less than 
ten percent of a typical time-based dataset are part of valid NTE 
events, and hence subject to the NTE standards; the remaining test data 
are excluded from consideration. We also found that emissions are high 
during many of the excluded periods of operation, such as when the 
aftertreatment temperature drops below the 250 [deg]C exclusion 
criterion. Our review of in-use data indicates that extended time at 
low load and idle operation results in low aftertreatment temperatures, 
which in turn lead to diesel engine SCR-based emission control systems 
not functioning over a significant fraction of real-world 
operation.\280\ \281\ \282\ Test data collected as part of EPA's 
manufacturer-run in-use testing program indicate that low-load 
operation could account for greater than 50 percent of the 
NOX emissions from a vehicle over a given workday.\283\
---------------------------------------------------------------------------

    \280\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of 
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel 
Engines Using Portable Emissions Measurement System (PEMS)''. 29th 
CRC Real World Emissions Workshop, March 10-13, 2019.
    \281\ Sandhu, Gurdas, et al. ``Identifying Areas of High 
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
    \282\ Sandhu, Gurdas, et al. ``In-Use Emission Rates for MY 
2010+ Heavy-Duty Diesel Vehicles''. 27th CRC Real-World Emissions 
Workshop, March 26-29, 2017.
    \283\ Sandhu, Gurdas, et al. ``Identifying Areas of High 
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
---------------------------------------------------------------------------

    For example, 96 percent of tests in response to 2014, 2015, and 
2016 EPA in-use testing orders passed with NOX emissions for 
valid NTE events well below the 0.3 g/hp-hr NOX NTE 
standard. When we used the same data to calculate NOX 
emissions over all operation measured, not limited to valid NTE events, 
the NOX emissions were more than double those within the 
valid NTE events (0.5 g/hp-hr).\284\ The results were even higher when 
we analyzed the data to consider only NOX emissions that 
occur during low load events.
---------------------------------------------------------------------------

    \284\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of 
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel 
Engines Using Portable Emissions Measurement System (PEMS)''. 29th 
CRC Real World Emissions Workshop, March 10-13, 2019.
---------------------------------------------------------------------------

    EPA and others have compared the performance of US-certified 
engines and those certified to European Union emission standards and 
concluded that the European engines' NOX emissions are lower 
in low-load conditions, but comparable to US-certified engines subject 
to MY 2010 standards under city and highway operation.\285\ This 
suggests that manufacturers are responding to the European 
certification standards by designing their emission controls to perform 
well under low-load operations, as well as highway operations.
---------------------------------------------------------------------------

    \285\ Rodriguez, F.; Posada, F. ``Future Heavy-Duty Emission 
Standards An Opportunity for International Harmonization''. The 
International Council on Clean Transportation. November 2019. 
Available online: https://theicct.org/sites/default/files/publications/Future%20_HDV_standards_opportunity_20191125.pdf.
---------------------------------------------------------------------------

    The European Union ``Euro VI'' emission standards for heavy-duty 
engines require manufacturers to check for ``in-service conformity'' by 
operating their engines over a mix of urban, rural, and motorway 
driving on prescribed routes using portable emission measurement system 
(PEMS) equipment to measure emissions.\286\ \287\ Compliance is 
determined using a work-based windows approach where emissions data are 
evaluated over segments or ``windows.'' A window consists of 
consecutive 1 Hz data points that are summed until the engine performs 
an amount of work equivalent to the European transient engine test 
cycle (World Harmonized Transient Cycle).
---------------------------------------------------------------------------

    \286\ COMMISSION REGULATION (EU) No 582/2011, May 25, 2011. 
Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:02011R0582-20180118&from=EN.
    \287\ COMMISSION REGULATION (EU) 2018/932, June 29, 2018. 
Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32018R0932&from=EN.
---------------------------------------------------------------------------

    EPA is finalizing new off-cycle test procedures similar to the 
European Euro VI in-service conformity program, with key distinctions 
that build upon the Euro VI approach, as discussed in the following 
section. This new approach will require manufacturers to account for a 
relatively larger proportion of engine operation and thereby further 
ensure that real-world emissions meet the off-cycle standards.
2. Off-Cycle Standards and Test Procedures
    We are replacing the NTE test procedures and standards (for 
NOX, PM, HC and CO) for model year 2027 and later engines. 
Under the final new off-cycle standards and test procedures, engine 
operation and emissions test data must be assessed in test intervals 
that consist of 300-second moving average windows (MAWs) of continuous 
engine operation. Our evaluation accounts for our current understanding 
that shorter windows are more sensitive to measurement variability and 
longer windows make it difficult to distinguish between duty cycles. In 
contrast to the current NTE approach that divides engine operation into 
two categories (in the NTE zone and out of the NTE zone), this approach 
will divide engine operation into two categories (or ``bins'') based on 
the time-weighted average engine power of each MAW of engine data, with 
some limited exclusions from the two bins, as described in more detail 
in the following discussion.
    In the NPRM, we requested comment on the proposed off-cycle 
standards and test procedures, including the 300 second length of the 
window. We first note that commenters broadly agree that the current 
NTE methodology should be revised, and that a MAW structure is 
preferable for off-cycle standards. Some commenters were concerned that 
individual seconds of data would be ``smeared,'' with the same 1-Hz 
data appearing in both bins as the 300 second windows are placed in the 
appropriate bin. We are finalizing the window length that we proposed, 
as the 300 second length provides an adequate averaging time to smooth 
any anomalous emission events and we anticipate that the final bin 
structure described in Section III.C.2.i. should also help address 
these concerns. See Response to Comments Section 11.1 through 11.3 for 
further details on these comments and EPA's response to these comments.
    Although this program has similarities to the European Euro VI 
approach, we are not limiting our off-

[[Page 4346]]

cycle standards and test procedures to operation on prescribed routes. 
Our current NTE program is not limited to prescribed routes, and we 
would consider it an unnecessary step backward to change that aspect of 
the procedure.
    In Section IV.G, we discuss the final rule updates to the ABT 
program to account for these new off-cycle standards.
i. Moving Average Window Operation Bins
    The final bin structure includes two bins of operation that 
represent two different domains of emission performance. Bin 1 
represents extended idle operation and other very low load operation 
where engine exhaust temperatures may drop below the optimal 
temperature for aftertreatment function. Bin 2 represents higher power 
operation including much of the operation currently covered by the NTE. 
Operation in bin 2 naturally involves higher exhaust temperatures and 
catalyst efficiencies. Because this approach divides 300 second windows 
into bins based on time-averaged engine power of the window, any of the 
bins could include some idle or high-power operation. Like the duty 
cycle standards, we believe more than a single standard is needed to 
apply to the entire range of operation that heavy-duty engines 
experience. A numerical standard that is technologically feasible under 
worst case conditions such as idle would necessarily be much higher 
than the levels that are achievable when the aftertreatment is 
functioning optimally. Section III.C.2.iii includes the final numeric 
off-cycle standards.
    Given the challenges of measuring engine power directly in-use, we 
are using the CO2 emission rate (grams per second) as a 
surrogate for engine power in defining the bins for an engine. We are 
further normalizing CO2 emission rates relative to the 
nominal maximum CO2 rate of the engine. So, if an engine 
with a maximum CO2 emission rate of 50 g/sec was found to be 
emitting CO2 at a rate of 10 g/sec, its normalized 
CO2 emission rate would be 20 percent. The maximum 
CO2 rate is defined as the engine's rated maximum power 
multiplied by the engine's CO2 family certification level 
(FCL) for the FTP certification cycle.
    In the proposal, we requested comment on whether the maximum 
CO2 mass emission rate should instead be determined from the 
steady-state fuel mapping procedure in 40 CFR 1036.535 or the torque 
mapping procedure defined in 40 CFR 1065.510. After considering 
comments, EPA is finalizing the use of the CO2 emission rate 
as a surrogate for engine power with the proposed approach to 
determining the maximum CO2 mass emission rate. We have two 
main reasons for finalizing the determination of maximum CO2 
mass emission rate as proposed. First, the FTP FCL and maximum engine 
power are already reported to the EPA, so no new requirements are 
needed under the finalized approach. Second, our assessment of the 
finalized approach has shown that this approach for the determination 
of maximum CO2 mass emission rate matches well with the 
other options we requested comment on. EPA believes that using the 
CO2 emission rate will automatically account for additional 
fuel usage not directly used for driveshaft torque and minimizes 
concerns about the accuracy and data alignment in the use of broadcast 
torque. EPA acknowledges that there is some small variation in 
efficiency, and thus CO2 emissions rates, among engines. 
However, the test procedure accounts for improvements to the engine 
efficiency by using the FTP FCL to convert CO2 specific 
NOX to work specific NOX. This is because the FTP 
FCL captures the efficiency of the engine over a wide range of 
operation, from cold start, idle and steady-state higher power 
operation. Furthermore, the FTP FCL can also capture the CO2 
improvements from hybrid technology when the powertrain test option 
described in preamble Section III.B.2.v is utilized.
    The bins are defined as follows:
     Bin 1: 300 second windows with normalized average 
CO2 rate <=6 percent.
     Bin 2: 300 second windows with normalized average 
CO2 rate >6 percent.
    The bin cut point of six percent is near the average power of the 
low-load cycle. In the NPRM, we proposed a three-bin structure and 
requested comment on the proposed number of bins and the value of the 
cut point(s). After considering comments, EPA agrees with commenters to 
the extent the commenters recommend combining the proposed bins 2 and 3 
into a single ``non-idle'' bin 2. Results from the EPA Stage 3 real 
world testing indicate that emissions in bins 2 and 3 (expressed as 
emissions/normalized CO2) are substantially similar, 
minimizing the advantage of separating these modes of operation. See 
Response to Comments Section 11.1 for further details on these comments 
and EPA's response to these comments.
    To ensure that there is adequate data in each of the bins to 
compare to the off-cycle standards, the final requirements specify that 
there must be a minimum of 2,400 moving average windows in bin 1 and 
10,000 moving average windows in bin 2. In the NPRM, we proposed a 
minimum of 2,400 windows for all bins and requested comment on the 
appropriate minimum number of windows required to sufficiently reduce 
variability in the results while not requiring an unnecessary number of 
shift days to be tested to meet the requirement. EPA received comments 
both supporting the proposed 2,400 window minimum and supporting an 
increase to 10,000 windows total for the non-idle bins (now a single 
bin 2 in this final rule). After considering comments, we believe 
requiring a minimum of 10,000 windows in final bin 2 to define a valid 
test is appropriate. Analysis of data from the EPA Stage 3 off-cycle 
test data has shown that emissions are stable after 6,000 windows of 
data at moderate temperatures but NOX emissions under low 
ambient temperatures need closer to 10,000 windows to be stable. EPA 
believes the larger number of required windows will better characterize 
the emissions performance of the engine.
    If during the first shift day any of the bins do not include at 
least the minimum number of windows, then the engine will need to be 
tested for additional day(s) until the minimum requirement is met. 
Additionally, the engine can be idled at the end of the shift day to 
meet the minimum window count requirement for the idle bin. This is to 
ensure that even for duty cycles that do not include significant idle 
operation the minimum window count requirement for the idle bin can be 
met without testing additional days.
    We received comments on the timing and duration of the optional 
end-of-day idle. After considering comments, the final requirements 
specify that the ability to add idle time is restricted to the end of 
the shift day, and manufacturers may extend this end-of-day idle period 
to be as long as they choose. Additional idle in the middle of the 
shift day is contrary to the intent of real-world testing, and the end 
of the shift day is the only realistic time to add windows. Since idle 
times of varying lengths are encountered in real-world operation, we do 
not think that requiring a specific length of idle time would 
necessarily make the resulting data set more representative.
    As described further in section III.C.2.ii, after consideration of 
comment, EPA is including requirements in 40 CFR 1036.420 that specify 
that during the end-of-day idle period, when testing vehicles with 
automated engine shutdown features, manufacturers will be required to 
override the automated shutdown feature where possible. This will 
ensure

[[Page 4347]]

that the test data will contain at least 2,400 windows in the idle bin, 
which otherwise would be unobtainable. For automated shutdown features 
that cannot be overridden, the manufacturer may populate the bin with 
zero emission values for idle until exactly 2,400 windows are achieved.
ii. Off-Cycle Test Procedures
    The final off-cycle test procedures include measuring off-cycle 
emissions using the existing test procedures that specify measurement 
equipment and the process of measuring emissions during testing in 40 
CFR part 1065. Part 1036, subpart E contains the process for recruiting 
test vehicles, how to test over the shift day, how to evaluate the 
data, what constitutes a valid test, and how to determine if an engine 
family passes. Measurements may use either the general laboratory test 
procedures or the field-testing procedures in 40 CFR part 1065, subpart 
J. However, we are finalizing special calculations for bin 2 in 40 CFR 
1036.530 that will supersede the brake-specific emission calculations 
in 40 CFR part 1065. The test procedures require second-by-second 
measurement of the following parameters:

 Molar concentration of CO2 (ppm)
 Molar concentration of NOX (ppm)
 Molar concentration of HC (ppm)
 Molar concentration of CO (ppm)
 Concentration of PM (g/m\3\)
 Exhaust flow rate (m\3\/s)

    Mass emissions of CO2 and each regulated pollutant are 
separately determined for each 300-second window and are binned based 
on the normalized CO2 rate for each window.
    Additionally, EPA agrees with commenters that the maximum allowable 
engine coolant temperature at the start of the day should be raised to 
40 degrees Celsius and we are finalizing this change in 40 CFR 
1036.530. In the NPRM, we proposed 30 [deg]C which is 86 [deg]F. It is 
possible that ambient temperatures in some regions of the United States 
won't drop below this overnight. We are therefore finalizing 40 [deg]C 
which is 104 [deg]F as this should ensure that high overnight ambient 
temperatures do not prevent a manufacturer from testing a vehicle.
    The standards described in Section III.C.2.iii are expressed in 
units of g/hr for bin 1 and mg/hp-hr for bin 2. However, unlike most of 
our exhaust standards, the hp-hr values for the off-cycle standards do 
not refer to actual brake work. Rather, they refer to nominal 
equivalent work calculated proportional to the CO2 emission 
rate. Thus, in 40 CFR 1036.530 the NOX emissions (``e'') in 
g/hp-hr are calculated as:
[GRAPHIC] [TIFF OMITTED] TR24JA23.000

    The final requirements include a limited number of exclusions (six 
total) in 40 CFR 1036.530(c)(3) that exclude some data from being 
subject to the off-cycle standards. The first exclusion in 40 CFR 
1036.530(c)(3)(i) is for data collected during periodic PEMS zero and 
span drift checks or calibrations, where the emission analyzers and/or 
flow meter are not available to measure emissions during that time and 
these checks/calibrations are needed to ensure the robustness of the 
data.
    The second exclusion in 40 CFR 1036.530(c)(3)(ii) is for data 
collected anytime the engine is off during the course of the shift day, 
with modifications from proposal that (1) this exclusion does not 
include engine off due to automated stop-start, and (2) specific 
requirements for vehicles with stop-start technology. In the NPRM, we 
proposed excluding data for vehicles with stop-start technology when 
the engine was off and requested comment on the appropriateness of this 
exclusion. We received comment suggesting provisions for vehicles 
equipped with automated stop-start technology. After considering 
comments, EPA has included in the final rule requirements applicable 
when testing vehicles with automatic engine shutdown (AES) and/or stop-
start technology. Under the final requirements, the manufacturer shall 
disable AES and/or stop-start if it is not tamper resistant as 
described in 40 CFR 1036.415(g), 1036.420(c), and 1036.530(c)(3). If 
stop-start is tamper resistant, the 1-Hz emission rate for all GHG and 
criteria pollutants shall be set to zero when AES and/or stop-start is 
active and the engine is off, and these data are included in the normal 
windowing process (i.e., the engine-off data are not treated as 
exclusions). If at the end of the shift day there are not 2,400 windows 
in bin 1 for a vehicle with AES and/or stop-start technology, the 
manufacturer must populate the bin with additional windows with the 
emission rate for each GHG and criteria pollutant set to zero to 
achieve exactly 2,400 idle bin windows. This process accounts for 
manufacturers who implement a start/stop mode that cannot be overridden 
and applies the windowing and binning process in a way that is similar 
to the process applied to a conventionally idling vehicle.
    The third exclusion in 40 CFR 1036.530(c)(3)(iii) is for data 
collected during infrequent regeneration events. The data collected for 
the test order may not collect enough operation to properly weight the 
emissions rates during an infrequent regeneration event with emissions 
that occur without an infrequent regeneration event.
    The fourth exclusion in 40 CFR 1036.530(c)(3)(iv) is for data 
collected when ambient temperatures are below 5 [deg]C (this aspect 
includes some modifications from proposal), or when ambient 
temperatures are above the altitude-based value determined using 
Equation 40 CFR 1036.530-1. The colder temperatures can significantly 
inhibit the engine's ability to maintain aftertreatment temperature 
above the minimum operating temperature of the SCR catalyst while the 
higher temperature conditions at altitude can limit the mass airflow 
through the engine, which can adversely affect the engine's ability to 
reduce engine out NOX through the use of exhaust gas 
recirculation (EGR). In addition to affecting EGR, the air-fuel ratio 
of the engine can decrease under high load, which can increase exhaust 
temperatures above the conditions where the SCR catalyst is most 
efficient at reducing NOX. However, we also do not want to 
select temperature limits that overly exclude operation, such as 
setting a cold temperature limit so high that it excludes important 
initial cold start operation from all tests, or a number of return to 
service events. These are important operational regimes, and the MAW 
protocol is intended to capture emissions over the entire operation of 
the vehicle. The final rule strikes an appropriate balance between 
these considerations.
    In the NPRM, we proposed excluding data when ambient temperatures 
were below -7 [deg]C and requested comment on the appropriateness of 
this exclusion. Several comments disagreed with the proposed low 
temperature exclusion level and recommended a higher

[[Page 4348]]

temperature of 20 [deg]C as well as additional exemptions for coolant 
and oil temperatures, and recommended low temperature exclusion 
temperatures that ranged from 20 to 70 [deg]C. After considering 
comments, we adjusted the final ambient temperature exclusion to 5 
[deg]C. We have additionally incorporated a temperature-based 
adjustment to the final numerical NOX standards, as 
described in Section III.C.iii. However, we have not incorporated 
exclusions based on coolant and oil temperatures. These changes are 
supported by data recently generated from testing at SwRI with the EPA 
Stage 3 engine at low temperatures over the CARB Southern Route Cycle 
and Low Load Cycle. This testing consisted of operation of the engine 
over the duty-cycle with the test cell ambient temperature set at 5 
[deg]C with air flow moving over the aftertreatment system to simulate 
the airflow over the aftertreatment during over the road operation. The 
results indicated that there were cold ambient air temperature effects 
on aftertreatment temperature that reduced NOX reduction 
efficiency, which supports that the temperature should be increased. 
With these changes, our analysis, as described in section III.C, shows 
that the off-cycle standards are achievable for MY 2027 and later 
engines down to 5 [deg]C, taking into account the temperature-based 
adjustment to the final numerical standards. We have concerns about 
whether the off-cycle standards could be met below 5 [deg]C after 
taking a closer look at all data regarding real world effects and based 
on this we are exempting data from operation below 5 [deg]C from being 
subject to the standards.
    The fifth exclusion in 40 CFR 1036.530(c)(3)(v) is for data 
collected where the altitude is greater than 5,500 feet above sea level 
for the same reasons as for the high temperatures at altitude 
exclusion.
    The sixth exclusion in 40 CFR 1036.530(c)(3)(vi) is for data 
collected when any approved Auxiliary Emission Control Device (AECD) 
for emergency vehicles are active because the engines are allowed to 
exceed the emission standards while these AECDs are active.
    To reduce the influence of environmental conditions on the accuracy 
and precision of the PEMS for off-cycle in-use testing, we are adding 
additional changes to those proposed in requirements in 40 CFR 
1065.910(b). These requirements are to minimize the influence of 
temperature, electromagnetic frequency, shock, and vibration on the 
emissions measurement. If the design of the PEMS or the installation of 
the PEMS does not minimize the influence of these environmental 
conditions, the final requirements specify that the PEMS must be 
installed in an environmental chamber during the off-cycle test to 
minimize these effects.
iii. Off-Cycle Standards
    For NOX, we are finalizing separate standards for 
distinct modes of operation. To ensure that the duty-cycle 
NOX standards and the off-cycle NOX standards are 
set at the same relative stringency level, the bin 1 standard is 
proportional to the Voluntary Idle standard discussed in Section 
III.B.2.iv, and the bin 2 standard is proportional to a weighted 
combination of the LLC standard discussed in Section III.B.2.iii and 
the SET standard discussed in Section III.B.2.ii. For bin 1, the 
NOX emission standard for all CI primary intended service 
classes is 10.0 g/hr starting in model year 2027. For PM, HC and CO we 
are not setting standards for bin 1 because the emissions from these 
pollutants are very small under idle conditions and idle operation is 
extensively covered by the SET, FTP, and LLC duty cycles discussed in 
Section III.B.2. The combined NOX bin 2 standard is weighted 
at 25 percent of the LLC standard and 75 percent of the SET standard, 
reflecting the nominal flow difference between the two cycles. For HC, 
the bin 2 standard is also set at values proportional to a 25 percent/
75 percent weighted combination of the LLC standard and the SET 
standard.\288\ For PM and CO, the SET, FTP, and LLC standards are the 
same numeric value, so bin 2 is proportional to that numeric standard. 
The numerical values of the off-cycle standards for bin 2 are shown in 
Table III-17.
---------------------------------------------------------------------------

    \288\ See Preamble Section III.B.2 for the HC standards for the 
SET and LLC.
---------------------------------------------------------------------------

    The final numerical off-cycle bin 1 NOX standard reflect 
a conformity factor of 1.0 times the Clean Idle standard discussed in 
Section III.B.2.iv. The final numerical off-cycle bin 2 standards for 
all pollutants reflect a conformity factor of 1.5 times the duty-cycle 
standards set for the LLC and SET cycles discussed in Section 
III.B.2.ii and Section III.B.2.iii. Additionally, as discussed in 
Section III.B.2, the in-use NOX off-cycle standard for 
Medium and Heavy HDE reflects an additional 15 mg/hp-hr NOX 
allowance above the bin 2 standard. Similar to the duty cycle 
standards, the off-cycle standards were set at a level that resulted in 
at least 40 percent compliance margin for the EPA Stage 3 engine. We 
requested and received comments on the appropriate scaling factors or 
other approaches to setting off-cycle standards. After consideration of 
the comments, we believe the final numerical standards are feasible and 
appropriate for certification and in-use testing. We note that the 
final standards are similar, but not identical to, the options proposed 
in the NPRM. As with the duty cycle standards discussed in Preamble 
Section III.B, the data from the EPA Stage 3 engine supported the most 
stringent numeric standards we proposed under low-load operation and 
the most stringent numeric standards we proposed for MY 2027 under high 
load operation. More discussion of the feasibility of these standards 
can be found in the following discussion and in Section III.C.3 and 
Response to Comments Section 11.3.1.

                                     Table III-17--Off-Cycle Bin 2 Standards
----------------------------------------------------------------------------------------------------------------
                       NOX  (mg/hp-hr)                          HC (mg/hp-hr)    PM (mg/hp-hr)     CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
58 \a\.......................................................             120              7.5                9
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR 1036, subpart
  E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR 1036.235(c) or
  selective enforcement audits described in 40 CFR part 1068.

    In the proposal, we requested comment on the in-use test conditions 
over which engines should be required to comply with the standard, 
asking commentors to take into consideration any tradeoffs that broader 
or narrower

[[Page 4349]]

conditions might have on the stringency of the standard we set. After 
considering comments on low ambient air temperature and the available 
data from the low-temperature Stage 3 testing at SwRI described in 
section III.C.2.ii, we are also incorporating an adjustment to the 
numerical off-cycle bin 1 and bin 2 standards for NOX as a 
function of ambient air temperature below 25 [deg]C. The results 
demonstrated higher NOX emissions at low temperatures, 
indicating that standards should be numerically higher to account for 
real-world temperature effects on the aftertreatment system. To 
determine the magnitude of this adjustment, we calculated the increase 
in the Stage 3 engine NOX emissions over the CARB Southern 
Route Cycle at low temperature over the NOX emissions at 25 
[deg]C. These values were linearly extrapolated to determine the 
projected increase at 5 [deg]C versus 25 [deg]C. Table III-18 presents 
the numerical value of each off-cycle bin 1 and bin 2 NOX 
standard at both 25 [deg]C and 5 [deg]C.
    Under the final requirements in 40 CFR 1036.104, the ambient 
temperature adjustment is applied based on the average 1-Hz ambient air 
temperature during the shift day for all data not excluded under 40 CFR 
1036.530(c), calculated as the time-averaged temperature of all 
included data points. If this average temperature is 25 [deg]C or 
above, no adjustment to the standard is made. If the average 
temperature is below 25 [deg]C, the applicable NOX standard 
is calculated using the equations in Table 3 to paragraph (a)(3) of 40 
CFR 1036.104 Table III-18 for the appropriate service class and bin.

                      Table III-18--Temperature Adjustments to the Off-Cycle NOX Standards
----------------------------------------------------------------------------------------------------------------
                                                                         NOX        NOX
                                                                       standard   standard
           Service class                Applicability         Bin       at 25       at 5       Applicable unit
                                                                        [deg]C     [deg]C
----------------------------------------------------------------------------------------------------------------
All...............................  All..................          1         10     \a\ 15  g/hr.
Light HDE.........................  Certification & In-            2         58    \a\ 102  mg/hp-hr.
                                     use.
Medium and Heavy HDE..............  Certification........          2         58    \a\ 102  mg/hp-hr.
Medium and Heavy HDE..............  In-Use...............          2     \a\ 73    \a\ 117  mg/hp-hr.
----------------------------------------------------------------------------------------------------------------
\a\ The Bin 1 and Bin 2 ambient temperature adjustment and the NOX compliance allowance for in-use testing do
  not scale with the FELFTPNOx.

3. Feasibility of the Diesel (Compression-Ignition) Off-Cycle Standards
i. Technologies
    As a starting point for our determination of the appropriate 
numeric levels of the off-cycle emission standards, we considered 
whether manufacturers could meet the duty-cycle standard corresponding 
to the type of engine operation included in a given bin,\289\ as 
follows:
---------------------------------------------------------------------------

    \289\ See preamble Section III.B.3 for details on EPA's 
assessment of the feasibility of the duty-cycle standards.
---------------------------------------------------------------------------

     Bin 1 operation is generally similar to operation at idle 
and the lower speed portions of the LLC.
     Bin 2 operation is generally similar to operation over the 
LLC, the FTP and much of the SET.
    An important question is whether the off-cycle standards would 
require technology beyond what we are projecting would be necessary to 
meet the duty-cycle standards. As described in this section, we do not 
expect the off-cycle standards to require different technologies.
    This is not to say that we expect manufacturers to be able to meet 
these standards with no additional work. Rather, we project that the 
off-cycle standards can be met primarily through additional effort to 
calibrate the duty-cycle technologies to function properly over the 
broader range of in-use conditions. We also recognize that 
manufacturers can choose to include additional technology, if it 
provided a less expensive or otherwise preferred option.
    When we evaluated the technologies discussed in Section III.B.3.i 
with emissions controls that were designed to cover a broad range of 
operation, it was clear that we should set the off-cycle standards to 
higher numerical values than the duty-cycle standards to take into 
account the broader operations covered by the off-cycle test 
procedures. Section III.C.3.ii explains how the technology and controls 
performed when testing with the off-cycle test procedures over a broad 
range of operation. The data presented in Section III.C.3.ii shows that 
even though there are similarities in the operation between the duty 
cycles (SET, FTP, and LLC) and the off-cycle bins 1 and 2, the broader 
range of operation covered by the off-cycle test procedure results in a 
broader range of emissions performance, which justifies setting the 
numeric off-cycle standards higher than the corresponding duty cycle 
standards for equivalent stringency. In addition to this, the off-cycle 
test procedures and standards cover a broader range of ambient 
temperature and pressure, which can also increase the emissions from 
the engine as discussed in Section III.C.2.ii.
ii. Summary of Feasibility Analysis
    To identify appropriate numerical levels for the off-cycle 
standards, we evaluated the performance of the EPA Stage 3 engine in 
the laboratory on five different cycles that were created from field 
data of HD engines that cover a range of off-cycle operation. These 
cycles are the CARB Southern Route Cycle, Grocery Delivery Truck Cycle, 
Drayage Truck Cycle, Euro-VI ISC Cycle (EU ISC) and the Advanced 
Collaborative Emissions Study (ACES) cycle. The CARB Southern Route 
Cycle is predominantly highway operation with elevation changes 
resulting in extended motoring sections followed by high power 
operation. The Grocery Delivery Truck Cycle represents goods delivery 
from regional warehouses to downtown and suburban supermarkets and 
extended engine-off events characteristic of unloading events at 
supermarkets. Drayage Truck Cycle includes near dock and local 
operation of drayage trucks, with extended idle and creep operation. 
Euro-VI ISC Cycle is modeled after Euro VI ISC route requirements with 
a mix of 30 percent urban, 25 percent rural and 45 percent highway 
operation. ACES Cycle is a 5-mode cycle developed as part of ACES 
program. Chapter 3 of the RIA includes figures that show the engine 
speed, engine torque and vehicle speed of the cycles.
    The engine was initially calibrated to minimize NOX 
emissions for the dynamometer duty cycles (SET, FTP, and LLC). It was 
then further calibrated to achieve more optimal performance over off-
cycle operation. The test results shown in Table III-19 provide a 
reasonable basis for evaluating the feasibility of controlling off-
cycle emissions to a useful life of 435,000 miles and 800,000 miles. 
Additionally,

[[Page 4350]]

the engine tested did not include the SCR catalyst volume that is 
included in our cost analysis and that we determined should enable 
lower bin 2 NOX emissions, further supporting that the final 
standards are feasible. Additionally, the 800,000 mile aged 
aftertreatment was tested over the CARB Southern Route Cycle with an 
ambient temperature between 2 [deg]C and 9 [deg]C (6.8 [deg]C average), 
the average of which is slightly above the 5 [deg]C minimum ambient 
temperature that the final requirements specify as the level below 
which test data are excluded.\290\ The summary of the results is in 
Chapter 3 of the RIA. For Light HDE standards, we looked at the data at 
the equivalent of 435,000 miles.\291\ For the Medium and Heavy HDE 
standards we looked at the data at the equivalent of 800,000 
miles.\292\
---------------------------------------------------------------------------

    \290\ The low ambient temperature exclusion was raised from the 
proposed level of -7 [deg]C to 5 [deg]C, since engines can continue 
to use EGR to reduce NOX without the use of an EGR cooler 
bypass at and above 5 [deg]C. See RIA Chapter 3.1.1.2.2 for a 
summary of data from the EPA Stage 3 engine with three different 
idle calibrations.
    \291\ See Section III.B.3.ii for an explanation on why we 
determined data at the equivalent of 435,000 miles was appropriate 
for determining the feasibility of the Light HDE standards.
    \292\ Similar to our reasoning in Section III.B.3.ii for using 
the interpolated data at the equivalent of 650,000 miles to 
determine the feasibility of the duty cycle standards for Medium and 
Heavy HDE, we determined the data at the equivalent of 800,000 was 
appropriate for determining the feasibility of the Medium and Heavy 
HDE off-cycle standards. The one difference is that emission data 
was not collected at the equivalent of 600,000 miles. Therefore, we 
used the data at the equivalent of 800,000 miles (rather than 
assuming the emissions performance changed linearly and 
interpolating the emissions from the data at the equivalent of 
435,000 and 800,000 miles) to determine the emissions performance at 
the equivalent of 650,000 miles. We think it's appropriate to use 
the data at the equivalent of 800,000 miles (rather than the 
interpolated data at the equivalent of 650,000 miles) to account for 
uncertainties in real world performance, particularly given the 
significant increases in useful life, decreases in the numeric 
levels of the standards, and the advanced nature of the 
technologies.

                         Table III-19--EPA Stage 3 NOX Emissions Off-Cycle Operation Without Adjustments for Crankcase Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                           CARB southern  Grocery deliv.
   Equivalent miles, ambient T ([deg]C)                Bin No.              route cycle        cycle           ACES           EU ISC          Drayage
--------------------------------------------------------------------------------------------------------------------------------------------------------
435,000, 25 [deg]C........................  1 (g/hr)....................             0.7             1.0             0.9             0.4             0.3
                                            2 (mg/hp-hr)................              32              21              20              31              19
800,000, 25 [deg]C........................  1 (g/hr)....................             0.7             3.3             1.5             0.4             1.1
                                            2 (mg/hp-hr)................              47              32              34              32              28
                                                                                         ---------------------------------------------------------------
800,000, 2 to 9 [deg]C....................  1 (g/hr)....................             1.4                            Not tested
                                                                                         ---------------------------------------------------------------
                                            2 (mg/hp-hr)................              87                            Not tested
--------------------------------------------------------------------------------------------------------------------------------------------------------

a. Bin 1 Evaluation
    Bin 1 includes the idle operation and some of the lower speed 
operation that occurs during the FTP and LLC. However, it also includes 
other types of low-load operation observed with in-use vehicles, such 
as operation involving longer idle times than occur in the LLC. To 
ensure that the bin 1 standard is feasible, we set the idle bin 
standard at the level projected to be achievable engine-out with 
exhaust temperatures below the aftertreatment light-off temperature. As 
can be seen from the results in Table III-19, the EPA Stage 3 engine 
performed well below the bin 1 NOX standards. The summary of 
the results is located in Chapter 3 of the RIA.
    For bin 1 we are finalizing NOX standard at a level 
above what we have demonstrated because there are conditions in the 
real world that may prevent the emissions control technology from being 
as effective as demonstrated with the EPA Stage 3 engine. For example, 
under extended idle operation the EGR rate may need to be reduced to 
maintain engine durability. Under extended idle operation with cold 
ambient temperatures, the aftertreatment system can lose NOX 
reduction efficiency which can also increase NOX emissions. 
Taking this under consideration, as well as other factors, we believe 
that the final bin 1 NOX standard in Table III-17 is the 
lowest achievable standard in MY 2027.
b. Bin 2 Evaluations
    As can be seen see from the results in Table III-19, the 
NOX emissions from the Stage 3 engine in bin 2 were below 
the final off-cycle standards for each of the off-cycle duty-cycles. 
The HC and CO emissions measured for each of these off-cycle duty 
cycles were well below the final off-cycle standards for bin 2. PM 
emissions were not measured during the off-cycle tests, but based on 
the effectiveness of DPFs over all engine operation as seen with the 
SET, FTP, and LLC, our assessment is that the final PM standards in Bin 
2 are feasible. The summary of the results is located in Chapter 3 of 
the RIA.
    For bin 2, all the 25 [deg]C off-cycle duty cycles at a full useful 
life of 800,000 miles had emission results below the NOX 
certification standard of 58 mg/hp-hr shown in Table III-19. 
Additionally, the CARB Southern Route Cycle run at ambient temperatures 
under 10 [deg]C had emission results below the Heavy HDE NOX 
in-use off-cycle standard of 106 mg/hp-hr which is the standard at 10 
[deg]C as determined from Equation 40 CFR 1036.104-2. While this cycle 
was run at temperatures above the minimum ambient temperature exclusion 
limit of 5 [deg]C that we are finalizing, we expect actual HDIUT 
testing to be less severe than the demonstration. Nonetheless, since 
the results of the low ambient temperature testing demonstrated higher 
NOX emissions at low temperatures, as shown in Table III-19, 
we have finalized standards that are numerically higher at lower 
temperatures to account for real-world temperature effects on the 
aftertreatment system.
    In the NPRM, we requested comment on the numerical values of the 
off-cycle standards, as well as the overall structure of the off-cycle 
program. We received comments recommending both lower and higher 
numerical standards than were proposed. After considering comments, we 
believe the off-cycle standards that we are finalizing are appropriate 
and feasible values. See Response to Comments Section 11.3.1 for 
further details on these comments and EPA's response to these comments.
4. Compliance and Flexibilities for Off-Cycle Standards
    Given the similarities of the off-cycle standards and test 
procedures to the current NTE requirements that we are

[[Page 4351]]

replacing starting in MY 2027, we evaluated the appropriateness of 
applying the current NTE compliance provisions to the off-cycle 
standards we are finalizing and determined which final compliance 
requirements and flexibilities are applicable to the new final off-
cycle standards, as discussed immediately below.
i. Relation of Off-Cycle Standards To Defeat Devices
    CAA section 203 prohibits bypassing or rendering inoperative a 
certified engine's emission controls. When the engine is designed or 
modified to do this, the engine is said to have a defeat device. With 
today's engines, the greatest risks with respect to defeat devices 
involve manipulation of the engine's electronic controls. EPA refers to 
an element of design that manipulates emission controls as an Auxiliary 
Emission Control Device (AECD).\293\ Unless explicitly permitted by 
EPA, AECDs that reduce the effectiveness of emission control systems 
under conditions which may reasonably be expected to be encountered in 
normal vehicle operation and use are prohibited as defeat devices under 
current 40 CFR 86.004-2.
---------------------------------------------------------------------------

    \293\ 40 CFR 86.082-2 defines Auxiliary Emission Control Device 
(AECD) to mean ``any element of design which senses temperature, 
vehicle speed, engine RPM, transmission gear, manifold vacuum, or 
any other parameter for the purpose of activating, modulating, 
delaying, or deactivating the operation of any part of the emission 
control system.''
---------------------------------------------------------------------------

    For certification, EPA requires manufacturers to identify and 
describe all AECDs.\294\ For any AECD that reduces the effectiveness of 
the emission control system under conditions which may reasonably be 
expected to be encountered in normal vehicle operation and use, 
manufacturers must provide a detailed justification.\295\ We are 
migrating the definition of defeat device from 40 CFR 86.004-2 to 40 
CFR 1036.115(h) and clarifying that an AECD is not a defeat device if 
such conditions are substantially included in the applicable procedure 
for duty-cycle testing as described in 40 CFR 1036, subpart F. Such 
AECDs are not treated as defeat devices because the manufacturer shows 
that their engines are able to meet standards during duty-cycle testing 
while the AECD is active. The AECD might reduce the effectiveness of 
emission controls, but not so much that the engine fails to meet the 
standards that apply.
---------------------------------------------------------------------------

    \294\ See 40 CFR 86.094-21(b)(1)(i)(A).
    \295\ See definition of ``defeat device'' in 40 CFR 86.004-2.
---------------------------------------------------------------------------

    We do not extend this same treatment to off-cycle testing, for two 
related reasons. First, we can have no assurance that the AECD is 
adequately exercised during any off-cycle operation to support the 
conclusion that the engine will consistently meet emission standards 
over all off-cycle operation. Second, off-cycle testing may involve 
operation over an infinite combination of engine speeds and loads, so 
excluding AECDs from consideration as defeat devices during off-cycle 
testing would make it practically impossible to conclude that an engine 
has a defeat device.
    If an engine meets duty-cycle standards and the engine has no 
defeat devices, we should be able to expect engines to achieve a 
comparable level of emission control for engine operation that is 
different than what is represented by the certification duty cycles. 
The off-cycle standards and measurement procedures allow for a modest 
increase in emissions for operation that is different than the duty 
cycle, but manufacturers may not change emission controls to increase 
emissions to the off-cycle standard if those controls were needed to 
meet the duty-cycle standards. The finalized off-cycle standards are 
set at a level that is feasible under all operating conditions, so we 
expect that under much of the engine operation the emissions are well 
below the final off-cycle standards.
ii. Heavy-Duty In-Use Testing Program
    Under the current manufacturer-run heavy-duty in-use testing 
(HDIUT) program, EPA annually selects engine families to evaluate 
whether engines are meeting current emissions standards. Once we submit 
a test order to the manufacturer to initiate testing, it must contact 
customers to recruit vehicles that use an engine from the selected 
engine family. The manufacturer generally selects five unique vehicles 
that have a good maintenance history, no malfunction indicators on, and 
are within the engine's regulatory useful life for the requested engine 
family. The tests require use of portable emissions measurement systems 
(PEMS) that meet the requirements of 40 CFR part 1065, subpart J. 
Manufacturers collect data from the selected vehicles over the course 
of a day while they are used for their normal work and operated by a 
regular driver, and then submit the data to EPA. Compliance is 
currently evaluated with respect to the NTE standards.
    With some modifications from proposal, we are continuing the HDIUT 
program, with compliance with respect to the new off-cycle standards 
and test procedures added to the program beginning with MY 2027 
engines. As proposed, we are not carrying forward the Phase 2 HDIUT 
requirements in 40 CFR 86.1915 once the NTE phases out after MY 2026. 
Under the current NTE based off-cycle test program, if a manufacturer 
is required to test ten engines under Phase 1 testing and less than 
eight fully comply with the vehicle pass criteria in 40 CFR 86.1912, we 
could require the manufacturer to initiate Phase 2 HDIUT testing which 
would require manufacturers to test an additional 10 engines. After 
consideration of comments, we are generally finalizing our overall long 
term HDIUT program's engine testing steps and pass/fail criteria as 
proposed; however, EPA believes that an interim approach in the initial 
two years of the program is appropriate, as manufacturers transition to 
the final standards, test procedures, and requirements, while still 
providing overall compliance assurance during that transition. More 
specifically, we are finalizing that compliance with the off-cycle 
standards would be determined by testing a maximum of fifteen engines 
for MYs 2027 and MY 2028 under the interim provisions, and ten engines 
for MYs 2029 and later. As noted in the proposal, the testing of a 
maximum of ten engines was the original limit under Phase 1 HDIUT 
testing in 40 CFR 86.1915. Similar to the current Phase 1 HDIUT 
requirements in 40 CFR 86.1912, the finalized 40 CFR 1036.425 and 
finalized interim provision in 40 CFR 1036.150(z) require initially 
testing five engines. Various outcomes are possible based on the 
observed number of vehicle passes or failures from manufacturer-run in-
use testing, as well as other supplemental information. Under the 
interim provisions for MYs 2027 and 2028, if four of the first test 
vehicles meet the off-cycle standards, testing stops, and no other 
action is required of the manufacturer for that diesel engine family. 
For MYs 2029 and later, if five of the first test vehicles meet the 
off-cycle standards, testing stops, and no other action is required of 
the manufacturer for that diesel engine family. For MYs 2027 and 2028, 
if two of those engines do not comply fully with the off-cycle bin 
standards, the manufacturer would then test five additional engines for 
a total of ten. For MYs 2029 and later, if one of those engines does 
not comply fully with the off-cycle bin standards, the manufacturer 
would then test a sixth engine. For MYs 2027 and 2028, if eight of the 
ten engines tested pass, testing stops, and no other action is required 
of the manufacturer for that diesel engine family under the program for 
that model

[[Page 4352]]

year. For MYs 2029 and later, if five of the six engines tested pass, 
testing stops, and no other action is required of the manufacturer for 
that diesel engine family under the program for that model year. For 
MYs 2027 and 2028, if three or more of the first ten engines tested do 
not pass, the manufacturer may test up to five additional engines until 
a maximum of fifteen engines have been tested. For MYs 2029 and later, 
when two or more of the first six engines tested do not pass, the 
manufacturer must test four additional engines until a total of ten 
engines have been tested. If the arithmetic mean of the emissions from 
the ten, or up to fifteen under the interim provisions, engine tests 
determined in Sec.  1036.530(g), or Sec.  1036.150(z) under the interim 
provisions, is at or below the off-cycle standard for each pollutant, 
the engine family passes and no other action is required of the 
manufacturer for that diesel engine family. If the arithmetic mean of 
the emissions from the ten, or up to fifteen under the interim 
provisions, engines for either of the two bins for any of the 
pollutants is above the respective off-cycle bin standard, the engine 
family fails and the manufacturer must join EPA in follow-up 
discussions to determine whether any further testing, investigations, 
data submissions, or other actions may be warranted. Under the final 
requirements, the manufacturer may accept a fail result for the engine 
family and discontinue testing at any point in the sequence of testing 
the specified number of engines.
    We received comment on the elimination of Phase 2 testing. See 
Response to Comment Section 11.5.1 for further information on these 
comments and EPA's response to these comments. As noted in the 
preceding paragraphs, we are finalizing elimination of Phase 2 testing. 
However, we also are clarifying what happens when an engine family 
fails under the final program. In such a case, three outcomes are 
possible. First, we may ultimately decide not to take further action if 
no nonconformity is indicated after a thorough evaluation of the causes 
or conditions that caused vehicles in the engine family to fail the 
off-cycle standards, and a review of any other supplemental information 
obtained separately by EPA or submitted by the manufacturer shows that 
no significant nonconformity exists. Testing would then stop, and no 
other action would be required of the manufacturer for that diesel 
engine family under the program for that year. Second, we may seek some 
form of remedial action from the manufacturer based on our evaluation 
of the test results and review of other supplemental information. 
Third, and finally, in situations where a significant nonconformity is 
observed during testing, we may order a recall action for the diesel 
engine family in question if the manufacturer does not voluntarily 
initiate an acceptable remedial action.
    In the NPRM, we proposed allowing manufacturers to test a minimum 
of 2 engines using PEMS, in response to a test order program, provided 
they measure, and report in-use data collected from the engine's on-
board NOX measurement system. EPA received comments 
expressing concerns on the feasibility of this alternate in-use testing 
option. Given meaningful uncertainties in whether technological 
advancement of measurement capabilities of these sensors will occur by 
MY 2027, at this time, EPA is not including the proposed option in 40 
CFR 1036.405(g) and not finalizing this alternative test program option 
in this action. The final in-use option for manufacturers to show 
compliance with the off-cycle standard will require the use of 
currently available PEMS to measure criteria pollutant emissions, with 
the sampling and measurement of emission concentrations in a manner 
similar to the current NTE in-use test program as described in 40 CFR 
part 1036, subpart E, and Section III.C of this preamble. See Response 
to Comment Section 11.5.3 for further information on these comments and 
EPA's response to these comments.
    In the NPRM, we proposed to not carry forward the provision in 40 
CFR 86.1908(a)(6) that considers an engine misfueled if operated on a 
biodiesel fuel blend that is either not listed as allowed or otherwise 
indicated to be an unacceptable fuel in the vehicle's owner or operator 
manual. We also proposed in 40 CFR 1036.415(c)(1) to allow vehicles to 
be tested for compliance with the new off-cycle standards on any 
commercially available biodiesel fuel blend that meets the 
specifications for ASTM D975 or ASTM D7467.
    We received comments on these proposed requirements. After 
considering the comments, we have altered provisions in the final rule 
from what was proposed. EPA agrees with the commenters' recommendation 
to restrict in-use off-cycle standards testing on vehicles that have 
been fueled with biodiesel to those that are either expressly allowed 
in the vehicle's owner or operator manual or not otherwise indicated as 
an unacceptable fuel in the vehicle's owner or operator manual or in 
the engine manufacturer's published fuel recommendations. EPA believes, 
as explained in section IV.H of this preamble, that data show biodiesel 
is compliant with ASTM D975, D7467 and D6751, that the occurrence of 
metal contamination in the fuel pool is extremely low, and that the 
metal content of biodiesel is low. However, EPA understands that 
manufacturers have little control over the quality of fuel that their 
engines will encounter over years of in-use operation.\296\ To address 
uncertainties, EPA is modifying the proposed approach to in-use off-
cycle standards testing and will allow manufacturers to continue to 
exempt engines from in-use off-cycle standards testing if the engine is 
being operated on biofuel that exceeds the manufacturers maximum 
allowable biodiesel percentage usable in their engines, as specified in 
the engine owner's manual. See 40 CFR 1036.415(c)(1).
---------------------------------------------------------------------------

    \296\ At this time, as explained in the proposed rule, EPA did 
not propose and is not taking final action to regulate biodiesel 
blend metal content because the available data does not indicate 
that there is widespread off-specification biodiesel blend stock or 
biodiesel blends in the marketplace. EPA also notes that the request 
to set a maximum nationwide biodiesel percentage of 20 percent is 
outside the scope of this final rule.
---------------------------------------------------------------------------

    EPA requested comment on a process for a manufacturer to receive 
EPA approval to exempt test results from in-use off-cycle standards 
testing from being considered for potential recall if an engine 
manufacturer can show that the vehicle was historically fueled with 
biodiesel blends whose B100 blendstock did not meet the ASTM D6751-20a 
limit for Na, K, Ca, and/or Mg metal (metals which are a byproduct of 
biodiesel production) or contaminated petroleum based fuels (i.e. if 
the manufacturer can show that the vehicle was misfueled), and the 
manufacturer can show that misfueling lead to degradation of the 
emission control system performance. 40 CFR 1068.505 describes how 
recall requirements apply for engines that have been properly 
maintained and used. Given the risk of metal contamination from 
biofuels and in some rare cases petroleum derived fuels, EPA will be 
willing to engage with any information manufacturers can share to 
demonstrate that the fueling history caused an engine to be 
noncompliant based on improper maintenance or use. It is envisioned 
that this engagement would include submission by the manufacturer of a 
comparison of the degraded emission control system to a representative 
compliant system of similar miles with respect to content of the 
contaminant, including an analysis of the level of the poisoning agents 
on the catalysts in the engine's aftertreatment system. This

[[Page 4353]]

process addresses concerns expressed by a commentor who stated that it 
would be difficult if not impossible for a manufacturer to provide 
``proof of source'' of the fuel contamination that led to the 
degradation in catalyst performance. This clarifies that the 
manufacturer must only determine the amount of poisoning agent present 
versus a baseline aftertreatment system.
    In the NPRM, we requested comment on the need to measure PM 
emissions during in-use off-cycle testing of engines that comply with 
MY 2027 or later standards if they are equipped with a DPF. PEMS 
measurement is more complicated and time-consuming for PM measurements 
than for gaseous pollutants such as NOX and eliminating it 
for some or all of in-use off-cycle standards testing would provide 
significant cost savings. We received comments both in support of and 
in opposition to continuing to require measurement of PM during in-use 
off-cycle standards testing. After considering these comments, EPA 
believes that historic test results from the manufacturer run in-use 
test program indicate that there is not a PM compliance problem for 
properly maintained engines. Additionally, we believe that removing the 
requirement for in-use off-cycle PM standards testing will not lead 
manufacturers to stop using wall flow DPF technology to meet the PM 
standards. Therefore, EPA is not including the proposed requirement for 
manufacturers to measure PM in the final 40 CFR 1036.415(d)(1) but is 
modifying that requirement from proposal to include a final provision 
in this paragraph that EPA may request PM measurement and that 
manufacturers must provide that measurement if EPA requests it. 
Generally, EPA expects that test orders issued by EPA under 40 CFR 
1036.405 will not include a requirement to measure PM.
    Furthermore, EPA received comments on the subject of the need to 
measure NMHC emissions during in-use off-cycle testing of engines that 
comply with MY 2027 or later standards. After considering comments, EPA 
believes that historic test results from the manufacturer run in-use 
test program indicate that there is not an NMHC compliance problem for 
properly maintained engines. EPA is not including the proposed 
requirement for manufacturers to measure NMHC in the final 40 CFR 
1036.415(d)(1) but is modifying that requirement from proposal to 
include a provision in this paragraph that EPA may request NMHC 
measurement and that manufacturers must provide that measurement if EPA 
requests it. Generally, EPA expects that test orders issued by EPA 
under 40 CFR 1036.405 will not include a requirement to measure NMHC. 
See Response to Comment Section 11.5.5 for further information on these 
comments and EPA's response to comments on the subject of in-use off-
cycle standards PM and NMHC testing.
iii. PEMS Accuracy Margin
    EPA worked with engine manufacturers on a joint test program to 
establish measurement allowance values to account for the measurement 
uncertainty associated with in-use testing in the 2007-time frame for 
gaseous emissions and the 2010-time frame for PM emissions to support 
NTE in-use testing.\297\ \298\ \299\ PEMS measurement allowance values 
in 40 CFR 86.1912 are 0.01 g/hp-hr for HC, 0.25 g/hp-hr for CO, 0.15 g/
hp-hr for NOX, and 0.006 g/hp-hr for PM. We are maintaining 
the same values for HC, CO, and PM in this rulemaking. For 
NOX we are finalizing an off-cycle NOX accuracy 
margin (formerly known as measurement allowance) that is 5 percent of 
the off-cycle standard for a given bin. This final accuracy margin is 
supported by PEMS accuracy margin work at SwRI. The SwRI PEMS accuracy 
margin testing was done on the Stage 3 engine, which was tested over 
five field cycles with three different commercially available PEMS. 
EPA's conclusion after assessing the results of that study, was that 
accuracy margins set at 0.4 g/hr for bin 1 and 5 mg/hp-hr for bin 2 
were appropriate.
---------------------------------------------------------------------------

    \297\ Feist, M.D.; Sharp, C.A; Mason, R.L.; and Buckingham, J.P. 
Determination of PEMS Measurement Allowances for Gaseous Emissions 
Regulated Under the Heavy-Duty Diesel Engine In-Use Testing Program. 
SwRI 12024, April 2007.
    \298\ Feist, M.D.; Mason, R.L.; and Buckingham, J.P. Additional 
Analyses of the Monte Carlo Model Developed for the Determination of 
PEMS Measurement Allowances for Gaseous Emissions Regulated Under 
the Heavy-Duty Diesel Engine In-Use Testing Program. SwRI[supreg] 
12859. July 2007.
    \299\ Khalek, I.A.; Bougher, T.L.; Mason, R.L.; and Buckingham, 
J.P. PM-PEMS Measurement Allowance Determination. SwRI Project 
03.14936.12. June 2010.
---------------------------------------------------------------------------

    The accuracy margins we are finalizing differ from the 10 percent 
of the standard margin proposed in the NPRM, which was based on an 
earlier study by JRC. This SwRI PEMS accuracy margin study was on-going 
at the time the NPRM was published, and the results were only available 
post-NPRM publication.\300\ However, the NPRM did note that we would 
consider the results of the SwRI PEMS study when they became available, 
and that the final off-cycle bin NOX standards could be 
higher or lower than what we proposed. EPA requested and received 
comments on the value of the PEMS accuracy margin for NOX; 
some commenters encouraged EPA to account for the SwRI PEMS accuracy 
work that was carried out on the Stage 3 engine. We initially planned 
to consider the results of this work and this was further supported 
through recommendations by some commentors; thus, we believe that 
incorporating the results of the latest study to determine an off-cycle 
NOX accuracy margin is appropriate. The SwRI PEMS study is 
further discussed in RIA Chapter 2. The study consisted of testing the 
Stage 3 engine with three commercially available PEMS units over 19 
different tests. These tests were 6 to 9 hours long, covering a wide 
range of field operation. In addition, the Stage 3 engine was tested in 
three different configurations to cover the range of emissions levels 
expected from an engine both meeting and failing the final standards. 
We believe, based on this robust data set that was evaluating using the 
finalized test procedures, the SwRI study provides a more accurate 
assessment of PEMS measurement uncertainty from field testing of heavy-
duty engines than what was determined from the JRC study that we relied 
on in the proposal for the proposed 10 percent margin. See Response to 
Comment Section 11.6 for further information on these comments and 
EPA's response to these comments.
---------------------------------------------------------------------------

    \300\ The data and the results from the study were added to the 
public docket prior to the signing of the final rule.
---------------------------------------------------------------------------

    It should be noted that our off-cycle test procedures already 
include a linear zero and span drift correction over at least the shift 
day, and we are finalizing requirements for at least hourly zero drift 
checks over the course of the shift day on purified air. We believe 
that the addition of these checks and the additional improvements we 
implemented helped facilitate a measurement error that is lower than 
the analytically derived JRC value of 10 percent.\301\
---------------------------------------------------------------------------

    \301\ Giechaskiel B., Valverde V., Clairotte M. 2020 Assessment 
of Portable Emissions Measurement Systems (PEMS) Measurement 
Uncertainty. JRC124017, EUR 30591 EN. https://publications.europa.eu/en/publications.
---------------------------------------------------------------------------

    We are updating 40 CFR 1065.935 to require hourly zeroing of the 
PEMS analyzers using purified air for all analyzers. We are also 
updating the drift limits for NOX analyzers to improve data 
quality. Specifically, for NOX analyzers, we are requiring 
an hourly or more frequent zero verification limit of 2.5 ppm, a zero-
drift limit over the entire shift day of 10 ppm, and a span drift limit 
between the beginning and end of the shift day or more frequent span 
verification(s) of 4 percent of the

[[Page 4354]]

measured span value. In the NPRM, we requested comment on the test 
procedure updates in 40 CFR 1065.935 and any changes that would reduce 
the PEMS measurement uncertainty. We received no comments on this topic 
other than a few minor edits and are finalizing these updates with 
minor edits for clarification.
iv. Demonstrating Off-Cycle Standards for Certification
    Consistent with current certification requirements in 40 CFR 
86.007-21(p)(1), we are finalizing a new paragraph in 40 CFR 
1036.205(p) that requires manufacturers to provide a statement in their 
application for certification that their engine complies with the off-
cycle standards, along with testing or other information to support 
that conclusion. We are finalizing this provision as proposed.

D. Summary of Spark-Ignition HDE Exhaust Emission Standards and Test 
Procedures

    This section summarizes the exhaust emission standards, test 
procedures, and other requirements and flexibilities we are finalizing 
for certain spark-ignition (SI) heavy-duty engines. The exhaust 
emission provisions in this section apply for SI engines installed in 
vehicles above 14,000 lb GVWR and incomplete vehicles at or below 
14,000 lb GVWR, but do not include engines voluntarily certified to or 
installed in vehicles subject to 40 CFR part 86, subpart S.
    As described in this Section III.D, Spark-ignition HDE 
certification will continue to be based on emission performance in lab-
based engine dynamometer testing, which will include a new SET duty 
cycle to address high load operation. High load temperature protection 
and idle emission control requirements are also added to supplement our 
current FTP and new SET duty cycles. We are also lengthening the useful 
life and emissions-related warranty periods for all heavy-duty engines, 
including Spark-ignition HDE, as detailed in Sections IV.A and IV.B.1 
of this preamble.
    The final exhaust emission standards in 40 CFR 1037.104 apply 
starting in MY 2027. This final rule includes new standards over the 
FTP duty cycle currently used for certification, as well as new 
standards over the SET duty cycle to ensure manufacturers of Spark-
ignition HDE are designing their engines to address emissions in during 
operation that is not covered by the FTP. The new standards are shown 
in Table III-20.

                                                            Table III-20--Final Duty Cycle Emission Standards for Spark-Ignition HDE
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                  Model year 2026 and earlier \a\                                    Model year 2027 and later
                                                                 -------------------------------------------------------------------------------------------------------------------------------
                           Duty cycle                              NOX  (mg/hp-                                                    NOX  (mg/hp-
                                                                        hr)        HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)         hr)        HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SET.............................................................  ..............  ..............  ..............  ..............              35              60               5            14.4
FTP.............................................................             200             140              10            14.4              35              60               5             6.0
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Current emission standards for NOX, HC, and PM were converted from g/hp-hr to mg/hp-hr to compare with the final standards.

    Our proposal included two options of fuel-neutral standards that 
applied the same numerical standards across all primary intended 
service classes. The proposed NOX and PM standards for the 
SET and FTP duty cycles were based on the emission performance of 
technologies evaluated in our HD CI engine technology demonstration 
program.\302\ We based the proposed SET and FTP standards for HC and CO 
on HD SI engine performance.
---------------------------------------------------------------------------

    \302\ Our assessment of the projected technology package for 
compression-ignition engines is based on both CARB's and EPA's 
technology demonstration programs. See Section III.B for a 
description of those technologies and test programs.
---------------------------------------------------------------------------

    Three organizations specifically expressed support for adopting the 
standards of proposed Option 1 for Spark-ignition HDE. The final 
standards are based largely on the emission levels of proposed Option 
1, with some revisions to account for a single-step program, starting 
in MY 2027. Some organizations commented that the proposed SI standards 
were challenging enough to need the flexibility of ABT for HC and CO. 
Consistent with the proposal for this rule, we are finalizing an ABT 
program for NOX credits only and are discontinuing the 
current options for manufacturers to generate HC and PM credits. We did 
not request comment on and are not finalizing an option for 
manufacturers to generate credits for CO. See Section IV.G of this 
preamble and section 12 of the Response to Comments document for more 
information on the final ABT program.
    We are remaining generally consistent with a fuel neutral approach 
in the final SET and FTP standards, with the exception of CO for Spark-
ignition HDE over the new SET duty cycle. We expand on our rationale 
for this deviation from fuel neutrality in Section III.D.1 where we 
also describe our rationale for the final program, including a summary 
of the feasibility demonstration, available data, and comments 
received.
    After considering comments, we are revising three other proposed 
provisions for Spark-ignition HDE as described in Section . Two new 
requirements in 40 CFR 1036.115(j) focus on ensuring catalyst 
efficiency at low loads and proper thermal management at high loads. We 
are finalizing, with additional clarification, a new OBD flexibility 
for ``sister vehicles''. We did not propose and are not finalizing 
separate off-cycle standards, manufacturer-run in-use testing 
requirements, or a low-load duty cycle for Spark-ignition HDE at this 
time.\303\
---------------------------------------------------------------------------

    \303\ See section 3 of the Response to Comments document for 
more information.
---------------------------------------------------------------------------

    The proposed rule provided an extensive discussion of the rationale 
and information supporting the proposed standards (87 FR 17479, March 
28, 2022). The RIA includes additional information related to the range 
of technologies to control criteria emissions, background on applicable 
test procedures, and the full feasibility analysis for Spark-ignition 
HDE. See also section 3 of the Response to Comments for a detailed 
discussion of the comments and how they have informed this final rule.
1. Basis of the Final Exhaust Emission Standards and Test Procedures
    EPA conducted a program with SwRI to better understand the 
emissions performance limitations of current heavy-duty SI engines as 
well as investigate the feasibility of advanced three-way catalyst 
aftertreatment and technologies and strategies to meet our proposed 
exhaust emission standards.\304\ Our demonstration included the use of 
advanced catalyst

[[Page 4355]]

technologies artificially aged to the equivalent of 250,000 miles and 
engine downspeeding. Our feasibility analyses for the exhaust emission 
standards are based on the SwRI demonstration program. Feasibility of 
the FTP standards is further supported by compliance data submitted by 
manufacturers for the 2019 model year. We also support the feasibility 
of the SET standards using engine fuel mapping data from a test program 
performed by the agency as part of the HD GHG Phase 2 rulemaking. See 
Chapter 3.2 of the RIA for more details related to the SwRI 
demonstration program and the two supporting datasets.
---------------------------------------------------------------------------

    \304\ Ross, M. (2022). Heavy-Duty Gasoline Engine Low 
NOX Demonstration. Southwest Research Institute. Final 
Report EPA Contract 68HERC20D0014.
---------------------------------------------------------------------------

    Results from our SI HDE technology demonstration program (see Table 
III-21 and Table III-22) show that the NOX standards based 
on our CI engine feasibility analysis are also feasible for SI HDEs 
over the SET and FTP duty cycles. The NOX standard was 
achieved in this test program by implementing an advanced catalyst with 
minor catalyst system design changes, and NOX levels were 
further improved with engine down-speeding. The emission control 
strategies that we evaluated did not specifically target PM emissions, 
but we note that PM emissions remained low in our demonstration. We 
project SI HDE manufacturers will maintain near-zero PM levels with 
limited effort. The following sections discuss the feasibility of the 
HC and CO standards over each of the duty cycles and the basis for our 
final numeric standards' levels.
i. Federal Test Procedure and Standards for Spark-Ignition HDE
    After considering comments, we are finalizing FTP standards that 
differ from our proposed options for Spark-ignition HDE. We are 
finalizing standards of 35 mg/hp-hr NOX, 5 mg/hp-hr PM, 60 
mg/hp-hr HC, and 6.0 g/hp-hr CO over the FTP duty cycle in a single 
step for MY 2027 and later engines. The NOX and HC standards 
match the MY 2027 step of proposed Option 1; the PM and CO standards 
match the MY 2031 step of Option 1. All of these standards were 
demonstrated to be technologically feasible in EPA's SI engine test 
program.
    As shown in Table III-21, use of advanced catalysts provided 
NOX emission levels over the FTP duty cycle well below 
today's standards and below the certification levels of some of the 
best performing engines certified in recent years.\305\ Engine down-
speeding further decreased CO emissions while maintaining 
NOX, NMHC, and PM control. Engine down-speeding also 
resulted in a small improvement in fuel consumption over the FTP duty 
cycle, with fuel consumption being reduced from 0.46 to 0.45 lb/hp-hr. 
See Chapter 3.2.3 of the RIA for an expanded description of the test 
program and results.
---------------------------------------------------------------------------

    \305\ As presented in Chapter 3.2 of the RIA, MY 2019 gasoline-
fueled HD SI engine certification results included NOX 
levels ranging from 40 to 240 mg/hp-hr at a useful life of 110,000 
miles. MY 2019-2021 alternative-fueled (CNG, LPG) HD SI engine 
certification results included NOx levels ranging from 6 to 70 mg/
hp-hr at the same useful life.

    Table III-21--Exhaust Emission Results From FTP Duty Cycle Testing in the HD SI Technology Demonstration
----------------------------------------------------------------------------------------------------------------
                                                   NOX  (mg/hp-
                                                        hr)        PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
Current Standards MY 2026 and earlier...........             200              10             140            14.4
Final Standards MY 2027 and later...............              35               5              60               6
Test Program Base Engine with Advanced Catalyst               19             4.8              32             4.9
 \a\............................................
Test Program Down-sped Engine with Advanced                   18             4.5              35            0.25
 Catalyst \b\...................................
----------------------------------------------------------------------------------------------------------------
\a\ Base engine's manufacturer-stated maximum test speed is 4715 RPM; advanced catalyst aged to 250,000 miles.
\b\ Down-sped engine's maximum test speed lowered to 4000 RPM; advanced catalyst aged to 250,000 miles.

    All SI HDEs currently on the market use a three-way catalyst (TWC) 
to simultaneously control NOX, HC, and CO emissions.\306\ We 
project most manufacturers will continue to use TWC technology and will 
also adopt advanced catalyst washcoat technologies and refine their 
existing catalyst thermal protection (fuel enrichment) strategies to 
prevent damage to engine and catalyst components over the longer useful 
life period we have finalized. We expect manufacturers, who design and 
have full access to the engine controls, could achieve similar emission 
performance as we demonstrated by adopting other, more targeted 
approaches, including a combination of calibration changes, optimized 
catalyst location, and fuel control strategies that EPA was unable to 
evaluate in our demonstration program due to limited access to 
proprietary engine controls.
---------------------------------------------------------------------------

    \306\ See Chapter 1.2 of the RIA for a detailed description of 
the TWC technology and other strategies HD SI manufacturers use to 
control criteria emissions.
---------------------------------------------------------------------------

    In the proposal we described how the FTP duty cycle did not 
sufficiently incentivize SI HDE manufacturers to address fuel 
enrichment and the associated CO emissions that are common under higher 
load operations in the real-world. In response to our proposed rule, 
one manufacturer shared technical information with us regarding an SI 
engine architecture under development that is expected to reduce or 
eliminate enrichment and the associated CO emissions.\307\ The company 
indicated that the low CO emissions may come at the expense of HC 
emission reduction in certain operation represented by the FTP duty 
cycle, and reiterated their request for an 80 mg/hp-hr HC standard, as 
was stated in their written comments. We are not finalizing an HC 
standard of 80 mg/hp-hr as requested in comment. For the FTP duty 
cycle, the EPA test program achieved HC levels more than half of the 
requested level without compromising NOX or CO emission 
control (see Table III-21), which clearly demonstrates feasibility.
---------------------------------------------------------------------------

    \307\ U.S. EPA. Stakeholder Meeting Log. December 2022.
---------------------------------------------------------------------------

    While we demonstrated emission levels below the final standards of 
60 mg HC/hp-hr and 35 mg NOX/hp-hr over the FTP duty cycle 
in our SI HDE testing program, we expect manufacturers to apply a 
compliance margin to their certification test results to account for 
uncertainties, such as production variation. Additionally, we believe 
manufacturers would have required additional lead time to implement the 
demonstrated emission levels broadly across all heavy-duty SI engine 
platforms for the final useful life periods. Since we are finalizing a 
single-step program starting in MY 2027, as discussed in Section 
III.A.3 of this preamble, we continue to consider 60 mg HC/hp-hr and 35 
mg NOX/hp-hr the appropriate level of the standards for

[[Page 4356]]

that model year, as proposed in the MY 2027 step of proposed Option 1.
ii. Supplemental Emission Test and Standards for Spark-Ignition HDE
    The existing SET duty cycle, currently only applicable to CI 
engines, is a ramped modal cycle covering 13 steady-state torque and 
engine speed points that is intended to exercise the engine over 
sustained higher load and higher speed operation. Historically, in 
light of the limited range of applications and sales volumes of SI 
heavy-duty engines, especially compared to CI engines, we believed the 
FTP duty cycle was sufficient to represent the high-load and high-speed 
operation of SI engine-powered heavy-duty vehicles. As the market for 
SI engines increases for use in larger vehicle classes, these engines 
are more likely to operate under extended high-load conditions. To 
address these market shifts, we proposed to apply the SET duty cycle 
and new SET standards to Spark-ignition HDE, starting in model year 
2027. This new cycle would ensure that emission controls are properly 
functioning in the high load and speed conditions covered by the SET.
    We are finalizing the addition of the SET duty cycle for the Spark-
ignition HDE primary intended service class, as proposed.\308\ We 
requested comment on revisions we should consider for the CI-based SET 
procedure to adapt it for SI engines. We received no comments on 
changes to the procedure itself and the SET standards for Spark-
ignition HDE are based on the same SET procedure as we are finalizing 
for heavy-duty CI engines. After considering comments, we are 
finalizing SET standards that differ from our proposed options for 
Spark-ignition HDE.
---------------------------------------------------------------------------

    \308\ See our updates to the SET test procedure in 40 CFR 
1036.505.
---------------------------------------------------------------------------

    The EPA HD SI technology demonstration program evaluated emission 
performance over the SET duty cycle. As shown in Table III-22, the 
NOX and NMHC emissions over the SET duty cycle were 
substantially lower than the emissions from the FTP duty cycle (see 
Table III-21). Lower levels of NMHC were demonstrated, but at the 
expense of increased CO emissions in those higher load operating 
conditions. Engine down-speeding improved CO emissions significantly, 
while NOX, NMHC, and PM remained low.\309\ The considerably 
lower NOX and HC in our SET duty cycle demonstration results 
leave enough room for manufacturers to calibrate the tradeoff in TWC 
emission control of NOX, HC, and CO to continue to fine-tune 
CO. See Chapter 3.2 of the RIA for an expanded description of the test 
program and results.
---------------------------------------------------------------------------

    \309\ Engine down-speeding also resulted in a small improvement 
in brake specific fuel consumption over the SET duty cycle reducing 
from 0.46 to 0.44 lb/hp-hr.

    Table III-22--Exhaust Emission Results From SET Duty Cycle Testing in the HD SI Technology Demonstration
----------------------------------------------------------------------------------------------------------------
                                                   NOX  (mg/hp-
                                                        hr)        PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
Final Standards MY 2027 and later...............              35               5              60            14.4
Test Program Base Engine with Advanced Catalyst                8           \c\ 7               6            36.7
 \a\............................................
Test Program Down-sped Engine with Advanced                    5               3               1            7.21
 Catalyst \b\...................................
----------------------------------------------------------------------------------------------------------------
\a\ Base engine's manufacturer-stated maximum test speed is 4715 RPM; advanced catalyst aged to 250,000 miles.
\b\ Down-sped engine's maximum test speed lowered to 4000 RPM; advanced catalyst aged to 250,000 miles.
\c\ As noted in Chapter 3.2 of the RIA, the higher PM value was due to material separating from the catalyst mat
  during the test and is not indicative of the engine's ability to control engine-generated PM emissions at the
  higher load conditions of the SET.

    Similar to our discussion related to the FTP standards, we expect 
manufacturers, who design and have full access to the engine controls, 
could achieve emission levels comparable to or lower than our 
feasibility demonstration over the SET duty cycle by adopting other 
approaches, including a combination of calibration changes, optimized 
catalyst location, and fuel control strategies that EPA was unable to 
evaluate due to limited access to proprietary engine controls. In fact, 
we are aware of advanced engine architectures that can reduce or 
eliminate enrichment, and the associated CO emissions, by maintaining 
closed loop operation.\310\
---------------------------------------------------------------------------

    \310\ See Chapter 1 of the RIA for a description of fuel 
enrichment, when engine operation deviates from closed loop, and its 
potential impact on emissions.
---------------------------------------------------------------------------

    We proposed Spark-ignition HDE standards for HC and CO emissions on 
the SET cycle that were numerically equivalent to the respective 
proposed FTP standards. Our intent was to ensure that SI engine 
manufacturers utilize emission control hardware and calibration 
strategies to control emissions during high load operation to levels 
similar to the FTP duty cycle.\311\ We retain this approach for HC, 
but, after considering comments, the final CO standard is revised from 
that proposed. One commenter indicated that manufacturers would need CO 
credits to achieve the proposed standards. Another commenter suggested 
that EPA underestimated the modifications manufacturers would need to 
make to fully transition away from the fuel enrichment strategies they 
currently use to protect their engines. The same commenter requested 
that EPA delay the SET to start in model year 2031 or temporarily 
exclude the highest load points over the test to provide additional 
lead time for manufacturers.
---------------------------------------------------------------------------

    \311\ Test results presented in Chapter 3.2 of the RIA indicate 
that these standards are achievable when the engine controls limit 
fuel enrichment and maintain closed loop control of the fuel-air 
ratio.
---------------------------------------------------------------------------

    We are not finalizing an option for manufacturers to generate CO 
credits. We believe a delayed implementation of SET, as requested, 
would further delay manufacturers' motivation to focus on high load 
operation to reduce enrichment and the associated emissions reductions 
that would result. Additionally, our objective for adding new standards 
over the SET duty cycle is to capture the prolonged, high-load 
operation not currently represented in the FTP duty cycle, and the 
commenter's recommendation to exclude the points of highest load would 
be counter to that objective.
    We agree with commenters that the new SET duty cycle and standards 
will be a challenge for heavy-duty SI manufacturers but maintain that 
setting a feasible technology-forcing CO standard is consistent with 
our authority under the CAA. After further considering the comments and 
assessing CO data from the EPA heavy-duty SI test program, the final 
new CO standard we

[[Page 4357]]

are adopting is less stringent than proposed to provide manufacturers 
additional margin for ensuring compliance with that pollutant's 
standard over the new test procedure for Spark-ignition HDE. Given this 
final standard, we determined that neither ABT or more lead time are 
appropriate or required. The Spark-ignition HDE standard for CO 
emissions on the SET duty-cycle established in this final rule is 
numerically equivalent to the current FTP standard of 14.4 g/hp-hr.
2. Other Provisions for Spark-Ignition HDE
    This Section III.D.2 describes other provisions we proposed and are 
finalizing with revisions from proposal in this rule. The following 
three provisions address information manufacturers will share with EPA 
as part of their certification and we are adding clarification where 
needed after considering comments. See also section 3 of the Response 
to Comments for a detailed discussion of the comments summarized in 
this section and how they have informed the updates we are finalizing 
for these three provisions.
Idle Control for Spark-Ignition HDE
    We proposed to add a new paragraph at 40 CFR 1036.115(j)(1) to 
require manufacturers to show how they maintain a catalyst bed 
temperature of 350 [deg]C in their application for certification or get 
approval for an alternative strategy that maintains low emissions 
during idle. As described in Chapter 3.2 of the RIA, prolonged idling 
events may allow the catalyst to cool and reduce its efficiency, 
resulting in emission increases until the catalyst temperatures 
increase. Our recent HD SI test program showed idle events that extend 
beyond four minutes allow the catalyst to cool below the light-off 
temperature of 350 [deg]C. The current heavy-duty SET and FTP duty 
cycles do not include sufficiently long idle periods to represent these 
real-world conditions where the exhaust system cools below the 
catalyst's light-off temperature.
    We continue to believe that a 350 [deg]C lower bound for catalysts 
will sufficiently ensure emission control is maintained during idle 
without additional manufacturer testing. We are finalizing the 350 
[deg]C target and the option for manufacturers to request approval for 
a different strategy, as proposed. We are revising the final 
requirement from our proposal to also allow manufacturers to request 
approval of a temperature lower than 350 [deg]C, after considering 
comments that requested that we replace the 350 [deg]C temperature with 
the more generic ``light-off temperature'' to account for catalysts 
with other formulations or locations relative to the engine.
i. Thermal Protection Temperature Modeling Validation
    The existing regulations require manufacturers to report any 
catalyst protection strategy that reduces the effectiveness of emission 
controls as an AECD in their application for certification.\312\ The 
engine controls used to implement these strategies often rely on a 
modeling algorithm to predict high exhaust temperatures and to disable 
the catalyst, which can change the emission control strategy and 
directly impact real world emissions. The accuracy of these models used 
by manufacturers is critical in both ensuring the durability of the 
emission control equipment and preventing excessive emissions that 
could result from unnecessary or premature activation of thermal 
protection strategies.
---------------------------------------------------------------------------

    \312\ See 40 CFR 86.094-21(b)(1)(i) and our migration of those 
provisions to final 40 CFR 1036.205(b).
---------------------------------------------------------------------------

    To ensure that a manufacturer's model accurately estimates the 
temperatures at which thermal protection modes are engaged, we proposed 
a validation process during certification in a new paragraph 40 CFR 
1036.115(j)(2) to demonstrate the model performance.
    Several commenters opposed the proposed requirement that 
manufacturers demonstrate a 5 [deg]C accuracy between modelled and 
actual exhaust and emission component temperatures and expressed 
concern with the ability to prove correlation at this level and lack of 
details on the procedure for measuring the temperatures. Our final, 
revised approach still ensures EPA has the information needed to 
appropriately assess a manufacturer's AECD strategy, without a specific 
accuracy requirement.
    Our final 40 CFR 1036.115(j)(2) clarifies that the new validation 
process is a requirement in addition to the requirements for any SI 
engine applications for certification that include an AECD for thermal 
protection.\313\ Instead of the proposed 5 [deg]C accuracy requirement, 
a manufacturer will describe why they rely on any AECDs, instead of 
other engine designs, for thermal protection of catalyst or other 
emission-related components. They will also describe the accuracy of 
any modeled or measured temperatures used to activate the AECD. Instead 
of requiring manufacturers to submit second-by-second data upfront in 
the application for certification to demonstrate a specific accuracy 
requirement is met, the final requirement gives EPA discretion to 
request the information at certification. We note that our final 
revised requirements apply the same validation process for modeled and 
measured temperatures that activate an AECD and that this requirement 
would not apply if manufacturers certify their engines without an AECD 
for enrichment as thermal protection.
---------------------------------------------------------------------------

    \313\ These requirements are in place today under existing 40 
CFR 86.094-21(b)(1)(i), which have been migrated to 40 CFR 
1036.205(b) in this final rule.
---------------------------------------------------------------------------

ii. OBD Flexibilities
    In recognition that there can be some significant overlap in the 
technologies and emission control systems adopted for products in the 
chassis-certified and engine-certified markets, we proposed an OBD 
flexibility to limit the data requirements for engine-certified 
products that use the same engines and generally share similar emission 
controls (i.e., are ``sister vehicles'') with chassis-certified 
products. Specifically, in a new 40 CFR 1036.110(a)(2), we proposed to 
allow vehicle manufacturers the option to request approval to certify 
the OBD of their SI, engine-certified products using data from similar 
chassis-certified Class 2b and Class 3 vehicles that meet the 
provisions of 40 CFR 86.1806-17.
    Two organizations commented in support of the proposed OBD 
flexibility and with one suggesting some revisions to the proposed 
regulatory language. The commenter suggested that the expression `share 
essential design characteristics' was too vague, and requested EPA 
provide more specific information on what EPA will use to make their 
determination. We disagree that more specific information is needed. We 
are relying on the manufacturers to identify the design characteristics 
and justify their request as part of the certification process. We are 
adjusting the final regulatory text to clarify how the vehicles above 
and below 14,000 lbs GVWR must use the same engine and share similar 
emission controls, but are otherwise finalizing this OBD flexibility as 
proposed.

E. Summary of Spark-Ignition HDV Refueling Emission Standards and Test 
Procedures

    All sizes of complete and incomplete heavy-duty vehicles have been 
subject to evaporative emission standards for many years. Similarly, 
all sizes of complete heavy-duty vehicles are subject to refueling 
standards. We most

[[Page 4358]]

recently applied the refueling standards to complete heavy-duty 
vehicles above 14,000 pounds GVWR starting with model year 2022 (81 FR 
74048, Oct. 25, 2016).
    We proposed to amend 40 CFR 1037.103 to apply the same refueling 
standard of 0.20 grams hydrocarbon per gallon of dispensed fuel to 
incomplete heavy-duty vehicles above 14,000 pounds GVWR starting with 
model year 2027 over a useful life of 150,000 miles or 15 years 
(whichever comes first). We further proposed to apply the same testing 
and certification procedures that currently apply for complete heavy-
duty vehicles. We are adopting this standard and testing and 
certification procedures as proposed, with some changes to the proposed 
rule as noted in this section. As noted in 40 CFR 1037.103(a)(2), the 
standards apply for vehicles that run on gasoline, other volatile 
liquid fuels, and gaseous fuels.
    The proposed rule provided an extensive discussion of the history 
of evaporative and refueling standards for heavy-duty vehicles, along 
with rationale and information supporting the proposed standards (87 FR 
17489, March 28, 2022). The RIA includes additional information related 
to control technology, feasibility, and test procedures. See also 
section 3 of the Response to Comments for a detailed discussion of the 
comments and the changes we made to the proposed rule.
    Some commenters advocated for applying the refueling standards also 
to incomplete heavy-duty vehicles at or below 14,000 pounds GVWR. 
Specifically, some manufacturers commented that they would need a 
phase-in schedule that allowed more lead time beyond the proposed MY 
2027 start of the refueling standards for incomplete vehicles above 
14,000 pounds GVWR, and that EPA should consider a longer phase-in that 
also included refueling standards for incomplete vehicles at or below 
14,000 pounds GVWR. In EPA's judgment, the design challenge for meeting 
the new refueling standards will mainly involve larger evaporative 
canisters, resizing purge valves, and recalibrating for higher flow of 
vapors from the evaporative canister into the engine's intake. Four 
years of lead time is adequate for designing, certifying, and 
implementing these design solutions. We are therefore finalizing the 
proposed start of refueling standards in MY 2027 for all incomplete 
heavy-duty vehicles above 14,000 pounds GVWR.
    At the same time, as manufacturers suggested, expanding the scope 
of certification over a longer time frame may be advantageous for 
implementing design changes across their product line in addition to 
the environmental gain from applying refueling controls to a greater 
number of vehicles. We did not propose refueling standards for vehicles 
at or below 14,000 pounds GVWR and we therefore do not adopt such 
standards in this final rule. However, the manufacturers' suggestion to 
consider a package of changes to both expand the scope of the standards 
and increase the lead time for meeting standards has led us to adopt an 
optional alternative phase-in. Under the alternative phase-in 
compliance pathway, instead of certifying all vehicles above 14,000 
pounds GVWR to the refueling standard in MY 2027, manufacturers can opt 
into the alternate phase-in that applies for all incomplete heavy-duty 
vehicles, regardless of GVWR. The alternative phase-in starts at 40 
percent of production in MYs 2026 and 2027, followed by 80 percent of 
production in MYs 2028 and 2029, ramping up to 100 percent of 
production in MY 2030. Phase-in calculations are based on projected 
nationwide production volume of all incomplete heavy-duty vehicles 
subject to refueling emission standards under 40 CFR 86.1813-17. 
Specifying the phase-in schedule in two-year increments allows 
manufacturers greater flexibility for integrating emission controls 
across their product line.
    Manufacturers may choose either schedule of standards; however, 
they must satisfy at least one of the two. That is, if manufacturers do 
not certify all their incomplete heavy-duty vehicles above 14,000 
pounds GVWR to the refueling standards in MY 2027, the alternate phase-
in schedule described in 40 CFR 86.1813-17(b) becomes mandatory to 
avoid noncompliance. Conversely, if manufacturers do not meet the 
alternative phase-in requirement for MY 2026, they must certify all 
their incomplete heavy-duty vehicles above 14,000 pounds GVWR to the 
refueling standard in MY 2027 to avoid noncompliance. See the final 40 
CFR 86.1813-17(b) for the detailed specifications for the alternative 
phase-in schedule.
    We received several comments suggesting that we adjust various 
aspects of the testing and certification procedures for heavy-duty 
vehicles meeting the evaporative and refueling standards. Consideration 
of these comments led us to include some changes from proposal for the 
final rule. First, we are revising 40 CFR 1037.103 to add a reference 
to the provisions from 40 CFR part 86, subpart S, that are related to 
the refueling standards. This is intended to make clear that the 
overall certification protocol from 40 CFR part 86, subpart S, applies 
for heavy-duty vehicles above 14,000 pounds GVWR (see also existing 40 
CFR 1037.201(h)). This applies, for example, for durability procedures, 
useful life, and information requirements for certifying vehicles. 
Along those lines, we are adding provisions to 40 CFR 86.1821-01 to 
clarify how manufacturers need to separately certify vehicles above 
14,000 pounds GVWR by dividing them into different families even if 
they have the same design characteristics as smaller vehicles. This is 
consistent with the way we have been certifying vehicles to evaporative 
and refueling standards.
    Second, we are modifying the test procedures for vehicles with fuel 
tank capacity above 50 gallons. These vehicles have very large 
quantities of vapor generation and correspondingly large evaporative 
and refueling canisters. The evaporative test procedures call for 
manufacturers to design their vehicles to purge a canister over about 
11 miles of driving (a single FTP duty cycle) before the diurnal test, 
which requires the vehicle to control the vapors generated over two 
simulated hot summer days of parking. We share manufacturers' concern 
that the operating characteristics of these engines and vehicles do not 
support achieving that level of emission control. We are therefore 
revising the two-day diurnal test procedure at 40 CFR 86.137-94(b)(24) 
and the Bleed Emission Test Procedure at 40 CFR 86.1813-17(a)(2)(iii) 
to include a second FTP duty cycle with an additional 11 miles of 
driving before starting the diurnal measurement procedure.
    Third, manufacturers pointed out that the existing test procedures 
don't adequately describe how to perform a refueling emission 
measurement with vehicles that have two fuel tanks with separate filler 
necks. We are amending the final rule to include a provision to direct 
manufacturers to use good engineering judgment for testing vehicles in 
a dual-tank configuration. It should be straightforward to do the 
testing with successive refills for the two tanks and combining the 
measured values into a single result. Rather than specifying detailed 
adjustments to the procedure, allowing manufacturers the discretion to 
perform that testing and computation consistent with good engineering 
judgment will be enough to ensure a proper outcome.
    Table III-23 summarizes the cost estimations for the different 
technological approaches to controlling refueling emissions that EPA 
evaluated. See Chapter 3.2.3.2 of the RIA for the

[[Page 4359]]

details. In calculating the overall cost, we used $25 (2019 dollars), 
the average of both approaches, to represent the cost for manufacturers 
to adopt the additional canister capacity and hardware to meet our new 
refueling emission standards for incomplete vehicles above 14,000 lb 
GVWR. See also Section V of this preamble for a summary of our overall 
program cost and Chapter 7 of the RIA for more details on our overall 
program cost.

          Table III-23--Summary of Projected Per-Vehicle Costs To Meet the Refueling Emission Standards
----------------------------------------------------------------------------------------------------------------
                                                            Liquid seal                   Mechanical seal
                                                 ---------------------------------------------------------------
                                                                   Dual existing                   Dual existing
                                                   New canister    canisters in    New canister    canisters in
                                                                      series                          series
----------------------------------------------------------------------------------------------------------------
Additional Canister Costs.......................             $20             $15              $8              $8
----------------------------------------------------------------------------------------------------------------
Additional Tooling \a\..........................               0.50
                                                               0.50
----------------------------------------------------------------------------------------------------------------
Flow Control Valves.............................               6.50
                                                               6.50
----------------------------------------------------------------------------------------------------------------
Seal............................................               0               0                10
----------------------------------------------------------------------------------------------------------------
    Total.......................................              27              22                25
----------------------------------------------------------------------------------------------------------------
a Assumes the retooling costs are spread over a five-year period.

    Incomplete vehicles above 14,000 lb GVWR with dual fuel tanks may 
require some unique accommodations to adopt onboard refueling vapor 
recovery (ORVR) systems. A chassis configuration with dual fuel tanks 
would need separate canisters and separate filler pipes and seals for 
each fuel tank. Depending on the design, a dual fuel tank chassis 
configuration may require a separate purge valve for each fuel tank. We 
assume manufacturers will install one additional purge valve for dual 
fuel tank applications that also incorporate independent canisters for 
the second fuel tank/canister configuration, and that manufacturers 
adopting a mechanical seal in their filler pipe will install an anti-
spitback valve for each filler pipe. See Chapter 1.2.4.5 of the RIA for 
a summary of the design considerations for these fuel tank 
configurations. We did not include an estimate of the impact of dual 
fuel tank vehicles in our cost analysis of the new refueling emission 
standards, as the population of these vehicles is very low and we 
expect minimal increase in the total average costs.

IV. Compliance Provisions and Flexibilities

    EPA certification is a fundamental requirement of the Clean Air Act 
for manufacturers of heavy-duty highway engines. EPA has employed 
significant discretion over the past several decades in designing and 
updating many aspects of our heavy-duty engine and vehicle 
certification and compliance programs. In the following sections, we 
discuss several revised provisions that we believe will increase the 
effectiveness of our regulations.
    As noted in Section I, we are migrating our criteria pollutant 
regulations for model years 2027 and later heavy-duty highway engines 
from their current location in 40 CFR part 86, subpart A, to 40 CFR 
part 1036.\314\ Consistent with this migration, the compliance 
provisions discussed in this section refer to the final regulations in 
their new location in part 1036. In general, this migration is not 
intended to change the compliance program specified in part 86, except 
as specifically finalized in this rulemaking. See Section III.A.1.
---------------------------------------------------------------------------

    \314\ As noted in the following sections, we are finalizing some 
updates to 40 CFR parts 1037, 1065, and 1068 to apply to other 
sectors in addition to heavy-duty highway engines.
---------------------------------------------------------------------------

A. Regulatory Useful Life

    Useful life represents the period over which emission standards 
apply for certified engines, and, practically, any difference between 
the regulatory useful life and the generally longer operational life of 
in-use engines represents miles and years of operation without an 
assurance that emission standards will continue to be met. In addition 
to promulgating new emission standards and promulgating new and 
updating existing test procedures described in Section III, we are 
updating regulatory useful life periods to further assure emission 
performance of heavy-duty highway engines. In this section, we present 
the updated regulatory useful life periods we are finalizing in this 
rule. In Section IV.A.1, we present our revised useful life periods 
that will apply for the new exhaust emission standards for criteria 
pollutants, OBD, and requirements related to crankcase emissions. In 
Section IV.A.2, we present the useful life periods that will apply for 
the new refueling emission standards for certain Spark-ignition HDE. As 
described in Section G.10 of this preamble, we are not finalizing the 
proposed allowance for manufacturers to generate NOX 
emissions credits from heavy-duty zero emissions vehicles (ZEVs) or the 
associated useful life requirements.
1. Regulatory Useful Life Periods by Primary Intended Service Class
    In this final rule, we are increasing the regulatory useful life 
mileage values for new heavy-duty engines to better reflect real-world 
usage, extend the emissions durability requirement for heavy-duty 
engines, and improve long-term emission performance. In this Section 
IV.1, we describe the regulatory useful life periods we are finalizing 
for the four primary intended service classes for heavy-duty highway 
engines.\315\ Our longer useful life periods vary by engine class to 
reflect the different lengths of their estimated operational lives. As 
described in the proposal for this rule, we continue to consider 
operational life to be the average mileage at rebuild for CI engines 
and the average mileage at replacement for SI engines.\316\
---------------------------------------------------------------------------

    \315\ The useful life periods we are finalizing in this rule 
apply for criteria pollutant standards; we did not propose and are 
not finalizing changes to the useful life periods that apply for GHG 
standards.
    \316\ See Chapter 2.4 of the RIA for a summary of the history of 
our regulatory useful life provisions and our estimate of the 
operational life for each heavy-duty engine class.
---------------------------------------------------------------------------

    In determining the appropriate longer useful life values to set in 
the final rule, we retain our proposed objective to set useful life 
periods that cover a significant portion of the engine's operational 
life. However, as explained in the proposal, we also maintain that

[[Page 4360]]

the emission standards presented in Section III must be considered 
together with their associated useful life periods. After further 
consideration of the basis for the proposal, comments received, 
supporting data available since the proposal, and the numeric level of 
the final standards, we are selecting final useful life values within 
the range of options proposed that cover a significant portion of the 
engine's operational life and take into account the combined effect of 
useful life and the final numeric standards on the overall stringency 
and emissions reductions of the program. As described in the final RIA, 
we concluded two engine test programs for this rule that demonstrated 
technologies that are capable of meeting lower emission levels at much 
longer mileages than current useful life periods. We evaluated a heavy-
duty diesel engine to a catalyst-aged equivalent of 800,000 miles for 
the compression-ignition demonstration program, and a heavy-duty 
gasoline engine to a catalyst-aged equivalent of 250,000 miles for the 
spark-ignition demonstration program. As described in Section III of 
this preamble, the results of those demonstration programs informed the 
appropriate standard levels for the useful life periods we are 
finalizing for each engine class. Our final useful life values were 
also informed by comments, including additional information on 
uncertainties and potential corresponding costs. We summarize key 
comments in Section IV.1.ii, and provide complete responses to useful 
life comments in section 3.8 of the Response to Comments document.
    Our final useful life periods for Spark-ignition HDE, Light HDE, 
Medium HDE, and Heavy HDE classes are presented in Table IV-1 and 
specified in a new 40 CFR 1036.104(e).\317\ The final useful life 
values that apply for Spark-ignition HDE, Light HDE, and Medium HDE 
starting in MY 2027 match the most stringent option we proposed, that 
is, MY 2031 step of proposed Option 1. The final useful life values for 
Heavy HDE, which has a distinctly longer operational life than the 
smaller engine classes, match the longest useful life mileage we 
proposed for model year 2027 (i.e., the Heavy HDE mileage of proposed 
Option 2). We are also increasing the years-based useful life from the 
current 10 years to values that vary by engine class and match the 
proposed value in the respective proposed option. After considering 
comments, we are also adding hours-based useful life values to all 
primary intended service classes based on a 20 mile per hour speed 
threshold and the corresponding final mileage values.
---------------------------------------------------------------------------

    \317\ We are migrating the current alternate standards for 
engines used in certain specialty vehicles from 40 CFR 86.007-11 and 
86.008-10 into 40 CFR 1036.605 without modification. See Section 
XI.B of this preamble for a discussion of these standards.

                                         Table IV-1--Final Useful Life Periods by Primary Intended Service Class
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                              Current                                    MY 2027 and later
             Primary intended service class              -----------------------------------------------------------------------------------------------
                                                               Miles           Years           Hours           Miles           Years           Hours
--------------------------------------------------------------------------------------------------------------------------------------------------------
Spark-ignition HDE \a\..................................         110,000              10  ..............         200,000              15          10,000
Light HDE \a\...........................................         110,000              10  ..............         270,000              15          13,000
Medium HDE..............................................         185,000              10  ..............         350,000              12          17,000
Heavy HDE...............................................         435,000              10          22,000         650,000              11          32,000
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Spark-ignition HDE and Light HDE for GHG emission standards is 15 years or 150,000 miles; we are not revising these
  useful life periods in this final rule. See 40 CFR 1036.108(d).

    For hybrid engines and powertrains, we are finalizing the proposal 
that manufacturers certifying hybrid engines and powertrains would 
declare the primary intended service class of their engine family using 
40 CFR 1036.140. Once a primary intended service class is declared, the 
engine configuration would be subject to the corresponding emission 
standards and useful life values from 40 CFR 1036.104.
i. Summary of the Useful Life Proposal
    For CI engines, the proposed Option 1 useful life periods included 
two steps in MYs 2027 and 2031 that aligned with the final useful life 
periods of CARB's HD Omnibus regulation, and the proposed MY 2031 
periods covered close to 80 percent of the expected operational life of 
CI engines based on mileage at out-of-frame rebuild. The useful life 
mileages of proposed Option 2, which was a single-step option starting 
in MY 2027, generally corresponded to the average mileages at which CI 
engines undergo the first in-frame rebuild. The rebuild data indicated 
that CI engines can last well beyond the in-frame rebuild mileages. We 
noted in the proposal that it was unlikely that we would finalize a 
single step program with useful life mileages shorter than proposed 
Option 2; instead, we signaled that we would likely adjust the numeric 
value of the standards to address any feasibility concerns.
    For Spark-ignition HDE, the useful life mileage in proposed Option 
1 was about 90 percent of the operational life of SI engines based on 
mileage at replacement. The useful life of proposed Option 2 aligned 
with the current SI engine useful life mileage that applies for GHG 
standards. In the proposal, we noted that proposed Option 2 also 
represented the lowest useful life mileage we would consider finalizing 
for Spark-ignition HDE.
    In proposed Option 1, we increased the years-based useful life 
values for all engine classes to account for engines that accumulate 
fewer miles annually. We also proposed to update the hours-based useful 
life criteria for the Heavy HDE class to account for engines that 
operated frequently, but accumulated relatively few miles due to lower 
vehicle speeds. We calculated the proposed hours values by applying the 
same 20 mile per hour conversion factor to the proposed mileages as was 
applied when calculating the useful life hours that currently apply for 
Heavy HDE.\318\ The proposed hours specification was limited to the 
Heavy HDE class to be consistent with current regulations, but we 
requested comment on adding hours-based useful life values to apply for 
the other service classes.
---------------------------------------------------------------------------

    \318\ U.S. EPA, ``Summary and Analysis of Comments: Control of 
Emissions of Air Pollution from Highway Heavy-Duty Engines'', EPA-
420-R-97-102, September 1997, pp 43-47.
---------------------------------------------------------------------------

ii. Basis for the Final Useful Life Periods
    In this Section IV.1.ii, we provide the rationale for our final 
useful life periods, including summaries and responses to certain 
comments that informed our final program. The complete set of useful 
life comments

[[Page 4361]]

and our responses are in section 3.8 of the Response to Comments 
document. As explained in the NPRM, CAA section 202(d) provides that 
the minimum useful life for heavy-duty vehicles and engines is a period 
of 10 years or 100,000 miles, whichever occurs first, and further 
authorizes EPA to adopt longer useful life periods that we determine to 
be appropriate.
    Many commenters expressed general support for our proposal to 
lengthen useful life periods in this rulemaking. Several commenters 
expressed specific support for the useful life periods of proposed 
Option 1 or proposed Option 2. Other commenters recommended EPA revise 
the proposal to either lengthen or shorten the useful life periods to 
values outside of the range of our proposed options.
    We are lengthening the current useful life mileages to capture the 
greatest amount of the operational life for each engine class that we 
have determined is appropriate at this time. We disagree with 
commenters recommending that we finalize useful life periods below the 
mileages of proposed Option 2. As noted in our proposal, proposed 
Option 2 represented the lower bound of useful life mileages we would 
consider finalizing for all engine classes. Furthermore, as described 
in Section III of this preamble and Chapter 3 of the RIA for this final 
rule, both of EPA's engine test programs successfully demonstrated that 
CI and SI engine technologies can achieve low emission levels at 
mileages (800,000 miles and 250,000 miles, respectively) well beyond 
Option 2. Even after taking into consideration uncertainties of the 
impacts of variability and real world operation on emission levels at 
the longest mileages, the test programs' data supports that mileages at 
least as long as Option 2 are appropriate, and the final standards are 
feasible at those mileages. We also disagree with commenters suggesting 
we finalize mileages longer than proposed Option 1. We did not propose 
and for the reasons just explained about impacts on emission level at 
the longest mileages do not believe it is appropriate at this time to 
require useful life periods beyond proposed Option 1.
    Organizations submitting adverse comments on useful life focused 
mostly on the useful life mileages proposed for the Heavy HDE service 
class. Technology suppliers and engine manufacturers expressed concern 
with the lack of data from engines at mileages well beyond the current 
useful life. Suppliers commented that it could be costly and 
challenging to design components without more information on component 
durability, failure modes, and use patterns at high mileages. Engine 
manufacturers claimed that some uncertainties relating to real world 
use would limit the feasibility of the proposed Option 1 useful life 
periods, including: The range of applications in which these engines 
are used, variable operator behavior (including 2nd and 3rd owners), 
and the use of new technology that is currently unproven in the field. 
In Sections III and IV.F of this preamble, we describe other areas 
where useful life plays a role and manufacturers expressed concern over 
uncertainties, including certification, DF testing, engine rating 
differences, lab-to-lab variability, production variability, and in-use 
engine variability. Due to these combined uncertainties, manufacturers 
stated that they expect to be conservative in their design and 
maintenance strategies, and some may opt to schedule aftertreatment 
replacement as a means to ensure compliance with new NOX 
emission standards, particularly for proposed Option 1 numeric 
standards and useful life values. Comments did not indicate a concern 
that manufacturers may schedule aftertreatment replacement for the 
smaller engine classes at the proposed Option 1 useful life periods.
    We agree that there are uncertainties associated with implementing 
new technology to meet new emission standards, and recognize that the 
uncertainties are highest for Heavy HDE that are expected to have the 
longest operational life and useful life periods. We acknowledge that 
higher useful life mileage is one factor that may contribute to a risk 
that manufacturers would schedule aftertreatment replacement to ensure 
compliance for the heaviest engine class. Specific to Heavy HDE, the 
final useful life mileage of 650,000 miles matches the longest useful 
life mileage we proposed for model year 2027 and we expect 
manufacturers have experience with their engines at this mileage 
through their extended warranty offerings, thus reducing uncertainties 
of real world operation compared to the longest useful life mileage we 
proposed (i.e., 800,000 miles).\319\ For Heavy HDE, the final numeric 
emission standards and useful life periods matching proposed Option 2, 
combined with other test procedure revisions to provide clarity and 
address variability, will require less conservative compliance 
strategies than proposed Option 1 and will not require manufacturers to 
plan for the replacement of the entire catalyst system. See Section III 
for further discussion on the basis and feasibility of the final 
emission standards.
---------------------------------------------------------------------------

    \319\ Brakora, Jessica. Memorandum to docket EPA-HQ-OAR-2019-
0055. ``Example Extended Warranty Packages for Heavy-duty Engines''. 
September 29, 2022.
---------------------------------------------------------------------------

    Many commenters supported proposed Option 1, including useful life 
periods out to 800,000 miles for the Heavy HDE class. Several 
commenters pointed to EPA's engine testing results on an engine aged to 
the equivalent of 800,000 miles as adequately demonstrating feasibility 
of an 800,000-mile useful life for Heavy HDE. We agree that CI engines 
are capable of meeting low emission levels at very high mileages in a 
controlled laboratory environment, but manufacturer liability for 
maintaining certified emission levels over the regulatory useful life 
period is not restricted to laboratory tests. Manufacturers expressed 
specific concern about the uncertainties outside the controlled 
laboratory environment after an engine enters commerce. In Sections III 
and IV.F of this preamble we summarize comments relating to how useful 
life factors into certification, DF testing, and in-use testing. In 
Section III.B, we describe a certification requirement we are 
finalizing for manufacturers to demonstrate the emission controls on 
Heavy HDE are durable through the equivalent of 750,000 miles; this 
durability demonstration will extend beyond the 650,000 mile useful 
life period for these engines. We expect this extended laboratory-based 
demonstration, in a controlled environment, will translate to greater 
assurance that an engine will maintain its certified emission levels in 
real world operation where conditions are more variable throughout the 
regulatory useful life. This greater assurance would be achieved while 
minimizing the compliance uncertainties identified by manufacturers in 
comments for the highest proposed useful life mileages.
    We believe manufacturers can adequately ensure the durability of 
their smaller engines over useful life periods that match proposed 
Option 1 both for meeting emission standards in the laboratory at 
certification and in the laboratory and applicable in-use testing after 
operation in the real world. The final durability demonstration 
requirements for Spark-ignition HDE, Light HDE, and Medium HDE match 
the final useful life periods for those smaller engines classes.
    As shown in Table IV-1, we are also finalizing useful life periods 
in years and hours for all primary intended service classes. We are 
updating the years values from the current 10 years to 15 years for 
Spark-ignition HDE and

[[Page 4362]]

Light HDE, 12 years for Medium HDE, and 11 years for Heavy HDE. The 
final years values match the years values we proposed and vary by 
engine class corresponding to the proposed mileage option we are 
finalizing. We are also adding hours as a useful life criteria for all 
engine classes. We received no adverse comments for hours-based useful 
life periods and are finalizing hours values by applying a 20-mph 
conversion factor, as proposed, to calculate hours values from the 
final mileage values.
    We have finalized a combination of emissions standards and useful 
life values that our analysis and supporting data demonstrate are 
feasible for all heavy-duty engine classes. We are lengthening the 
existing useful life mileages to capture the greatest amount of the 
operational life for each engine class that we have determined is 
appropriate at this time, while considering the impact of useful life 
length on the stringency of the standards and other requirements of 
this final rule. Preamble Section III describes how our analysis and 
the EPA engine test programs demonstrated feasibility of the standards 
at these useful life values, including data on emission levels at the 
equivalent useful life mileages.
2. Useful Life for Incomplete Vehicle Refueling Emission Standards
    As described in Section III.E., we are finalizing a refueling 
emission standard for incomplete vehicles above 14,000 lb GVWR. 
Manufacturers would meet the refueling emission standard by installing 
onboard refueling vapor recovery (ORVR) systems on these incomplete 
vehicles. Since ORVR systems are based on the same carbon canister 
technology that manufacturers currently use to control evaporative 
emissions on these incomplete vehicles, we proposed to align the useful 
life periods for the two systems. In 40 CFR 1037.103(f), we are 
finalizing a useful life of 15 years or 150,000 miles, whichever comes 
first, for refueling standards for incomplete vehicles above 14,000 lb 
GVWR, as proposed.
    Evaporative emission control systems are currently part of the fuel 
system of incomplete vehicles, and manufacturers are meeting applicable 
standards and useful life requirements for evaporative systems today. 
ORVR is a mature technology that has been installed on complete 
vehicles for many years, and incomplete vehicle manufacturers have 
experience with ORVR systems through their complete vehicle 
applications. Considering the manufacturers' experience with 
evaporative emission standards for incomplete vehicles, and their 
familiarity with ORVR systems, we continue to believe it would be 
feasible for manufacturers to apply the same evaporative emission 
standard useful life periods to refueling standards. We received no 
adverse comments relating to the proposed 15 years/150,000 miles useful 
life for refueling standards, and several manufacturers commented in 
support of our proposed periods.

B. Ensuring Long-Term In-Use Emissions Performance

    In the proposal, we introduced several ideas for an enhanced, 
comprehensive strategy to ensure in-use emissions performance over more 
of an engine's operational life. In this section, we discuss the final 
provisions to lengthen emission-related warranty periods, update 
maintenance requirements, and improve serviceability in this rule. 
Taken together, these updates are intended to increase the likelihood 
that engine emission controls will be maintained properly through more 
of the service life of heavy-duty engines and vehicles, including 
beyond useful life.
1. Emission-Related Warranty
    The emission-related warranty period is the period over which CAA 
section 207 requires an engine manufacturer to warrant to a purchaser 
that the engine is designed, built, and equipped so as to conform with 
applicable regulations under CAA section 202 and is free from defects 
in materials or workmanship which would cause the engine not to conform 
with applicable regulations for the warranty period. If an emission-
related component fails during the regulatory emission warranty period, 
the manufacturer is required to pay for the cost of repair or 
replacement. A manufacturer's general emissions warranty 
responsibilities are currently set out in 40 CFR 1068.115. Note that 
while an emission warranty provides protection to the owner against 
emission-related repair costs during the warranty period, the owner is 
responsible for properly maintaining the engine (40 CFR 1068.110(e)), 
and the manufacturer may deny warranty claims for failures that have 
been caused by the owner's or operator's improper maintenance or use 
(40 CFR 1068.115(a)).
    In this section, we present the updated emission-related warranty 
periods we are finalizing for heavy-duty highway engines and vehicles 
included in this rule. As described in Section G.10 of this preamble, 
we are not finalizing the proposed allowance for manufacturers to 
generate NOX emissions credits from heavy-duty zero 
emissions vehicles (ZEVs) or the associated warranty requirements.
i. Final Warranty Periods by Primary Intended Service Class
    We are updating and significantly strengthening our emission-
related warranty periods for model year 2027 and later heavy-duty 
engines.\320\ We are finalizing most of the emission-related warranty 
provisions of 40 CFR 1036.120 as proposed. Following our approach for 
useful life, we are revising the proposed warranty periods for each 
primary intended service class to reflect the difference in average 
operational life of each class and after considering additional 
information provided by commenters. See section 4 of the Response to 
Comments document for our detailed responses, including descriptions of 
revisions to the proposed regulatory text in response to commenter 
requests for clarification.
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    \320\ Emission-related components for only criteria pollutant 
emissions or both greenhouse gas (i.e., CO2, N2O, and CH4) and 
criteria pollutant emissions would be subject to the final warranty 
periods of 40 CFR 1036.120. See 40 CFR 1036.150(w).
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    EPA's current emissions-related warranty periods for heavy-duty 
engines range from 22 percent to 54 percent of the current regulatory 
useful life; the warranty periods have not changed since 1983 even as 
the useful life periods were lengthened.\321\ The revised warranty 
periods are expected to result in better engine maintenance and less 
tampering, which would help to maintain the benefits of the emission 
controls. In addition, longer regulatory warranty periods may lead 
engine manufacturers to simplify repair processes and make them more 
aware of system defects that need to be tracked and reported to EPA.
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    \321\ The useful life for heavy heavy-duty engines was increased 
from 290,000 miles to 435,000 miles for 2004 and later model years 
(62 FR 54694, October 21, 1997).
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    Our final emission-related warranty periods for heavy-duty engines 
are presented in Table IV-2 and specified in a new 40 CFR 
1036.120.322 323 The final warranty mileages that apply 
starting in MY 2027 for Spark-ignition HDE, Light HDE, and Medium HDE 
match the longest warranty mileages proposed (i.e., MY 2031 step of 
proposed Option 1) for these primary intended service

[[Page 4363]]

classes. For Heavy HDE, the final warranty mileage matches the longest 
warranty mileage proposed for MY 2027 (i.e., MY 2027 step of proposed 
Option 1). We are also increasing the years-based warranty from the 
current 5 years to 10 years for all engine classes. After considering 
comments, we are also adding hours-based warranty values to all primary 
intended service classes based on a 20 mile per hour speed threshold 
and the corresponding final mileage values. Consistent with current 
warranty provisions, the warranty period would be whichever warranty 
value (i.e., mileage, hours, or years) occurs first. We summarize key 
comments in Section IV.B.1.i.a, and provide complete responses to 
warranty comments in section 4 of the Response to Comments document.
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    \322\ All engines covered by a primary intended service class 
would be subject to the corresponding warranty period, regardless of 
fuel used.
    \323\ We are migrating the current alternate standards for 
engines used in certain specialty vehicles from 40 CFR 86.007-11 and 
86.008-10 into 40 CFR 1036.605 without modifying those alternate 
standards, as proposed. See Section XI.B of this preamble for a 
discussion of these standards.

                                  Table IV-2--Final Emission-Related Warranty Periods by Primary Intended Service Class
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                              Current                                Model year 2027 and later
             Primary intended service class              -----------------------------------------------------------------------------------------------
                                                              Mileage          Years           Hours          Mileage          Years           Hours
--------------------------------------------------------------------------------------------------------------------------------------------------------
Spark-Ignition HDE......................................          50,000               5  ..............         160,000              10           8,000
Light HDE...............................................          50,000               5  ..............         210,000              10          10,000
Medium HDE..............................................         100,000               5  ..............         280,000              10          14,000
Heavy HDE...............................................         100,000               5  ..............         450,000              10          22,000
--------------------------------------------------------------------------------------------------------------------------------------------------------

    We note that we are finalizing as proposed that when a 
manufacturer's certified configuration includes hybrid system 
components (e.g., batteries, electric motors, and inverters), those 
components are considered emission-related components, which would be 
covered under the warranty requirements in new 40 CFR 1036.120.\324\ 
Similar to the approach for useful life in Section IV.A, a manufacturer 
certifying a hybrid engine or hybrid powertrain would declare a primary 
intended service class for the engine family and apply the 
corresponding warranty periods in 40 CFR 1036.120 when certifying the 
engine configuration.\325\ This approach to clarify that hybrid 
components are part of the broader engine configuration provides 
vehicle owners and operators with consistent warranty coverage based on 
the intended vehicle application.
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    \324\ See our new definition of ``emission-related component'' 
in 40 CFR 1036.801. Defects or failures of hybrid system components 
can result in the engine operating more, and thus increase 
emissions.
    \325\ As described in 40 CFR 1036.140, the primary intended 
service classes are partially based on the GVWR of the vehicle in 
which the configuration is intended to be used. See also the update 
to definition of ``engine configuration'' in 40 CFR 1036.801 to 
clarify that an engine configuration would include hybrid components 
if it is certified as a hybrid engine or hybrid powertrain.
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    We estimated the emissions impacts of the final warranty periods in 
our inventory analysis, which is summarized in Section VI and discussed 
in detail in Chapter 5 of our RIA. In Section V, we estimate costs 
associated with the final warranty periods, including indirect costs 
for manufacturers and operating costs for owners and operators.
a. Summary of the Emission-Related Warranty Proposal
    In the proposal, we included several justifications for lengthened 
warranty periods that continue to apply for the final provisions. 
First, we expected longer emission-related warranty periods would lead 
owners to continue maintain their engines and vehicles over a longer 
period of time and ensure longer-term benefits of emission 
controls.\326\ Since emission-related repairs would be covered by 
manufacturers for a longer period of time, an owner would be more 
likely to have systems repaired and less likely to tamper to avoid the 
cost of a repair.\327\
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    \326\ See Chapter 5 of the RIA for a discussion of mal-
maintenance and tampering effects in our emission inventory 
estimates.
    \327\ Existing warranty provisions specify that owners are 
responsible for properly maintaining their engines (40 CFR 
1068.110(e)) and manufacturers may deny warranty claims for failures 
that have been caused by the owner's or operator's improper 
maintenance or use (40 CFR 1068.115(a)). See Section IV.B.2 for a 
description of updates to the allowable maintenance provisions.
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    Second, emission-related repair processes may get more attention 
from manufacturers if they are responsible for repairs over a longer 
period of time. The current, relatively short warranty periods provide 
little incentive for manufacturers to evaluate the complexity of their 
repair processes, since the owner pays for the repairs after the 
warranty period ends. As manufacturers try to remain competitive, 
longer emission warranty periods may lead manufacturers to simplify 
repair processes and provide better training to technicians in an 
effort to reduce their warranty repair costs. Simplifying repair 
processes could include modifying emission control components in terms 
of how systems are serviced and how components are replaced (e.g., 
modular sub-assemblies that could be replaced individually, resulting 
in a quicker, less expensive repair). Improved technician training may 
also reduce warranty repair costs by improving identification and 
diagnosing component failures more quickly and accurately, thus 
reducing downtime for owners and avoiding repeated failures, 
misdiagnoses of failures, and higher costs from repeat repair events at 
service facilities.
    Finally, longer regulatory emission warranty periods would increase 
the period over which the engine manufacturer would be made aware of 
emission-related defects. Manufacturers are currently required to track 
and report defects to the Agency under the defect reporting provisions 
of 40 CFR part 1068. Under 40 CFR 1068.501(b), manufacturers 
investigate possible defects whenever a warranty claim is submitted for 
a component. Therefore, manufacturers can easily monitor defect 
information from dealers and repair shops who are performing those 
warranty repair services, but after the warranty period ends, the 
manufacturer would not necessarily know about these events, since 
repair facilities are less likely to be in contact with the 
manufacturers and they are less likely to use OEM parts. A longer 
warranty period would allow manufacturers to have access to better 
defect information over a period of time more consistent with engine 
useful life.
    In the proposal, we also highlighted that a longer warranty period 
would encourage owners of vehicles powered by SI engines (as for CI 
engines) to follow manufacturer-prescribed maintenance procedures for a 
longer period of time, as failure to do so would void the warranty. We 
noted that the impact of a longer emissions warranty period may be 
slightly different for SI engines from a tampering perspective. Spark-
ignition engine systems rely on mature technologies, including 
evaporative emission systems and three-way catalyst-based emission 
controls, that have been consistently reliable for light-duty and 
heavy-duty vehicle

[[Page 4364]]

owners.\328\ SI engine owners may not currently be motivated to tamper 
with their catalyst systems to avoid repairs, but they may purchase 
defeat devices intended to disable emission controls to boost the 
performance of their engines. We expected SI engine owners may be less 
inclined to install such defeat devices during a longer warranty 
period.
---------------------------------------------------------------------------

    \328\ The last U.S. EPA enforcement action against a 
manufacturer for three-way catalysts was settled with 
DaimlerChrylser Corporation Settlement on December 21, 2005. 
Available online: https://www.epa.gov/enforcement/daimlerchrysler-corporation-settlement.
---------------------------------------------------------------------------

    We proposed two options that generally represented the range of 
revised emission warranty periods we considered adopting in the final 
rule. Proposed Option 1 included warranty periods that aligned with the 
MY 2027 and MY 2031 periods of the CARB HD Omnibus program and were 
close to 80 percent of useful life. At the time of the proposal, we 
assumed most manufacturers would continue to certify 50-state compliant 
engines in MY 2027 and later, and it would simplify the certification 
process if there would be consistency between CARB and Federal 
requirements. The warranty periods of proposed Option 2 were proposed 
to apply in a single step beginning in model year 2027 and to match 
CARB's Step 1 warranty periods for engines sold in California.\329\ The 
proposed Option 2 mileages covered 40 to 55 percent of the proposed 
Option 1 MY 2031 useful life mileages and represented an appropriate 
lower end of the range of the revised regulatory emission warranty 
periods we considered.
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    \329\ Since the CARB Step 1 warranty program did not include 
updates to warranty for SI engines, the proposed Option 2 warranty 
mileage for that the Spark-ignition HDE class matched the current 
useful life for those engines, consistent with the approach for 
Light HDE proposed Option 2 warranty.
---------------------------------------------------------------------------

    While we noted that a majority of engines would reach the warranty 
mileage in a reasonable amount of time, some applications may have very 
low annual mileage due to infrequent use or low speed operation and may 
not reach the warranty mileage for many years. To ensure manufacturers 
are not indefinitely responsible for components covered under emissions 
warranty in these situations, we proposed to revise the years-based 
warranty periods and proposed hours-based warranty periods for all 
engine classes in proposed Option 1.
    For the years-based period, which would likely be reached first by 
engines with lower annual mileage due to infrequent use, we proposed to 
increase the current period from 5 years to 7 years for MY 2027 through 
2030, and to 10 years starting with MY 2031. We also proposed to add an 
hours-based warranty period to cover engines that operate at low speed 
and/or are frequently in idle mode.\330\ In contrast to infrequent use, 
low speed and frequent idle operation can strain emission control 
components. We proposed an hours-based warranty period to allow 
manufacturers to factor gradually-accumulated work into their warranty 
obligations.
---------------------------------------------------------------------------

    \330\ We proposed warranty hours for all primary intended 
service classes based on a 20 mile per hour average vehicle speed 
threshold to convert from the proposed mileage values.
---------------------------------------------------------------------------

b. Basis for the Final Emission-Related Warranty Periods
    As detailed in section 4 of the Response to Comments document for 
this rule, commenter support for lengthening emission-related warranty 
periods varied. Many commenters expressed general support for our 
proposal to lengthen warranty periods in this rulemaking. Several 
commenters expressed specific support for the warranty periods of 
proposed Option 1 or proposed Option 2. Other commenters recommended 
EPA revise the proposal to either lengthen or shorten the warranty 
periods to values outside of the range of our proposed options.
    Our final warranty periods continue to be influenced by the 
potential beneficial outcomes of lengthening emission-related warranty 
periods that we discussed in the proposal. Specifically, we continue to 
believe lengthened warranty periods will effectively assure owners 
properly maintain and repair their emission controls over a longer 
period, reduce the likelihood of tampering, provide additional 
information on failure modes, and create a greater incentive for 
manufacturers to simplify repair processes to reduce costs. Several 
commenters agreed with our list of potential outcomes, with some noting 
that any associated emissions benefits would be accelerated by pulling 
ahead the warranty periods of the MY 2031 step of proposed Option 1 to 
begin in MY 2027.
    Organizations submitting adverse comments on lengthening warranty 
periods focused mostly the warranty mileages proposed for the Heavy HDE 
service class. Technology suppliers and engine manufacturers expressed 
concern with the lack of data from engines at high mileages, including 
uncertainties related to frequency and cause of failures, varying 
vehicle applications, and operational changes as the engine ages. We 
considered commenters' concerns regarding how uncertainties for the 
highest mileages of proposed Option 1 could cause manufacturers to 
respond by conservatively estimating their warranty cost. We continue 
to expect, as noted in the proposal, that manufacturers are likely to 
recoup the costs of warranty by increasing the purchase price of their 
products. We agree with comments indicating that increases in purchase 
price can increase the risk of pre-buy or low-buy, especially for the 
heaviest engine class, Heavy HDE.
    As described in this section, the final warranty periods are within 
the range of periods over which we expect manufacturers have access to 
failure data, which should limit the need for manufacturers to 
conservatively estimate warranty costs. We summarize our updated cost 
and economic impact analyses, which reflect the final warranty periods, 
in Sections V and X of this preamble, respectively. For more 
information, see our complete assessments of costs in Chapter 7 and 
economic impacts in Chapter 10 of the Regulatory Impact Analysis for 
this final rule.
    We retain our proposed objectives to lengthen warranty periods to 
cover a larger portion of the operational lives and to be more 
consistent with the final useful life periods. Similar to our approach 
for the useful life mileages in this final rule (see Section IV.A of 
this preamble), we believe it is appropriate to pull ahead the longest 
proposed MY 2031 warranty periods to apply in MY 2027 for the smaller 
engine classes. For Spark-ignition HDE, Light HDE, and Medium HDE, the 
final warranty mileages are 160,000 miles, 210,000 miles, and 280,000 
miles, respectively, which cover about 80 percent of the corresponding 
final useful life mileages. In response to commenters concerned with 
data limitations, we expect any component failure and wear data 
available from engines in the largest engine class would be applicable 
to the smaller engine classes. As such, manufacturers and suppliers 
have access to failure and wear data at the mileages we are finalizing 
for the smaller engine classes through their current R&D and in-use 
programs evaluating components for larger engines that currently have a 
435,000 mile useful life.
    We are not applying the same pull-ahead approach for the Heavy HDE 
warranty mileage. We do not believe it is appropriate at this time to 
finalize a 600,000-mile warranty for the Heavy HDE class that would 
uniquely cover greater than 90 percent of the 650,000-

[[Page 4365]]

mile final useful life, especially considering the comments pointing to 
uncertainties, lack of data, and potential high costs specific to Heavy 
HDE. We are also not applying the approach of adopting the warranty 
mileage of proposed Option 2, as was done for Heavy HDE useful life, as 
we do not believe the proposed Option 2 warranty of 350,000 miles would 
provide emission control assurance over a sufficient portion of the 
useful life. Instead, we are finalizing a warranty mileage that matches 
the longest mileage proposed for MY 2027 (450,000 miles), covering a 
percentage of the final useful life that is more consistent with the 
warranty periods of the smaller engine classes. The final warranty 
mileage for Heavy HDE is only 15,000 miles longer than the current 
useful life for this engine class. As noted for the warranties of the 
smaller engine classes, we expect manufacturers and suppliers have 
access to failure data nearing 450,000 miles through their R&D programs 
evaluating Heavy HDE over their current useful life. We expect 
manufacturers also have experience with their engines at this mileage 
through their extended warranty offerings; thus, they already possess 
real world operational data in addition to their internal 
evaluations.\331\
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    \331\ Brakora, Jessica. Memorandum to docket EPA-HQ-OAR-2019-
0055. ``Example Extended Warranty Packages for Heavy-duty Engines''. 
September 29, 2022.
---------------------------------------------------------------------------

    Several organizations commented on the proposed years or hours 
criteria for warranty. One supplier noted that analyses focused on 
tractors and their relatively high mileages may not accurately predict 
the use of vocational vehicles that are more limited by hours of 
operation. The same supplier suggested EPA should further differentiate 
warranties by vehicles classes and vocations. Another organization 
cautioned against warranty periods that are one-size-fits-all. Two 
organizations supported applying an hours-based warranty period for all 
engine classes to cover lower-speed applications and the 20-mph 
conversion factor that we proposed.
    We agree that vocational vehicles have distinct use patterns; 
however, we did not propose and are not finalizing warranty periods at 
the vehicle level to distinguish between vehicle types in this rule. We 
are finalizing three warranty thresholds for each heavy-duty engine 
class: A mileage threshold that is likely to reached first by vehicles 
driving many miles annually, a years threshold that is likely to be 
reached first by vehicles that drive infrequently or seasonally, and an 
hours threshold that is likely to be reached first by vehicles that 
drive frequently at lower speeds or with significant idling. We believe 
adding an hours threshold in the final rule to the mileage- and years-
based warranty periods for all engine classes will lead to more 
equitable warranty obligations across the range of possible vehicle 
applications for which a heavy-duty engine may be used.
ii. Warranty for Incomplete Vehicle Refueling Emission Controls
    As noted in Section III.E, we are finalizing refueling emission 
standards for Spark-ignition HDE that are certified as incomplete 
vehicles above 14,000 lb GVWR.\332\ Our refueling standards are 
equivalent to the refueling standards that are in effect for light- and 
heavy-duty complete Spark-ignition HDVs. We project manufacturers would 
meet the new refueling standards by adapting the existing onboard 
refueling vapor recovery (ORVR) systems from systems designed for 
complete vehicles. The new ORVR systems will likely supplement existing 
evaporative emission control systems installed on these vehicles.
---------------------------------------------------------------------------

    \332\ See the final updates to 40 CFR 1037.103.
---------------------------------------------------------------------------

    We are finalizing warranty periods for the ORVR systems of 
incomplete vehicles above 14,000 lb GVWR that align with the current 
warranty periods for the evaporative systems on those vehicles. 
Specifically, warranty periods for refueling emission controls would be 
5 years or 50,000 miles on incomplete Light HDV, and 5 years or 100,000 
miles on incomplete Medium HDV and Heavy HDV, as proposed. See our 
final updates to 40 CFR 1037.120. Our approach to apply the existing 
warranty periods for evaporative emission control systems to the ORVR 
systems is similar to our approach to the final regulatory useful life 
periods associated with our final refueling standards discussed in 
Section IV.A. We received no adverse comments on our proposed warranty 
periods for refueling emission controls.
2. Maintenance
    In this section, we describe the migrated and updated maintenance 
provisions we are finalizing for heavy-duty highway engines. Section 
IV.F of this preamble summarizes the current durability demonstration 
requirements and our final updates.
    Our final maintenance provisions, in a new section 40 CFR 1036.125, 
combine and amend the existing criteria pollutant maintenance 
provisions from 40 CFR 86.004-25 and 86.010-38. Similar to other part 
1036 sections we are adding in this rule, the structure of the new 40 
CFR 1036.125 is consistent with the maintenance sections in the 
standard-setting parts of other sectors (e.g., nonroad compression-
ignition engines in 40 CFR 1039.125). In 40 CFR 1036.205(i), we are 
codifying the current manufacturer practice of including maintenance 
instructions in their application for certification such that approval 
of those instructions would be part of a manufacturer's certification 
process.\333\ We are also finalizing a new paragraph 40 CFR 1036.125(h) 
outlining several owner's manual requirements, including migrated and 
updated provisions from 40 CFR 86.010-38(a).
---------------------------------------------------------------------------

    \333\ The current submission of maintenance instructions 
provisions in 40 CFR 86.079-39 are migrated into the requirements 
for an application for certification provisions in 40 CFR 1036.205.
---------------------------------------------------------------------------

    This section summarizes the final provisions that clarify the types 
of maintenance, update the options for demonstrating critical emission-
related maintenance will occur and the minimum scheduled maintenance 
intervals for certain components, and specify the requirements for 
maintenance instructions. The proposed rule provided an extensive 
discussion of the rationale and information supporting the proposed 
maintenance provisions (87 FR 17520, March 28, 2022). See also section 
6 of the Response to Comments for a detailed discussion of the comments 
and how they may have informed changes we are making to the proposal in 
this final rule.
i. Types of Maintenance
    The new 40 CFR 1036.125 clarifies that maintenance includes any 
inspection, adjustment, cleaning, repair, or replacement of components 
and, consistent with 40 CFR 86.004-25(a)(2), broadly classifies 
maintenance as emission-related or non-emission-related and scheduled 
or unscheduled.\334\ As proposed, we are finalizing five types of 
maintenance that manufacturers may choose to schedule: Critical 
emission-related maintenance, recommended additional maintenance, 
special maintenance, noncritical emission-related maintenance, and non-
emission-related maintenance. As we explained in the proposal, 
identifying and defining these maintenance categories in final 40 CFR 
1036.125 distinguishes between the types of maintenance manufacturers 
may choose to recommend to owners in

[[Page 4366]]

maintenance instructions, identifies the requirements that apply to 
maintenance performed during certification durability demonstrations, 
and clarifies the relationship between the different types of 
maintenance, emissions warranty requirements, and in-use testing 
requirements. The final provisions thus also specify the conditions for 
scheduling each of these five maintenance categories.
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    \334\ We include repairs as a part of maintenance because proper 
maintenance would require owners to repair failed or malfunctioning 
components. We note that repairs are considered unscheduled 
maintenance that would not be performed during durability testing 
and may be covered under warranty.
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    We summarize several revisions to the proposed critical emission-
related maintenance provisions in Section 0 with additional details in 
section 6 of the Response to Comments document. As proposed, the four 
other types of maintenance will require varying levels of EPA approval. 
In 40 CFR 1036.125(b), we propose to define recommended additional 
maintenance as maintenance that manufacturers recommend owners perform 
for critical emission-related components in addition to what is 
approved for those components under 40 CFR 1036.125(a). We are 
finalizing this provision as proposed except for a clarification in 
wording to connect additional recommended maintenance and critical 
emission-related maintenance more clearly. Under the final provisions, 
a manufacturer may recommend that owners replace a critical emission-
related component at a shorter interval than the manufacturer received 
approval to schedule for critical emission-related maintenance; 
however, the manufacturer will have to clearly distinguish their 
recommended intervals from the critical emission-related scheduled 
maintenance in their maintenance instructions. As described in this 
Section III.B.2 and the proposal, recommended additional maintenance is 
not performed in the durability demonstration and cannot be used to 
deny a warranty claim, so manufacturers will not be limited by the 
minimum maintenance intervals or need the same approval from EPA by 
demonstrating the maintenance would occur.
    In 40 CFR 1036.125(c), we proposed that special maintenance would 
be more frequent maintenance approved at shorter intervals to address 
special situations, such as atypical engine operation. We received one 
comment requesting we clarify special maintenance in proposed 40 CFR 
1036.125(c) and we are finalizing this provision as proposed except 
that we are including an example of biodiesel use in the final 
paragraph (c). Under the final provisions, manufacturers will clearly 
state that the maintenance is associated with a special situation in 
the maintenance instructions provided to EPA and owners.
    In 40 CFR 1036.125(d), as proposed, we are finalizing that 
noncritical emission-related maintenance includes inspections and 
maintenance that is performed on emission-related components but is 
considered ``noncritical'' because emission control will be unaffected 
(consistent with existing 40 CFR 86.010-38(d)). Under this final 
provision, manufacturers may recommend noncritical emission-related 
inspections and maintenance in their maintenance instructions if they 
clearly state that it is not required to maintain the emissions 
warranty.
    In 40 CFR 1036.125(e), we are updating the paragraph heading from 
nonemission-related maintenance to maintenance that is not emission-
related to be consistent with other sectors. The final provision, as 
proposed, describes the maintenance as unrelated to emission controls 
(e.g., oil changes) and states that manufacturers' maintenance 
instructions can include any amount of maintenance unrelated to 
emission controls that is needed for proper functioning of the engine.
Critical Emission-Related Components
    Consistent with the existing and proposed maintenance provisions, 
the final provisions continue to distinguish certain components as 
critical emission-related components. The proposal did not migrate the 
specific list of components defined as ``critical emission-related 
components'' from 40 CFR 86.004-25(b)(6)(i); instead, we proposed and 
are finalizing that manufacturers identify their specific critical 
components by obtaining EPA's approval for critical emission-related 
maintenance using 40 CFR 1036.125(a). Separately, we also proposed a 
new definition for critical emission-related components in 40 CFR 
1068.30 and are finalizing with revision. The final definition is 
consistent with paragraph 40 CFR 86.004-25(b)(6)(i)(I) and the current 
paragraph IV of 40 CFR part 1068, appendix A, as proposed.\335\ We are 
removing the proposed reference to 40 CFR 1068, appendix A, in the 
final definition, since appendix A specifies emission-related 
components more generally. To avoid having similar text in two 
locations, we are also replacing the current text of paragraph IV of 40 
CFR 1068, appendix A, with a reference to the new part 1068 definition 
of critical emission-related components.
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    \335\ Paragraph (b)(6)(i)(I) concludes the list of critical 
emission-related components in 40 CFR 86.004-25 with a general 
description stating: ``Any other component whose primary purpose is 
to reduce emissions or whose failure would commonly increase 
emissions of any regulated pollutant without significantly degrading 
engine performance.'' The existing paragraph (IV) of 40 CFR 1068, 
appendix A similarly states: ``Emission-related components also 
include any other part whose primary purpose is to reduce emissions 
or whose failure would commonly increase emissions without 
significantly degrading engine/equipment performance.''
---------------------------------------------------------------------------

ii. Critical Emission-Related Maintenance
    A primary focus of the final maintenance provisions is critical 
emission-related maintenance. Critical emission-related maintenance 
includes any adjustment, cleaning, repair, or replacement of emission-
related components that manufacturers identify as having a critical 
role in the emission control of their engines. The final 40 CFR 
1036.125(a), consistent with current maintenance provisions in 40 CFR 
part 86 and the proposal, will continue to allow manufacturers to seek 
advance approval from EPA for new emission-related maintenance they 
wish to include in maintenance instructions and perform during 
durability demonstration. The final 40 CFR 1036.125(a) retains the same 
proposed structure that includes a maintenance demonstration and 
minimum maintenance intervals, and a pathway for new technology that 
may be applied in engines after model year 2020.
    We are finalizing with revision the maintenance demonstration 
proposed in 40 CFR 1036.125(a)(1). The final provision includes the 
five proposed options for manufacturers to demonstrate the maintenance 
is reasonably likely to be performed in-use, with several clarifying 
edits detailed in the Response to Comments document .\336\ As further 
discussed in Section IV.D, we are finalizing the separate statement in 
40 CFR 1036.125(a)(1) that points to the final inducement provisions, 
noting that we will accept DEF replenishment as reasonably likely to 
occur if an engine meets the specifications in proposed 40 CFR 
1036.111; we are not setting a minimum maintenance interval for DEF 
replenishment. Also, as noted in the proposal and reiterated here, the 
first maintenance demonstration option, described in 40 CFR 
1036.125(a)(1)(i), is intended to cover emission control technologies 
that have an inherent performance degradation that coincides with 
emission increases, such as back pressure resulting from a clogged DPF.
---------------------------------------------------------------------------

    \336\ The five maintenance demonstration options are consistent 
with current maintenance demonstration requirements in 40 CFR 
86.004-25 and 86.094-25.
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    Consistent with the current and proposed maintenance provisions, we 
are specifying minimum maintenance

[[Page 4367]]

intervals for certain emission-related components, such that 
manufacturers may not schedule more frequent maintenance than we allow. 
In 40 CFR 1036.125(a)(2), we are updating the list of components with 
minimum maintenance intervals to more accurately reflect components in 
use today and extending the replacement intervals such that they 
reflect replacement intervals currently scheduled for those components. 
See the NPRM preamble for a discussion of our justification for 
terminology changes we are applying in the final rule, and the list of 
components that we are not migrating from 40 CFR part 86 because they 
are obsolete or covered by other parts.
    Consistent with current maintenance provisions, we proposed to 
disallow replacement of catalyst beds and particulate filter elements 
within the regulatory useful life of the engine.\337\ We are removing 
reference to catalyst beds and particular filter elements in the 
introductory text of paragraph (a)(2) and instead are adding them, with 
updated terminology, as a separate line in the list of components in 
Table 1 of 40 CFR 1036.125(a)(2) with minimum maintenance intervals 
matching the final useful life values of this rule.\338\ Including 
catalyst substrates and particulate filter substrates directly in the 
table of minimum maintenance intervals more clearly connects the 
intervals to the useful life values. In response to manufacturer 
comments requesting clarification, we are also adding a reference to 40 
CFR 1036.125(g) in paragraph (a)(2) to clarify that manufacturers are 
not restricted from scheduling maintenance more frequent than the 
minimum intervals, including replacement of catalyst substrates and 
particulate filter substrates, if they pay for it.
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    \337\ Existing 40 CFR 86.004-25(b)(4)(iii) states that only 
adjustment and cleaning are allowed for catalyst beds and 
particulate filter elements and that replacement is not allowed 
during the useful life. Existing 40 CFR 86.004 25(i) clarifies that 
these components could be replaced or repaired if manufacturers 
demonstrate the maintenance will occur and the manufacturer pays for 
it.
    \338\ In the final provision, we replaced ``catalyst bed'' with 
``catalyst substrate'' and ``particulate filter element'' with 
``particulate filter substrate''.
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    We are finalizing as proposed the addition of minimum intervals for 
replacing hybrid system components in engine configurations certified 
as hybrid engines or hybrid powertrains, which would include the 
rechargeable energy storage system (RESS). Our final minimum intervals 
for hybrid system components equal the current useful life for the 
primary intended service classes of the engines that these electric 
power systems are intended to supplement or replace.\339\
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    \339\ We note that Table IV-3 and the corresponding Table 1 of 
40 CFR 1036.125(a)(2) include a reference to ``hybrid system 
components'', which we inadvertently omitted from the tables in the 
proposed rule.
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    Table IV-3 summarizes the minimum replacement intervals we are 
finalizing in a new table in 40 CFR 1036.125(a)(2). As explained in the 
proposal, we believe it is appropriate to account for replacement 
intervals that manufacturers have already identified and demonstrated 
will occur for these components and the final replacement intervals 
generally match the shortest mileage interval (i.e., most frequent 
maintenance) of the published values, with some adjustments after 
considering comments. Commenters noted that some sensors are not 
integrated with a listed system and requested EPA retain a discrete set 
of minimum intervals for sensors, actuators, and related ECMs. We agree 
and are specifying minimum intervals that match the current intervals 
for sensors, actuators, and related control modules that are not 
integrated into other systems. We are retaining the proposed text to 
indicate that intervals specified for a given system would apply for 
all to actuators, sensors, tubing, valves, and wiring associated with 
that component associated with that system. We are also revising the 
minimum intervals for ignition wires from the proposed 100,000 miles to 
50,000 miles to match the current intervals and adding an interval for 
ignition coils at the same 50,000 miles after considering comments. See 
section 6 of the Response to Comments document for other comments we 
considered when developing the final maintenance provisions.
    We proposed to retain the maintenance intervals specified in 40 CFR 
86.004-25 for adjusting or cleaning components as part of critical 
emission-related maintenance. We are finalizing the proposed 
maintenance intervals for adjusting and cleaning with one correction. 
Commenters noted that the proposal omitted an initial minimum interval 
for adjusting or cleaning EGR system components. Consistent with 40 CFR 
86.004-25(b), we are correcting the proposed intervals for several 
components (catalyst system components, EGR system components (other 
than filters or coolers), particulate filtration system components, and 
turbochargers) from 150,000 miles or 4,500 hours to include an initial 
interval of 100,000 miles or 3,000 hours, with subsequent intervals of 
150,000 miles or 4,500 hours. We did not reproduce the new Table 2 from 
40 CFR 1036.125(a)(2) showing the minimum intervals for adjusting or 
cleaning components in this preamble.

 Table IV-3--Minimum Scheduled Maintenance Intervals in Miles (or Hours) for Replacing Critical Emission-Related
                                          Components in 40 CR 1036.125
----------------------------------------------------------------------------------------------------------------
                                           Spark-ignition
               Components                        HDE            Light HDE        Medium HDE         Heavy HDE
----------------------------------------------------------------------------------------------------------------
Spark plugs.............................      25,000 (750)  ................  ................  ................
DEF filters.............................  ................   100,000 (3,000)   100,000 (3,000)   100,000 (3,000)
Crankcase ventilation valves and filters    60,000 (1,800)    60,000 (1,800)    60,000 (1,800)    60,000 (1,800)
 .......................................
Ignition wires and coils................    50,000 (1,500)  ................  ................  ................
Oxygen sensors..........................    80,000 (2,400)  ................  ................  ................
Air injection system components.........   110,000 (3,300)  ................  ................  ................
Sensors, actuators, and related control    100,000 (3,000)   100,000 (3,000)   150,000 (4,500)   150,000 (4,500)
 modules that are not integrated into
 other systems..........................
Particulate filtration systems (other      100,000 (3,000)   100,000 (3,000)   250,000 (7,500)   250,000 (7,500)
 than filter substrates)................
Catalyst systems (other than catalyst      110,000 (3,300)   110,000 (3,300)   185,000 (5,550)  435,000 (13,050)
 substrates), fuel injectors, electronic
 control modules, hybrid system
 components, turbochargers, and EGR
 system components (including filters
 and coolers)...........................
Catalyst substrates and particulate       200,000 (10,000)  270,000 (13,000)  350,000 (17,000)  650,000 (32,000)
 filter substrates......................
----------------------------------------------------------------------------------------------------------------


[[Page 4368]]

    We received no adverse comments on the proposed approach to 
calculate the corresponding hours values for each minimum maintenance 
interval. Consistent with our current maintenance provisions and the 
proposal, we are finalizing minimum hours values based on the final 
mileage and a 33 miles per hour vehicle speed (e.g., 150,000 miles 
would equate to 4,500 hours).\340\ Consistent with the current 
maintenance intervals specified in part 86 and the proposal, we are not 
including year-based minimum intervals; OEMs can use good engineering 
judgment if they choose to include a scheduled maintenance interval 
based on years in their owner's manuals.
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    \340\ The minimum hours-based intervals for catalyst substrates 
and particulate filter substrates match the useful life hours that 
apply for each primary intended service class to ensure these 
components are not replaced within the regulatory useful life of the 
engine, consistent with existing maintenance provisions. The useful 
life hours are calculated using a 22 miles per hour conversion 
factor as described in Section IV.A of this preamble.
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    For new technology, not used on engines before model year 2020, we 
are providing a process for manufacturers to seek approval for new 
scheduled maintenance, consistent with the current maintenance 
provisions. We received no adverse comment on the proposal to migrate 
40 CFR 86.094-25(b)(7)(ii), which specifies a process for approval of 
new critical emission-related maintenance associated with new 
technology, and 40 CFR 86.094-25(b)(7)(iii), which allows manufacturers 
to ask for a hearing if they object to our decision.\341\ We are 
finalizing a new 40 CFR 1036.125(a)(3), as proposed.
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    \341\ Hearing procedures are specified in 40 CFR 1036.820 and 40 
CFR part 1068, subpart G.
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iii. Source of Parts and Repairs
    Consistent with CAA section 207 \342\ and our existing regulations 
for heavy duty vehicles under part 1037, we proposed a new paragraph 40 
CFR 1036.125(f) to clarify that manufacturers' written instructions for 
proper maintenance and use, discussed further in Section IV.B.2.vi, 
generally cannot limit the source of parts and service owners use for 
maintenance unless the component or service is provided without charge 
under the purchase agreement, with two specified exceptions.\343\ We 
are moving, with revisions, the content of the proposed paragraph (f) 
to 40 CFR 1036.125(h)(2). See section 6 of the Response to Comments. 
Consistent with the proposal, we are finalizing that manufacturers 
cannot specify a particular brand, trade, or corporate name for 
components or service and cannot deny a warranty claim due to 
``improper maintenance'' based on owners choosing not to use a 
franchised dealer or service facility or a specific brand of part 
unless the component or service is provided without charge under the 
purchase agreement. Consistent with current maintenance provisions and 
CAA section 207(c)(3)(B), a second exception is that manufacturers can 
specify a particular service facility and brand of parts only if the 
manufacturer convinces EPA during the approval process that the engine 
will only work properly with the identified service or component. We 
are not finalizing at this time the proposed 40 CFR 1036.125(f) 
requirement regarding specific statements on the first page of written 
maintenance instructions; after consideration of comments, we agree 
with commenters that the final regulatory text accomplishes the intent 
of our proposal without the additional proposed first sentence.
---------------------------------------------------------------------------

    \342\ See, e.g., CAA section 207(c)(3)(B) and (g).
    \343\ This provision has been adopted in the standard-setting 
parts of several other sectors (see 1037.125(f)).
---------------------------------------------------------------------------

iv. Payment for Scheduled Maintenance
    We proposed 40 CFR 1036.125(g) to allow manufacturers to schedule 
maintenance not otherwise allowed by 40 CFR 1036.125(a)(2) if they pay 
for it. The proposed paragraph (g) also included four criteria to 
identify components for which we would require manufacturers to pay for 
any scheduled maintenance within the regulatory useful life. The four 
criteria, which are based on current provisions that apply for nonroad 
compression-ignition engines, would require manufacturers to pay for 
components that were not in general use on similar engines before 1980, 
whose primary purpose is to reduce emissions, where the cost of the 
scheduled maintenance is more than 2 percent of the price of the 
engine, and where failure to perform the scheduled maintenance would 
not significantly degrade engine performance.\344\ We continue to 
believe that components meeting the four criteria are less likely to be 
maintained without the incentive of manufacturers paying for it and we 
are finalizing 40 CFR 1036.125(g) as proposed.
---------------------------------------------------------------------------

    \344\ See 40 CFR 1039.125(g).
---------------------------------------------------------------------------

    As noted in Section IV.B.2.ii, manufacturers cannot schedule 
replacement of catalyst substrates or particulate filter substrates 
within the regulatory useful life of the engine unless they pay for it. 
As explained in the proposed rule, in addition to catalyst substrates 
and particulate filter substrates, we expect that replacement of EGR 
valves, EGR coolers, and RESS of certain hybrid systems also meet the 
40 CFR 1036.125(g) criteria and manufacturers will only be able to 
schedule replacement of these components if the manufacturer pays for 
it.
    In the proposal, we requested comment on restricting the 
replacement of turbochargers irrespective of the four criteria of 
proposed 40 CFR 1036.125(g). One commenter suggested that EPA should 
follow the CARB approach that requires manufacturers to pay for 
scheduled maintenance of turbochargers within the regulatory useful 
life. The comment indicated the cost of repairs and ``significant 
impact'' of a failed turbocharger on emissions justify requiring that 
manufacturers pay for replacement. We disagree and are not finalizing a 
separate requirement for turbochargers. Turbochargers are not added to 
engines specifically to control emissions and we expect the performance 
degredation associated with a failing turbocharger is likely to 
motivate owners to fix the problem. We continue to believe the four 
criteria in 40 CFR 1036.125(g) are an appropriate means of 
distinguishing components for which manufacturers should pay in order 
to ensure the components are maintained.
v. Maintenance Instructions
    As proposed, our final 40 CFR 1036.125 preserves the requirement 
that the manufacturer provide written instructions for properly 
maintaining and using the engine and emission control system, 
consistent with CAA section 207(c)(3)(A).\345\ The new 40 CFR 
1036.125(h) describes the information that we are requiring 
manufacturers to include in an owner's manual, consistent with CAA 
sections 202 and 207. The new 40 CFR 1036.125(h)(1) generally migrates 
the existing maintenance instruction provisions specified in 40 CFR 
86.010-38(a). As described in Section IV.B.2.iii, final 40 CFR 
1036.125(h)(2) includes revised content from proposed 40 CFR 
1036.125(f). The final paragraph (h)(2) is also revised from the 
proposed regulatory text to clarify that EPA did not intend the 
proposed paragraph as a requirement for owners to maintain

[[Page 4369]]

records in order to make a warranty claim. While 40 CFR 1036.120(d) 
allows manufacturers to deny warranty claims for improper maintenance 
and use, owners have expressed concern that it is unclear what 
recordkeeping is needed to document proper maintenance and use, and 
both the proposed and final 40 CFR 1036.125(h)(2) are intended to 
ensure manufacturers are communicating their expectations to owners.
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    \345\ CAA section 207(c)(3)(A) states that the manufacturer 
shall furnish with each new motor vehicle or motor vehicle engine 
written instructions for the proper maintenance and use of the 
vehicle or engine by the ultimate purchaser and that such 
instructions shall correspond to regulations which the Administrator 
shall promulgate.
---------------------------------------------------------------------------

    Consistent with the current 40 CFR 86.010-38(a)(2), our final 40 
CFR 1036.125(h)(2) also requires manufacturers to describe in the 
owner's manual if manufacturers expect owners to maintain any 
documentation to show the engine and emission control system have been 
properly maintained and, if so, to specify what documentation. 
Manufacturers should be able to identify their expectations for 
documenting routine maintenance and repairs related to warranty claims. 
For instance, if a manufacturer requires a maintenance log as part of 
their process for reviewing warranty claims and determining whether the 
engine was properly maintained, we expect the owner's manual would 
provide an example log with a clear statement that warranty claims 
require an up-to-date maintenance record. We note that 40 CFR 1036.125 
specifies minimum maintenance intervals for critical emission-related 
maintenance, and limits manufacturers from invalidating warranty if 
certain other types of allowable maintenance are not performed (i.e., 
recommended additional maintenance and noncritical emission-related 
maintenance). Any required maintenance tasks and intervals must be 
consistent with the requirements and limitations in 40 CFR 1036.125. As 
explained at proposal, we may review a manufacturer's information 
describing the parameters and documentation for demonstrating proper 
maintenance before granting certification for an engine family.
    The maintenance instructions requirements we are finalizing for the 
remainder of 40 CFR 1036.125(h) are covered in the serviceability 
discussion in Section IV.B.3 and inducements discussion in Section IV.C 
of this preamble. As noted in Section IV.B.3, our serviceability 
provisions supplement the service information provisions specified in 
40 CFR 86.010-38(j).\346\
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    \346\ We are not migrating the service information provisions 
into 40 CFR part 1036 in this rule.
---------------------------------------------------------------------------

vi. Performing Scheduled Maintenance on Test Engines
    We are finalizing our proposed update to 40 CFR 1065.410(c) to 
clarify that inspections performed during testing include electronic 
monitoring of engine parameters. While we intended the proposed update 
to include prognostic systems, the proposed text referred only to 
electronic tools, and we are revising from the proposed text in the 
final provision to include ``or internal engine systems'' to clarify. 
Manufacturers that include prognostic systems as part of their engine 
packages to identify or predict malfunctioning components may use those 
systems during durability testing and would describe any maintenance 
performed as a result of those systems, consistent with 40 CFR 
1065.410(d), in their application for certification. We note that, to 
apply these electronic monitoring systems in testing, the inspection 
tool (e.g., prognostic system) must be readable without specialized 
equipment so it is available to all customers or accessible at 
dealerships and other service outlets consistent with CAA sections 
202(m) and 206.
3. Serviceability
    This Section IV.B.3 describes the provisions we are finalizing to 
improve serviceability, reduce mal-maintenance, and ensure owners are 
able to maintain emission control performance throughout the entire in-
use life of heavy-duty engines. See section IV.B.2 of this preamble for 
a discussion of manufacturers' obligations to provide maintenance 
instructions to operators. Also see the preamble of the proposed rule 
for further discussion of why EPA proposed these serviceability and 
maintenance information provisions.\347\ The final serviceability and 
maintenance information provisions were informed by comments, and we 
summarize key comments in this section.\348\ We provide complete 
responses to the serviceability-related comments in section 5 of the 
Response to Comments.
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    \347\ See section IV.B.3. of the proposed preamble (87 FR 17517, 
March 28, 2022).
    \348\ While we requested comment on several potential approaches 
to improve serviceability of electric vehicles in the proposal (87 
FR 17517, March 28, 2022), EPA is not taking final action on any 
requirements related to this request at this time; we may consider 
the comments provided on improved serviceability of electric 
vehicles in future rulemakings relevant to electric vehicles. See 
section 5.3 of the Response to Comments document for details on 
comments received.
---------------------------------------------------------------------------

i. Background
    Without proper maintenance, the emission controls on heavy-duty 
engines may not function as intended, which can result in increased 
emissions. Mal-maintenance, which includes delayed or improper repairs 
and delayed or unperformed maintenance, can be intentional (e.g., 
deferring repairs due to costs) or unintentional (e.g., not being able 
to diagnose the actual problem and make the proper repair).
    In the NPRM, EPA discussed stakeholder concerns with the 
reliability of MY 2010 and later heavy-duty engines, and significant 
frustration expressed by owners concerning their experiences with 
emission control systems on such engines. EPA explained that 
stakeholders have communicated to EPA that, although significant 
improvements have been made to emission control systems since they were 
first introduced into the market, reliability and serviceability 
continue to cause them concern. EPA received comments on the NPRM 
further highlighting problems from fleets, owners, and operators. 
Commenters noted issues with a range of emission-related components, 
including: Sensors (DPF and SCR-related), DEF dosers, hoses, filters, 
EGR valves, EGR coolers and EGR actuators, SCR catalysts, DOC, turbos, 
wiring, decomposition tubes, cylinder heads, and DPFs. Specifically, 
for example, comments included described experiences with 
aftertreatment wiring harness failures, DEF nozzles plugging or over-
injecting, NOX sensor failures, defective DEF pumps and 
level sensors, systems being less reliable in rain and cold weather, 
more frequent required cleaning of DPFs than anticipated, and problems 
related to DEF build-up. See section 5 of the Response to Comment for 
further information and the detailed comments.
    In addition to existing labeling, diagnostic, and service 
information requirements, EPA proposed to require important maintenance 
information be made available in the owner's manual as a way to improve 
factors that may contribute to mal-maintenance. The proposed 
serviceability provisions were expected to result in better service 
experiences for independent repair technicians, specialized repair 
technicians, owners who repair their own equipment, and possibly 
vehicle inspection and maintenance technicians. Furthermore, the 
proposed provisions were intended to improve owner experiences 
operating and maintaining heavy-duty engines and provide greater 
assurance of long-term in-use emission reductions by reducing the 
likelihood of occurrences of tampering.
    Given the importance and complexity of emission control systems and 
the

[[Page 4370]]

impact to drivers for failing to maintain such systems (e.g., 
inducements), EPA believes it is critical to include additional 
information about emission control systems in the owner's manual. We 
proposed to require manufacturers to provide more information 
concerning the emission control system in the owner's manual to include 
descriptions of how the emissions systems operate, troubleshooting 
information, and diagrams. EPA has imposed similar requirements in the 
past, such as when EPA required vacuum hose diagrams be included on the 
emission label to improve serviceability and help inspection and 
maintenance facilities identify concerns with that system.\349\
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    \349\ See 53 FR 7675, March 9, 1988, and 55 FR 7177, February 
29. 1990 for more information.
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ii. Final Maintenance Information Requirements for Improved 
Serviceability
    EPA received both supportive and adverse comments from a number of 
stakeholders on the serviceability proposals (see section 5 of the 
Response to Comments). For example, comments from service providers and 
manufacturers largely objected to the proposed serviceability 
requirements, while owners and operators supported the proposed 
requirements. EPA is finalizing requirements for improved 
serviceability so that owners and operators can more easily understand 
advanced emission control system operation and identify issues in such 
systems as they arise during operation. To the extent EPA can ensure 
this information is harmonized among manufacturers, we believe this 
will improve the experiences of owners, operators, parts counter 
specialists, and repair technicians, and reduce frustration that could 
otherwise create an incentive to tamper.
    CAA section 207(c)(3)(A) requires manufacturers to provide 
instructions for the proper maintenance and use of a vehicle or engine 
by the ultimate purchaser and requires such instructions to correspond 
to EPA regulations. The final rule includes maintenance provisions 
migrated and updated from 40 CFR part 86, subpart A, to a new 40 CFR 
1036.125, that specify the maintenance instructions manufacturers must 
provide in an owner's manual to ensure that owners can properly 
maintain their vehicles (see Section IV.B.2). Additionally, as a part 
of the new 40 CFR 1036.125(h), we are finalizing specific maintenance 
information manufacturers must provide in the owner's manual to improve 
serviceability:
     EPA is finalizing with revision the proposed requirement 
for manufacturers to provide a description of how the owner can use the 
OBD system to troubleshoot problems and access emission-related 
diagnostic information and codes stored in onboard monitoring systems. 
The revision replaces the proposed requirement that the owner's manual 
include general information on how to read and understand OBD codes 
with a more specific set of required information. The final requirement 
specifies that, at a minimum, manufacturers provide a description of 
how to use the OBD system to troubleshoot and access information and 
codes, including (1) identification of the OBD communication protocol 
used, (2) location and type of OBD connector, (3) a brief description 
of what OBD is (including type of information stored, what a 
malfunction indicator light (MIL) is, explanation that some MILs may 
self-extinguish), and (4) a note that certain engine and emission data 
is publicly available using any scan tool, as required by EPA. As we 
describe further in section IV.C.1.iii, we are not taking final action 
on the proposed health monitors. Therefore, we are also not requiring 
manufacturers to provide information about the role of the health 
monitor to help owners service their engines before components fail in 
the description of the OBD system.
     EPA is finalizing as proposed, with a few clarifications 
in wording, a requirement for manufacturers to identify critical 
emission systems and components, describe how they work, and provide a 
general description of how the emission control systems operate.
     EPA is finalizing as proposed the requirement for 
manufacturers to include one or more diagrams of the engine and its 
emission-related components, with two exceptions: (1) We are not 
finalizing the proposed requirements to include the identity, location, 
and arrangement of wiring in the diagram, and we are not requiring 
information related to the expected pressures at the particulate filter 
and exhaust temperatures throughout the aftertreatment system. The 
final requirement specifies the following information is required, as 
proposed:
    [cir] The flow path for intake air and exhaust gas.
    [cir] The flow path of evaporative and refueling emissions for 
spark-ignition engines, and DEF for compression-ignition engines, as 
applicable.
    [cir] The flow path of engine coolant if it is part of the emission 
control system described in the application for certification.
    [cir] The identity, location, and arrangement of relevant emission 
sensors, DEF heater and other DEF delivery components, and other 
critical emission-related components.
    [cir] Terminology to identify components must be consistent with 
codes the manufacturer uses for the OBD system.
     EPA is revising the proposed requirement relating to 
exploded-view drawings and basic assembly requirements in the owner's 
manual. The final provision replaces a general reference to 
aftertreatment devices with a specific list of components that should 
be included in one or more diagrams in the owner's manual, including: 
EGR Valve, EGR actuator, EGR cooler, all emission sensors (e.g., 
NOX, soot sensors, etc.), temperature and pressure sensors 
(EGR, DPF, DOC, and SCR-related, including DEF-related temperature and 
pressure sensors), fuel (DPF-related) and DEF dosing units and 
components (e.g., pumps, filters, metering units, nozzles, valves, 
injectors), DEF quality sensors, DPF filter, DOC, SCR catalyst, 
aftertreatment-related control modules, any other DEF delivery-related 
components (e.g., lines and freeze protection components), and 
aftertreatment-related wiring harnesses if replaceable separately. The 
revision also notes that the information could be provided in multiple 
diagrams. We are also revising the proposed requirement to include part 
numbers for all components in the drawings and instead are only 
requiring part numbers for sensors and filters related to SCR or DPF 
systems. We are not finalizing at this time the broader requirement 
that this information include enough detail to allow a mechanic to 
replace any of these components. Finally, once published for a given 
model year, manufacturers will not be required to revise their owner's 
manual with updated part numbers if a part is updated in that model 
year. We recognize that manufacturers are able to use outdated part 
numbers to find updated parts.
     EPA is finalizing as proposed the requirement for 
manufacturers to provide a statement instructing owners or service 
technicians where and how to find emission recall and technical repair 
information available without charge from the National Highway Traffic 
Safety Administration.\350\
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    \350\ NHTSA provides this information at https://www.nhtsa.gov/recalls. For example, manufacturers should specify if the 
information would be listed under ``Vehicle'' or ``Equipment.''
---------------------------------------------------------------------------

     EPA is finalizing with some modifications from the 
proposal the requirement for manufacturers to

[[Page 4371]]

include a troubleshooting guide to address SCR inducement-related and 
DPF regeneration-related warning signals. For the SCR system this 
requirement includes:
    [cir] The inducement derate schedule (including indication that DEF 
quantity-related inducements will be triggered prior to the DEF tank 
being completely empty).
    [cir] The meaning of any trouble lights that indicate specific 
problems (e.g., DEF level).
    [cir] A description of the three types of SCR-related derates (DEF 
quantity, DEF quality and tampering) and a notice that further 
information on the cause of (e.g., trouble codes) is available using 
the OBD system.
     For the DPF system the troubleshooting guide requirement 
includes:
    [cir] Information on the occurrence of DPF-related derates.
    [cir] EPA is finalizing in 40 CFR 1036.110(c) that certain 
information must be displayed on-demand for operators. Specifically, 
EPA is finalizing the requirement that for SCR-related inducements, 
information such as the derate and associated fault code must be 
displayed on-demand for operators (see section IV.D.3 for further 
information). EPA is also finalizing requirements that the number of 
DPF regenerations, DEF consumption rate, and the type of derate (e.g., 
DPF- or SCR-related) and associated fault code for other types of 
emission-related derates be displayed on-demand for operators (see 
section IV.C.1.iii for further information).
    EPA proposed that manufacturers include a Quick Response (QR) code 
on the emission label that would direct repair technicians, owners, and 
inspection and maintenance facilities to a website providing critical 
emission systems information at no cost. We are not taking final action 
at this time on the proposed requirement to include QR codes on the 
emission control information label. After considering manufacturers' 
comments, we intend to engage in further outreach and analysis before 
adopting electronic labeling requirements, such as QR codes. In this 
rule, we are instead finalizing that the owner's manual must include a 
URL directing owners to a web location for the manufacturer's service 
information required in 40 CFR 86.010-38(j). We recognize the potential 
for electronic labels with QR codes or similar technology to provide 
useful information for operators, inspectors, and others. Manufacturers 
from multiple industry sectors are actively pursuing alternative 
electronic labeling. In the absence of new requirements for electronic 
labeling, manufacturers must continue to meet requirements for applying 
physical labels to their engines. Manufacturers may include on the 
vehicle or engine any QR codes or other electronic labeling information 
that goes beyond what is required for the physical emission control 
information label. EPA is also not taking final action at this time on 
the proposed requirement to include a basic wiring diagram for 
aftertreatment-related components in the owner's manual. Finally, EPA 
is not taking final action at this time on requirements related to DPF 
cleaning; instead, EPA intends to continue to follow the work CARB has 
undertaken in this area and may consider taking action in a future 
rule.
iii. Other Emission Controls Education Options
    In addition to our proposed provisions to provide more easily 
accessible service information for operators, we sought comment on 
whether educational programs and voluntary incentives could lead to 
better maintenance and real-world emission benefits. We received 
comments in response to the NPRM supportive of improving such 
educational opportunities to promote an understanding of how advanced 
emission control technologies function and the importance of emissions 
controls as they relate to the broader economy and the environment (see 
section 5.4 of the Response to Comment for further details). EPA is not 
finalizing any requirements related to this request for comment at this 
time but will look for future opportunities to improve the availability 
of information on emission control systems.

C. Onboard Diagnostics

    As used here, the terms ``onboard diagnostics'' and ``OBD'' refer 
to systems of electronic controllers and sensors required by regulation 
to detect malfunctions of engines and emission controls. EPA's OBD 
regulations for heavy-duty engines are contained in 40 CFR 86.010-18, 
which were initially promulgated on February 24, 2009 (74 FR 8310). 
Those requirements were harmonized with CARB's OBD program then in 
place. Consistent with our authority under CAA section 202(m), EPA is 
finalizing an update to our OBD regulations in 40 CFR 1036.110 to align 
with existing CARB OBD requirements as appropriate, better address 
newer diagnostic methods and available technologies, and to streamline 
provisions.
1. Incorporation of California OBD Regulations by Reference
    CARB OBD regulations for heavy-duty engines are codified in title 
13, California Code of Regulations, sections 1968.2, 1968.5, 1971.1, 
and 1971.5. EPA is finalizing our proposal to incorporate by reference 
in 40 CFR 1036.810 the OBD requirements CARB adopted October 3, 
2019.351 352 In response to the NPRM, EPA received a number 
of comments supportive of EPA's adoption of the revised CARB OBD 
program, including the 2019 rule amendments. As discussed in this 
section and reflected in final 40 CFR 1036.110(b), our final rule will 
harmonize with the majority of CARB's existing OBD regulations, as 
appropriate and consistent with the CAA, and make these final 
requirements mandatory beginning in MY 2027 and optional in earlier 
model years. These new requirements better address newer diagnostic 
methods and available technologies and have the additional benefit of 
being familiar to industry. For example, the new tracking requirements 
contained in CARB's updated OBD program, known as the Real Emissions 
Assessment Logging (``REAL'') program, track real-world emissions 
systems performance of heavy-duty engines. The REAL tracking 
requirements include the collection of onboard data using existing OBD 
sensors and other vehicle performance parameters, which will better 
allow the assessment of real world, in-use emission performance.
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    \351\ This CARB rulemaking became effective the same day and 
began to phase in under CARB's regulations with MY 2022. The CARB 
regulations we are adopting are available at: https://ww2.arb.ca.gov/resources/documents/heavy-duty-obd-regulations-and-rulemaking.
    \352\ The legal effect of incorporation by reference is that the 
material is treated as if it were published in the Federal Register 
and CFR. This material, like any other properly issued rule, has the 
force and effect of law. Congress authorized incorporation by 
reference in the Freedom of Information Act to reduce the volume of 
material published in the Federal Register and CFR. (See 5 U.S.C. 
552(a) and 1 CFR part 51). See https://www.archives.gov/federal-register/cfr/ibr-locations.html for additional information.
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    EPA's final OBD requirements are closely aligned with CARB's 
existing requirements with a few exceptions, as further described in 
Section IV.C.1.i. We are finalizing exclusions to certain provisions 
that are not appropriate for a Federal program and including additional 
elements to improve on the usefulness of OBD systems for operators.

[[Page 4372]]

i. CARB OBD Provisions Revised or Not Included in the Finalized Federal 
Program
    CARB's 2019 OBD program includes some provisions that may not be 
appropriate for the Federal regulations.\353\ In a new 40 CFR 
1036.110(b), we are finalizing the following clarifications and changes 
to the 2019 CARB regulations that we are otherwise incorporating by 
reference:
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    \353\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule; note, we are making no 
determination in this action about the appropriateness of these 
provisions for CARB's regulation.
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    1. Modifying the threshold requirements contained in the 2019 CARB 
OBD standards we are adopting (as discussed in Section IV.C.1.ii),
    2. Providing flexibilities to delay compliance up to three model 
years for small manufacturers who have not previously certified an 
engine in California,
    3. Allowing good engineering judgment to correlate the CARB OBD 
standards with EPA OBD standards,
    4. Clarifying that engines must comply with OBD requirements 
throughout EPA's useful life as specified in 40 CFR 1036.104, which may 
differ from CARB's required useful life for some model years,
    5. Clarifying that the purpose and applicability statements in 13 
CCR 1971.1(a) and (b) do not apply,
    6. Not requiring the manufacturer self-testing and reporting 
requirements in 13 CCR 1971.1(l)(4) ``Verification of In-Use 
Compliance'' and 1971.5(c) ``Manufacturer Self-Testing'' (note, in the 
proposal we inadvertently cited incorrect CARB provisions for the 
intended referenced requirements),
    7. Retaining our existing deficiency policy (which we are also 
migrating into 40 CFR 1036.110(d)), adjusting our deficiency timing 
language to match CARB's, and specifying that the deficiency provisions 
in 13 CCR 1971.1(k) do not apply,
    8. Requiring additional freeze frame data requirements (as further 
explained in Section IV.C.1.iii),
    9. Requiring additional data stream parameters for compression- and 
spark-ignition engines (as further explained in Section IV.C.1.iii), 
and
    10. Providing flexibilities to reduce redundant demonstration 
testing requirements for engines certified to CARB OBD requirements.
    With regard to the second through the fifth items, EPA is 
finalizing these requirements as proposed for the reasons stated in the 
proposal. For the sixth item, EPA is finalizing this requirement for 
the reasons stated in the proposal and as proposed with the exception 
of a correction to the CARB reference we cited.
    EPA received supportive comment from manufacturers on our proposal 
to migrate our existing deficiency requirements, and adverse comment 
from manufacturers and CARB requesting that EPA harmonize with CARB's 
retroactive deficiency provisions. CARB's deficiency requirements are 
described in 13 CCR 1971.1(k) and include descriptions of requirements 
such as how deficiencies are granted, fines charged for deficiencies, 
allowable timelines, and the application of retroactive deficiencies. 
We are finalizing as proposed to migrate our existing approach to 
deficiency provisions in 40 CFR 86.010-18(n) into 40 CFR 
1036.110(d).\354\ See section 7.1 of the Response to Comments for 
further details on comments received and EPA's responses.
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    \354\ See 74 FR 8310, 8349 (February 24, 2009).
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    EPA also received comment concerned with EPA's regulatory language 
describing the allowable timeframe for deficiencies. Commenters said 
EPA's proposed deficiency timeline is shorter than CARB's and that EPA 
should harmonize with CARB and provide manufacturers with 3 years to 
make hardware-related changes. EPA is finalizing a change to 40 CFR 
1036.110(d)(3) to ensure our language is consistent with CARB's 
deficiency timeline in 13 CCR 1971.1(k)(4).
    EPA received supportive and adverse comment on the proposal to 
require additional freeze frame data requirements, including that the 
reference in our regulations was overly broad and possibly in error. 
EPA is finalizing these requirements with revisions to those proposed 
in 40 CFR 1036.110(b)(8) to be more targeted. It is critical for there 
to be sufficient emissions-related parameters captured in freeze frame 
data to enable proper repairs.
    EPA received supportive and adverse comment on the proposal to 
require additional data stream parameter requirements, including 
comment that our regulations needed to be more specific. EPA is 
finalizing these requirements with revisions to those proposed in 40 
CFR 1036.110(b)(9) to properly capture the additional elements we 
intended to add to the freeze frame and to ensure these additional 
parameters are interpreted properly as an expansion of the existing 
data stream requirements in 13 CCR 1971.1(h)(4.2). Access to important 
emissions-related data parameters is critical for prompt and proper 
repairs.
    EPA is finalizing flexibilities to reduce redundant demonstration 
testing requirements for engines certified to CARB OBD requirements, 
see section IV.C.1.iv. of this preamble for further discussion on what 
we are finalizing.
    It is important to emphasize that by not incorporating certain 
existing CARB OBD requirements (e.g., the ``Manufacturer Self-Testing'' 
requirements) into our regulations, we are not waiving our authority to 
require such testing on a case-by-case basis. CAA section 208 gives EPA 
broad authority to require manufacturers to perform testing not 
specified in the regulations in such circumstances. Thus, should we 
determine in the future that such testing is needed, we would retain 
the authority to require it pursuant to CAA section 208.
ii. OBD Threshold Requirements
a. Malfunction Criteria Thresholds
    Existing OBD requirements specify how OBD systems must monitor 
certain components and indicate a malfunction prior to when emissions 
would exceed emission standards by a certain amount, known as an 
emission threshold. Emission thresholds for these components under the 
existing requirements in the 2019 CARB OBD update that we are 
incorporating by reference are generally either an additive or 
multiplicative value above the applicable exhaust emission standard. 
EPA proposed to modify the threshold requirements in the 2019 CARB OBD 
update to be consistent with the provisions finalized by CARB in their 
Omnibus rule in December of 2021 and not tighten threshold requirements 
while finalizing lower emission standards.\355\ \356\ This meant, for 
example, that for monitors required to detect a malfunction before 
NOX emissions exceed 1.75 times the applicable existing 
NOX standard, the manufacturer would continue to use the 
same numeric threshold (e.g., 0.35 g/bhp-hr NOX) for the new 
emission standards finalized in this rule.
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    \355\ California Air Resources Board. Staff Report: Addendum to 
the Final Statement of Reasons for Rulemaking--Public Hearing to 
Consider the Proposed Heavy-Duty Engine and Vehicle Omnibus 
Regulation and Associated Amendments. December 20, 2021. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2020/hdomnibuslownox/fsoraddendum.pdf.
    \356\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule; note, we are making no 
determination in this action about the appropriateness of these 
provisions for CARB's regulation.
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    EPA received comments from manufacturers and operators in support

[[Page 4373]]

of finalizing the threshold provisions as proposed, and a comment from 
CARB stating that three engine families have recently been certified to 
lower FELs indicating EPA should finalize lower thresholds. We note 
that CARB stated that two of these engine families were certified with 
deficiencies, and thus these engines did not fully meet all specific 
OBD requirements (see section 7.1 of the Response to Comment for 
further detail about these comments and EPA's responses). EPA is 
finalizing with minor revision future numerical values for OBD 
NOX and PM thresholds that align with the numerical value 
that results under today's NOX and PM emissions 
requirements.
    We are finalizing as proposed a NOX threshold of 0.40 g/
hp-hr and a PM threshold of 0.03 g/hp-hr for compression-ignition 
engines for operation on the FTP and SET duty cycles. We are finalizing 
as proposed a PM threshold of 0.015 g/hp-hr for spark-ignition engines 
for operation on the FTP and SET duty cycles. For spark-ignition 
engines, we proposed NOX thresholds of 0.30 and 0.35 g/hp-hr 
for monitors detecting a malfunction before NOX emissions 
exceed 1.5 and 1.75 times the applicable standard, respectively. We are 
finalizing these numeric threshold values without reference to what 
percent exceedance is relevant and instead are clarifying that the 
0.35g/hp-hr standard applies for catalyst monitors and that 0.30g/hp-hr 
applies for all other monitors, to ensure the proper numeric thresholds 
can be applied to engines certified under 13 CCR 1968.2 and 1971.1.. 
EPA intends to continue to evaluate the capability of HD OBD monitors 
to accommodate lower thresholds to correspond to the lower emission 
levels for the final emission standards and may consider updating 
threshold requirements in the future as more in-use data becomes 
available.
    We also inadvertently omitted from the proposed 40 CFR 1036.110(b) 
the specific threshold criteria for SI and CI engine HC and CO 
emissions that coincided with our overall expressed intent to harmonize 
with the threshold requirements included in CARB's Omnibus rule and not 
tighten OBD emission thresholds.\357\ Consistent with this intent, we 
are finalizing a provision in 40 CFR 1036.110(b)(5) that instructs 
manufacturers to use numeric values that correspond to existing HC and 
CO standards (0.14 g/hp-hr for HC, 15.5 g/hp-hr for CO from 
compression-ignition engines, and 14.4 g/hp/hr for spark-ignition 
engines) to determine the required thresholds. Applying this 
methodology will result in calculations that produce thresholds 
equivalent to existing thresholds. Including this clarification avoids 
unintentionally lowering such thresholds.
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    \357\ While CARB standards refer to nonmethane hydrocarbon 
standards as ``NMHC'' EPA's regulation refers to ``HC'' generically 
for such standards, but we define HC in 40 CFR 1036.104 to be NMHC 
for gasoline- and diesel-fueled engines.
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b. Test-Out Criteria
    CARB OBD requirements include ``test-out'' provisions in 13 CCR 
1968.2 and 1971.1 which allow manufacturers to be exempt from 
monitoring certain components if failure of these components meets 
specified criteria.\358\ EPA is adopting these test-out provisions 
through the incorporation by reference of CARB's updated 2019 OBD 
requirements. Similar to the revisions we proposed and are finalizing 
for malfunction criteria, EPA's assessment is that for compression 
ignition engines test-out criteria should also not be tightened at this 
time. However, we inadvertently omitted from the proposed 40 CFR 
1036.110(b) the specific adjustments to test-out criteria for 
compression-ignition engines included in CARB's Omnibus rule that are 
necessary to result in such criteria not being tightened. Consistent 
with our overall expressed intent to (1) not tighten OBD requirements, 
and (2) modify the 2019 CARB requirements we are adopting by 
harmonizing with the numeric values included in CARB's Omnibus rule, we 
are finalizing a revision from the proposal to include test-out 
criteria calculation instructions into our regulations.
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    \358\ ``Test-out'' provisions may be identified in CARB OBD 
regulations specifically as ``test-out'' requirements or through 
language describing that certain components or systems are ``exempt 
from monitoring'' if manufacturers can demonstrate certain 
conditions are met.
---------------------------------------------------------------------------

    Specifically, we are finalizing a provision that manufacturers 
seeking to use the test-out criteria to exempt engines from certain 
monitoring in the incorporated by reference 2019 CARB regulations 13 
CCR 1968.2 and 1971.1 must calculate the criteria based on specified 
values provided in 40 CFR 1036.110(b)(5). For example, 13 CCR 
1971.1(e)(3.2.6) specifies that one of the requirements for an EGR 
catalyst to be exempt from monitoring is if no malfunction of the EGR 
catalyst can cause emissions to increase by 15 percent or more of the 
applicable standard as measured from the appropriate test cycle. The 
requirement we are finalizing in 40 CFR 1036.110(b)(5) instructs 
manufacturers to use specific values for that ``applicable standard'' 
to calculate the required test-out criteria. For example, for the EGR 
catalyst test-out provision, this would result in a NOX 
test-out criterion of 0.03 g/hp-hr (0.2 g/hp-hr  0.15). 
Including this provision is consistent with the intent of our proposal 
and avoids unintentionally lowering such test-out criteria that would 
render such test-out criteria generally inconsistent with the other 
provisions we are finalizing in 40 CFR 1036.110(b)(5), and enables 
manufacturers to continue using these provisions.
c. Applicable Thresholds for Engines Certified to 40 CFR Part 1036 Used 
in Heavy-Duty Vehicles Less Than 14,000 Pounds GVWR
    We are finalizing as proposed that engines installed in vehicles at 
or below 14,000 lbs GVWR are subject to OBD requirements under the 
light-duty program in 40 CFR 86.1806-17. Commenters pointed out that 
the proposed rule did not specify alternative thresholds for engines 
certified to 40 CFR part 1036 on an engine dynamometer that are subject 
to OBD requirements under 40 CFR 86.1806-17. Without such a provision, 
manufacturers would be subject to the existing thresholds in 40 CFR 
86.1806-17 that are based on standards set for light-duty chassis-
certified vehicles. Consistent with our statements in the NPRM that our 
proposal intended to harmonize with the threshold requirements included 
in CARB's Omnibus policy and not lower emission threshold levels in our 
proposed OBD regulations, we are clarifying in 40 CFR 86.1806-17(b)(9) 
that the thresholds we are finalizing in 40 CFR 1036.110(b)(5) apply 
equally for engines certified under 40 CFR part 1036 that are used in 
vehicles at or below 14,000 lbs GVWR.
iii. Additional OBD Provisions in the Proposed Federal Program
    In the NPRM, EPA proposed to include additional requirements to 
ensure that OBD can be used to properly diagnose and maintain emission 
control systems to avoid increased real-world emissions. This was also 
a part of our effort to update EPA's OBD program and respond to 
numerous concerns raised in the ANPR about the difficulty of diagnosing 
and maintaining proper functionality of advanced emission control 
technologies and the important role accessible and robust diagnostics 
play in this process. At this time, after consideration of comments, we 
are finalizing a limited set of these proposed provisions (see section 
7 of the Response to Comments documents for further detail on comments 
and

[[Page 4374]]

EPA's responses). Where OBD requirements between EPA and CARB may 
differ, EPA is finalizing as proposed provisions allowing us to accept 
CARB OBD approval as long as a manufacturer can demonstrate that the 
CARB program meets the intent of EPA OBD requirements and submits 
documentation as specified in 40 CFR 1036.110(b).
    In this section we describe the final additional EPA certification 
requirements in 40 CFR 1036.110 for OBD systems, which, consistent with 
CAA section 202(m),\359\ are intended to provide more information and 
value to the operator and play an important role in ensuring expected 
in-use emission reductions are achieved long-term. With respect to our 
proposed provisions to require additional information from OBD systems 
be made publicly available, we received supportive comments from 
operators and adverse comments from manufacturers. After considering 
these comments, we are revising our final provision from those 
proposed, as summarized here and provide in more detail in section 7 of 
the Response to Comments document. We are not taking final action at 
this time on the proposed requirement to include health monitors. In 
addition to driver information requirements we are adopting to increase 
the availability of serviceability and inducement-related information 
(see section IV.B.3 and IV.D.3 respectively of this preamble), we are 
also finalizing in 40 CFR 1036.110(c) that the following information 
must be made available in the cab on-demand in lieu of the proposed 
health monitors:
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    \359\ For example, CAA section 202(m)(5) specifies that by 
regulation EPA shall require (subject to an exception where 
information is entitled to protection as trade secrets) 
manufacturers to provide promptly to any person engaged in the 
repairing or servicing of heavy-duty engines with any and all 
information needed to make use of the emission control diagnostics 
system required under CAA section 202 and such other information 
including instructions for making emission related diagnosis and 
repairs.
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     The total number of diesel particulate filter regeneration 
events that have taken place since installing the current particulate 
filter.
     Historical and current rate of DEF consumption (e.g., 
gallons of DEF consumed per mile or gallons of DEF consumed per gallon 
of diesel fuel consumed.) This information is designed such that 
operators can reset it as needed to capture specific data for 
comparison purposes.
     For AECD conditions (outside of inducements) related to 
SCR or DPF systems that derate the engine (e.g., either a speed or 
torque reduction), the fault code for the detected problem, a 
description of the fault code, and the current restriction.
    For all other health monitor provisions proposed in 40 CFR 
1036.110(c)(3), we are not taking final action on those proposed 
provisions at this time.
    In addition to incorporating an improved list of publicly available 
data parameters by harmonizing with updated CARB OBD requirements, in 
40 CFR 1036.110(b)(9) EPA is finalizing as proposed for the reasons 
explained further in the proposal to add signals to the list, including 
to specifically require that all parameters related to fault conditions 
that trigger vehicle inducement also be made readily available using 
generic scan tools. EPA expects that each of these additional 
requirements will be addressed even where manufacturers relied in part 
on a CARB OBD approval to satisfy Federal requirements in order to 
demonstrate under 40 CFR 1036.110(b) that the engine meets the intent 
of 40 CFR 1036.110. The purpose of including additional parameters is 
to make it easier to identify malfunctions of critical aftertreatment 
related components, especially where failure of such components would 
trigger an inducement. We are revising the proposed new parameters for 
HD SI engines in 40 CFR 1036.110(b)(10) after considering comments. See 
section 3 of the Response to Comments.
    We are also finalizing a general requirement in 40 CFR 
1036.110(b)(9)(vi) to make all parameters available that are used as 
the basis for the decision to put a vehicle into an SCR- or DPF-related 
derate. For example, if the failure of an open-circuit check for a DEF 
quality sensor leads to an engine inducement, the owner/operator would 
be able to identify this fault condition using a generic scan tool. We 
are finalizing a requirement that manufacturers make additional 
parameters available for all engines so equipped,\360\ including:
---------------------------------------------------------------------------

    \360\ Memorandum to Docket EPA-HQ-OAR-2019-0055: ``Example 
Additional OBD Parameters''. Neil Miller, Amy Kopin. November 21, 
2022.
---------------------------------------------------------------------------

      For Compression Ignition engines:

[cir] Inlet DOC and Outlet DOC pressure and temperature
[cir] DPF Filter Soot Load (for all installed DPFs)
[cir] DPF Filter Ash Load (for all installed DPFs)
[cir] Engine Exhaust Gas Recirculation Differential Pressure
[cir] DEF quality-related signals
[cir] Parking Brake, Neutral Switch, Brake Switch, and Clutch Switch 
Status
[cir] Aftertreatment Dosing Quantity Commanded and Actual
[cir] Wastegate Control Solenoid Output
[cir] Wastegate Position Commanded and Actual
[cir] DEF Tank Temperature
[cir] DEF Doser Control Status
[cir] DEF System Pressure
[cir] DEF Pump Commanded Percentage
[cir] DEF Coolant Control Valve Control Position Commanded and Actual
[cir] DEF Line Heater Control Outputs
[cir] Speed and output shaft torque consistent with 40 CFR 1036.115(d)

     For Spark Ignition Engines:

[cir] Air/Fuel Enrichment Enable flags: Throttle based, Load based, 
Catalyst protection based
[cir] Percent of time not in stoichiometric operation (including per 
trip and since new)

    One of the more useful features in the CARB OBD program for 
diagnosing and repairing emissions components is the requirement for 
``freeze frame'' data to be stored by the system. To comply with this 
requirement, manufacturers must capture and store certain data 
parameters (e.g., vehicle operating conditions such as the 
NOX sensor output reading) within 10 seconds of the system 
detecting a malfunction. The purpose of storing this data is in part to 
record the likely area of malfunction. EPA is finalizing a requirement 
in 40 CFR 1036.110(b)(8) to require that manufacturers capture the 
following elements as freeze frame data: Those data parameters 
specified in 1971.1(h)(4.2.3)(E), 1971.1(h)(4.2.3)(F), and 
1971.1(h)(4.2.3)(G). We are also specifying that these additional 
parameters would be added according to the specifications in 13 CCR 
1971.1(h)(4.3). EPA believes this is essential information to make 
available to operators for proper maintenance.
iv. Demonstration Testing Requirements
    Existing requirements of 40 CFR 86.010-18(l) and 13 CCR 1971.1(l) 
specify the number of test engines for which a manufacturer must submit 
monitoring system demonstration emissions data. Specifically, a 
manufacturer certifying one to five engine families in a given model 
year must provide emissions test data for a single test engine from one 
engine rating, a manufacturer certifying six to ten engine families in 
a given model year must provide emissions test data for a single test 
engine from two different engine ratings, and a manufacturer certifying 
eleven or more engine families in a given model year must provide 
emissions test data for a single test engine from three different 
engine ratings.
    EPA received supportive and adverse comment on a proposed 
flexibility to

[[Page 4375]]

reduce redundant demonstration testing requirements for certain engines 
where an OBD system designed to comply with California OBD requirements 
is being used in both a CARB proposed family and a proposed EPA-only 
family and the two families are also identical in all aspects material 
to expected emission characteristics. EPA issued guidance last year on 
this issue.\361\ We are finalizing as proposed to codify this guidance 
as a provision, subject to certain information submission requirements 
for EPA to evaluate if this provision's requirements have been met, for 
model years 2027 and later engines in 40 CFR 1036.110(b)(11). 
Manufacturers may also use the flexibility in earlier model years. More 
specifically, we are finalizing the provision as proposed to count two 
equivalent engines families as one for the purposes of determining OBD 
demonstration testing requirements, where equivalent means they are 
identical in all aspects material to emission characteristics, as such, 
testing is not necessary to ensure a robust OBD program. 40 CFR 
1036.110(b)(11) requires manufacturers to submit additional information 
as needed to demonstrate that the engines meet the requirements of 40 
CFR 1036.110 that are not covered by the California Executive order, as 
well as results from any testing performed for certifying engine 
families (including equivalent engine families) with the California Air 
Resources Board and any additional information we request as needed to 
evaluate whether the requirements of this provision are met.
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    \361\ EPA Guidance Document CD-2021-04 (HD Highway), April 26, 
2021, ``Information on OBD Monitoring System Demonstration for Pairs 
of EPA and CARB Families Identical in All Aspects Other Than 
Warranty.'' Available here:  https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=52574&flag=1.
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    We took comment on and are finalizing language that this 
flexibility will apply for cases where equivalent engine families also 
have different inducement strategies. We are aware that the auxiliary 
emission control devices (AECDs) needed to implement the engine 
derating associated with inducements do not affect engine calibrations 
in a way that would prevent OBD systems from detecting when emissions 
exceed specified levels. Rather, those AECDs simply limit the range of 
engine operation that is available to the driver. Thus, testing of 
different inducement strategies in these AECDs would also not be 
necessary to ensure a robust OBD program and we would consider such 
differences between engines to not be material to emission 
characteristics relevant to these OBD testing requirements. Any 
difference in impacts between the engines would be a consequence of the 
driver's response to the inducement itself, which could also occur even 
with the same inducement strategy, rather than a difference in the 
functioning of the OBD systems in the engines. In that way, inducements 
are analogous to warranty for purposes of counting engine families for 
OBD testing requirements. See section 8 of the Response to Comments for 
details on the comments received and EPA's responses.
v. Use of CARB OBD Approval for EPA OBD Certification
    Existing EPA OBD regulations allow manufacturers seeking an EPA 
certificate of conformity to comply with the Federal OBD requirements 
by demonstrating to EPA how the OBD system they have designed to comply 
with California OBD requirements also meets the intent behind Federal 
OBD requirements, as long as the manufacturer complies with certain 
certification documentation requirements. EPA has implemented these 
requirements by allowing a manufacturer to submit an OBD approval 
letter from CARB for the equivalent engine family where a manufacturer 
can demonstrate that the CARB OBD program has met the intent of the EPA 
OBD program. In other words, EPA has interpreted these requirements to 
allow OBD approval from CARB to be submitted to EPA for approval. We 
are finalizing as proposed to migrate the language from 40 CFR 86.010-
18(a)(5) to 40 CFR 1036.110(b) to allow manufacturers to continue to 
use a CARB OBD approval letter to demonstrate compliance with Federal 
OBD regulations for an equivalent engine family where manufacturers can 
demonstrate that the CARB OBD program has met the intent of the EPA OBD 
program.
    To demonstrate that your engine meets the intent of EPA OBD 
requirements, we are finalizing as proposed that the OBD system must 
address all the provisions described in 40 CFR 1036.110(b) and (c) and 
adding clarification in 40 CFR 1036.110(b) that manufacturers must 
submit information demonstrating that all EPA requirements are met. In 
the case where a manufacturer chooses not to include information 
showing compliance with additional EPA OBD requirements in their CARB 
certification package (e.g., not including the additional EPA data 
parameters in their CARB certification documentation), EPA expects 
manufacturers to provide separate documentation along with the CARB OBD 
approval letter to show they have met all EPA OBD requirements. This 
process also applies in potential future cases where CARB has further 
modified their OBD requirements such that they are different from but 
meet the intent of existing EPA OBD requirements. EPA expects 
manufacturers to submit documentation as is currently required by 40 
CFR 86.010-18(m)(3), detailing how the system meets the intent of EPA 
OBD requirements and information on any system deficiencies. As a part 
of this update to EPA OBD regulations, we are clarifying as proposed in 
40 CFR 1036.110(b)(11)(iii) that we can request that manufacturers send 
us information needed for us to evaluate how they meet the intent of 
our OBD program using this pathway. This would often mean sending EPA a 
copy of documents submitted to CARB during the certification process.
vi. Use of the SAE J1979-2 Communications Protocol
    In a February 2020 workshop, CARB indicated their intent to propose 
allowing the use of Unified Diagnostic Services (``UDS'') through the 
SAE J1979-2 communications protocol for heavy-duty OBD with an optional 
implementation as early as MY 2023.\362 363\ The CARB OBD update that 
includes this UDS proposal has not yet been finalized, but was 
submitted to California's Office of Administrative Law for approval in 
July of 2022.\364\ CARB stated that engine manufacturers are concerned 
about the limited number of remaining undefined 2-byte diagnostic 
trouble codes (``DTC'') and the need for additional DTCs for hybrid 
vehicles. SAE J1979-2 provides 3-byte DTCs, significantly increasing 
the number of DTCs that can be defined. In addition, this change would 
provide additional features for data access that improve the usefulness 
of generic scan tools to repair vehicles.
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    \362\ SAE J1979-2 was issued on April 22, 2021 and is available 
here: https://www.sae.org/standards/content/j1979-2_202104/.
    \363\ CARB Workshop for 2020 OBD Regulations Update, February 
27, 2020. Available here: https://ww3.arb.ca.gov/msprog/obdprog/obd_feb2020wspresentation.pdf.
    \364\ CARB Proposed Revisions to the On-Board Diagnostic System 
Requirements and Associated Enforcement Provisions for Passenger 
Cars, Light-Duty Trucks, Medium-Duty Vehicles and Engines, and 
Heavy-Duty Engines, available: https://ww2.arb.ca.gov/rulemaking/2021/obd2021.
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    This update has not been finalized by CARB in time for us to 
include it in this final rule. In consideration of manufacturers who 
want to certify their engine families in the future for

[[Page 4376]]

nationwide use, and after consideration of expected environmental 
benefits associated with the use of this updated protocol, we are 
finalizing as proposed a process for reviewing and approving 
manufacturers' requests to comply using the alternative communications 
protocol.
    While EPA believes our existing requirements in 40 CFR 86.010-
18(a)(5) allow us to accept OBD systems using SAE J1979-2 that have 
been approved by CARB, there may be OEMs that want to obtain an EPA-
only certificate (i.e., does not include certification to California 
standards) for engines that do not have CARB OBD approval for MYs prior 
to MY 2027 (i.e., prior to when the 40 CFR part 1036 OBD provisions of 
this final rule become mandatory). EPA is finalizing as proposed to 
allow the use of SAE J1979-2 for manufacturers seeking EPA OBD 
approval. We are adopting this as an interim provision in 40 CFR 
1036.150(v) to address the immediate concern for model year 2026 and 
earlier engines. Once EPA's updated OBD requirements are in effect for 
MY 2027, we expect to be able to allow the use of SAE J1979-2 based on 
the final language in 40 CFR 1036.110(b); however, we do not specify an 
end date for the provision in 40 CFR 1036.150(v) to make sure there is 
a smooth transition toward using SAE J1979-2 for model years 2027 and 
later. This provides manufacturers the option to upgrade their OBD 
protocol to significantly increase the amount of OBD data available to 
owners and repair facilities.
    CAA section 202(m)(4)(C) requires that the output of the data from 
the emission control diagnostic system through such connectors shall be 
usable without the need for any unique decoding information or device, 
and it is not expected that the use of SAE J1979-2 would conflict with 
this requirement. Further, CAA section 202(m)(5) requires manufacturers 
to provide promptly to any person engaged in the repairing or servicing 
of motor vehicles or motor vehicle engines, and the Administrator for 
use by any such persons, with any and all information needed to make 
use of the emission control diagnostics system prescribed under this 
subsection and such other information including instructions for making 
emission related diagnosis and repairs. Manufacturers that voluntarily 
use J1979-2 as early as MY 2022 under interim provision 40 CFR 
1036.150(v) would need to provide access to systems using this 
alternative protocol at that time and meet all the relevant 
requirements in 40 CFR 86.010-18 and 1036.110. EPA did not receive 
adverse comment on the availability of tools that can read the new 
protocol from manufacturers or tool providers. CARB commented that 
staff anticipates tool vendors will be able to fully support the SAE 
J1979-2 protocol at a fair and reasonable price for the vehicle repair 
industry and consumers.
2. Cost Impacts
    Heavy-duty engine manufacturers currently certify their engines to 
meet CARB's OBD regulations before obtaining EPA certification for a 
50-state OBD approval. We anticipate most manufacturers will continue 
to certify with CARB and that they will certify to CARB's 2019 updated 
OBD regulations well in advance of the EPA program taking effect; 
therefore, we anticipate the incorporation by reference of CARB's 2019 
OBD requirements will not result in any additional costs. EPA does not 
believe the additional OBD requirements described here will result in 
any significant costs, as there are no requirements for: New monitors, 
new data parameters, new hardware, or new testing included in this 
rule. However, EPA has accounted for possible additional costs that may 
result from the final expanded list of public OBD parameters in the 
``Research and Development Costs'' of our cost analysis in Section V. 
EPA recognizes that there could be cost savings associated with reduced 
OBD testing requirements under final 40 CFR 1036.110(c)(11). For 
example, cost savings could come from the provision to not count engine 
families certified separately by EPA and CARB, but otherwise identical 
in all aspects material to expected emission characteristics, as 
different families when determining OBD demonstration testing (see 
section IV.C.1.iv of this document for further discussion on this 
provision). This potential reduction in demonstration testing burden 
could reduce costs such as labor and test cell time. However, 
manufacturers may choose not to certify engine families in this manner 
which would not translate to cost savings. Therefore, given the 
uncertainty in the potential for savings, we did not quantify the costs 
savings associated with this final provision.
D. Inducements
    Manufacturers have deployed urea-based SCR systems to meet the 
existing heavy-duty engine emission standards. EPA anticipates that 
manufacturers will continue to use this technology to meet the new 
NOX standards finalized in this rule. SCR is very different 
from other emission control technologies in that it requires operators 
to maintain an adequate supply of diesel exhaust fluid (DEF), which is 
generally a water-based solution with 32.5 percent urea. Operating an 
SCR-equipped engine without DEF or certain components like an SCR 
catalyst could cause NOX emissions to increase to levels 
comparable to having no NOX controls at all.
    The proposed rule described two key aspects of how our regulations 
currently require manufacturers to ensure engines will operate with an 
adequate supply of high-quality DEF, which we proposed to update and 
further codify. First, manufacturers currently must demonstrate 
compliance with our critical emissions-related schedule maintenance 
requirements, including 40 CFR 86.004-25(b). EPA has approved DEF 
refills as part of manufacturers' scheduled maintenance. EPA's approval 
is conditioned on manufacturers demonstrating that operators are 
reasonably likely to perform such maintenance. Manufacturers have 
consistently made this demonstration by designing their engines to go 
into a disabled mode that decreases a vehicle's maximum speed if the 
engine detects that operators are failing to provide an adequate supply 
of DEF. More specifically, manufacturers have generally complied by 
programming engines to restrict peak vehicle speeds after detecting 
that such maintenance has not been performed or detecting that 
tampering with the SCR system may have occurred. We refer to this 
strategy of derating engine power and vehicle speed as an 
``inducement.''
    Second, EPA's current regulations in 40 CFR 86.094-22(e) require 
that manufacturers comply with emission standards over the full 
adjustable range of ``adjustable parameters,'' and that, in determining 
the parameters subject to adjustment, EPA considers the likelihood that 
settings other than the manufacturer's recommended setting will occur 
in-use, including the effect of settings other than the manufacturer's 
recommended settings on engine performance. We have historically 
considered DEF level and quality as parameters that can be physically 
adjusted and may significantly affect emissions. EPA generally has 
approved manufacturers strategies consistent with guidance that 
described recommendations on ways manufacturers could meet adjustable 
parameter requirements when using SCR systems.\365\ This guidance 
states that manufacturers should demonstrate that operators are being 
made aware that DEF needs to be replaced through warnings and vehicle 
performance

[[Page 4377]]

deterioration that should not create undue safety concerns but be 
onerous enough to discourage drivers from operating without DEF (i.e., 
through inducement). See the proposed rule preamble for further 
background and discussion of the basis of EPA's proposed inducement 
regulations.
---------------------------------------------------------------------------

    \365\ See CISD-09-04 REVISED.
---------------------------------------------------------------------------

    With some modification from the proposal, EPA is adopting final 
inducement regulations in this final rule. The regulatory provisions 
also include changes compared to existing inducement guidance after 
consideration of manufacturer designs and operator experiences with SCR 
over the last several years. The inducement requirements included in 
this final rule supersede the existing guidance and are mandatory 
beginning in MY 2027 and voluntary prior to that and are intended to-
     Ensure that all critical emission-related scheduled 
maintenance has a reasonable likelihood of being performed while also 
deterring tampering of the SCR system.
     Set an appropriate inducement speed derating schedule that 
reflects experience gained over the past decade with SCR systems.
     Recognize the diversity of the real-world fleet with 
derate schedules that are tailored to a vehicle's operating 
characteristics.
     Improve the type and amount of information operators 
receive from the vehicle to both understand inducement actions and to 
help avoid or quickly remedy a problem that is causing an inducement.
     Allow operators to perform an inducement reset by using a 
generic scan tool or allowing for the engine to self-heal during normal 
driving.
     Address operator frustration with false inducements and 
low inducement speed restrictions that occur quickly, in part due to 
concern that such frustration may potentially lead to in-use tampering 
of the SCR system.
    This final rule includes several changes from the proposed rule 
after consideration of numerous comments. See section 8 of the Response 
to Comments for the detailed comments and EPA's response to those 
comments, including further discussion of the changes in the final rule 
compared to the proposed rule. As an overview, EPA is adopting as a 
maintenance requirement, as proposed, in 40 CFR 1036.125(a)(1) that 
manufacturers must meet the specifications in new 40 CFR 1036.111, 
which contains requirements for inducements related to SCR, to 
demonstrate that timely replenishment with high-quality DEF is 
reasonably likely to occur on in-use engines and that adjustable 
parameter requirements will be met. Specifically, EPA is finalizing as 
proposed to specify in 40 CFR 1036.115(f) that DEF supply and DEF 
quality are adjustable parameters. Regarding DEF supply, we are 
finalizing as proposed that the physically adjustable range includes 
any amount of DEF that the engine's diagnostic system does not 
recognize as a fault condition under new 40 CFR 1036.111. We are 
adopting a requirement under new 40 CFR 1036.115(i) for manufacturers 
to size DEF tanks corresponding to refueling events, which is 
consistent with the regulation we are replacing under 40 CFR 86.004-
25(b)(4)(v). Under the final requirements, manufacturers can no longer 
use the alternative option in 40 CFR 86.004-25(b)(6)(ii)(F) to 
demonstrate high-quality DEF replenishment is reasonably likely to be 
performed in use. As described in the proposed rule, EPA plans to 
continue to rely on the existing guidance in CD-13-13 that describes 
how manufacturers of heavy-duty highway engines determine the 
practically adjustable range for DEF quality. We inadvertently proposed 
to require that manufacturers use the physically adjustable range for 
DEF quality as the basis for defining a fault condition for inducements 
under 40 CFR 1036.111. Since we intended for the existing guidance to 
addresses issues related to the physically adjustable range for DEF 
quality, we are not finalizing the proposed provision in 40 CFR 
1036.115(f)(2) for DEF quality. EPA intends further consider the 
relationship between inducements and the practically adjustable range 
for DEF quality and may consider updating this guidance in the future.
    EPA is adopting requirements that inducements be triggered for 
three types of fault conditions: (1) DEF supply is low, (2) DEF quality 
does not meet manufacturer specifications, or (3) tampering with the 
SCR system. EPA is not taking final action at this time on the proposed 
requirement for manufacturers to include a NOX override to 
prevent false inducements. After consideration of public comments, the 
final inducement provisions at 40 CFR 1036.111 include updates from the 
proposed inducement schedules; more specifically, EPA is adopting 
separate inducement schedules for low-, medium-, and high-speed 
vehicles. EPA is also finalizing requirements for manufacturers to 
improve information provided to operators regarding inducements. The 
final rule also includes a requirement for manufacturers to design 
their engines to remove inducements after proper repairs are made, 
through self-healing or with the use of a generic scan tool to ensure 
that operators have performed the proper maintenance.
    These requirements apply starting in MY 2027, though manufacturers 
may optionally comply with these 40 CFR part 1036 requirements in lieu 
of provisions that apply under 40 CFR part 86 early. The following 
sections describe the inducement requirements for the final rule in 
greater detail.
1. Inducement Triggers
    Three types of fault conditions trigger inducements under 40 CFR 
1036.111. The first triggering condition is DEF quantity. Specifically, 
we require that SCR-equipped engines trigger an inducement when the 
amount of DEF in the tank has been reduced to a level corresponding to 
three remaining hours of engine operation. This triggering condition 
ensures that operators will be compelled to perform the necessary 
maintenance before the DEF supply runs out, which would cause emissions 
to increase significantly.
    The second triggering condition is DEF quality failing to meet 
manufacturer concentration specifications. This triggering condition 
ensures high quality DEF is used.
    Third, EPA is requiring inducements to ensure that SCR systems are 
designed to be tamper-resistant. We are requiring that manufacturers 
design their engines to monitor for and trigger an inducement for open-
circuit fault conditions for the following components: (1) DEF tank 
level sensor, (2) DEF pump, (3) DEF quality sensor, (4) SCR wiring 
harness, (5) NOX sensors, (6) DEF dosing valve, (7) DEF tank 
heater, (8) DEF tank temperature sensor, and (9) aftertreatment control 
module (ACM). EPA is also requiring that manufacturers monitor for and 
trigger an inducement if the OBD system has any signal indicating that 
a catalyst is missing (see OBD requirements for this monitor in 13 CCR 
1971.1(i)(3.1.6)). This list is the same as the list from the proposed 
rule, with two exceptions after consideration of comments. First, we 
are adding the DEF tank temperature sensor in the final rule. This 
additional sensor is on par with the DEF tank heater for ensuring that 
SCR systems are capable of monitoring for freezing conditions. Second, 
in consideration of comment, we are removing blocked DEF lines or 
dosing valves as a triggering condition because such a condition could 
be caused by crystallized DEF rather than any operator action and thus 
is not directly related to protecting against tampering with the SCR-
system. We believe this standardized list of required

[[Page 4378]]

tampering inducement triggers will be important for owners, operators, 
and fleets in repairing their vehicles by avoiding excessive cost and 
time to determine the reason for inducement.
2. Derate Schedule
    We are finalizing a different set of schedules than we proposed. 
First, we are adding a new category for medium-speed vehicles. Second, 
we are adjusting the low-speed category to have a lower final speed 
compared to the proposal and a lower average operating speed to 
identify this category. Third, we increased the average operating speed 
that qualifies a vehicle to be in the high-speed category. We are 
adopting derate schedules for low-, medium- and high-speed vehicles as 
shown in Table IV-13. Similar to the proposal, we differentiate these 
three vehicle categories based on a vehicle's calculated average speed 
for the preceding 30 hours of non-idle operation. Low-speed vehicles 
are those with an average operating speed below 15 mph. Medium-speed 
vehicles are those with average operating speeds at or above 15 and 
below 25 mph. High-speed vehicles are those with average operating 
speeds at or above 25 mph. Excluding idle from the calculation of 
vehicle speed allows us to more effectively evaluate each vehicle's 
speed profile; in contrast, time spent at idle would not help to give 
an indication of a vehicle's operating characteristics for purposes of 
selecting the appropriate derate schedule. EPA chose these final speeds 
after consideration of stakeholder comments (see section 8.3 of the 
Response to Comments for further information on comments received) and 
an updated analysis of real-world vehicle speed activity data from the 
FleetDNA database maintained by the National Renewable Energy 
Laboratory (NREL).366 367 Our analyses provided us with 
insight into the optimum way to characterize vehicles in a way to 
ensure these categories received appropriate inducements that would be 
neither ineffective nor overly restrictive.
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    \366\ EPA's original analysis of NREL data can be found here: 
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055-
0981. ``Review and analysis of vehicle speed activity data from the 
FleetDNA database.'' October 1, 2021.
    \367\ EPA's updated analysis of NREL data can be found here: 
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055. 
``Updated review and analysis of vehicle speed activity data from 
the FleetDNA database.'' October 13, 2022.

                                                            Table IV-13--Inducement Schedules
--------------------------------------------------------------------------------------------------------------------------------------------------------
                           High-speed vehicles                                     Medium-speed vehicles                    Low-speed vehicles
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                      Maximum speed (mi/   Hours of non-idle  Maximum speed (mi/   Hours of non-idle  Maximum speed (mi/
         Hours of non-idle engine operation                   hr)          engine operation           hr)          engine operation           hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
0...................................................                  65                   0                  55                   0                  45
6...................................................                  60                   6                  50                   5                  40
12..................................................                  55                  12                  45                  10                  35
60..................................................                  50                  45                  40                  30                  25
86..................................................                  45                  70                  35  ..................  ..................
119.................................................                  40                  90                  25  ..................  ..................
144.................................................                  35  ..................  ..................  ..................  ..................
164.................................................                  25  ..................  ..................  ..................  ..................
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The derate schedule for each vehicle category is set up with 
progressively increasing severity to induce the owner or operator to 
efficiently address conditions that trigger inducements. Table IV-13 
shows the derate schedules in cumulative hours. The initial inducement 
applies immediately when the OBD system detects any of the triggering 
fault conditions identified in section IV.D.1. The inducement schedule 
then steps down over time to result in the final inducement speed 
corresponding to each vehicle category. The inducement schedule 
includes a gradual transition (1mph every 5 minutes) at the beginning 
of each step of derate and prior to any repeat inducement occurring 
after a failed repair to avoid abrupt changes, as the step down in 
derate speeds in the schedules will be implemented while the vehicle is 
in motion. Inducements are intended to deteriorate vehicle performance 
to a point unacceptable for typical driving in a manner that is safe 
but onerous enough to discourage vehicles from being operated (i.e., 
impact the ability to perform work), such that operators will be 
compelled to replenish the DEF tank with high-quality DEF and not 
tamper with the SCR system's ability to detect whether there is 
adequate high-quality DEF. To this end, as explained in the proposal, 
our analyses of vehicle operational data from NREL show that even 
vehicles whose operation is focused on local or intracity travel depend 
on frequently operating at highway speeds to complete commercial 
work.\368\ Vehicles in an inducement under the schedules we are 
finalizing would not be able to maintain commercial functions. Our 
analysis of the NREL data also show that even medium- and low-speed 
vehicles travel at speeds up to 70 mph and indicate that it is likely 
regular highway travel is critical for low-speed vehicles to complete 
their work; for example, refuse trucks need to drop off collected waste 
at a landfill or transfer station before returning to neighborhoods.
---------------------------------------------------------------------------

    \368\ EPA's updated analysis of NREL data can be found here: 
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055. 
``Updated review and analysis of vehicle speed activity data from 
the FleetDNA database.'' October 13, 2022.
---------------------------------------------------------------------------

    Motorcoach operators submitted comments describing a greater 
sensitivity to any speed derate because of a much greater 
responsibility for carrying people safely to their intended 
destinations over longer distances, including their role in emergency 
response and national defense operations. After consideration of these 
comments, we are allowing manufacturers to design and produce engines 
that will be installed in motorcoaches with an alternative derate 
schedule that starts with a 65 mi/hr derate when a fault condition is 
first detected, steps down to 50 mi/hr after 80 hours, and concludes 
with a final derate speed of 25 mi/hr after 180 hours of non-idle 
operation. EPA is defining motorcoaches in 40 CFR 1036.801 to include 
buses that are designed to travel long distances with row seating for 
at least 30 passengers. This is intended to include charter services 
available to the general public.
    Comments on the proposed inducement policy ranged from

[[Page 4379]]

objecting to any speed restrictions to advocating that we adopt a 5 mph 
final derate speed. Some commenters supported the proposed rule, and 
some commenters asserted that decreasing final derate speeds would 
provide for greater assurance that operators would perform the 
necessary maintenance. There was a similar range of comments regarding 
the time specified for escalating the speed restrictions, with some 
commenters agreeing with the proposed schedule, and other commenters 
suggesting substantially more or less time.
    We made several changes from proposal after consideration of 
comments, including three main changes. First, as noted in the 
preceding paragraphs, the final rule includes a medium-speed vehicle 
category. This allows us to adjust the qualifying criterion for high-
speed vehicles to finalize a derate schedule similar to that proposed 
for vehicles that are clearly operating mostly on interstate highways 
over long distances. Similarly, the added vehicle category allows us to 
adjust the qualifying criterion for low-speed vehicles and adopt an 
appropriately more restrictive final derate schedule for those vehicles 
that are operating at lower speeds in local service.
    Second, we developed unique schedules for escalating the speed 
restrictions for medium-speed and low-speed vehicles; this change was 
based on the expectation that vehicles with lower average speeds spend 
less time operating at highway speeds characteristic of inter-city 
driving and will therefore not need to travel substantial distances to 
return home for scheduling repair.
    Third, we added derate speeds that go beyond the first four stages 
of derating that we proposed for high-speed vehicles, essentially 
reducing the final inducement speeds for all vehicles to be the same as 
low-speed vehicles. In other words, as shown in Table IV-13, both high- 
and medium-speed vehicles eventually derate to the same speeds as low-
speed vehicles, after additional transition time after the derate 
begins. For example, the final derate schedule for high-speed vehicles 
goes through the proposed four derate stages for high-speed vehicles. 
At the fifth derate stage the vehicle begins to be treated like a 
medium-speed vehicle, starting at the third derate stage for medium-
speed vehicles and progressing through the fifth derate stage for 
medium-speed vehicles. At the fifth derate stage the vehicle begins to 
be treated like a low-speed vehicle, similarly starting at the third 
derate stage for low-speed vehicles. A similar step-down approach 
applies for medium-speed vehicles, transitioning down to the derate 
stages for low-speed vehicles. This progression is intended to address 
the concern that vehicle owners might reassign vehicles in their fleet 
to lower-speed service, or sell vehicles to someone who would use the 
vehicle for different purposes that don't depend on higher-speed 
operations. Our assessment is that the NREL data show that no matter 
what category vehicles are, they do not travel exclusively at or below 
25 mph, indicating that vehicles derated to 25 mph cannot be operated 
commercially.
    For the simplest type of maintenance, DEF refills, we fully expect 
that the initial stage of derated vehicle speed will be sufficient to 
compel vehicle operators to meet their maintenance obligations. We 
expect operators will add DEF routinely to avoid inducements; however, 
inducements begin three hours prior to the DEF tank being empty to 
better ensure operation with an empty DEF tank is avoided.
    We expect that the derate schedules in this final rule will be 
fully effective in compelling operators to perform needed maintenance. 
This effectiveness will be comparable to the current approach under 
existing guidance, but will reduce operating costs to operators. We 
believe this measured approach will also result in lower tampering 
rates involving time.
3. Driver Information
    In addition to the driver information requirements we are adopting 
to improve serviceability and OBD (see section IV.B.3 and IV.C.1.iii 
respectively of this preamble for more details on these provisions), we 
are also adopting improved driver information requirements for 
inducements. Specifically, we are adopting as proposed the requirement 
for manufacturers to increase the amount of information provided to the 
driver about inducements, including: (1) The condition causing the 
derate (i.e., DEF quality, DEF quantity or tampering), (2) the fault 
code and description of the code associated with the inducement, (3) 
the current derate speed restriction, (4) hours until the next derate 
speed decrease, and (5) what the next derate speed will be. It is 
critical that operators have clear and ready access to information 
regarding inducements to reduce concerns over progressive engine 
derates (which can lead to motivations to tamper) as well as to allow 
operators to make timely informed decisions, especially since 
inducements are used by manufacturers to demonstrate that critical 
emissions-related maintenance is reasonably likely to occur in-use. We 
note that we are finalizing this requirement at 40 CFR 1036.110(c), in 
a different regulatory section than proposed; however, the substance of 
the requirement is the same as at proposal.
    EPA is requiring that all inducement-related diagnostic data 
parameters be made available with generic scan tools to help operators 
promptly respond when the engine detects fault condition requiring 
repair or other maintenance (see section IV.C.1.iii. for further 
information).
4. Clearing an Inducement Condition
    Following restorative maintenance, EPA is requiring that the engine 
would allow the vehicle to self-heal if it confirms that the fault 
condition is resolved. The engine would then remove the inducement, 
which would allow the vehicle to resume unrestricted engine operation. 
EPA is also requiring that generic scan tools be able to remove an 
inducement condition after a successful repair. After clearing 
inducement-related fault codes, all fault codes are subject to 
immediate reevaluation that would lead to resuming the derate schedule 
where it was at the time the codes were cleared if the fault persists. 
Therefore, there is no need to limit the number of times a scan tool 
can clear codes. Use of a generic scan tool to clear inducements would 
allow owners who repair vehicles outside of commercial facilities to 
complete the repair without delay (e.g., flushing and refilling a DEF 
tank where contaminated DEF was discovered). However, if the same fault 
condition repeats within 40 hours of engine operation (e.g., in 
response to a DEF quantity fault an owner adds a small but insufficient 
quantity of DEF), this will be considered a repeat faut. In response to 
a repeat fault, the system will immediately resume the derate at the 
same point in the derate schedule when the original fault was 
deactivated. This is less time than the 80 hours EPA proposed in the 
NPRM, but it is consistent with existing EPA guidance. After 
consideration of comments, we believe that the shorter interval is long 
enough to give a reliable confirmation that a repair has properly 
addressed the fault condition, and are concerned that 80 hours would 
risk treating an unrelated occurrence of a fault condition as if it 
were a continuation of the same fault.
    EPA is not finalizing the proposed provision that an inducement 
schedule is applied and tracked independently for each fault if 
multiple fault conditions are detected due to the software complexity 
for the

[[Page 4380]]

manufacturer in applying and tracking the occurrence of multiple derate 
schedules. Section 4 of the Response to Comments for further discussion 
of EPA's thinking to assist manufacturers regarding consideration for 
programming diagnostic systems to handle overlapping fault conditions.
5. Further Considerations
    EPA is not taking final action at this time on the proposed 
NOX override provision, which was proposed to prevent speed 
derates for fault conditions that are caused by component failures if 
the catalyst is nevertheless functioning normally. We received comments 
describing concerns with our proposed methodology, including the 
reliability of NOX sensors and use of OBD REAL 
NOX data, and concerns that reliance in this way on the 
NOX sensor could result in easier tampering. We are 
continuing to consider these issues and comments. We may consider such 
a provision in an appropriate future action. Our final inducement 
regulations will reduce the risk of false inducements and provide 
increased certainty during repairs by limiting inducements to well-
defined fault conditions that focus appropriately on DEF supply, DEF 
quality, and tampering (open-circuit faults associated with missing 
aftertreatment hardware).
    We have also learned from the last several years that it is 
important to monitor in-use experiences to evaluate whether the 
inducement provisions are striking the intended balance of ensuring an 
adequate supply of high-quality DEF in a way that is allowing for safe 
and timely resolution, even for cases involving difficult 
circumstances. For example, we might hypothetically learn from in-use 
experiences that component malfunctions, part shortages, or other 
circumstances are leaving operators in a place where inducements 
prevent them from operating and they are unable to perform maintenance 
that is needed to resolve the fault condition. Conversely, we might 
hypothetically learn that operators are routinely driving vehicles with 
active derates. Information from those in-use experiences may be 
helpful for future assessments of whether we should pursue adjustments 
to the derate schedules or other inducement provisions we are adopting 
in this final rule.
6. In-Use Retrofits To Update Existing Inducement Algorithms
    In the NPRM, we sought comment on whether it would be appropriate 
to allow engine manufacturers to modify earlier model year engines to 
align with the new regulatory specifications. We did not propose 
changes to existing regulations to address this concern. Specifically, 
we sought comment on whether and how manufacturers might use field-fix 
practices under EPA's field fix guidance to modify in-use engines with 
algorithms that incorporate some or all the inducement provisions in 
the final rule. We received numerous comments on the need to modify 
existing inducement speeds and schedules from operator groups and at 
least one manufacturer.\369\ We received comment on the use of field-
fixes for this purpose from CARB, stating that CARB staff does not 
support the SCR inducement strategy proposed by EPA and does not 
support allowing field fixes for in-use vehicles or to amend the 
certification application of current model year engines for the NPRM 
inducement strategy. CARB staff also commented that they would support 
allowing field fixes for in-use vehicles or amending current 
certification applications only if EPA adopts an inducement strategy 
identical or similar to the one CARB proposed in their comments on the 
proposed rule.\370\ For example, CARB suggested an inducement strategy 
with a 5 mph inducement after 10 hours, following an engine restart.
---------------------------------------------------------------------------

    \369\ See, for example, comments from the National Association 
of Small Trucking Companies, EPA-HQ-OAR-2019-0055-1130.
    \370\ See comments from California Air Resources Board, EPA-HQ-
OAR-2019-0055-1186.
---------------------------------------------------------------------------

    EPA believes field fixes with updated inducement algorithms may 
fall within EPA's field fix guidance for engines that have EPA-only 
certification (i.e., does not include certification to California 
standards), but has concerns about such field fixes falling within the 
scope of the guidance for engines also certified by CARB if CARB 
considers such changes to be tampering with respect to requirements 
that apply in California. EPA intends to also consider alternative 
field fix inducement approaches that manufacturers choose to develop 
and propose to CARB and EPA, for engines certified by both EPA and 
CARB, such as approaches that provide a more balanced inducement 
strategy than that used in current certifications while still being 
effective.

E. Fuel Quality

    EPA has long recognized the importance of fuel quality on motor 
vehicle emissions and has regulated fuel quality to enable compliance 
with emission standards. In 1993, EPA limited diesel sulfur content to 
a maximum of 500 ppm and put into place a minimum cetane index of 40. 
Starting in 2006 with the establishment of more stringent heavy-duty 
highway PM, NOX and hydrocarbon emission standards, EPA 
phased-in a 15-ppm maximum diesel fuel sulfur standard to enable heavy-
duty diesel engine compliance with the more stringent emission 
standards.\371\
---------------------------------------------------------------------------

    \371\ 66 FR 5002 January 18, 2001.
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    EPA continues to recognize the importance of fuel quality on heavy-
duty vehicle emissions and is not currently aware of any additional 
diesel fuel quality requirements necessary for controlling criteria 
pollutant emissions from these vehicles.
1. Biodiesel Fuel Quality
    As discussed in Chapter 2.3.2 of the RIA, metals (e.g., Na, K, Ca, 
Mg) can enter the biodiesel production stream and can adversely affect 
emission control system performance if not sufficiently removed during 
production. Our review of data collected by NREL, EPA, and CARB 
indicates that biodiesel is compliant with the ASTM D6751-18 limits for 
Na, K, Ca, and Mg. As we explained in the proposed rule, the available 
data does not indicate that there is widespread off specification 
biodiesel blend stock or biodiesel blends in the marketplace. We did 
not propose and are not including at this time in this final rule 
requirements for biodiesel blend metal content.
    While occasionally there are biodiesel blends with elevated levels 
of these metals, they are the exception. Data in the literature 
indicates that Na, K, Ca, and Mg levels in these fuels are less than 
100 ppb on average. Data further suggests that the low levels measured 
in today's fuels are not enough to adversely affect emission control 
system performance when the engine manufacturer properly sizes the 
catalyst to account for low-level exposure.
    Given the low levels measured in today's fuels, however, we are 
aware that ASTM is currently evaluating a possible revision to the 
measurement method for Na, K, Ca, and Mg in D6751-20a from EN14538 to a 
method that has lower detection limits (e.g., ASTM D7111-16, or a 
method based on the ICP-MS method used in the 2016 NREL study). We 
anticipate that ASTM will likely specify Na, K, Ca, and Mg limits in a 
future update to ASTM 7467-19 for B6 to B20 blends that is an 
extrapolation of the B100 limits (see RIA Chapter 2.3.2 for additional 
discussion of ASTM test methods, as well as available data on levels of 
metal in biodiesel and potential impacts on emission control systems).

[[Page 4381]]

2. Compliance Issues Related to Biodiesel Fuel Quality
    Given the concerns we raised in the ANPR and NPRM regarding the 
possibility of catalyst poisoning from metals contained in biodiesel 
blends and specifically heavy-duty vehicles fueled on biodiesel blends, 
and after consideration of comments on the NPRM, EPA is finalizing a 
process where we will consider the possibility that an engine was not 
properly maintained under the provisions of 40 CFR part 1068, subpart 
F, if an engine manufacturer demonstrates that the vehicle was 
misfueled in a way that exposed the engine and its aftertreatment 
components to metal contaminants and that misfueling degraded the 
emission control system performance. This allows a manufacturer to 
receive EPA approval to exempt test results from being considered for 
potential recall. For example, a manufacturer might request EPA 
approval through this process for a vehicle that was historically 
fueled on biodiesel blends whose B100 blend stock did not meet the ASTM 
D6751-20a limit for Na, K, Ca, and/or Mg (metals which are a byproduct 
of current biodiesel production methods). This process requires the 
engine manufacturer to provide proof of historic misfueling with off-
specification fuels; more specifically, to qualify for the test result 
exemption(s), a manufacturer must provide documentation that compares 
the degraded system to a representative compliant system of similar 
miles with respect to the content and amount of the contaminant. We are 
also finalizing a change from the proposal in the fuel requirements 
relevant to conducting in-use testing and to recruitment of vehicles 
for in-use testing. The new provision in 40 CFR 1036.415(c)(1) states 
that the person conducting the in-use testing may use any commercially 
available biodiesel fuel blend that meets the specifications for ASTM 
D975 or ASTM D7467 that is either expressly allowed or not otherwise 
indicated as an unacceptable fuel in the vehicle's owner or operator 
manual or in the engine manufacturer's published fuel recommendations. 
As specified in final 40 CFR 1036.410, if the engine manufacturer finds 
that the engine was fueled with fuel not meeting the specifications in 
40 CFR 1036.415(c)(1), they may disqualify the vehicle from in-use 
testing and replace it with another one.

F. Durability Testing

    In this section, we describe the final deterioration factor (DF) 
provisions for heavy-duty highway engines, including migration and 
updates from their current location in 40 CFR 86.004-26(c) and (d) and 
86.004-28(c) and (d) to 40 CFR 1036.245 and 1036.246. EPA regulations 
require that a heavy-duty engine manufacturer's application for 
certification include a demonstration that the engines will meet 
applicable emission standards throughout their regulatory useful life. 
This is often called the durability demonstration. Manufacturers 
typically complete this demonstration by following regulatory 
procedures to calculate a DF. Deterioration factors are additive or 
multiplicative adjustments applied to the results from manufacturer 
testing to quantify the emissions deterioration over useful life.\372\
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    \372\ See 40 CFR 1036.240(c) and the definition of 
``deterioration factor'' in 40 CFR 1036.801, which, as proposed, are 
migrated and updated from 40 CFR 86.004-26 and 86.004-28 in this 
final rule.
---------------------------------------------------------------------------

    Currently, a DF is determined directly by aging an engine and 
exhaust aftertreatment system to useful life on an engine dynamometer. 
This time-consuming service accumulation process requires manufacturers 
to commit to product configurations well ahead of their pre-production 
certification testing to complete the durability testing so EPA can 
review the test results before issuing the certificate of conformity. 
Some manufacturers run multiple, staggered durability tests in parallel 
in case a component failure occurs that may require a complete restart 
of the aging process.\373\
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    \373\ See 40 CFR 1065.415.
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    As explained in the NPRM, EPA recognizes that durability testing 
over a regulatory useful life is a significant undertaking, which can 
involve more than a full year of continuous engine operation for Heavy 
HDE to test to the equivalent of the current useful life of 435,000 
miles. Manufacturers have been approved, on a case-by-case basis, to 
age their systems to between 35 and 50 percent of the current full 
useful life on an engine dynamometer, and then extrapolate the test 
results to full useful life.\374\ This extrapolation reduces the time 
to complete the aging process, but data from a test program shared with 
EPA show that while engine out emissions for SCR-equipped engines were 
predictable and consistent, actual tailpipe emission levels were higher 
by the end of useful life when compared to emission levels extrapolated 
to useful life from service accumulation of 75 or lower percent useful 
life.375 376 In response to the new data indicating DFs 
generated by manufacturers using service accumulation less than useful 
life may not be fully representative of useful life deterioration, EPA 
initially worked with manufacturers and CARB to address this concern 
through guidance for MY 2020 and later engines.
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    \374\ See 40 CFR 86.004-26.
    \375\ U.S. EPA. ``Guidance on Deterioration Factor Validation 
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel 
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad). 
November 17, 2020.
    \376\ Truck and Engine Manufacturers Association. ``EMA DF Test 
Program.'' August 1, 2017.
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    While the current DF guidance is specific to SCR-equipped engines, 
in this final rule we are updating our DF provisions to apply certain 
aspects of the current DF guidance to all engine families starting in 
model year 2027.\377\ We also are finalizing as proposed that 
manufacturers may optionally use these provisions to determine their 
deterioration factors for earlier model years. As noted in the 
following section, as proposed, we are continuing the option for Spark-
ignition HDE manufacturers to request approval of an accelerated aging 
DF determination, as is allowed in our current regulations (see 40 CFR 
86.004-26(c)(2)), and our final provision extends this option to all 
primary intended service classes. We are not finalizing any changes to 
the existing compliance demonstration provision in 40 CFR 1037.103(c) 
for evaporative and refueling emission standards. As introduced in 
Section III.E, in this rule we are also promulgating refueling emission 
standards for incomplete vehicles above 14,000 lb GVWR. As proposed, we 
are finalizing that incomplete vehicle manufacturers certifying to the 
refueling emission standards for the first time have the option to use 
engineering analyses to demonstrate durability using the same 
procedures that apply for the evaporative systems on their vehicles 
today.
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    \377\ As noted in Section III.A, the final update to the 
definition of ``engine configuration'' in 40 CFR 1036.801, as 
proposed, clarifies that hybrid engines and powertrains are part of 
a certified configuration and subject to all of the criteria 
pollutant emission standards and other requirements; thus the DF 
provisions for heavy-duty engines discussed in this subsection will 
apply to configurations that include hybrid components.
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    In Section IV.F.1, we are finalizing two methods for determining 
DFs in a new 40 CFR 1036.245 with some modifications from those 
proposed, including a new option to bench-age the aftertreatment system 
to limit the burden of generating a DF over the lengthened useful life 
periods in Section IV.A.3. We are also codifying two DF verification 
options available to

[[Page 4382]]

manufacturers in the recent DF guidance, with some modifications from 
our proposed DF verification requirements. As described in Section 
IV.F.2, under the final 40 CFR 1036.245 and 40 CFR 1036.246, the final 
provisions include two options for DF verification to confirm the 
accuracy of the DF values submitted by manufacturers for certification, 
and will be required upon request from EPA. In Section IV.F.3, we 
introduce a test program to evaluate a rapid-aging protocol for diesel 
catalysts, the results of which we used to develop a rapid-aging test 
procedure for CI engine manufacturers to be able to use in their 
durability demonstration under 40 CFR 1036.245(c)(6). We are finalizing 
this procedure in 40 CFR part 1065, subpart L, as new sections 40 CFR 
1065.1131 through 40 CFR 1065.1145.
    At this time we are not finalizing any additional testing 
requirements for manufacturers to demonstrate durability of other key 
components included in a hybrid configuration (e.g., battery durability 
testing). We will consider additional requirements in a future rule as 
we pursue other durability-related provisions for EVs, PHEVs, etc.
    As described in Section XI.A.8, we are also finalizing as proposed 
that manufacturers of nonroad engines may use the procedures described 
in this section to establish deterioration factors based on bench-aged 
aftertreatment, along with any EPA-requested in-use verification 
testing.
1. Options for Determining Deterioration Factor
    Accurate methods to demonstrate emission durability are key to 
ensuring certified emission levels represent real world emissions, and 
the efficiency of those methods is especially important in light of the 
lengthening of useful life periods in this final rule. To address these 
needs, we are migrating our existing regulatory option from part 86 to 
part 1036 and including a new option for heavy-duty highway engine 
manufacturers to determine DFs for certification. We note that 
manufacturers apply these deterioration factors to determine whether 
their engines meet the duty cycle standards.
    Consistent with existing regulations, final 40 CFR 1036.245 allows 
manufacturers to continue the current practice of determining DFs based 
on engine dynamometer-based aging of the complete engine and 
aftertreatment system out to regulatory useful life. In addition, under 
the new DF determination option, which includes some modifications from 
that proposed and which are described in this section, manufacturers 
perform dynamometer testing of an engine and aftertreatment system to a 
minimum required mileage that is less than regulatory useful life. 
Manufacturers then bench age the aftertreatment system to regulatory 
useful life and combine the aftertreatment system with an engine that 
represents the engine family. Manufacturers run the combined engine and 
bench-aged aftertreatment for at least 100 hours before collecting 
emission data for determination of the deterioration factor. Under this 
option, the manufacturer can use the accelerated bench-aging of diesel 
aftertreatment procedure described in Section IV.F.3 that is codified 
in the new sections 40 CFR 1065.1131 through 40 CFR 1065.1145 or 
propose an equivalent bench-aging procedure and obtain prior approval 
from the Agency. For example, a manufacturer might propose a different, 
established bench-aging procedure for other engines or vehicles (e.g., 
procedures that apply for light-duty vehicles under 40 CFR part 86, 
subpart S).
    We requested comment on whether the new bench-aged aftertreatment 
option accurately evaluates the durability of the emission-related 
components in a certified configuration, including the allowance for 
manufacturers to define and seek approval for a less-than-useful life 
mileage for the dynamometer portion of the bench-aging option. This 
request for comment specifically included whether or not there is a 
need to define a minimum number of engine hours of dynamometer testing 
beyond what is required to stabilize the engine before bench-aging the 
aftertreatment, noting that EPA's bench-aging proposal focused on 
deterioration of emission control components.\378\ We requested comment 
on including a more comprehensive durability demonstration of the whole 
engine, such as the recent diesel test procedures from CARB's Omnibus 
regulation that includes dynamometer-based service accumulation of 
2,100 hours or more based on engine class and other factors.\379\ We 
also requested comment on whether EPA should prescribe a standardized 
aging cycle for the dynamometer portion, as was done by CARB in the 
Omnibus rule with their Service Accumulation Cycles 1 and 2.\380\ We 
also requested cost and time data corresponding to the current DF 
procedures, and projections of cost and time for the proposed new DF 
options at the proposed new useful life mileages.
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    \378\ We are updating, as proposed, the definition of ``low-
hour'' in 40 CFR 1036.801 to include 300 hours of operation for 
engines with NOX aftertreatment to be considered 
stabilized.
    \379\ California Air Resources Board, '' Appendix B-1 Proposed 
30-Day Modifications to the Diesel Test Procedures'', May 5, 2021, 
Available online: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2020/hdomnibuslownox/30dayappb1.pdf, page 54.
    \380\ California Air Resources Board, ``Staff Report: Initial 
Statement of Reasons for Proposed Rulemaking, Public Hearing to 
Consider the Proposed Heavy-duty Engine and Vehicle Omnibus 
Regulation and Associated Amendments,'' June 23, 2020. Available 
online: https://ww3.arb.ca.gov/regact/2020/hdomnibuslownox/isor.pdf, 
page III-80.
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    Some commentors supported the removal of the fuel-based accelerated 
DF determination method, noting that it has been shown to underestimate 
emission control system deterioration. Other commentors requested that 
EPA retain the option, noting that it has been historically allowed. 
Fuel-based accelerated aging accelerates the service accumulation using 
higher-load operation based on equivalent total fuel flow on a 
dynamometer. The engine is only operated out to around 35 percent of UL 
based on operating hours, however the high-load operation is intended 
to result in an equivalent aging out to full UL. EPA has assessed data 
from the EMA DF test program and determined that the data indicated 
that the aging mechanism of accelerating the aging at higher load 
differs from the actual in-use deterioration 
mechanism.381 382 We are not including this option in the 
final provisions for determining DF based on our assessment of the 
available data and have removed the option in final 40 CFR 1036.245.
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    \381\ U.S. EPA. ``Guidance on Deterioration Factor Validation 
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel 
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad). 
November 17, 2020.
    \382\ Truck and Engine Manufacturers Association. ``EMA DF Test 
Program.'' August 1, 2017.
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    We also received general support of the use of accelerated aging 
cycles to manage the total cost and duration of the DF test, in 
addition to some commenters stating that the CARB DF determination 
procedure in the CARB Omnibus regulation is superior to the accelerated 
aging procedure EPA proposed in 40 CFR 1036.245(b)(2). The required 
hours of engine dynamometer aging in the CARB Omnibus procedure 
(roughly out to 20 percent of UL for a HHD engine) provide limited 
assurance on the performance of engine components out to UL, and thus 
primarily provide a short-term quality assurance durability program for 
engine hardware. While the purpose of EPA's DF determination procedure 
is to

[[Page 4383]]

determine emission performance degradation over the useful life of the 
engine, we acknowledge that there is value in performing some engine 
dynamometer aging. We are finalizing an option to use accelerated 
reactor bench-aging of the emission control system that is ten times a 
dynamometer or field test (1,000 hours of accelerated aging would be 
equivalent to 10,000 hours of standard aging), requiring a minimum 
number of testing hours on an engine dynamometer, with the allowance 
for the manufacturer to add additional hours of engine dynamometer-
aging at their discretion. The minimum required hours are by primary 
intended service class and follow: 300 hours for SI, 1,250 hours for 
Light HDE, and 1,500 hours for Medium HDE and Heavy HDE. This option 
allows the DF determination to be completed within a maximum of 180 
days for a Heavy HDE. We recognize that a different approach, that uses 
the same aging duty-cycle for all manufacturers, would provide more 
consistency across engine manufacturers. However, no data was provided 
by commentors showing that the Service Accumulation Cycles 1 and 2 in 
the CARB Omnibus rule are any more effective at determining 
deterioration than cycles developed by the manufacturer and submitted 
to EPA for approval. EPA is also concerned regarding the amount of idle 
contained in each of the CARB Omnibus rule cycles. We realize that this 
idle operation was included to target the degradation mechanism that 
plagued the SAPO-34 SCR formulations used by manufacturers in the 
2010s, however the catalyst developers are aware of this issue now and 
have developed formulations that are free from this degradation 
mechanism. The two most predominant degradation mechanisms are time at 
high temperature and sulfur exposure, including the effects of catalyst 
desulfation, and as such EPA favors duty-cycles with more aggressive 
aftertreatment temperature profiles. We understand that catalyst 
manufacturers now bench test the catalyst formulations under the 
conditions that led to the SAPO-34 degradation to ensure that this 
degradation mechanism is not present in newly developed SCR 
formulations. After taking all of the comments received into 
consideration, EPA has added two specified duty-cycle options in 40 CFR 
1036.245(c) for DF determination, that are identical to CARB's Service 
Accumulation Cycles 1 and 2. Cycle 1 consists of a combination of FTP, 
RMC, LLC and extended idle, while Cycle 2 consists of a combination of 
HDTT, 55-cruise, 65-cruise, LLC, and extended idle. In the case of the 
second option, the manufacturer is required to use good engineering 
judgment to choose the vehicle subcategory and vehicle configuration 
that yields the highest load factor using the GEM model. EPA is also 
providing an option for manufacturers to use their own duty cycles for 
DF determination subject to EPA approval and we expect a manufacturer 
to include light-load operation if it is deemed to contribute to 
degradation of the aftertreatment performance. We also note that we are 
finalizing requirements to stop, cooldown, and restart the engine 
during service accumulation when using the options that correspond to 
CARB Service Accumulation Cycles 1 and 2 for harmonization purposes, 
however we note that manufacturers may make a request to EPA to remove 
this requirement on a case-by-case basis.
    We are finalizing critical emission-related maintenance as 
described in 40 CFR 1036.125(a)(2) and 1036.245(c) in this final rule. 
Under this final rule, manufacturers may make requests to EPA for 
approval for additional emission-related maintenance actions beyond 
what is listed in 40 CFR 1036.125(a)(2), as described in 40 CFR 
1036.125(a)(1) and as allowed during deterioration testing under 40 CFR 
1036.245(c).
2. Options for Verifying Deterioration Factors
    We are finalizing, with some modifications from proposal, a new 40 
CFR 1036.246 where, at EPA's request, the manufacturers would be 
required to verify an engine family's deterioration factor for each 
duty cycle up to 85 percent of useful life. Because the manufacturer 
must comply with emission standards out to useful life, we retain the 
authority to verify DF. We proposed requiring upfront verification for 
all engine families, but have decided to make this required only in the 
event that EPA requests verification. We intend to make such a request 
primarily when EPA becomes aware of information suggesting that there 
is an issue with the DF generated by the manufacturer. EPA anticipates 
that a DF verification request may be appropriate due to consideration 
of, for example: (1) Information indicating that a substantial number 
of in-use engines tested under subpart E of this part failed to meet 
emission standards, (2) information from any other test program or any 
other technical information indicating that engines will not meet 
emission standards throughout the useful life, (3) a filed defect 
report relating to the engine family, (4) a change in the technical 
specifications for any critical emission-related components, and (5) 
the addition of a new or modified engine configuration such that the 
test data from the original emission-data engine do not clearly 
continue to serve as worst-case testing for certification. We are 
finalizing as proposed that manufacturers may request use of an 
approved DF on future model year engines for that engine family, using 
the final updates to carryover engine data provisions in 40 CFR 
1036.235(d), with the final provision clarifying that we may request DF 
verification for the production year of that new model year as 
specified in the new 40 CFR 1036.246. As also further discussed in the 
following paragraphs, we are not finalizing at this time certain DF 
verification provisions that we had proposed regarding timing of when 
EPA may request DF verification and certain provisions for the first 
model year after a failed result. Our revisions from proposal 
appropriately provide flexibility for EPA to gather information based 
on DF concerns. The final provisions specify that we will discuss with 
the manufacturer the selection criteria for vehicles with respect to 
the target vehicle mileage(s) and production model year(s) that we want 
the manufacturer to test. We are finalizing that we will not require 
the manufacturer to select vehicles whose mileage or age exceeds 10 
years or 85 percent of useful life.
    We originally included three testing options in our proposed DF 
verification provisions. We are finalizing two of these options and we 
are not including the option to verify DF by measuring NOX 
emissions using the vehicle's on-board NOX measurement 
system at this time. For the two options we are finalizing, 
manufacturers select in-use engines meeting the criteria in 40 CFR 
1036.246(a), including the appropriate mileage specified by EPA 
corresponding to the production year of the engine family.
    Under the first verification option in 40 CFR 1036.246(b)(1), 
manufacturers test at least two in-use engines over all duty cycles 
with brake-specific emission standards in 40 CFR 1036.104(a) by 
removing each engine from the vehicle to install it on an engine 
dynamometer and measure emissions. Manufacturers determine compliance 
with the emission standards after applying infrequent regeneration 
adjustment factors to their measured results, just as they did when 
they originally certified the engine family. We are also finalizing a 
requirement under this option to allow EPA to request that 
manufacturers

[[Page 4384]]

perform a new determination of infrequent regeneration adjustment 
factors to apply to the emissions from the engine dynamometer-based 
testing. Consistent with the proposal, the engine family passes the DF 
verification if 70 percent or more of the engines tested meet the duty-
cycle emission standards in 40 CFR 1036.104(a), including any 
associated compliance allowance, for each pollutant over all duty 
cycles. If a manufacturer chooses to test two engines under this 
option, both engines have to meet the standards. Under this option, the 
aftertreatment system, including all the associated wiring, sensors, 
and related hardware or software is installed on the test engine. We 
are finalizing an allowance in 40 CFR 1036.246(a) for the manufacturer 
to use hardware or software in testing that differs from those used for 
engine family and power rating with EPA approval.
    Under the second verification option in 40 CFR 1036.246(b)(2), as 
proposed, manufacturers test at least five in-use engines, to account 
for the increased variability of vehicle-level measurement, while 
installed in the vehicle using a PEMS. Manufacturers bin and report the 
emissions following the in-use testing provisions in 40 CFR part 1036, 
subpart E. Compliance is determined by comparing emission results to 
the off-cycle emission standards in 40 CFR 1036.104(a) with any 
associated compliance allowance, mean ambient temperature adjustment, 
and, accuracy margin for each pollutant for each bin after adjusting 
for infrequent regeneration.\383\ As proposed, the engine family passes 
the DF verification if 70 percent or more of the engines tested meet 
the off-cycle standards for each pollutant for each bin. In the event 
that EPA requested DF verification and a DF verification fails under 
the PEMS option, consistent with the proposal the manufacturer can 
reverse a fail determination for the PEMS-based testing and verify the 
DF using the engine dynamometer testing option in 40 CFR 
1036.246(b)(1).
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    \383\ For Spark-ignition HDE, we are not finalizing off-cycle 
standards; however, for the in-use DF verification options, a 
manufacturer compares the engine's emission results to the duty 
cycle standards applying a 1.5 multiplier for model years 2027 and 
later.
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    EPA is not including the third option we proposed, to verify DF 
using the vehicle's on-board NOX measurement system (i.e., a 
NOX sensor), in the final provisions, as we have concerns 
that the technology has not matured enough to make this method viable 
for DF verification at this time. We did not receive any comments that 
supported the availability of technology to enable accurate on-board 
NOX measurement at a level needed to show compliance with 
the standard. EPA acknowledges the challenges associated with the 
development of a functional onboard NOX measurement method, 
including data acquisition and telematic system capabilities, and may 
reconsider this option in the future if the technology evolves.
    As noted in the preceding paragraphs, we are not taking final 
action at this time on the proposed 40 CFR 1036.246(h) provision that 
proposed a process for the first MY after a DF verification resulted in 
failure. Instead, we are adopting a process for DF verification 
failures similar to the existing process used for manufacturer run in-
use testing failures under 40 CFR part 1036, subpart E, such that a 
failure may result in an expanded discovery process that could 
eventually lead to recall under our existing provisions in 40 CFR part 
1068, subpart F. EPA is making this change from proposal because this 
approach provides consistency with and builds upon existing processes.
    The final 40 CFR 1036.246(a) specifies how to select and prepare 
engines for testing. Manufacturers may exclude selected engines from 
testing if they have not been properly maintained or used and the 
engine tested must be in a certified configuration, including its 
original aftertreatment components. Manufacturers may test engines that 
have undergone critical emission-related maintenance as allowed in 40 
CFR 1065.410(d), but may not test an engine if its critical emission-
related components had any other major repair.
3. Accelerated Deterioration Factor Determination
    As discussed in Section IV.F.1, we are finalizing a deterioration 
factor procedure where manufacturers use engine dynamometer testing for 
the required minimum number of hours given in Table 1 to Paragraph 
(c)(2) of 40 CFR 1036.245 in combination with an accelerated 
aftertreatment catalyst aging protocol in their demonstration of heavy-
duty diesel engine aftertreatment durability through useful life. EPA 
has approved accelerated aging protocols for spark-ignition engine 
manufacturers to apply in their durability demonstrations for many 
years. Historically, while CI engine manufacturers have the ability to 
request EPA approval of an accelerated aging procedure, CI engine 
manufacturers have largely opted to seek EPA approval to use a service 
accumulation fuel based accelerated test with reduce mileage and 
extrapolate to determine their DF.
    Other regulatory agencies have promulgated accelerated aging 
protocols,384 385 and we have evaluated how these or similar 
protocols apply to our heavy-duty highway engine compliance program. 
EPA has validated and is finalizing an accelerated aging procedure in 
40 CFR part 1065, subpart L, as new sections 40 CFR 1065.1131 through 
40 CFR 1065.1145 that CI engine manufacturers can choose to use in lieu 
of developing their own protocol as described in 40 CFR 1036.245. The 
test program that validated the diesel aftertreatment rapid-aging 
protocol (DARAP) was built on existing accelerated aging protocols 
designed for light-duty gasoline vehicles (64 FR 23906, May 4, 1999) 
and heavy-duty engines.\386\
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    \384\ California Air Resources Board. California Evaluation 
Procedure For New Aftermarket Diesel Particulate Filters Intended As 
Modified Parts For 2007 Through 2009 Model Year On-Road Heavy-Duty 
Diesel Engines, March 1, 2017. Available online: https://ww3.arb.ca.gov/regact/2016/aftermarket2016/amprcert.pdf.
    \385\ European Commission. Amending Regulation (EU) No 583/2011, 
20 September 2016. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32016R1718&from=HU.
    \386\ Eakle, S and Bartley, G (2014), ``The DAAAC Protocol for 
Diesel Aftertreatment System Accelerated Aging''.
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i. Diesel Aftertreatment Rapid Aging Protocol
    The objective of the DARAP validation program was to artificially 
recreate the three primary catalytic deterioration processes observed 
in field-aged aftertreatment components: Thermal aging based on time at 
high temperature, chemical aging that accounts for poisoning due to 
fuel and oil contamination, and deposits. The validation program had 
access to three baseline engines that were field-aged to the model year 
2026 and earlier useful life of 435,000 miles. Engines and their 
corresponding aftertreatment systems were aged using the current, 
engine dynamometer-based durability test procedure for comparison of 
the results to the accelerated aging procedure. We performed 
accelerated aging of the catalyst-based aftertreatment systems using 
two different methods with one utilizing a burner \387\ and the other 
using an engine as the source of aftertreatment aging conditions. The 
validation test plan compared emissions at the following approximate 
intervals: 0 percent, 25 percent, 50 percent, 75 percent, and 100 
percent of the model year 2026 and earlier useful life of 435,000 
miles. At proposal, we included

[[Page 4385]]

additional details of our DARAP test program in a memo to the 
docket.\388\
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    \387\ A burner is a computer controlled multi-fuel reactor 
designed to simulate engine aging conditions.
    \388\ Memorandum to Docket EPA-HQ-OAR-2019-0055: ``Diesel 
Aftertreatment Rapid Aging Program''. George Mitchell. May 5, 2021.
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    The DARAP validation program has completed testing of two rapidly 
aged aftertreatment systems, engine and burner, and two engines, a 
single FUL aged engine and a 300-hour aged engine. Our memo to the 
docket includes a summary of the validation results from this program. 
The results show that both accelerated aging pathways, burner and 
engine, produced rapidly aged aftertreatment system results that were 
not statistically significant when compared to the 9,800-hour 
dynamometer aged reference system. We are currently completing 
postmortem testing to evaluate the deposition of chemical poisoning on 
the surface of the substrates to see how this compares to the 
dynamometer aged reference system. The complete results from our 
validation program are contained in a final report in the docket.\389\
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    \389\ Sharp, C. (2022). Demonstration of Low NOX 
Technologies and Assessment of Low NOX Measurements in 
Support of EPA's 2027 Heavy Duty Rulemaking. Southwest Research 
Institute. Final Report EPA Contract 68HERC20D0014.
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ii. Diesel Aftertreatment Accelerated Aging Test Procedure
    The final provisions include an option for manufacturers to use the 
method from the DARAP test program for DF determination and streamline 
approval under 40 CFR 1036.245(c). This accelerated aging method we are 
finalizing in 40 CFR part 1065, subpart L, as new sections 40 CFR 
1065.1131 through 40 CFR 1065.1145 is a protocol for translating field 
data that represents a given application (e.g., engine family) into an 
accelerated aging cycle for that given application, as well as methods 
for carrying out reactor or engine accelerated aging using that cycle. 
While this testing can be carried out on an engine as well as reactor 
bench, the engine option should not be confused with standard engine 
dynamometer aging out to useful life or the historic fuel-based engine 
dynamometer accelerated aging typically done out to 35 percent of 
useful life approach that EPA will no longer allow under this final 
rule. The engine option in this procedure uses the engine (1) as a 
source of accelerated sulfur from the combusted fuel, (2) as a source 
for exhaust gas, and (3) to generate heat. The catalyst poisoning 
agents (oil and sulfur) as well as the temperature exposure are the 
same between the two methods and the DARAP test program data 
corroborates this. This protocol is intended to be representative of 
field aging, includes exposure to elements of both thermal and chemical 
aging, and is designed to achieve an acceleration of aging that is ten 
times a dynamometer or field test (1,000 hours of accelerated aging 
would be equivalent to 10,000 hours of standard aging).
    The initial step in the method requires the gathering and analysis 
of input field data that represent a greater than average exposure to 
potential field aging factors. The field aging factors consist of 
thermal, oil, and sulfur exposure. The thermal exposure is based on the 
average exhaust temperature; however, if the engine family incorporates 
a periodic infrequent regeneration event that involves exposure to 
higher temperatures than are observed during normal (non-regeneration) 
operation, then this temperature is used. Oil exposure is based on 
field and laboratory measurements to determine an average rate of oil 
consumption in grams per hour that reaches the exhaust. Sulfur exposure 
is based on the sum of fuel- and oil-related sulfur consumption rates 
for the engine family. The procedure provides details on how to gather 
data from field vehicles to support the generation and analysis of the 
field data.
    Next, the method requires determination of key components for 
aging. Most diesel aftertreatment systems contain multiple catalysts, 
each with their own aging characteristics. This accelerated aging 
procedure ages the system, not component-by-component. Therefore, it is 
necessary to determine which catalyst components are the key components 
that will be used for deriving and scaling the aging cycle. This 
includes identification of the primary and secondary catalysts in the 
aftertreatment system, where the primary is the catalyst that is 
directly responsible for most of the NOX reduction, such as 
a urea SCR catalyst in a compression-ignition aftertreatment system. 
The secondary is the catalyst that is intended to either alter exhaust 
characteristics or generate elevated temperature upstream of the 
primary catalyst, such as a DOC placed upstream of an SCR catalyst, 
with or without a DPF in between.
    The next step in the process is to determine the thermal 
deactivation rate constant(s) for each key component. This is used for 
the thermal heat load calculation in the accelerated aging protocol. 
The calculations for thermal degradation are based on the use of an 
Arrhenius rate law function to model cumulative thermal degradation due 
to heat exposure. The process of determining the thermal deactivation 
rate constant begins with determining what catalyst characteristic will 
be tracked as the basis for measuring thermal deactivation. Generally, 
ammonia storage is the key aging metric for zeolite-based SCR 
catalysts, NOX reduction efficiency at low temperature for 
vanadium-based SCR catalysts, conversion rate of NO to NO2 
for DOCs with a downstream SCR catalyst, and HC reduction efficiency 
(as measured using ethylene) at 200 [deg]C for DOCs where the 
aftertreatment system does not contain an SCR catalyst for 
NOX reduction. Thermal degradation experiments are then 
carried out over at least three different temperatures that accelerate 
thermal deactivation such that measurable changes in the aging metric 
can be observed at multiple time points over the course of no more than 
50 hours. During these experiments it is important to void temperatures 
that are too high to prevent rapid catalyst failure by a mechanism that 
does not represent normal aging.
    Generation of the accelerated aging cycle for a given application 
involves analysis of the field data to determine a set of aging modes 
that will represent that field operation. There are two methods of 
cycle generation in 40 CFR 1065.1139, each of which is described 
separately. Method 1 involves the direct application of field data and 
is used when the recorded data includes sufficient exhaust flow and 
temperature data to allow for determination of aging conditions 
directly from the field data set. Method 2 is meant to be used when 
insufficient flow and temperature data is available from the field 
data. In Method 2, the field data is used to weight a set of modes 
derived from the laboratory certification cycles for a given 
application. These weighted modes are then combined with laboratory 
recorded flow and temperatures on the certification cycles to derive 
aging modes. There are two different cases to consider for aging cycle 
generation, depending on whether or not a given aftertreatment system 
incorporates the use of a periodic regeneration event. For the purposes 
of cycle generation, a regeneration is any event where the operating 
temperature of some part of the aftertreatment system is raised beyond 
levels that are observed during normal (non-regeneration) operation. 
The analysis of regeneration data is considered separately from normal 
operating data.
    The process of cycle generation begins with the determination of 
the number of bench aging hours. The input into this calculation is the 
number of real or field

[[Page 4386]]

hours that represent the useful life for the target application. The 
target for the accelerated aging protocol is a 10-time acceleration of 
the aging process, therefore the total number of aging hours is set at 
service accumulation hours minus required engine dynamometer aging 
hours divided by 10. The hours will then be among different operating 
modes that will be arranged to result in repetitive temperature cycling 
over that period. For systems that incorporate periodic regeneration, 
the total duration will be split between regeneration and normal (non-
regeneration) operation. The analysis of the operation data develops a 
reduced set of aging modes that represent normal operation using either 
Method 1 or Method 2. Method 1 is a direct clustering method and 
involves three steps: Clustering analysis, mode consolidation, and 
cycle building.\390\ This method is used when sufficient exhaust flow 
and temperature data are available directly from the field data. Method 
2 is a cluster-based weighting of certification cycle modes when there 
is insufficient exhaust flow and temperature data from the field at the 
time the cycle is being developed. The initial candidate mode 
conditions are temperature and flow rate combinations that are the 
centroids from the analysis of each cluster.
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    \390\ https://documentation.sas.com/doc/en/emref/14.3/
n1dm4owbc3ka5jn11yjkod7ov1va.htm#:~:text=The%20cubic%20clustering%20c
riterion%20(CCC,evaluated%20by%20Monte%20Carlo%20methods.
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    The target for accelerated aging cycle operation is to run all the 
regenerations that would be expected over the course of useful life and 
the procedure provides a process for determining a representative 
regeneration profile that will be used during aging. Heat load 
calculation and cycle tuning are performed after the preliminary cycles 
have been developed for both normal and regeneration operation. The 
target cumulative deactivation is determined from the input field data, 
and then a similar calculation is performed for the preliminary aging 
cycle. If the cumulative deactivation for the preliminary cycle does 
not match cumulative deactivation from the field data, then the cycle 
is tuned over a series of steps described in 40 CFR 1065.1139 until the 
target is matched.
    The final assembly of the candidate accelerated aging cycle 
involves the assembly of the target modes into a schedule of modes laid 
out on a time basis that can be repeated until the target number of 
aging hours has been reached. For cycles that incorporate periodic 
regeneration modes, the regeneration frequency and duration, including 
any regeneration extension added to reach thermal targets, will be used 
to determine the length of the overall cycle. The number of these 
cycles that is run is equal to the total number of regenerations over 
full useful life. The duration of each cycle is total number of 
accelerated aging hours divided by the total number of regenerations. 
For multiple components with differing regeneration schedules, this 
calculation is performed using the component with the fewest total 
number of regenerations. The regeneration events for the more 
frequently regenerating components should be spaced evenly throughout 
each cycle to achieve the appropriate regeneration frequency and 
duration.
    The regeneration duration (including extension) is then subtracted 
from the base cycle duration to calculate the duration of normal (non-
regeneration) operation in seconds. This time is split among the normal 
(non-regeneration) modes in proportion to the overall target aging time 
in each mode. These modes are then split and arranged to achieve the 
maximum thermal cycling between high and low temperatures. No mode may 
have a duration shorter than 900 seconds, not including transition 
time. Mode transitions must be at least 60 seconds long and must be no 
longer than 300 seconds. The transition period is considered complete 
when you are within 5 [deg]C of the target temperature for the primary 
key component. For modes longer than 1800 seconds, you may count the 
transition time as time in mode. For modes shorter than 1800 seconds, 
under the procedure you must not count the transition time as time in 
mode. Modes are arranged in alternating order starting with the lowest 
temperature mode and proceeding to the highest temperature mode, 
followed by the next lowest temperature mode, and so forth.
    The final cycle is expressed as a schedule of target temperature, 
exhaust flow rate, and NOX. For a burner-based platform with 
independent control of these parameters, this cycle can be used 
directly. For an engine-based platform, it is necessary to develop a 
schedule of speed and load targets that will produce the target exhaust 
conditions based on the capabilities of the engine platform.
    The accelerated oil consumption target is calculated at 10 times 
the field average oil consumption that was determined from the field 
data and/or laboratory measurements. Under the procedure, this oil 
consumption rate must be achieved on average over the aging cycle, and 
it must at least be performed during all non-regeneration modes. Under 
the procedure, the lubricating oil chosen must meet the normal in-use 
specifications and it cannot be altered. The oil is introduced by two 
pathways, a bulk pathway and a volatile pathway. The bulk pathway 
involves introduction of oil in a manner that represents oil passing 
the piston rings, and the volatile pathway involves adding small amount 
of lubricating oil to the fuel. Under the procedure, the oil introduced 
by the volatile pathway must be between 10 percent and 30 percent of 
the total accelerated oil consumption.
    Sulfur exposure related to oil is already taken care of via 
acceleration of the oil consumption itself. The target cumulative fuel 
sulfur exposure is calculated using the field recorded average fuel 
rate data and total field hours assuming a 10-ppm fuel sulfur level 
(which was determined as the 90th percentile of available fuel survey 
data).
    For an engine-based accelerated aging platform where the engine is 
used as the exhaust gas source, accelerated fuel sulfur is introduced 
by increasing the fuel sulfur level. The cycle average fuel rate over 
the final aging cycle is determined once that target modes have been 
converted into an engine speed and load schedule. The target aging fuel 
sulfur level that results in reaching the target cumulative fuel sulfur 
exposure is determined from the field data using the aging cycle 
average fuel rate and the total number of accelerated aging hours.
    For a burner-based platform, accelerated fuel sulfur is introduced 
directly as gaseous SO2. Under the procedure, the 
SO2 must be introduced in a manner that does not impede any 
burner combustion, and only in a location that represents the exhaust 
conditions entering the aftertreatment system. Under the procedure, the 
mass rate of sulfur that must be introduced on a cycle average basis to 
reach the target cumulative fuel sulfur exposure from the field data is 
determined after the final aging cycle has been generated.
    The accelerated aging protocol is run on a bench aging platform 
that includes features necessary to successfully achieve accelerated 
aging of thermal and chemical aging factors. This aging bench can be 
built around either an engine or a burner as the core heat generating 
element. The requirements for both kinds of bench aging platform are 
described in the following paragraphs.
    The engine-based accelerated aging platform is built around the use 
of a diesel engine for generation of heat and flow. The engine used 
does not need to be the same engine as the application that is being 
aged. Any diesel engine can be used, and the engine may be

[[Page 4387]]

modified as needed to support meeting the aging procedure requirements. 
You may use the same bench aging engine for deterioration factor 
determination from multiple engine families. The engine must be capable 
of reaching the combination of temperature, flow, NOX, and 
oil consumption targets required. Using an engine platform larger than 
the target application for a given aftertreatment system can provide 
more flexibility to achieve the target conditions and oil consumption 
rates.
    To increase the range of flexibility of the bench aging engine 
platform, the test cell setup should include additional elements to 
allow more independent control of exhaust temperature and flow than 
would be available from the engine alone. For example, exhaust heat 
exchangers and/or the use of cooled and uncooled exhaust pipe can be 
useful to provide needed flexibility. When using heat exchangers under 
this procedure, you must ensure that you avoid condensation in any part 
of the exhaust system prior to the aftertreatment. You can also control 
engine parameters and the calibration on the engine to achieve 
additional flexibility needed to reach the target exhaust conditions.
    Under this procedure, oil consumption must be increased from normal 
levels to reach the target of 10 times oil consumption. As noted 
earlier, oil must be introduced through a combination of a bulk 
pathway, which represents the majority of oil consumption past the 
piston rings, and a volatile pathway, which is achieved by adding small 
amounts of lube oil to the fuel. The total oil exposure via the 
volatile pathway must be between 10 percent and 30 percent of the total 
accelerated oil consumption. Under this procedure, the remainder of the 
oil consumption must be introduced via the bulk pathway. The volatile 
portion of the oil consumption should be introduced and monitored 
continuously via a mass flow meter or controller.
    Under this procedure, the engine will need to be modified to 
increase oil consumption via the bulk pathway. This increase is 
generally achieved through a combination of engine modifications and 
the selection of aging speed/load combinations that will result in 
increased oil consumption rates. To achieve this, you may modify the 
engine in a fashion that will increase oil consumption in a manner such 
that the oil consumption is still generally representative of oil 
passing the piston rings into the cylinder. Inversion of the top 
compression rings as a method which has been used to increase oil 
consumption successfully for the DAAAC aging program at SwRI. A 
secondary method that has been used in combination with the primary 
method involves the modification of the oil control rings in one or 
more cylinders to create small notches or gaps (usually no more than 
two per cylinder) in the top portion of the oil control rings that 
contact the cylinder liner (care must be taken to avoid compromising 
the structural integrity of the ring itself).
    Under this procedure, oil consumption for the engine-based platform 
must be tracked at least periodically via a drain and weigh process, to 
ensure that the proper amount of oil consumption has been achieved. It 
is recommended that the test stand include a constant volume oil system 
with a sufficiently large oil reservoir to avoid oil ``top-offs'' 
between oil change intervals. Under this procedure, periodic oil 
changes will be necessary on any engine platform, and it is recommended 
that the engine be run for at least 72 hours following an oil change 
with engine exhaust not flowing through the aftertreatment system to 
stabilize oil consumption behavior before resuming aging. A secondary 
method for tracking oil consumption is to use clean DPF weights to 
track ash loading, and compare this mass of ash to the amount predicted 
using the measured oil consumption mass and the oil ash concentration. 
The mass of ash found by DPF weight should fall within a range of 55 
percent to 70 percent of the of mass predicted from oil consumption 
measurements.
    The engine should also include a means of introducing supplemental 
fuel to the exhaust to support regeneration if regeneration events are 
part of the aging. This can be done either via post-injection from the 
engine or using in-exhaust injection. The method and location of 
supplemental fuel introduction should be representative of the approach 
used on the target application, but manufacturers may adjust this 
methodology as needed on the engine-based aging platform to achieve the 
target regeneration temperature conditions.
    The burner-based aging platform is built around a fuel-fired burner 
as the primary heat generation mechanism. For the accelerated aging 
application under this procedure, the burner must utilize diesel fuel 
and it must produce a lean exhaust gas mixture. Under this procedure, 
the burner must have the ability to control temperature, exhaust flow 
rate, NOX, oxygen, and water to produce a representative 
exhaust mixture that meets the accelerated aging cycle targets for the 
aftertreatment system to be aged. Under this procedure, the burner must 
include a means to monitor these constituents in real time, except in 
the case of water where the system's water metering may be verified via 
measurements made prior to the start of aging (such as with an FTIR) 
and should be checked periodically by the same method. Under this 
procedure, the accelerated aging cycle for burner-based aging must also 
include representative mode targets for oxygen and water, because these 
will not necessarily be met by the burner itself through combustion. As 
a result, for this procedure the burner will need features to allow the 
addition of water and the displacement of oxygen to reach 
representative target levels of both. During non-regeneration modes, it 
is recommended that the burner be operated in a manner to generate a 
small amount of soot to facilitate proper ash distribution in the DPF 
system.
    The burner-based platform requires methods for oil introduction for 
both the bulk pathway and the volatile pathway. For the bulk pathway, 
manufacturers may implement a method that introduces lubricating oil in 
a region of the burner that does not result in complete combustion of 
the oil, but at the same time is hot enough to oxidize oil and oil 
additives in a manner similar to what occurs when oil enters the 
cylinder of an engine past the piston rings. Care must be taken to 
ensure the oil is properly atomized and mixed into the post-combustion 
burner gases before they have cooled to normal exhaust temperatures, to 
insure proper digestion and oxidation of the oil constituents. The 
volatile pathway oil is mixed into the burner fuel supply and combusted 
in the burner. As noted earlier, under this procedure total oil 
exposure via the volatile pathway must be between 10 percent and 30 
percent of the total accelerated oil consumption. The consumption of 
oil in both pathways should be monitored continuously via mass flow 
meters or controllers. A secondary method of tracking oil consumption 
is to use clean DPF weights to track ash loading and compare this mass 
of ash to the amount predicted using the measured oil consumption mass 
and the oil ash concentration. The mass of ash found by DPF weight 
should fall within a range of 55 percent to 70 percent of the of mass 
predicted from oil consumption measurements. This will also ensure that 
injected oil mass is actually done in a representative manner so that 
it reaches the aftertreatment system.
    Under this procedure, the burner-based platform will also need a 
method to introduce and mix gaseous SO2 to achieve the 
accelerated sulfur targets. Under this procedure, the consumption

[[Page 4388]]

of SO2 must be monitored continuously via a mass flow meter 
or controller. SO2 does not need to be injected during 
regeneration modes.
    The burner-based platform should also include a means of 
introducing supplemental fuel to the exhaust to support regeneration if 
regeneration events are part of the aging. We recommend that the method 
and location of supplemental fuel introduction be representative of the 
approach used on the target application, but manufacturers may adjust 
this methodology as needed on the bench engine platform to achieve the 
target regeneration temperature conditions. For example, to simulate 
post-injected fuel we recommend to introduce the supplemental fuel into 
the post-combustion burner gases to achieve partial oxidation that will 
produce more light and partially oxidized hydrocarbons similar to post-
injection.
    There are specific requirements for the implementation, running, 
and validation of an accelerated aging cycle developed using the 
processes described in this section. Some of these requirements are 
common to both engine-based and burner-based platforms, but others are 
specific to one platform type or the other.
    We recommended carrying out one or more practice aging cycles to 
help tune the cycle and aging platform to meet the cycle requirements. 
These runs can be considered part of the de-greening of test parts, or 
these can be conducted on a separate aftertreatment.
    The final target cycle is used to calculate a cumulative target 
deactivation for key aftertreatment components. Manufacturers must also 
generate a cumulative deactivation target line describing the linear 
relationship between aging hours and cumulative deactivation. The 
temperature of all key components is monitored during the actual aging 
test and the actual cumulative deactivation based on actual recorded 
temperatures is calculated. The cumulative deactivation must be 
maintained to within 3 percent of the target line over the course of 
the aging run and if you are exceeding these limits, you must adjust 
the aging stand parameters to ensure that you remain within these 
limits. Under this procedure, you must stay within these limits for all 
primary key components. It should be noted that any adjustments made 
may require adjustment of the heat rejection through the system if you 
are seeing different behavior than the target cycle suggests based on 
the field data. If you are unable to meet this requirement for any 
tracked secondary system (for example for a DOC where the SCR is the 
primary component), you may instead track the aging metric directly and 
show that you are within 3 percent of the target aging metric. Note 
that this is more likely to occur when there is a large difference 
between the thermal reactivity coefficients of different components.
    Calculate a target line for oil accumulation and sulfur 
accumulation showing a linear relationship between aging hours and the 
cumulative oil exposure on a mass basis. Under this procedure, you must 
stay within 10 percent of this target line for oil 
accumulation, and within 5 percent of this target line for 
sulfur accumulation. In the case of engine-based bulk oil accumulation 
you will only be able to track this based on periodic drain and weigh 
measurements. For all other chemical aging components, track exposure 
based on the continuous data from the mass flow meters for these 
chemical components. If your system includes a DPF, it is recommend 
that you implement the secondary tracking of oil consumption using DPF 
ash loading measurements as describe earlier.
    For the engine-based platform, it will be necessary under this 
procedure to develop a schedule of engine operating modes that achieve 
the combined temperature, flow, and oil consumption targets. You may 
deviate from target NOX levels as needed to achieve these 
other targets, but we recommend that you maintain a NOX 
level representative of the target application or higher on a cycle 
average basis. Note that the need to operate at modes that can reach 
the target oil consumption will leverage the flexibility of the engine 
stand, and you may need to iterate on the accelerated oil consumption 
modifications to achieve a final target configuration. You may need to 
adjust the cycle or modify the oil consumption acceleration to stay 
within the 10 percent target. In the even that you find 
that actual fuel consumption varies from original assumptions, you may 
need to adjust the doped fuel sulfur level periodically to maintain the 
sulfur exposure within the 5 percent limit.
    If the application uses DEF, it must be introduced to the exhaust 
stream in a manner that represents the target application. You may use 
hardware that is not identical to the production hardware but ensure 
that hardware produces representative performance. Similarly, you may 
use hardware that is not identical to production hardware for fuel 
introduction into the exhaust as long you ensure that the performance 
is representative.
    Under this procedure, for the burner-based platform, you will be 
able to directly implement the temperature, flow, NOX, 
sulfur, and oil consumption targets. You will also need to implement 
water and O2 targets to reach levels representative of 
diesel exhaust. We recommend that you monitor and adjust oil and sulfur 
dosing on a continuous basis to stay within targets. You must verify 
the performance of the oil exposure system via the secondary tracking 
of oil exposure via DPF ash loading and weighing measurements. This 
will ensure that your oil introduction system is functioning correctly. 
If you use a reductant, such as DEF, for NOX reduction, use 
good engineering judgement to introduce DEF in a manner that represents 
the target application. You may use hardware that is not identical to 
the production hardware but ensure that the hardware produces 
representative performance. Similarly, you may use hardware that is not 
identical to production hardware for fuel introduction into the exhaust 
as long you ensure that the performance is representative.
    The implementation and carrying out of these procedures will enable 
acceleration of the deterioration factor determination testing, and 
generally allow the determination of the deterioration factor out to 
useful life, over 90 days of testing.

G. Averaging, Banking, and Trading

    EPA is finalizing an averaging, banking, and trading (ABT) program 
for heavy-duty engines that provides manufacturers with flexibility in 
their product planning while encouraging the early introduction of 
emissions control technologies and maintaining the expected emissions 
reductions from the program. Several core aspects of the ABT program we 
are finalizing are consistent with the proposed ABT program, but the 
final ABT program includes several updates after consideration of 
public comments. In particular, EPA requested comment on and agrees 
with commenters that a lower family emission limit (FEL) cap than 
proposed is appropriate for the final rule. Further, after 
consideration of public comments, EPA is not finalizing at this time 
the proposed Early Adoption Incentives program, and in turn we are not 
including emissions credit multipliers in the final program. Rather, we 
are finalizing an updated version of the proposed transitional credit 
program under the ABT program. As described in preamble Section IV.G.7, 
the revised transitional credit program that we are finalizing provides 
four pathways to generate straight NOX

[[Page 4389]]

emissions credits (i.e., no credit multipliers) that are valued based 
on the extent to which the engines generating credits comply with the 
requirements we are finalizing for MY 2027 and later (e.g., credits 
discounted at a rate of 40 percent for engines meeting a lower numeric 
standard but none of the other MY 2027 and later requirements) (see 
section 12 of the Response to Comments document and preamble Section 
IV.G.7 for more details). In addition, we are finalizing a production 
volume allowance for MYs 2027 through 2029 that is consistent with the 
proposal but different in several key aspects, including that 
manufacturers will be required to use NOX emissions credits 
to certify heavy heavy-duty engines compliant with MY 2010 requirements 
in MYs 2027 through 2029 (see Section IV.G.9 for details). Finally, we 
are not finalizing the proposed allowance for manufacturers to generate 
NOX emissions credits from heavy-duty zero emissions 
vehicles (ZEVs) (see Section IV.G.10).
    Consistent with the proposed ABT program, the final ABT program 
will maintain several aspects of the ABT program currently specified in 
40 CFR 86.007-15, including:
     Allowing ABT of NOX credits with no expiration 
of the ABT program,
     calculating NOX credits based on a single 
NOX FEL for an engine family,
     specifying FELs to the same number of decimal places as 
the applicable standards, and
     calculating credits based on the work and miles of the FTP 
cycle.
    In this Section we briefly describe the proposed ABT program, the 
comments received on the proposed ABT program, and EPA's response to 
those comments. Subsequent subsections provide additional details on 
the restrictions we are finalizing for using emission credits in model 
years 2027 and later, such as averaging sets (Section IV.G.2), FEL caps 
(Section IV.G.4), and limited credit life (Section IV.G.4). See the 
proposed rule preamble (87 FR 17550, March 28, 2022) for additional 
discussion on the proposed ABT program and the history of ABT for 
heavy-duty engines.
    The proposed ABT program allowed averaging, banking, and trading of 
NOX credits generated against applicable heavy-duty engine 
NOX standards, while discontinuing a credit program for HC 
and PM. We also proposed new provisions to clarify how FELs apply for 
additional duty cycles. The proposed program included restrictions to 
limit the production of new engines with higher emissions than the 
standards; these restrictions included FEL caps, credit life for 
credits generated for use in MYs 2027 and later, and the expiration of 
currently banked credits. These provisions were included in proposed 40 
CFR part 1036, subpart H. and 40 CFR 1036.104(c). In addition, we 
proposed interim provisions in 40 CFR 1036.150(a)(1) describing how 
manufacturers could generate credits in MY 2024 through 2026 to apply 
in MYs 2027 and later. We requested comment on several aspects of the 
proposed ABT program that we are updating in the final rule, including 
the transitional credit program and level of the FEL cap, which 
restrict the use of credits in MY 2027 and later.
    Many commenters provided perspectives on the proposed ABT program. 
The majority of commenters supported the proposed ABT program, although 
several suggested adjustments for EPA to consider in the final rule. In 
contrast, a number of commenters opposed the proposed ABT program and 
argued that EPA should eliminate the NOX ABT program in the 
final rule. Perspectives from commenters supporting and opposing the 
proposed ABT program are briefly summarized in this section with 
additional details in section 12 of the Response to Comments document.
    Commenters supporting the ABT program stated that it provides an 
important flexibility to manufacturers for product planning during a 
transition to more stringent standards. They further stated that a 
NOX ABT program would allow manufacturers to continue 
offering a complete portfolio of products, while still providing real 
NOX emissions reductions. In contrast, commenters opposing 
the ABT program argued EPA should eliminate the NOX ABT 
program in order to maximize NOX emissions reductions 
nationwide, particularly in environmental justice communities and other 
areas impacted by freight industry. These commenters stated that the 
NOX standards are feasible without the use of credits, and 
that eliminating the credit flexibilities of an ABT program would be 
most consistent with EPA's legal obligations under the CAA.
    EPA agrees with those commenters who support a well-designed ABT 
program as a way to help us meet our emission reduction goals at a 
faster pace while providing flexibilities to manufacturers to meet new, 
more stringent emission standards. For example, averaging, banking, and 
trading can result in emissions reductions by encouraging the 
development and use of new and improved emission control technology, 
which results in lower emissions. The introduction of new emission 
control technologies can occur either in model years prior to the 
introduction of new standards, or during periods when there is no 
change in emissions standards but manufacturers still find it useful to 
generate credits for their overall product planning. In either case, 
allowing banking and trading can result in emissions reductions earlier 
in time, which leads to greater public health benefits sooner than 
would otherwise occur; benefits realized sooner in time are generally 
worth more to society than those deferred to a later time.\391\ These 
public health benefits are further ensured through the use of 
restrictions on how and when credits may be used (e.g., averaging sets, 
credit life), which are discussed further in this Section IV.G. For 
manufacturers, averaging, banking, and trading provides additional 
flexibility in their product planning by providing additional lead time 
before all of their engine families must comply with all the new 
requirements without the use of credits. For periods when no changes in 
emission standards are involved, banking can provide manufacturers 
additional flexibility, provide assurance against any unforeseen 
emissions-related problems that may arise, and in general provide a 
means to encourage the development and introduction of new engine 
technology (see 55 FR 30585, July 26, 1990, for additional discussion 
on potential benefits of an ABT program).
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    \391\ Consistent with economic theory, we assume that people 
generally prefer present to future consumption. We refer to this as 
the time value of money, which means money received in the future is 
not worth as much as an equal amount received today. This time 
preference also applies to emissions reductions that result in the 
health benefits that accrue from regulation. People have been 
observed to prefer health gains that occur immediately to identical 
health gains that occur in the future. Health benefits realized in 
the near term are therefore worth more to society than those 
deferred to a later time.
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    While EPA also agrees with those commenters stating that the 
standards in the final rule are feasible without the use of credits, as 
described in Section III of this preamble, given the technology-forcing 
nature of the final standards we disagree that providing an optional 
compliance pathway through the final rule's ABT program is inconsistent 
with requirements under CAA section 202(a)(3)(A).\392\ The final ABT 
program appropriately balances flexibilities for manufacturers to 
generate NOX

[[Page 4390]]

emissions credits with updated final restrictions (e.g., credit life, 
averaging sets, and family emissions limit (FEL) caps) that in our 
judgement both ensure that available emissions control technologies are 
adopted and maintain the emissions reductions expected from the final 
standards.\393\ An ABT program is also an important foundation for 
targeted incentives to encourage manufacturers to adopt advanced 
technology before required compliance dates, which we discuss further 
in preamble Section IV.G.7 and Section 12 of the Response to Comments 
document.
---------------------------------------------------------------------------

    \392\ See NRDC v. Thomas, 805 F. 2d 410, 425 (D.C. Cir. 1986), 
which upheld emissions averaging after concluding that ``EPA's 
argument that averaging will allow manufacturers more flexibility in 
cost allocation while ensuring that a manufacturer's overall fleet 
still meets the emissions reduction standards makes sense''.
    \393\ As discussed in Section IV.G.9, we are finalizing an 
allowance for manufacturers to continue to produce a small number (5 
percent of production volume) of engines that meet the current 
standards for a few model years (i.e., through MY 2030). See Section 
IV.G.9 for details on our approach and rationale for including this 
allowance in the final rule.
---------------------------------------------------------------------------

    One commenter opposing EPA's proposed NOX emissions ABT 
program provided analyses for EPA to consider in developing the final 
rule. EPA has evaluated the three approaches to generating credits in 
the commenter's analysis: (1) Engines certified below today's standards 
which qualify for the proposed transitional credit program, (2) engines 
certified to the CARB Omnibus standards which would quality for the 
proposed transitional program or on average achieve a standard below 
Federal requirements, and (3) ZEVs. For the first category (the 
transitional credit program), we considered several factors when 
designing the final transitional credit program that are more fully 
described in preamble Section IV.G.7; briefly, the transitional credit 
program we are finalizing will discount the credits manufacturers 
generated from engines certified to levels below today's standards 
unless manufacturers can meet all of the requirements in the final MY 
2027 and later standards. This includes meeting standards such as the 
final low load cycle (LLC), which requires demonstration of emissions 
control in additional engine operations (i.e., low load) compared to 
today's test cycles. For the second category in the commenter's 
analysis (engines certified to Omnibus standards), we recognize that 
our proposed rule preamble may have been unclear regarding how the 
existing regulations in part 86 and part 1036 apply for purposes of 
participation in the Federal ABT program to engines that are certified 
to state standards that are different than the Federal standards. We 
proposed to migrate without substantive modification the definition of 
``U.S.-directed production'' in 40 CFR 86.004-2 to 40 CFR part 1036.801 
for criteria pollutant engine requirements, to match the existing 
definition for GHG engine requirements, which excludes engines 
certified to state emission standards that are different than the 
Federal standards.\394\ The relevant existing NOX ABT credit 
program requirements, and the relevant program requirements we are 
finalizing as proposed, specify that compliance through ABT does not 
allow credit calculations to include engines excluded from the 
definition of U.S.-directed production volume.\395\ For the third 
category in the commenter's analysis (ZEVs), as discussed in preamble 
Section IV.G.10 and section 12 of the Response to Comments document, we 
are not finalizing the proposed allowance for manufacturers to generate 
NOX credits from ZEVs. For these reasons, EPA believes the 
final ABT program will at a minimum maintain the emissions reductions 
projected from the final rule, and in fact could result in greater 
public health benefits by resulting in emissions reductions earlier in 
time than they would occur without banking or trading. Further, if 
manufacturers generate NOX emissions credits that they do 
not subsequently use (e.g., due to transitioning product lines to 
ZEVs), then the early emissions reductions from generating these 
credits will result in more emission reductions than our current 
estimates reflect. In addition, the final ABT program provides an 
important flexibility for manufacturers, which we expect will help to 
ensure a smooth transition to the new standards and avoid delayed 
emissions reductions due to slower fleet turnover than may occur 
without the flexibility of the final ABT program.
---------------------------------------------------------------------------

    \394\ See Section XI.B.4 for additional information.
    \395\ See final part 1036, subpart H. Existing 40 CFR 
1036.705(c) states the following, which we are finalizing as 
proposed as also applicable to NOX ABT: ``As described in 
Sec.  1036.730, compliance with the requirements of this subpart is 
determined at the end of the model year based on actual U.S.-
directed production volumes. Keep appropriate records to document 
these production volumes. Do not include any of the following 
engines to calculate emission credits: . . . (4) Any other engines 
if we indicate elsewhere in this part 1036 that they are not to be 
included in the calculations of this subpart.'' See also existing 40 
CFR 86.007-15 (regarding U.S.-directed production engines for the 
purpose of using or generating credits during a phase-in of new 
standards) and 66 FR 5114, January 18, 2001.
---------------------------------------------------------------------------

    In the subsections that follow we briefly summarize and provide 
responses to comments on several more specific topics, including: ABT 
for pollutants other than NOX (IV.G.1), Applying the ABT 
provisions to multiple NOX duty-cycle standards (IV.G.2), 
Averaging Sets (IV.G.3), FEL caps (IV.G.4), Credit Life (IV.G.5), 
Existing credits (IV.G.6), Transitional Credits (IV.G.7), the proposed 
Early Adoption Incentives (IV.G.8), and a Production Volume Allowance 
under ABT (IV.G.9). The final ABT program is specified in 40 CFR part 
1036, subpart H.\396\ Consistent with the proposal, we are also 
finalizing a new paragraph at 40 CFR 1036.104(c) to specify how the ABT 
provisions will apply for MY 2027 and later heavy-duty engines subject 
to the final criteria pollutant standards in 40 CFR 1036.104(a). The 
Transitional Credit program in the final rule is described in the 
interim provision in 40 CFR 1036.150(a)(1), which we are finalizing 
with revisions from the proposal.
---------------------------------------------------------------------------

    \396\ As proposed, the final rule does not include substantive 
revisions to the existing GHG provisions in 40 CFR 1036, subpart H; 
as proposed, the final revisions clarify whether paragraphs apply 
for criteria pollutant standards or GHG standards.
---------------------------------------------------------------------------

1. ABT for Pollutants Other Than NOX
    After consideration of public comments, EPA is choosing to finalize 
as proposed an ABT program that will not allow averaging, banking, or 
trading for HC (including NOX+NMHC) or PM for MY 2027 and 
later engines. This includes not allowing HC and PM emissions credits 
from prior model years to be used for MY 2027 and later engines. For 
engines certified to MY 2027 or later standards, manufacturers must 
demonstrate in their application for certification that they meet the 
final PM, HC, and CO emission standards in 40 CFR 1036.104(a) without 
using emission credits.
    Several commenters supported EPA's proposal to discontinue ABT for 
HC and PM. These commenters stated that current heavy-duty engine 
technologies can easily meet the proposed HC and PM standards, and 
therefore an ABT program for these pollutants is not necessary. Some 
commenters urged EPA to provide ABT programs for HC and CO based on the 
stringency of the standards for these pollutants, particularly for 
Spark-ignition HDE. Another commenter did not indicate support or 
opposition to an HC ABT flexibility in general, but stated that EPA 
should not base the final HC standard on the use of HC emissions 
credits since doing so could lead to competitive disruptions between SI 
engine manufacturers. One commenter also urged EPA to consider ABT 
programs for regulated pollutant emissions other than NOX, 
including HC, PM, CO, and N2O.
    As discussed in preamble Section III, EPA demonstrated that the 
final standards for NOX, HC, CO, and PM area feasible for 
all engine classes, and we

[[Page 4391]]

set the numeric values without assuming manufacturers would require the 
use of credits to comply. We proposed to retain and revise the 
NOX ABT program and we are updating from our proposal in 
this final rule as described in the following sections.
    For PM, manufacturers are submitting certification data to the 
agency for current production engines well below the final PM standard 
over the FTP duty cycle; the final standard ensures that future engines 
will maintain the low level of PM emissions of the current engines. 
Manufacturers are not using PM credits to certify today and we received 
no new data showing manufacturers would generate or use PM credits 
starting in MY 2027; therefore, we are finalizing as proposed.
    We disagree with commenters indicating that credits will be needed 
for Spark-ignition HDE to meet the final HC and CO standards. Our SI 
engine demonstration program data show feasibility of the final 
standards (see preamble Section III.D for details). Furthermore, as 
described in Section IV.G.3, we are retaining the current ABT 
provisions that restrict credit use to within averaging sets and we 
expect SI engine manufacturers, who have few heavy-duty engine 
families, will have limited ability to generate and use credits. See 
preamble Section III.D for a discussion of the final numeric levels of 
the Spark-ignition HDE standards and adjustments we made to the 
proposed HC and CO stringencies after further consideration.
    We did not propose or request comment on expanding the heavy-duty 
engine ABT program to include other regulated pollutant emissions, such 
as N2O, and thus are not including additional pollutants in 
the final ABT program.
2. Multiple Standards and Duty Cycles for NOX ABT
    Under the current and final ABT provisions, FELs serve as the 
emission standards for the engine family for compliance testing 
purposes.\397\ We are finalizing as proposed new provisions to ensure 
the NOX emission performance over the FTP is proportionally 
reflected in the range of cycles included in the final rule for heavy-
duty engines.\398\ Specifically, manufacturers will declare a FEL to 
apply for the FTP standards and then they will calculate a 
NOX FEL for the other applicable cycles by applying an 
adjustment factor based on their declared FELFTP. As 
proposed, the adjustment factor in the final rule is a ratio of the 
declared NOX FELFTP to the FTP NOX 
standard to scale the NOX FEL of the other duty cycle or 
off-cycle standards.\399\ For example, if a manufacturer declares an 
FELFTP of 25 mg NOX/hp-hr in MY 2027 for a Medium 
HDE, where the final NOX standard is 35 mg/hp-hr, a ratio of 
25/35 or 0.71 will be applied to calculate a FEL to replace each 
NOX standard that applies for these engines in the proposed 
40 CFR 1036.104(a). Specifically, for this example, a Medium HDE 
manufacturer would replace the full useful life standards for SET, LLC, 
and the three off-cycle bins with values that are 0.71 of the final 
standards. For an SI engine manufacturer that declares an 
FELFTP of 15 mg NOX/hp-hr compared to the final 
MY 2027 standard of 35 mg/hp-hr, a ratio of 15/35 or 0.43 would be 
applied to the SET duty cycle standard to calculate an 
FELSET. Note that an FELFTP can also be higher 
than the NOX standard in an ABT program if it is offset by 
lower-emitting engines in an engine family that generates equivalent or 
more credits in the averaging set (see 40 CFR 1036.710). For a FEL 
higher than the NOX standard, the adjustment factor will 
proportionally increase the emission levels allowed when manufacturers 
demonstrate compliance over the other applicable cycles. Manufacturers 
are required to set the FEL for credit generation such that the engine 
family's measured emissions are at or below the respective FEL of all 
the duty-cycle and off-cycle standards. For instance, if a CI engine 
manufacturer demonstrates NOX emissions on the FTP that is 
25 percent lower than the standard but can only achieve 10 percent 
lower NOX emissions for the low load cycle, the declared FEL 
could be no less than 10 percent below the FTP standard, to ensure the 
proportional FELLLC would be met.
---------------------------------------------------------------------------

    \397\ The FELs serves as the emission standard for compliance 
testing instead of the standards specified in 40 CFR 1036.104(a); 
the manufacturer agrees to meet the FELs declared whenever the 
engine is tested over the applicable duty- or off-cycle test 
procedures.
    \398\ See the proposed rule preamble (87 FR 17550, March 28, 
2022) for discussion on the relationship between the current FTP 
standards and other duty- or off-cycle standards.
    \399\ As proposed, we will require manufacturers to declare the 
NOX FEL for the FTP duty cycle in their application for 
certification. Manufacturers and EPA will calculate FELs for the 
other applicable cycles using the procedures specified in 40 CFR 
1036.104(c)(3) to evaluate compliance with the other cycles; 
manufacturers will not be required to report the calculated FELs for 
the other applicable cycles. As noted previously, manufacturers will 
demonstrate they meet the standards for PM, CO, and HC and will not 
calculate or report FELs for those pollutants.
---------------------------------------------------------------------------

    In the final program, manufacturers will include test results in 
the certification application to demonstrate their engines meet the 
declared FEL values for all applicable duty cycles (see 40 CFR 
1036.240(a), finalized as proposed). For off-cycle standards, we are 
also finalizing as proposed the requirement for manufacturers to 
demonstrate that all the CI engines in the engine family comply with 
the final off-cycle emission standards (or the corresponding FELs for 
the off-cycle bins) for all normal operation and use by describing in 
sufficient detail any relevant testing, engineering analysis, or other 
information (see 40 CFR 1036.205(p)). These same bin standards (or 
FELs) apply for the in-use testing provisions finalized in 40 CFR part 
1036, subpart E, and for the PEM-based DF verification in the finalized 
40 CFR 1036.246(b)(2), if applicable.\400\ In addition, as discussed in 
Section III, we are finalizing a compliance margin for Heavy HDE to 
account for additional variability that can occur in-use over the 
useful life of HHDEs; the same 15 mg/hp-hr in-use compliance margin for 
HHDEs will be added to declared FELs when verifying in-use compliance 
for each of the duty-cycles (i.e., compliance with duty-cycle standards 
once the engine has entered commerce) (see 40 CFR 1036.104(a)). 
Similarly, the same in-use compliance margin will be applied when 
verifying in-use compliance over off-cycle standards (see preamble 
Section III.C for discussion).
---------------------------------------------------------------------------

    \400\ We did not propose and are not finalizing off-cycle 
standards for SI engines; if EPA requests SI engine manufacturers to 
perform PEMS-based DF verification as set forth in the final 40 CFR 
1036.246(b)(2), then the SI engine manufacturer would use their FEL 
to calculate the effective in-use standard for those procedures.
---------------------------------------------------------------------------

    Once FEL values are established, credits are calculated based on 
the FTP duty cycle. We did not propose substantive revisions to the 
equation that applies for calculating emission credits in 40 CFR 
1036.705, but we are finalizing, as proposed, to update the variable 
names and descriptions to apply for both GHG and criteria pollutant 
calculations.\401\ In Equation IV-1, we reproduce the equation of 40 
CFR 1036.705 to emphasize how the FTP duty cycle applies for 
NOX credits. Credits are calculated as megagrams (i.e., 
metric tons) based on the emission rate over the FTP cycle. The 
emission credit calculation represents the emission impact that would 
occur if an engine operated over the FTP cycle for its full useful 
life. The difference between the FTP standard and the FEL is multiplied 
by a conversion factor that represents the average work performed

[[Page 4392]]

over the FTP duty cycle to get the per-engine emission rate over the 
cycle. This value is then multiplied by the production volume of 
engines in the engine family and the applicable useful life mileage. 
Credits are calculated at the end of the model year using actual U.S. 
production volumes for the engine family. The credit calculations are 
submitted to EPA as part of a manufacturer's ABT report (see 40 CFR 
1036.730).
---------------------------------------------------------------------------

    \401\ The emission credits equations in the final 40 CFR 
1036.705 and the current 40 CFR 86.007-15(c)(1)(i) are functionally 
the same.
[GRAPHIC] [TIFF OMITTED] TR24JA23.001

---------------------------------------------------------------------------
Where:

StdFTP = the FTP duty cycle NOX emission 
standard, in mg/hp-hr, that applies for engines not participating in 
the ABT program
FEL = the engine family's FEL for NOX, in mg/hp-hr.
WorkFTP = the total integrated horsepower-hour over the 
FTP duty cycle.
MilesFTP = the miles of the FTP duty cycle. For Spark-
ignition HDE, use 6.3 miles. For Light HDE, Medium HDE, and Heavy 
HDE, use 6.5 miles.
Volume = the number of engine eligible to participate in the ABT 
program within the given engine family during the model year, as 
described in 40 CFR 1036.705(c).
UL = the useful life for the standard that applies for a given 
engine family, in miles.

    We did not receive specific comments on the proposed approach to 
calculate a NOX FEL for the other applicable cycles by 
applying an adjustment factor based on the declared FELFTP. 
As such, we are finalizing the approach as proposed.
3. Averaging Sets
    After consideration of public comments, we are finalizing, as 
proposed, to allow averaging, banking, and trading only within 
specified ``averaging sets'' for heavy-duty engine emission standards. 
Specifically, the final rule will use engine averaging sets that 
correspond to the four primary intended service classes,\402\ namely:
---------------------------------------------------------------------------

    \402\ Primary intended service class is defined in 40 CFR 
1036.140, which is referenced in the current 40 CFR 86.004-2.

 Spark-ignition HDE
 Light HDE
 Medium HDE
 Heavy HDE

    Some commenters urged EPA to allow manufacturers to move credits 
between the current averaging sets (e.g., credits generated by medium 
heavy-duty engines could be used by heavy heavy-duty engines), while 
other commenters recommended that EPA finalize the proposal to maintain 
restrictions that do not allow movement of credits between the current 
averaging sets. Those supporting movement of credits between averaging 
sets stated that doing so would reduce the likelihood that a 
manufacturer would develop two engines to address regulatory 
requirements when they could invest in only one engine if they were 
able to move credits between averaging sets; commenters also stated 
that restrictions on ABT decrease a manufacturer's ability to respond 
to changes in emissions standards. Those supporting the current 
restrictions that do not allow movement of credits between averaging 
sets stated that maintaining the averaging sets was important to avoid 
competitive disruptions between manufacturers.
    EPA agrees that maintaining the current averaging sets is important 
to avoid competitive disruptions between manufacturers; this is 
consistent with our current and historical approach to avoid creating 
unfair competitive advantages or environmental risks due to credit 
inconsistency.\403\ As described throughout this Section IV.G, we 
believe that the final ABT program, including this limitation, 
appropriately balances providing manufacturers with flexibility in 
their product planning, while maintaining the expected emissions 
reductions from the program. As we describe further in Section IV.G.7, 
we provide one exception to this limitation for one of the Transitional 
Credit pathways for reasons special to that program.\404\
---------------------------------------------------------------------------

    \403\ 55 FR 30585, July 26, 1990, 66 FR 5002 January 18, 2001 
and 81 FR 73478 October 25, 2016.
    \404\ As discussed in Section IV.G.7, one of the transitional 
credit pathways we are finalizing allows limited movement of 
discounted credits between a subset of averaging sets. The 
combination of discounting credits moved between averaging sets 
combined with the additional limitations included in this 
transitional pathway are intended to address the potential for 
competitive disadvantages or environmental risks from allowing 
credit movement between averaging sets.
---------------------------------------------------------------------------

4. FEL Caps
    As proposed, the final ABT program includes Family Emissions Limit 
(FEL) caps; however, after further consideration, including 
consideration of public comments, we are choosing to finalize lower FEL 
caps than proposed. The FEL caps in the final rule are 65 mg/hp-hr for 
MY 2027 through 2030, and 50 mg/hp-hr for MY 2031 and later (see 40 CFR 
1036.104(c)(2)). In this section, IV.G.4, we briefly summarize our 
proposed FEL caps, stakeholder comments on the proposed FEL caps, and 
then discuss EPA's responses to comments along with our rationale for 
the FEL caps in the final rule.
    We proposed maximum NOX FELFTP values of 150 
mg/hp-hr under both proposed Option 1 (for model year 2027 through 
2030), and proposed Option 2 (for model year 2027 and later). This 
value is consistent with the average NOX emission levels 
achieved by recently certified CI engines (see Chapter 3.1.2 of the 
RIA). We believed a cap based on the average NOX emission 
levels of recent engines would be more appropriate than a cap at the 
current standard of 0.2 g/hp-hr (200 mg/hp-hr), particularly when 
considering the potential for manufacturers to apply NOX 
credits generated from electric vehicles for the first time.\405\ For 
MY 2031 and later under Option 1, we proposed a consistent 30 mg/hp-hr 
allowance for each primary intended service class added to each full 
useful life standard.
---------------------------------------------------------------------------

    \405\ Note that the current g/hp-hr emission standards are 
rounded to two decimal places, which allow emission levels to be 
rounded down by as much as 5 mg/hp-hr (i.e., with rounding the 
current standard is 205 mg/hp-hr).
---------------------------------------------------------------------------

    We requested comment on our proposed FEL caps, including our 
approach to base the cap for MY 2027 through 2030 under Option 1, or MY 
2027 and later under Option 2, on the recent average NOX 
emission levels. We also requested comment on whether the 
NOX FELFTP cap in MY 2027 should be set at a 
different value, ranging from the current Federal NOX 
standard of approximately 200 mg/hp-hr to the 50 mg/hp-hr standard in 
CARB's HD Omnibus rule starting in MY 2024.406 407

[[Page 4393]]

We further requested comment on the proposal to set MY 2031 
NOX FEL caps at 30 mg/hp-hr above the full useful life 
standards under proposed Option 1. Finally, we requested comment on 
whether different FEL caps should be considered if we finalize 
standards other than those proposed (i.e., within the range between the 
standards of proposed Options 1 and 2) (See 87 FR 17550, March 28, 
2022, for additional discussion on our proposed FEL caps and historical 
perspective on FEL caps).
---------------------------------------------------------------------------

    \406\ California Air Resources Board, ``California Exhaust 
Emission Standards and Test Procedures for 2004 and Subsequent Model 
Heavy-Duty Diesel Engines and Vehicles,'' August 27, 2020. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2020/hdomnibuslownox/frob-1.pdf, page 19. Last accessed September 8, 
2022.
    \407\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule.
---------------------------------------------------------------------------

    Several commenters provided perspectives on the proposed FEL caps. 
All commenters urged EPA to finalize a lower FEL cap than proposed; 
there was broad agreement that the FEL cap in the final rule should be 
100 mg/hp-hr or lower.
    One commenter stated that a FEL cap at the level of the current 
standard would not meet the CAA 202(a)(3)(A) requirement to set 
``standards which reflect the greatest degree of emission reduction 
achievable through the application of technology which the 
Administrator determines will be available for the model year to which 
such standards apply''. Similarly, many commenters stated that EPA 
should finalize FEL caps that match the CARB Omnibus FEL caps (i.e., 
100 mg-hp-hr in 2024-2026 for all engine classes; 50 mg/hp-hr in 2027 
and later for LHDEs and MHDE and 65 mg/hp-hr in 2027-2030 and 70 mg/hp-
hr in 2031 and later for HHDEs). These commenters argue that aligning 
the FEL caps in the EPA final rule with those in the CARB Omnibus would 
reflect the technologies available in 2027 and later, and better align 
with the CAA 202(a)(3)(A) requirement for standards that reflect the 
greatest degree of emission reduction achievable. Commenters provide 
several lines of support that the CARB Omnibus FEL caps should provide 
the technical maximum for the EPA FEL caps. Namely, commenters stated 
that manufacturers will have been producing products to meet CARB 
Omnibus standard of 50 mg/hp-hr starting in 2024. They further state 
that two diesel engine families have been certified with CA for MY2022 
at a FEL of 160 mg/hp-hr, which is only slightly higher than the FEL 
EPA proposed under option 1 for MY 2027 and would continue under the 
proposed FEL cap until MY2030. Finally, a commenter pointed to SwRI 
data showing that 50 mg/hp-hr can be achieved with what the commenter 
considers to be ``minor changes to engine configuration.''
    Commenters further argue that EPA should not base the FEL cap in 
the final rule on the average performance of recently certified engines 
since these engines were designed to comply with the current standards, 
which were set over 20 years ago, and do not utilize the emissions 
controls technologies that would be available in 2027. Commenters 
stated that EPA did not consider the extent to which the proposed FEL 
cap could adversely affect the emissions reductions expected from the 
rule. Commenters note that although EPA has previously set the FEL cap 
at the level of the previous standard, the current FEL cap was set 
lower than the previous standard due to the 90 percent reduction 
between the previous standard and the current standard. Commenters 
argue that EPA should similarly set the FEL cap below the current 
standard given the same magnitude in reduction between the current and 
proposed standards, and the greater level of certainty in the 
technologies available to meet the standards in this rule compared to 
previous rules.
    Other commenters stated that a FEL cap of 100 mg/hp-hr, or between 
50 and 100 mg/hp-hr, would help to prevent competitive disruptions. 
Additional details on comments received on the proposed FEL caps are 
available in section 12.2 of the Response to Comments document.
    Our analysis and rationale for finalizing FEL caps of 65 mg/hp-hr 
in MY 2027 through 2030, and 50 mg/hp-hr in MY 2031and later includes 
several factors. First, we agree with commenters that the difference 
between the current (0.2 g/hp-hr) standard and the standards we are 
finalizing for MY 2027 and later suggests that FEL caps lower than the 
current standard are appropriate to ensure that available emissions 
control technologies are adopted. This is consistent with our past 
practice when issuing rules for heavy-duty onroad engines or nonroad 
engines in which there was a substantial (i.e., greater than 50 
percent) difference between the numeric levels of the existing and new 
standards (69 FR 38997, June 29, 2004; 66 FR 5111, January 18, 2001). 
Specifically, by finalizing FEL caps below the current standards, we 
are ensuring that the vast majority of new engines introduced into 
commerce include updated emissions control technologies compared to the 
emissions control technologies manufacturers use to meet the current 
standards.\408\
---------------------------------------------------------------------------

    \408\ As discussed in Section IV.G.9, we are finalizing an 
allowance for manufacturers to continue to produce a small number (5 
percent of production volume) of engines that meet the current 
standards for a few model years (i.e., through MY 2029); thus, the 
vast majority of, but not all, new engines will need to include 
updated emissions control technologies compared to those used to 
meet today's standards until MY 2031, when all engines will need 
updated emissions control technologies to comply with the final 
standards. See Section IV.G.9 for details on our approach and 
rationale for including this allowance in the final rule.
---------------------------------------------------------------------------

    Second, finalizing FEL caps below the current standard is 
consistent with comments from manufacturers stating that a FEL cap of 
100 mg/hp-hr or between 50 and 100 mg/hp-hr would help to prevent 
competitive disruptions (i.e., require all manufactures to make 
improvements in their emissions control technologies).
    The specific numeric levels of the final FEL caps were also 
selected to balance several factors. These factors include providing 
sufficient assurance that low-emissions technologies will be introduced 
in a timely manner, which is consistent with our past practice (69 FR 
38997, June 29, 2004), and providing manufacturers with flexibility in 
their product planning or assurance against unforeseen emissions-
related problems that may arise. In the early years of the program 
(i.e., MY2027 through 2030), we are finalizing a FEL cap of 65 mg/hp-hr 
to place more emphasis on providing manufacturers flexibility and 
assurance against unforeseen emissions control issues in order to 
ensure a smooth transition to the new standards and avoid market 
disruptions. A smooth transition in the early years of the program will 
help ensure the public health benefits of the final program by avoiding 
delayed emissions reductions due to slower fleet turnover than may 
occur without the flexibility of the final ABT. Thus, the final FEL cap 
in MY 2027 through 2030 can help to ensure the expected emissions 
reductions by providing manufacturers with flexibility to meet the 
final standards through the use of credits up to the FEL cap. In the 
later years of the program (i.e., MY 2031 and later), we are finalizing 
a FEL cap of 50 mg/hp-hr to place more emphasis on ensuring continued 
improvements in the emissions control technologies installed on new 
engines.
    We disagree with certain commenters stating that a certain numeric 
level of the FEL cap does or does not align with the CAA requirement to 
set ``standards which reflect the greatest degree of emission reduction 
achievable through the application of technology which the 
Administrator determines will be available for the model year to which 
such standards apply''; rather, given the technology-forcing nature of 
the final standards, an optional compliance

[[Page 4394]]

pathway, including the FEL caps and other elements of the ABT program, 
through the final rule is consistent with requirements under CAA 
section 202(a)(3)(A).\409\ Nevertheless, as described in this Section 
IV.G.4, we are finalizing lower FEL caps than proposed as part of a 
carefully balanced final ABT program that provides flexibilities for 
manufacturers to generate NOX emissions credits while 
assuring that available emissions control technologies are adopted and 
the emissions reductions expected from the final program are realized.
---------------------------------------------------------------------------

    \409\ See NRDC v. Thomas, 805 F. 2d 410, 425 (D.C. Cir. 1986) 
(upholding averaging as a reasonable and permissible means of 
implementing a statutory provision requiring technology-forcing 
standards).
---------------------------------------------------------------------------

    Finally, we disagree with commenters stating a FEL cap can 
adversely affect the emissions reductions expected from the final rule. 
Inherent in the ABT program is the requirement for manufacturers 
producing engines above the emissions standard to also produce engines 
below the standard or to purchase credits from another manufacturer who 
has produced lower emitting engines. As such, while the FEL cap 
constrains the extent to which engines can emit above the level of the 
standard, it does not reduce the expected emissions reductions because 
higher emitting engines must be balanced by lower emitting engines. 
Without credit multipliers, an ABT program, and the associated FEL cap, 
may impact when emissions reductions occur due to manufacturers 
choosing to certify some engines to a more stringent standard and then 
later use credits generated from those engines, but it does not impact 
the absolute value of the emissions reductions. Rather, to the extent 
that credits are banked, there would be greater emissions reductions 
earlier in the program, which leads to greater public health benefits 
sooner than would otherwise occur; as discussed earlier in this Section 
IV.G, benefits realized in the near term are worth more to society than 
those deferred to a later time.
    The FEL caps for the final rule have been set at a level to ensure 
sizeable emission reductions from the existing 2010 standards, while 
providing manufacturers with flexibility to meet the final standards. 
When combined with the other restrictions in the final ABT program 
(e.g., credit life, averaging sets, expiration of existing credit 
balances), we believe the final FEL caps of 65 mg/hp-hr in MY 2027 
through 2030, and 50 mg/hp-hr in MY 2031 and later avoid potential 
adverse effects on the emissions reductions expected from the final 
program.
5. Credit Life for MY 2027 and Later Credits
    As proposed, we are finalizing a five-year credit life for 
NOX emissions credits generated and used in MY 2027 and 
later, which is consistent with the existing credit life for 
CO2. In this section, IV.G.5, we briefly summarize our 
proposed credit life, stakeholder comments on the proposed credit life, 
and then discuss EPA's responses to comments along with our rationale 
for credit life in the final rule. Section IV.G.7 discusses credit life 
of credits generated in MYs 2022 through 2026 for use in 2027.
    We proposed to update the existing credit life provisions in 40 CFR 
1036.740(d) to apply for both CO2 and NOX 
credits. The proposal updated the current unlimited credit life for 
NOX credits such that NOX emission credits 
generated for use in MY 2027 and later could be used for five model 
years after the year in which they are generated.\410\ For example, 
under the proposal credits generated in model year 2027 could be used 
to demonstrate compliance with emission standards through model year 
2032. We also requested comment on our proposed five-year credit life.
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    \410\ As discussed in Section IV.G.10, we are not finalizing the 
proposed allowance for manufacturers to generate credits from BEVs 
or FCEVs, and thus the credit life provisions in 40 CFR 1036.740(d) 
do not apply to BEVs or FCEVs.
---------------------------------------------------------------------------

    Several commenters provided perspectives on the proposal to revise 
the credit life of NOX emissions credits from unlimited to 
five years. Commenters took several different positions, including 
supporting the proposed five-year credit life, arguing that three 
years, not five, is the more appropriate credit life period, and 
arguing that credit life should be unlimited. Additional details and a 
summary of comments received on the proposed credit life are available 
in section 12 of the Response to Comments document.
    The commenter supporting the proposed five-year credit life, rather 
than an unlimited credit life, states that they conducted an analysis 
that showed manufacturers had accrued credits from 2007-2009 MYs, which 
could have been used to certify engines up to the FEL cap in the 
Omnibus 2024-2026 program and would have delayed emissions reductions 
in those years. They further state that unlimited credit life would 
allow manufacturers to produce higher emitting engines against more 
stringent standards for many years (e.g., in MY2030).
    The commenter arguing that three (not five) years is an appropriate 
credit life to average out year-to-year variability stated that three 
years aligns with the CAA requirement for three years of stability 
between changes in standards, and it represents the pace of improvement 
that manufacturers include in their product planning. The commenter 
argues that three years would be more protective under the CAA and is 
the duration that EPA previously used for NOX and PM 
emissions credits. Finally, the commenter states that EPA has not 
justified its choice of five years.
    Commenters who urged EPA to finalize an unlimited credit life for 
NOX emissions credits did not provide data or rationale to 
support their assertion.
    After further consideration, including consideration of public 
comments, EPA is finalizing as proposed a five-year credit life for 
credits generated and used in MY 2027 and later. The credit life in the 
final rule is based on consideration of several factors. First, 
consistent with our proposal, we continue to believe a limited credit 
life, rather than an unlimited credit life suggested by some 
commenters, is necessary to prevent large numbers of credits 
accumulating early in the program from interfering with the incentive 
to develop and transition to other more advanced emissions control 
technologies later in the program. Further, as discussed in Section 
IV.G.7, we believe the transitional credit program in the final rule 
addresses key aspects of manufacturers' requests for longer credit 
life. Second, as explained in the proposal, we believe a five-year 
credit life adequately covers a transition period for manufacturers in 
the early years of the program, while continuing to encourage 
technology development in later years.
    We disagree with one commenter who stated that a three-year credit 
life is more appropriate than a five-year credit life. Rather, we 
believe five years appropriately balances providing flexibility in 
manufacturers product planning with ensuring available emissions 
control technologies are adopted. Further, as discussed in Section 
IV.G.4, inherent in an ABT program is the requirement for manufacturers 
producing engines above the emissions standard to also produce engines 
below the standard or to purchase credits from another manufacturer who 
has produced lower emitting engines. As such, while the five-year 
credit life in the final rule constrains the time period over which 
manufacturers can use credits, it does not impact the overall emissions

[[Page 4395]]

reductions from the final rule. In addition, to the extent that credits 
are banked for five-years, the emissions reductions from those credits 
occur five-years earlier, and as discussed earlier in this Section 
IV.G, benefits realized in the near term are worth more to society than 
those deferred to a later time. Finally, a five-year credit life is 
consistent with our approach in the existing light-duty criteria and 
GHG programs, as well as our heavy-duty GHG program (see 40 CFR 
86.1861-17, 86.1865-12, and 1037.740(c)).
    As discussed in Section IV.G.7, we are finalizing a shorter credit 
life for credits generated in 2022 through 2026 with engines certified 
to a FEL below the current MY 2010 emissions standards, while complying 
with all other MY 2010 requirements, since these credits are generated 
from engines that do not meet the MY 2027 and later requirements. We 
are also finalizing longer credit life values for engines meeting all, 
or some of the key, MY 2027 and later requirements to further 
incentivize emissions reductions before the new standards begin (see 
IV.G.7 for details).
6. Existing Credit Balances
    After further consideration, including information received in 
public comments, the final rule will allow manufacturers to generate 
credits in MYs 2022 and later for use in MYs 2027 and later, as 
described further in the following Section IV.G.7. Consistent with the 
proposal, in the final program, manufacturers will not be allowed to 
use credits generated prior to model year 2022 when certifying to model 
year 2027 and later requirements.
    We proposed that while emission credits generated prior to MY 2027 
could continue to be used to meet the existing emission standards 
through MY 2026 under 40 CFR part 86, subpart A, those banked credits 
could not be used to meet the proposed MYs 2027 and later standards 
(except as specified in 1036.150(a)(3) for transitional and early 
credits in 1036.150(a)(1) and (2)). Our rationale included that the 
currently banked NOX emissions credits are not equivalent to 
credits that would be generated under the new program (e.g., credits 
were generated without demonstrating emissions control under all test 
conditions of the new program), and that EPA did not rely on the use of 
existing credit balances to demonstrate feasibility of the proposed 
standards.
    Some commenters urged EPA to allow the use of existing credits, or 
credits generated after the release of the CTI ANPR, to be used in MYs 
2027 and later. Commenters stated that EPA has not demonstrated the 
standards are feasible without the use of credits, and that the credits 
were from engines with improved emissions that provide real-world 
NOX benefits, even if they are not certified to all of the 
test conditions of the proposed program. They further stated that not 
allowing the use of existing credits in 2027 and later could discourage 
manufacturers from proactively improving emissions performance. In 
contrast, other commenters support the proposal to discontinue the use 
of old credits (e.g., those generated before 2010) since allowing the 
use of these credits would delay emissions reductions and prevent a 
timely transition to new standards.
    EPA did not rely on the use of existing or prior to MY 2027 credit 
balances to demonstrate feasibility of the proposed standards (see 
Section III) and continues to believe that credits from older model 
years should not be used to meet the final MY 2027 and later standards. 
Credits from older model years (i.e., MY 2009 or prior) were generated 
as manufacturers transitioned to the current standards, and thus would 
not require manufacturers to introduce new emissions control 
technologies to generate credits leading up to MY 2027. However, EPA 
agrees with some commenters that credits generated in model years 
leading up to MY 2027 are from engines with improved emissions controls 
and provide some real-world NOX benefits, even if they are 
not certified to all of the test conditions of the model year 2027 and 
later program. Therefore, the transitional credit program we are 
finalizing allows manufacturers to generate credits starting in model 
year 2022 for use in MYs 2027 and later; however, credits generated 
from engines in MYs 2022-2026 that do not meet all of the MY 2027 and 
later requirements are discounted to account for the differences in 
emissions controls between those engines and engines meeting all 2027 
and later requirements (see Section IV.G.7 and Section 12 of the RTC 
for details). For credits generated in model years prior to MY 2022, we 
are finalizing that such emission credits could continue to be used to 
meet the existing emission standards through MY 2026 under 40 CFR part 
86, subpart A.
    We selected model year 2022 for two reasons. First, allowing MY 
2022 and later credits inherently precludes emissions credits from the 
oldest model years (i.e., MY 2009 or prior). These oldest years are 
when the vast majority of existing credit balances were accumulated, to 
create flexibility in transitioning to the MY 2007-2010 standards.\411\ 
The oldest model year credits were not generated with current emissions 
control technologies and are therefore quite distinct from credits 
generated under the final standards. Second, regarding both the oldest 
MY credits and those few generated in more recent years, allowing only 
MY 2022 and later credits incentivizes manufacturers to maximize their 
development and introduction of the best available emissions control 
technologies ahead of when they are required to do so in MY2027. As 
discussed in IV.G.7, this not only provides a stepping-stone to the 
broader introduction of this technology soon thereafter, but also 
encourages the early production of cleaner vehicles, which enhances the 
early benefits of our program. If we were to allow manufacturers to use 
emissions credits from older model years then there would be no 
incentive to apply new emissions control technologies in the years 
leading up to MY 2027. Further, we recognize that some manufacturers 
have begun to modernize some of their emissions controls in 
anticipation of needing to comply with the CARB Omnibus standards that 
begin in 2024,\412\ or potential future Federal standards under this 
final rule, and agree with commenters that it's appropriate to 
recognize the effort to proactively improve emissions performance.\413\ 
Thus, allowing credits generated in MY 2022 and later both recognizes 
improvements in emissions controls beyond what is needed to meet the 
current standards, and ensures that only credits generated in the model 
years leading up to 2027 can be used to meet the standards finalized in 
this rule.
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    \411\ EPA compliance data shows that prior to MY 2022, the 
majority of heavy-duty on-highway engine manufacturers were not 
generating NOX emissions credits in recent model years 
(i.e., since model year 2009).
    \412\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule.
    \413\ As discussed in this Section IV.G, the final ABT program 
does not allow manufacturers to generate emissions credits from 
engines certified to state emission standards that are different 
than the federal standards; however, as discussed in IV.G.7, 
manufacturers could generate emissions credits if they produce 
larger volumes of engines to sell outside of those states that have 
adopted emission standards that are different than the federal 
standards.
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7. Transitional Credits Generated in MYs 2022 Through 2026
    We are finalizing a transitional credit program that includes 
several pathways for manufacturers to generate transitional credits in 
MYs 2022 through 2026 that they can then use in MYs 2027 and later. The 
transitional credit pathways differ in several ways from

[[Page 4396]]

what we proposed based on further consideration, including the 
consideration of public comments. In this section, IV.G.7, we briefly 
summarize our proposed transitional credit program, stakeholder 
comments on the proposed transitional credit program, and then discuss 
EPA's responses to comments along with our rationale for the 
transitional credit pathways in the final rule.
    Under the proposed transitional credit program, manufacturers would 
generate transitional credits in model years 2024 through 2026. As 
proposed, manufacturers would have calculated transitional credits 
based on the current NOX emissions standards and useful life 
periods; however, manufacturers would have been required to certify to 
the other model year 2027 and later requirements, including the LLC and 
off-cycle test procedures. We proposed the same five-year credit life 
for transitional credits as other credits in the proposed general ABT 
program (see 87 FR 17553-17554 March 28, 2022, for additional details 
of the proposed transitional credits).
    We requested comment on our proposed approach to offer transitional 
NOX emission credits that incentivize manufacturers to adopt 
the proposed test procedures earlier than required in MY 2027. We also 
requested comment on whether CI engines should be required to meet the 
proposed off-cycle standards to qualify for the transitional credits, 
and were specifically interested in comments on other approaches to 
calculating transitional credits before MY 2027 that would account for 
the differences in our current and proposed compliance programs. In 
addition, we requested comment on our proposed five-year credit life 
for transitional NOX emission credits. Finally, we also 
requested comment related to our proposed Early Adoption Incentives on 
whether EPA should adopt an incentive that reflects the MY 2024 Omnibus 
requirements being a step more stringent than our current standards, 
but less comprehensive than the proposed MY 2027 requirements.
    Several commenters provided perspectives on the proposed 
transitional credit program under the ABT program. Most commenters 
either opposed allowing manufacturers to generate NOX 
emissions credits, or suggested additional requirements for generating 
credits that could be used in MYs 2027 and later. One commenter stated 
that due to lead time and resource constraints, manufacturers would not 
be able to participate in the proposed transitional credit program. 
Another commenter supported the proposed transitional credit program. 
One commenter also stated that incentives for compliant vehicles, not 
just ZEVs, purchased prior to the MY 2027 will bring tremendous health 
benefits to at-risk communities and the nation. Similarly, one 
commenter encouraged EPA to further incentivize emissions reductions 
prior to the start of the new standards by providing additional 
flexibilities to use credits in MY 2027 and later if manufacturers were 
able to certify prior to MY 2027 a large volume of engines (i.e., an 
entire engine service class) to almost all MY2027 and later 
requirements.
    Commenters who opposed allowing manufacturers to generate 
NOX emissions credits prior to MY2027 were concerned that 
the difference between Federal and state (i.e., CARB Omnibus) standards 
would result in ``windfall of credits'' that would allow a large 
fraction of engines to emit at the FEL cap into MY2030 and later. One 
commenter stated that EPA has not adequately assessed the potential 
erosion of emissions reductions from credits generated by engines 
certifying to the CARB Omnibus standards. Another commenter stated that 
manufacturers are already certifying to levels below the current MY2010 
standards, and they believe that certifying to the new test procedures 
will take little effort for manufacturers. The commenter stated that 
there is no need to incentivize manufacturers to adopt proposed test 
procedures ahead of MY2027 because they will already be doing so under 
the Omnibus program. They argued that rather than requiring new 
testing, EPA should encourage new technology adoption. Commenters 
opposing the transitional credit program stated that EPA should 
eliminate the transitional credit program, or if EPA choses to finalize 
the transitional credit program, then EPA should adjust the final 
standards to account for the transitional credit program impacts, or 
revise the transitional credit program (e.g., shorten credit life to 
three years, establish a separate bank for credits generated by engines 
in states adopting the Omnibus standards). Two commenters stated that 
EPA should require engines generating credits prior to 2027 to meet all 
of the requirements of 2027 and beyond; they highlighted the importance 
of the 2027 and later low-load cycle and off-cycle standards to ensure 
real-world reductions on the road, and stated that there should be 
consistency in the way credits are generated and the way they are used. 
Similarly, these commenters oppose credits for legacy engines or legacy 
technologies (i.e., engines or technologies used to meet the current 
emissions standards).
    The commenter who stated that manufacturers would be unable to 
generate credits under the proposed transitional credit due to lead 
time and resource constraints argued that manufacturers would be unable 
to adjust their engine development plans to meet the new LLC and off-
cycle test standards in MY 2024. They further stated that in many cases 
deterioration factor (DF) testing has already started for MY 2024 
engines. The commenter also argued that they view the ABT program as 
part of the emissions standards, and the proposed transitional credit 
program provided less than the four-year lead time that the CAA 
requires when setting heavy-duty criteria pollutant emissions 
standards. In addition, the commenter stated that the proposed 
transitional credit program would disincentivize manufacturers to make 
real-world NOX emissions reductions ahead of when new 
standards are in place because they would not be able to design and 
validate their engines to meet the requirements to generate credits.
    Finally, a commenter suggested EPA further encourage additional 
emissions reductions prior to the start of new standards by providing 
greater flexibility to use credits in MYs 2027 and later.\414\ 
Specifically, this commenter suggested that EPA provide a longer credit 
life (e.g., ten years compared to the five years proposed for the ABT 
program) and also allow the movement of credits between averaging sets. 
The commenter stated that in order to generate credits with these 
additional flexibilities manufacturers would need to certify an entire 
engine service class (e.g., all heavy heavy-duty engines a manufacturer 
produced) in a given model year to a FEL of 50 mg/hp-hr or less, and 
meet all other MY 2027 and later requirements. They further stated that 
it may not be appropriate for natural gas engines to generate credits 
with these additional flexibilities since natural gas engines can meet 
a 50 mg/hp-hr FEL today. Finally, the commenter stated that engines 
using these credits in MYs 2027 and later should be required to certify 
to a FEL of 50 mg/hp-hr or less. Additional details on comments 
regarding the proposed transitional credit program are included in 
section 12 of the Response to Comments document.
---------------------------------------------------------------------------

    \414\ U.S. EPA. Stakeholder Meeting Log. December 2022.
---------------------------------------------------------------------------

    After considering comments on the proposed transitional credit 
program, we are choosing to finalize a revised

[[Page 4397]]

version of the proposed transitional credit program. Similar to the 
proposed rule, we are finalizing an optional transitional credit 
program to help us meet our emission reduction goals at a faster pace, 
while also providing flexibilities to manufacturers to meet new, more 
stringent emission standards. Building on the ABT program as whole, the 
transitional credit program in the final rule can benefit the 
environment and public health in two ways. First, early introduction of 
new emission control technologies can accelerate the entrance of lower-
emitting engines and vehicles into the heavy-duty vehicle fleet, 
thereby reducing NOX emissions from the heavy-duty sector 
and lowering its contributions to ozone and PM formation before new 
standards are in place. Second, the earlier improvements in ambient air 
quality will result in public health benefits sooner than they would 
otherwise occur; these benefits are worth more to society than those 
deferred to a later time, and could be particularly impactful for 
communities already overburdened with pollution. As discussed in 
Section II, many state and local agencies have asked the EPA to further 
reduce NOX emissions, specifically from heavy-duty engines, 
because such reductions will be a critical part of many areas' 
strategies to attain and maintain the ozone and PM2.5 NAAQS. 
Several of these areas are working to attain or maintain NAAQS in 
timeframes leading up to and immediately following the required 
compliance dates of the final standards, which underscores the 
importance of the early introduction of lower-emitting vehicles.
    The transitional credit program is voluntary and as such no 
manufacturer is required to participate in the transitional credit 
program. The transitional credit program in the final rule will provide 
four pathways for manufacturers to generate credits in MYs 2022 through 
2026 for use in MYs 2027 and later: (1) In MY 2026, certify all engines 
in the manufacturer's heavy heavy-duty service class to a FEL of 50 mg/
hp-hr or less and meet all other EPA requirements for MYs 2027 and 
later to generate undiscounted credits that have additional 
flexibilities for use in MYs 2027 and later (2026 Service Class Pull 
Ahead Credits); (2) starting in MY 2024, certify one or more engine 
family(ies) to a FEL below the current MY2010 emissions standards and 
meet all other EPA requirements for MYs 2027 and later to generate 
undiscounted credits based on the longer UL periods included in the 
2027 and later program (Full Credits); (3) starting in MY 2024, certify 
one or more engine family(ies) to a FEL below the current MY2010 
emissions standards and meet several of the key requirements for MYs 
2027 and later, while meeting the current useful life and warranty 
requirements to generate undiscounted credits based on the shorter UL 
period (Partial Credits); (4) starting in MY 2022, certify one or more 
engine family(ies) to a FEL below the current MY2010 emissions 
standards, while complying with all other MY2010 requirements, to 
generate discounted credits (Discounted Credits).
    All credits generated in the first pathway have an eight-year 
credit life and can therefore be used through MY 2034. All credits 
generated under the second or third pathways will expire by MY2033; all 
credits generated in the fourth pathway will expire by MY 2030. We 
further describe each pathway and our rationale for each pathway in 
this section (see the final interim provisions in 40 CFR 1036.150(a) 
for additional details).\415\ In Section IV.G.8 we discuss our decision 
to finalize the transitional credit pathways in lieu of the proposed 
Early Adoption Incentives program (section 12 of the Response to 
Comments document includes additional details on the comments received 
on the proposed Early Adoption Incentives program).
---------------------------------------------------------------------------

    \415\ We are finalizing as proposed a requirement that, to 
generate transitional NOX emission credits, manufacturers 
must meet the applicable PM, HC, and CO emission standards without 
generating or using emission credits. For the first and second 
pathways, applicable PM, HC, and CO emission standards are in 40 CFR 
1036.104. For the third and fourth pathways (Partial and Discounted 
Credits), applicable PM, HC, and CO emission standards are in 40 CFR 
86.007-11 or 86.008-10.
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    In developing the final transitional credit program and each 
individual pathway, we considered several factors. For instance, for 
the transitional credit program as a whole, one commenter stated that 
there should be consistency in the way the credits are generated and 
the way they are used; several commenters urged EPA to only provide 
transitional credits to engines meeting all the 2027 and later 
requirements. The transitional credit program acknowledges these 
commenters' input by only providing full credit value to engines 
meeting all the 2027 and later requirements [i.e., 2026 Service Class 
Pull Ahead Credits and Full Credits pathways], while providing a lesser 
value for credits generated from engines that do not meet all of the 
2027 and later requirements but still demonstrate improved emissions 
performance compared to the current standards.
    We now turn to discussing in detail each pathway, and the factors 
we considered in developing each pathway. The first pathway 
acknowledges the significant emissions reductions that would occur if 
manufacturers were to certify an entire service class of heavy heavy-
duty engines to a much lower numeric standard than the current 
standards and meet all other MY 2027 requirements prior to the start of 
the new standards. Specifically, compared to the emissions reductions 
expected from the final rule, our assessment shows significant, 
additional reductions in the early years of the program from certifying 
the entire heavy heavy-duty engine fleet to a FEL of 50 mg/hp-hr or 
less and meeting all other MY2027 requirements in MY 2026, one model 
year prior to the start of the new standards.\416\ As discussed 
throughout this Section IV.G, emissions reductions, and the resulting 
public health benefits, that are realized earlier in time are worth 
more to society than those deferred to a later time. Based on the 
potential for additional, early emissions reductions, we are finalizing 
the 2026 Service Class Pull Ahead Credits pathway with two additional 
flexibilities for manufacturers to use the credits in MYs 2027 and 
later. First, 2026 Service Class Pull Ahead Credits have an eight-year 
credit life (i.e., expire in MY 2034), which is longer than credits 
generated in the other transitional credit pathways, or under the main 
ABT program. Second, we are allowing 2026 Service Class Pull Ahead 
Credits to move from a heavy heavy-duty to a medium heavy-duty 
averaging set; however, credits moved between averaging sets will be 
discounted at 10 percent. We note that a recent assessment by an 
independent NGO shows that allowing credits to move between service 
classes could reduce the overall monetized health benefits of a program 
similar to the one in this final rule; however, the 10 percent discount 
rate that we are apply would more than offset the potential for reduced 
emissions reductions. Moreover, as noted in this section, the early 
emissions reductions from this transitional credit program would 
provide important positive benefits, particularly in communities

[[Page 4398]]

overburdened with pollution.\417\ Further, we are balancing these 
additional flexibilities with restrictions on which engines can 
participate in the 2026 Service Class Pull Ahead Credits pathway. 
Specifically, only heavy heavy-duty engines may generate 2026 Service 
Class Pull Ahead Credits; we expect a much lower level of investment 
would be required for natural gas-fueled engines, light heavy-duty 
engines, and SI engines to meet the 2026 Service Class Pull Ahead 
Credits requirements compared to the investment needed for heavy- 
heavy-duty engines. We expect that the combination of discounting 
credits moved across averaging sets and only allowing the heavy heavy-
duty engine service class to participate in the 2026 Service Class Pull 
Ahead Credits pathway will appropriately balance the potential for 
meaningful emissions reductions in the early years of the program with 
the potential for adverse competitive disadvantages or environmental 
risks from either unequal investments to generate credits or producing 
large volumes of credits from engines that could easily meet the 
requirements of the 2026 Service Class Pull Ahead Credits pathway. 
Finally, engines certified using 2026 Service Class Pull Ahead Credits 
in 2027 through 2034 will need to meet a FEL of 50 mg/hp-hr or less; 
this requirement helps to ensure that these credits are used only to 
certify engines that are at least as low emitting as the engines that 
generated the credits.
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    \416\ See RIA Chapter 5.5.5 for additional details on our 
assessment of emissions reductions projected to occur from 
certifying engines to a FEL of 50 mg/hp-hr and meeting all other 
2027 requirements in MY 2026. Note that for the purposes of bounding 
the potential emissions impacts, we assumed all heavy heavy-duty 
engines would participate in the 2026 Service Class Pull Ahead 
Credits pathway, and that those credits would be used by both medium 
and heavy heavy-duty engines in MY 2027 and later, until 
manufacturers used all of the credits.
    \417\ See U.S. EPA. Stakeholder Meeting Log. December 2022 for 
details of the assessment by the independent NGO (ICCT).
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    The second pathway (Full Credits) acknowledges the emissions 
reductions that could be achieved prior to the start of new standards 
if manufacturers certify to a FEL lower than today's standard and meet 
all other MY 2027 and later requirements, although without doing so for 
an entire engine service class. This pathway is similar to our proposed 
transitional credit program and is consistent with input from 
commenters who highlighted the importance of meeting MY 2027 and later 
requirements such as the low-load cycle and off-cycle standards to 
ensure real-world reductions on the road. As proposed, all heavy-duty 
engine service classes, including heavy-duty natural gas engines in the 
respective service classes, can participate in this pathway.
    The third pathway (Partial Credits) incentivizes manufacturers to 
produce engines that meet several of the key final requirements for MY 
2027 and later, including the LLC and off-cycle standards for 
NOX, while meeting the existing useful life and warranty 
periods.\418\ This pathway allows manufacturers to adopt new emissions 
control technologies without demonstrating durability over the longer 
useful life periods required in MY 2027 and later, or certifying to the 
longer warranty periods in the final rule. We expect that some 
manufacturers may already be planning to produce such engines in order 
to comply with 2024 California Omnibus program; however, this 
transitional pathway would incentivize manufacturers to produce greater 
volumes of these engines than they would otherwise do to comply in 
states adopting the Omnibus standards. Some commenters were concerned 
that the proposed transitional credit program would result in 
``windfall credits'' due to manufacturers generating credits from 
engines produced to comply with more stringent state standards. As 
discussed in IV.G, the final program will not allow manufacturers to 
generate credits from engines certified to meet state standards that 
are different from the Federal standards.\419\ The Partial Credits 
pathway thus avoids ``windfall credits'' because manufacturers are not 
allowed to generate credits from engines produced to meet the more 
stringent 2024 Omnibus requirements, but rather are incentivized to 
produce cleaner engines that would benefit areas of the country where 
such engines may not otherwise be made available (i.e., outside of 
states adopting the Omnibus program).\420\ Further, because engines 
participating in this pathway will be certified to shorter useful life 
periods, they will generate fewer credits than engines participating in 
the third and fourth pathways (Full Credits and 2026 Service Class Pull 
Ahead Credits).
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    \418\ Engines earning Partial Credits must comply with 
NOX standards over the Low Load Cycle and the off-cycle 
standards. The family emission limits for the Low Load Cycle and 
off-cycle standards are calculated relative to the family emission 
limit the manufacturer declares for FTP testing, as described in 40 
CFR 1036.104(c). If we direct a manufacturer to do in-use testing 
for an engine family earning Partial Credits, we may direct the 
manufacturer to follow either the in-use testing program specified 
in 40 CFR part 1036 for NOX, or the in-use testing 
program in 40 CFR part 86 for all criteria pollutants. Except for 
the NOX standards for the Low Load Cycle and for off-
cycle testing, engines generating Partial Credits would be subject 
to all the certification and testing requirements from 40 CFR part 
86.
    \419\ See final part 1036, subpart H, and 40 CFR 1036.801 (which 
EPA did not propose any revisions to in the proposed migration from 
part 86, subpart A, to part 1036). See also the substantively 
similar definition of U.S.-directed production in current 40 CFR 
86.004-2. Under 40 CFR 1036.705(c), which we are also finalizing as 
proposed as applicable for NOX ABT, compliance through 
ABT does not allow credit calculations to include engines excluded 
from the definition of U.S.-directed production volume: ``As 
described in Sec.  1036.730, compliance with the requirements of 
this subpart is determined at the end of the model year based on 
actual U.S.-directed production volumes. Keep appropriate records to 
document these production volumes. Do not include any of the 
following engines to calculate emission credits: . . . (4) Any other 
engines if we indicate elsewhere in this part 1036 that they are not 
to be included in the calculations of this subpart.''
    \420\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule.
---------------------------------------------------------------------------

    The first, second, and third pathways all include meeting the LLC 
requirements for MY 2027 and later. One commenter suggested meeting the 
LLC would require manufacturers to simply meet a lower numeric standard 
than the current standard; however, EPA disagrees. Certifying to the 
LLC will require more than simply meeting a lower numeric standard 
since the LLC is a new test cycle that requires demonstration of 
emissions control in additional engine operations (i.e., low load) 
compared to today's test cycles (see preamble Section III and section 3 
of the Response to Comments document and for more discussion on the 
LLC).
    Finally, the fourth pathway (Discounted Credits) allows 
manufacturers to generate credits for use in MY 2027 and later with 
engines that are not designed to meet the LLC and off-cycle standards 
and so could provide additional compliance flexibility for meeting the 
final standards; however, since the engines are not meeting the full 
requirements of the MY 2027 and later program the credits are 
discounted and will expire before credits generated in the other 
transitional credit pathways. This Discounted Credits pathway includes 
consideration of input from one commenter who stated that it would be 
infeasible for manufacturers to comply with the new LLC and off-cycle 
test procedures in MY 2024 in order to generate credits under the 
proposed credit program; they further argued that for manufacturers 
relying on credits to comply with the final standards, the proposed 
transitional credit program would not provide the lead time required by 
the CAA. As described in Section III of this preamble, the new 
standards in the final rule are feasible without the ABT program and 
without the use of transitional credits; participation in ABT is 
voluntary and is intended to provide additional flexibility to 
manufacturers through an optional compliance pathway. While 
manufacturers have the option of generating NOX emissions 
credits under the transitional credit program in the final rule, they 
are not required to do so. The four-year lead time requirement under 
CAA 202(a)(3) does not apply to these ABT provisions.

[[Page 4399]]

    Nevertheless, the final rule allows credits generated under this 
Discounted Credits pathway to incentivize improvements in emissions 
controls, even if the engines are not certified to the full MY2027 and 
later requirements. Credits will be discounted by 40 percent to account 
for differences in NOX emissions during low-load and off-
cycle operations between current engines and engines certifying to the 
model year 2027 and later requirements. While we expect that 
manufacturers certifying to a FEL below the current 200 mg/hp-hr 
standard will reflect improvement in emissions control over the FTP and 
SET duty-cycles, the discount applied to the credits accounts for the 
fact that these engines are not required to maintain the same level of 
emissions control over all operations of the off-cycle standards, or 
during the low-load operations of the LLC. For example, a manufacturer 
certifying a HHDE engine family to a FEL of 150 mg/hp-hr and all other 
MY 2010 requirements with a U.S.-directed production volume of 50,000 
engines in 2024 would generate approximately 5,000 credits (see 
Equation IV-1), which they would then multiply by 0.6 to result in a 
final credit value of 3,000 credits. See the final, revised from 
proposal, interim provision in 40 CFR 1036.150(a)(1) for additional 
details on the calculation of discounted credits.
    Credits generated under this Discounted Credits pathway could be 
used in MY 2027 through MY 2029. The combination of the discount and 
limited number of model years in which manufacturers are allowed to use 
these credits is consistent with our past practice and helps to 
addresses some commenters' concerns about allowing legacy engines to 
generate credits, or credits generated under the transitional credit 
program eroding emissions reductions expected from the rule (55 FR 
30584-30585, July 26,1990). There are two primary ways that the 
Discounted Credits pathway results in positive public health impacts. 
First, an immediate added benefit to the environment is the discounting 
of credits, which ensures that there will be a reduction of the overall 
emission level. The 40 percent discount provides a significant public 
health benefit, while not being so substantial that it would discourage 
the voluntary initiatives and innovation the transitional ABT program 
is designed to elicit. Second, consistent with the benefits of the 
overall transitional credit program, when the ``time value'' of 
benefits (i.e., their present value) is taken into account, benefits 
realized in the near term are worth more to society than those deferred 
to a later time. The earlier expiration date of credits in the 
Discounted Pathway reflects that these credits are intended to help 
manufacturers transition in the early years of the program, but we 
don't think they are appropriate for use in later years of the program. 
The earlier expiration of credits is also consistent with comments that 
we should finalize a 3-year credit life for transitional credits (i.e., 
credits can be used for 3-years once the new standards begin).
    As discussed earlier in this Section IV.G.7, credits generated 
under the first pathway (2026 Service Class Pull Ahead Credits) can be 
used for eight years, through MY 2034; we selected this expiration date 
to balance incentivizing manufacturers to participate in the 2026 
Credits pathway and thereby realize the potential for additional, early 
emissions reductions, with continuing to encourage the introduction of 
improved emissions controls, particularly as the heavy-duty fleet 
continues to transition into zero emissions technologies.\421\ As 
stated in the preceding paragraphs, all credits generated in the second 
and third pathways can be used through MY 2032. Our rationale for this 
expiration date is two-fold. First, providing a six-year credit life 
from when the new standards begin provides a longer credit life than 
provided in the final ABT program for credits generated in MY 2027 and 
later; similar to the first pathway, this longer credit life 
incentivizes manufacturers to produce engines that emit lower levels of 
NOX earlier than required. Second, the six-year credit life 
balances additional flexibility for manufacturers to transition over 
all of their product lines with the environmental and human health 
benefits of early emissions reductions. This transitional period 
acknowledges that resource constraints may make it challenging to 
convert over all product lines immediately when new standards begin, 
but maintains emission reductions projected from program by requiring 
the use of credits to certify engines that emit above the level of the 
new standard. While some commenters stated that manufacturers will have 
been complying with the CARB Omnibus program starting in 2024, we 
acknowledge that complying with the 2027 and later Federal standards 
will require another step in technology and thus think it is 
appropriate to provide additional flexibility for manufacturers to 
transition to the new standards through the use of emissions credits in 
the ABT program.
---------------------------------------------------------------------------

    \421\ As discussed in RIA 5.5.5, our evaluation shows that 
manufacturers would use all 2026 Service Class Pull Ahead Credits in 
about an eight-year period, which further supports the eight-year 
credit life of the 2026 Service Class Pull Ahead Credits pathway.
---------------------------------------------------------------------------

    This section describes how to generate credits for MY 2026 and 
earlier engines that are certified to standards under 40 CFR part 86, 
subpart A. As noted in Section III.A.3, we are allowing manufacturers 
to continue to certify engines to the existing standards for the first 
part of model year 2027. While those engines continue to be subject to 
standards under 40 CFR part 86, subpart A, we are not allowing those 
engines to generate credits that carry forward for certifying engines 
under 40 CFR part 1036.\422\ Manufacturers may only generate 
NOX emissions credits under transitional credit pathways for 
MY 2024-2026 engines since one purpose of transitional credits is to 
incentivize emission reductions in the model years leading up to MY 
2027. To the extent manufacturers choose to split MY 2027, the engines 
produced in the first part of the split MY are produced very close in 
time to when the new standards will apply, and thus we expect that 
rather than incentivizing earlier emission reductions, providing an 
allowance to generate NOX emission credits would incentivize 
production at higher volumes during the first part of the split MY than 
would otherwise occur (i.e., incentivizing more of the MY 2027 
production before the final standards apply). The higher production 
volume of engines in the first part of the split MY could thereby 
result in additional NOX emission credits without additional 
emission reductions that would otherwise occur. See preamble Section 
III.A.3 for details on the split model year provision in this final 
rule.
---------------------------------------------------------------------------

    \422\ MY 2027 engines produced prior to four years after the 
date that the final rule is promulgated and certified to the 
existing 40 CFR part 86 standards cannot participate in the part 
1036 ABT program; however, MY 2027 engines certified to 40 CFR part 
1036 standards and requirements may participate in the ABT program 
specified in 40 CFR part 1036, subpart H.
---------------------------------------------------------------------------

8. Early Adoption Incentives
    EPA is choosing not to finalize the Early Adoption Incentives 
program as proposed. This includes a decision not to include emissions 
credit multipliers in the final ABT program. Rather, we are finalizing 
a revised version of the transitional credit program under the ABT 
program as described above in Section IV.G.7. In this Section IV.G.8 we 
briefly describe the proposed Early Adoption Incentives program, 
stakeholder comments on the proposed Early Adoption Incentives program, 
and then discuss EPA's responses to comments along with our rationale 
for

[[Page 4400]]

choosing not to finalize the Early Adoption Incentives program.
    We proposed an early adoption incentive program that would allow 
manufacturers who demonstrated early compliance with all of the final 
MY 2027 standards (or MY 2031 standards under proposed Option 1) to 
include Early Adoption Multiplier values of 1.5 or 2.0 when calculating 
NOX emissions credits. In the proposed Early Adoption 
Incentives program, manufacturers could generate credits in MYs 2024 
through 2026 and use those credits in MYs 2027 and later.
    We requested comment on all aspects of our proposed early adoption 
incentive program. We were aware that some aspects of the proposed 
requirements could be challenging to meet ahead of the required 
compliance dates, and thus requested comment on any needed 
flexibilities that we should include in the early adoption incentive 
program in the final rule. See 87 FR 17555, March 28, 2022, for 
additional discussion on the proposed Early Adoption Incentives 
program, including specifics of our requests for comment.
    Several commenters provided general comments on the proposed Early 
Adoption Incentive program. Although many of the commenters generally 
supported incentives such as emissions credit multipliers to encourage 
early investments in emissions reductions technology, several were 
concerned that the emissions credit multipliers would result in an 
excess of credits that would undermine some of the benefits of the 
rule; other commenters were concerned that the multipliers would 
incentivize some technologies (e.g., hybrid powertrains, natural gas 
engines) over others (e.g., battery-electric vehicles).
    As described in preamble Section IV.G.7, the revised transitional 
credit program that we are finalizing provides discounted credits for 
engines that do not comply with all of the MY 2027 and later 
requirements. In addition, after consideration of comments responding 
to our request for comment about incentivizing early reductions through 
our proposed transitional and Early Adoption Incentive program, the 
final transitional credit program includes an additional pathway that 
incentivizes manufacturers to produce engines that meet several of the 
key final requirements for MY 2027 and later, including the LLC and 
off-cycle standards for NOX, while meeting the current 
useful life and warranty periods. We expect that this transitional 
credit pathway will incentivize manufacturers to produce greater 
volumes of the same or similar engines that they plan to produce to 
comply with the MY 2024 Omnibus requirements. By choosing not to 
finalize the Early Adoption Incentives program and instead finalizing a 
modified version of the Transitional Credit program, we are avoiding 
the potential concern some commenters raised that the credit 
multipliers would result in a higher volume or magnitude of higher-
emitting MY 2027 and later engines compared to a program without 
emission credit multipliers. We believe the Transitional Credit program 
we are finalizing will better balance incentivizing emissions reduction 
technologies prior to MY 2027 against avoiding an excess of emissions 
credits that leads to much greater volumes or magnitudes of higher-
emitting engines in MYs 2027 and later. Moreover, by not finalizing the 
Early Adoption Incentive program we are avoiding any concerns that the 
emissions credit multipliers would incentivize some technologies over 
others (see section 12.5 of the Response to Comments and preamble 
Section IV.G.10 for additional discussion on battery-electric and fuel 
cell electric vehicles in the final rule; see section 3 of the Response 
to Comments for discussion on additional technology pathways).
9. Production Volume Allowance
    After further consideration, including consideration of public 
comments, EPA is finalizing an interim production volume allowance for 
MYs 2027 through 2029 in 40 CFR 1036.150(k) that is consistent with our 
request for comment in the proposal, but different in several key 
aspects. In particular, the production volume allowance we are 
finalizing allows manufacturers to use NOX emissions credits 
to certify a limited volume of heavy heavy-duty engines compliant with 
pre-MY 2027 requirements in MYs 2027 through 2029.\423\ In addition, 
since we are requiring the use of credits to certify MY 2010 compliant 
heavy heavy-duty engines in the early years of the final program, and 
to aid in implementation, we are choosing to not limit the applications 
that are eligible for this production volume allowance. Finally, the 
production volume allowance in the final rule will be five percent of 
the average U.S.-directed production volumes of Heavy HDE over three 
model years, see 40 CFR 1036.801, and thus excludes engines certified 
to different emission standards in CA or other states adopting the 
Omnibus program. In this section, IV.G.9, we summarize our request for 
comment on a production volume allowance, related stakeholder comments, 
and EPA's responses to comments along with our rationale for the 
production volume allowance in the final rule.
---------------------------------------------------------------------------

    \423\ Engines certified under this production volume allowance 
would meet the current, pre-MY 2027 engine provisions of 40 CFR part 
86, subpart A.
---------------------------------------------------------------------------

    In the proposal we stated that we were considering a flexibility to 
allow engine manufacturers, for model years 2027 through 2029 only, to 
certify up to five percent of their total production volume of heavy-
duty highway CI engines in a given model year to the current, pre-MY 
2027 engine provisions of 40 CFR part 86, subpart A. We stated the 
allowance would be limited to Medium HDE or Heavy HDE engine families 
that manufacturers show would be used in low volume, specialty 
vocational vehicles. We noted that such an allowance from the MY 2027 
criteria pollutant standards may be necessary to provide engine and 
vehicle manufacturers additional lead time and flexibility to redesign 
some low sales volume products to accommodate the technologies needed 
to meet the proposed more stringent engine emission standards.
    We requested comment on the potential option of a three-year 
allowance from the proposed MY 2027 criteria pollutant standards for 
engines installed in specialty vocational vehicles, including whether 
and why the flexibility would be warranted and whether 5 percent of a 
manufacturers engine production volume is an appropriate value for such 
an interim provision. In addition, we requested comment on whether the 
flexibility should be limited to specific vocational vehicle regulatory 
subcategories and the engines used in them.
    Several commenters provided perspectives on our request for comment 
on providing an additional flexibility that would allow manufacturers 
to certify up to five percent of their total production volume of 2027 
through 2029 MY medium and heavy HDEs to the current Federal engine 
provisions. Many environmental and state organizations opposed the 
potential production volume allowance, while most manufacturers and one 
supplier generally supported the potential allowance although they 
suggested changes to the parameters included in the proposal.
    Commenters opposing the production volume allowance had two primary 
concerns. First, they stated that the production volume flexibility is 
not needed because there is enough lead time between now and MY 2027 to 
develop the technologies and overcome any packaging challenges. One 
commenter further noted that the CARB

[[Page 4401]]

Omnibus standards would already be in effect in 15 percent of the 
market. Second, commenters argued that the production volume allowance 
would result in high NOX emissions and adverse health 
effects, particularly in high-risk areas, which would undermine the 
effectiveness of the rule to reduce emissions and protect public 
health. One commenter noted that HHDEs last for many years before being 
scrapped and that the production volume allowance, combined with other 
flexibilities in the proposal, could result in significant emissions 
impacts for many years to follow, which would create extreme difficulty 
for California and other impacted states to achieve air quality goals. 
Another commenter estimated that in MY 2027 through 2029, the 
production volume allowance would result in 20,000 vehicles emitting 
nearly 6 times more NOX on the FTP cycle than proposed 
Option 1, and that these vehicles could represent 20-25 percent of the 
total NOX emissions from MY 2027 through 2029 vehicles. 
Still another commenter stated that the production volume allowance 
would result in up to a 45 percent increase in NOX emissions 
inventory for each applicable model year's production from a 
manufacturer with products in a single useful life and power rating 
category; the commenter noted that the emissions inventory impact could 
be even greater if a manufacturer used the five percent allowance for 
engines with longer useful life periods and higher power ratings. One 
commenter opposing the production volume allowance stated that EPA 
should not exempt any engines from complying with the adopted new 
emission standards for any amount of time. Other commenters opposing 
the production volume allowance stated that if EPA chose to finalize a 
production allowance then emissions from those engines should be offset 
with ABT emission credits to protect vulnerable impacted communities. 
Finally, one commenter opposing the production volume allowance state 
that if EPA chose to finalize the production allowance then the Agency 
should provide strong technical justification for each engine category 
subject to the provision.
    Commenters generally supporting the production volume allowance 
suggested several ways to further limit the flexibility, or suggested 
additional flexibilities based on the CARB Omnibus program. For 
instance, several engine manufacturers and their trade association 
suggested limiting the provision to include only engines with low 
annual miles traveled to minimize the emissions inventory impacts. 
These commenters suggested limiting the allowance to engines with 
greater than or equal to 525 hp or 510 hp in specific vehicle 
applications, namely: Heavy-haul tractors and custom chassis motor 
homes, concrete mixers, and emergency vehicles. Two engine 
manufacturers further suggested the production volume allowance include 
vehicles where aftertreatment is mounted off the frame rails, or that 
EPA review and approve applications demonstrating severe packaging 
constraints for low volume, highly specialized vocational applications. 
Another engine manufacturer argued that manufacturers need to be able 
to carry over some existing engines into MY 2027 and later for a few 
years in order to adequately manage investments and prioritize ultra-
low NOX and ZEV technology adoption in the applications that 
make the most sense. They further stated that EPA should consider 
alternate credit program options that can be used to truly manage 
investment and to prioritize appropriate applications by allowing 
manufacturers to leverage credits to stage development programs. One 
engine manufacturer and one supplier suggested EPA consider programs 
similar to the CARB Omnibus' separate certification paths for `legacy 
engines,' emergency vehicles, and low-volume high horsepower engines. 
Additional details on comments received on the request for comment on a 
potential production volume allowance are available in section 12.7 of 
the Response to Comments.
    After considering comments on the proposed production volume 
allowance, we are finalizing an allowance in MY 2027 through 2029 for 
manufacturers to certify up to five percent of their Heavy HDE U.S.-
directed production volume averaged over three model years (MY 2023 
through 2025) as compliant with the standards and other requirements of 
MY 2026 (i.e., the current, pre-MY 2027 engine provisions of 40 CFR 
part 86, subpart A). As explained earlier in this Section IV.G, U.S.-
directed production volume excludes engines certified to different 
state emission standards (e.g., would exclude engines certified to CARB 
Omnibus standards if EPA grants the pending waiver request), and thus 
would be a smaller total volume than all Heavy HDE engine production in 
a given model year.424 425 By finalizing a production volume 
allowance based on the average U.S.-directed production volume over 
three model years (MY 2023 through 2025), rather than an allowance that 
varies by production volume in each of the model years included in the 
allowance period (MY 2027 through 2029), we are providing greater 
certainty to manufacturers and other stakeholders regarding the number 
of engines that could be produced under this allowance. Further, we 
avoid the potential for economic conditions in any one year to unduly 
influence the volume of engines that could be certified under this 
allowance. Based on EPA certification data, we estimate that five 
percent MY 2021 Heavy HDE would result in approximately 12,000 engines 
per year permitted under this allowance.\426\
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    \424\ See final part 1036, subpart H, and 40 CFR 1036.801.
    \425\ EPA is reviewing a waiver request under CAA section 209(b) 
from California for the Omnibus rule.
    \426\ We note that there would be fewer engines eligible for 
this allowance in the event we approve the pending waiver request 
since our existing regulations provide that the production volume 
allowance would exclude engines certified to state emission 
standards that are different than the federal standards.
---------------------------------------------------------------------------

    We are limiting the final production volume allowance to Heavy HDE, 
rather than Heavy HDE and Medium HDE as proposed, because comments from 
manufacturers generally pointed to Heavy HDE applications or otherwise 
suggested limiting the allowance to larger engines (e.g., greater than 
510 hp). After considering comments on the vehicle categories to 
include in the production volume allowance, we are choosing not to 
specify the vehicle categories for engines certified under this 
production volume. Our rationale includes three main factors. First, we 
are requiring manufacturers to use credits to certify engines under the 
production volume allowance, which will inherently result in the 
production of lower-emitting engines to generate the necessary credits. 
We believe requiring emission credits to certify engines under the 
production volume allowance better protects the expected emission 
reductions from the final rule than limiting the production allowance 
to specific vehicle categories. Our approach is consistent with some 
commenters' recommendation to finalize a program that required the use 
of emission credits to protect vulnerable impacted communities by 
ensuring that lower-emitting engines are produced earlier to generate 
the credits necessary to produce engines certified under this 
allowance. Second, a variety of vehicle categories were identified in 
comments as vehicle categories for which manufacturers may need 
additional lead time and flexibility to redesign to accommodate the 
technologies needed to meet the final emission standards. We expect 
that the specific vehicle

[[Page 4402]]

category(ies) for which additional lead time and flexibility is of 
interest will vary by manufacturer, and thus are choosing not to 
specify vehicle categories to avoid competitive disruptions. Finally, 
we are choosing not to limit the production volume allowance to 
specific vehicle categories to simplify and streamline implementation; 
the specific vehicle in which an engine will be installed is not always 
known when an engine is produced, which would make implementing 
restrictions on engines installed in specific vehicle categories 
challenging for both EPA and manufacturers.
    We continue to believe it is important to ensure that technology 
turns over in a timely manner and that manufacturers do not continue 
producing large numbers of higher-emitting pre-MY 2027 compliant 
engines once the MY 2027 standards are in place. The combination of a 
limited production volume (i.e., five percent of the average U.S.-
directed production volume over three model years, (MY 2023 through 
2025, in MYs 2027 through 2029) and a requirement to use credits will 
prevent the production of large numbers of these higher emitting 
engines, while providing additional flexibility for manufacturers to 
redesign engine product lines to accommodate the technologies needed to 
meet the final emission standards.
    For engines certified under the production volume allowance, 
manufacturers would need to meet the standards and related requirements 
that apply for model year 2026 engines under 40 CFR part 86, subpart A. 
Engine families must be certified as separate engine families that 
qualify for carryover certification, which means that the engine family 
would still be properly represented by test data submitted in an 
earlier model year.
    Manufacturers would need to declare a NOX family 
emission limit (FEL) that is at or below the standard specified in 40 
CFR 86.007-11 and calculate negative credits by comparing the declared 
NOX FEL to the FTP emission standard for model year 2027 
engines. In addition, manufacturers would calculate negative credits 
using a value for useful life of 650,000 miles to align with the credit 
calculation for engines that will be generating credits under 40 CFR 
part 1036 starting in model year 2027 (see Equation IV-I for credit 
calculation). The inclusion of useful life and work produced over the 
FTP in the calculation of credits addresses some commenters' concern 
regarding the production of engines with higher power ratings and 
longer useful life periods under the production volume allowance. 
Manufacturers would need to demonstrate compliance with credit 
accounting based on the same ABT reporting requirements that apply for 
certified engines under 40 CFR part 1036.
    See 40 CFR 1036.150(k) for additional details on the limited 
production volume allowance in the final rule.
10. Zero Emission Vehicle NOX Emission Credits
    After further consideration, including consideration of public 
comments, EPA is not finalizing the proposed allowance for 
manufacturers to generate NOX emissions credits from heavy-
duty zero emissions vehicles (ZEVs). Rather, the current 40 CFR 86.016-
1(d)(4), which specifies that heavy-duty ZEVs may not generate 
NOX or PM emission credits, will continue to apply through 
MY 2026, after which 40 CFR 1037.1 will apply. The final 40 CFR 1037.1 
migrates without revisions the text of 40 CFR 86.016-1(d)(4), rather 
than the revisions we proposed to allow manufacturers to generate 
NOX emissions credits from ZEVs.427 428 In this 
Section IV.G.10, we briefly describe the proposal to allow 
manufacturers to generate NOX emissions credits from ZEVs; 
the comments received on the proposal to allow ZEV NOX 
credits; and EPA's response to those comments, which includes our 
rationale for the approach to ZEV NOX credits in the final 
rule.
---------------------------------------------------------------------------

    \427\ At the time of proposal, we referred to battery-electric 
vehicles (BEVs) and fuel cell electric vehicles (FCEVs); in this 
final rule we generally use the term zero emissions vehicles (ZEVs) 
to collectively refer to both BEVs and FCEVs.
    \428\ As proposed, we are consolidating certification 
requirements for BEVs and FCEVs over 14,000 pounds GVWR in 40 CFR 
part 1037 such that manufacturers of BEVs and FCEVs over 14,000 
pounds GVWR would certify to meeting the emission standards and 
requirements of part 1037, as provided in the current 40 CFR 1037.1. 
The final 1037.1 migrates without revisions the text of 40 CFR 
86.016-1(d)(4), rather than the revisions we proposed to allow 
manufacturers to generate NOX emissions credits from BEVs 
and FCEVs. See preamble Section III for additional details on the 
migration of 40 CFR 86.016-1(d)(4) to 40 CFR 1037.1.
---------------------------------------------------------------------------

    We proposed that if manufacturers met certain requirements, then 
they could generate NOX emissions credits from battery-
electric vehicles, BEVs, and fuel cell electric vehicles, FCEVs; we 
refer to BEVs and FCEVs collectively as zero emissions vehicles, 
ZEVs.\429\ Under the proposal, manufacturers would calculate the value 
of NOX emission credits generated from ZEVs using the same 
equation provided for engine emission credits (see Equation IV-1 in 
final preamble Section IV.G.2). To generate the inputs to the equation, 
we proposed that manufacturers would submit test data at the time of 
certification, which is consistent with requirements for CI and SI 
engine manufacturers to generate NOX emissions credits. We 
proposed that vehicle manufacturers, rather than powertrain 
manufacturers, would generate vehicle credits for ZEVs since vehicle 
manufacturers already certify ZEVs to GHG standards under 40 CFR part 
1037. To ensure that ZEV NOX credits were calculated 
accurately, and reflected the environmental and public health benefits 
of vehicles with zero tailpipe emissions over their full useful life, 
we proposed that in MY 2024 and beyond, ZEVs used to generate 
NOX emission credits would need to meet certain battery and 
fuel cell performance requirements over the useful life period (i.e., 
durability requirements).
---------------------------------------------------------------------------

    \429\ We also proposed to allow manufacturers to optionally test 
the hybrid engine and powertrain together, rather than testing the 
engine alone, to demonstrate the NOX emission performance 
of hybrid electric vehicle (HEV) technologies; if the emissions 
results of testing the hybrid engine and powertrain together showed 
NOX emissions lower than the final standards, then 
manufacturers could choose to participate in the NOX ABT 
program; see preamble Section III.A for details on HEVs in the final 
rule.
---------------------------------------------------------------------------

    We requested comment on the general proposed approach of allowing 
ZEVs to generate NOX credits, which could then be used in 
the heavy-duty engine ABT program. We also requested comment on several 
specific aspects of our proposal. See 87 FR 17558, March 28, 2022, for 
additional discussion on the proposal to allow manufacturers to 
generate NOX emissions credits from ZEVs if those vehicles 
met the specified requirements.
    Numerous commenters provided feedback on EPA's proposal to allow 
manufacturers to generate NOX emissions credits from ZEVs. 
The majority of commenters oppose allowing manufacturers to generate 
NOX emissions credits from ZEVs. Several additional 
commenters oppose ZEV NOX emissions credits unless there 
were restrictions on the credits (e.g., shorter credit life, sunsetting 
credit generation in 2026). Other commenters support allowing 
manufacturers to generate NOX emissions credits from 
electric vehicles. Arguments from each of these commenter groups are 
summarized immediately below.
    Commenters opposing NOX emissions credits for ZEVs 
present several lines of argument, including the potential for: (1) 
Substantial impacts on the emissions reductions expected from the 
proposed rule, which could also result in disproportionate impacts in 
disadvantaged communities already

[[Page 4403]]

overburdened with pollution; (2) a lack of improvements in conventional 
engine technologies; and (3) ZEV NOX credits to result 
higher emissions from internal combustion engines, rather than further 
incentivizing additional ZEVs (further noting that other State and 
Federal actions are providing more meaningful and less environmentally 
costly HD ZEV incentives). Stakeholders opposing NOX 
emissions credits from ZEVs were generally environmental or state 
organizations, or suppliers of heavy-duty engine and vehicle 
components.
    In contrast, several commenters support allowing manufacturers to 
generate these credits. Many of these commenters are heavy-duty engine 
and vehicle manufacturers. Commenters supporting an allowance to 
generate NOX emissions credits from ZEVs also provided 
several lines of argument, including the potential for: (1) ZEVs to 
help meet emissions reductions and air quality goals; (2) ZEV 
NOX credits to be essential to the achievability of the 
standards for some manufacturers; and (3) ZEV NOX credits to 
allow manufacturers to manage investments across different products and 
ultimately result in increased ZEV deployment. Each of these topic 
areas is discussed further in section 12.5 of the Response to Comments 
document.
    Three considerations resulted in our decision not to finalize at 
this time the allowance for manufacturers to generate NOX 
emissions credits from heavy-duty ZEVs. First, the standards in the 
final rule are technology-forcing, yet achievable for MY2027 and later 
internal combustion engines without this flexibility. Second, since the 
final standards are not based on projected utilization of ZEV 
technology, and given that we believe there will be increased 
penetration of ZEVs in the HD fleet by MY2027 and later, we are 
concerned that allowing NOX emissions credits would result 
in fewer emissions reductions than intended from this rule.\430\ For 
example, by allowing manufacturers to generate ZEV NOX 
credits, EPA would be allowing higher emissions (through engines using 
credits to emit up to the FEL cap) in MY 2027 and later, without 
requiring commensurate emissions reductions (through additional ZEVs 
beyond those already entering the market without this rule), which 
could be particularly impactful in communities already overburdened by 
pollution. Third, we continue to believe that testing requirements to 
ensure continued battery and fuel cell performance over the useful life 
of a ZEV may be important to ensure the zero-emissions tailpipe 
performance for which they are generating NOX credits; 
however, after further consideration, including consideration of public 
comments, we believe it is appropriate to take additional time to work 
with industry and other stakeholders on any test procedures and other 
specifications for ZEV battery and fuel cell performance over the 
useful life period of the ZEV (see section 12.6 of the Response to 
Comments document for additional detail on comments and EPA responses 
to comments on the proposed ZEV testing and useful life and warranty 
requirements).
---------------------------------------------------------------------------

    \430\ For example, the recently passed Inflation Reduction Act 
(IRA) has many incentives for promoting zero-emission vehicles, see 
Sections 13403 (Qualified Clean Vehicles), 13404 (Alternative Fuel 
Refueling Property Credit), 60101 (Clean Heavy-Duty Vehicles), 60102 
(Grants to Reduce Air Pollution at Ports), and 70002 (United States 
Postal Service Clean Fleets) of H.R. 5376.
---------------------------------------------------------------------------

    In section 12.6 of the Response to Comments document, we further 
discuss each of these considerations in our decision not to finalize 
the allowance for manufacturers to generate NOX emissions 
credits from ZEVs. Additional detail on comments received and EPA 
responses to comments, including comments on more specific aspects of 
comments on the proposed allowance for ZEV NOX emissions 
credits, such as testing, useful life, and warranty requirements for 
ZEVs, are also available in section 12.6 of the Response to Comments 
document. Our responses to comments on the proposed vehicle 
certification for ZEVs are summarized in preamble Section III, with 
additional detail in section 12.6.3 of the Response to Comments 
document.

V. Program Costs

    In Chapter 3 of the RIA, we differentiate between direct, indirect, 
and operating costs when estimating the costs of the rule. ``Direct'' 
costs represent the direct manufacturing costs of the technologies we 
expect to be used to comply with the final standards over the final 
useful lives; these costs accrue to the manufacturer. In this section 
we use those costs to estimate the year-over-year manufacturing costs 
going forward from the first year of implementation. ``Indirect'' 
costs, i.e., research and development (R&D), administrative costs, 
marketing, and other costs of running a company, are associated with 
the application of the expected technologies and also accrue to the 
manufacturer. Like direct costs, indirect costs are expected to 
increase under the final standards, in part due to the useful life 
provisions. Indirect costs are also expected to increase under the 
final program due to the warranty provisions. We term the sum of these 
direct and indirect costs ``technology costs'' or ``technology package 
costs.'' They represent the costs incurred by manufacturers--i.e., 
regulated entities--to comply with the final program.\431\ 
``Operating'' costs represent the costs of using the technology in the 
field. Operating costs include, for example, changes in diesel exhaust 
fluid (DEF) consumption or fuel consumption. These costs accrue to the 
owner/operator of MY 2027 and later heavy-duty vehicles.\432\ We 
present total costs associated with the final program in Section V.C. 
All costs are presented in 2017 dollars consistent with the proposed 
cost analysis, unless noted otherwise.
---------------------------------------------------------------------------

    \431\ More precisely, these technology costs represent costs 
that manufacturers are expected to attempt to recapture via new 
vehicle sales. As such, profits are included in the indirect cost 
calculation. Clearly, profits are not a ``cost'' of compliance--EPA 
is not imposing new regulations to force manufacturers to make a 
profit. However, profits are necessary for manufacturers in the 
heavy-duty industry, a competitive for-profit industry, to sustain 
their operations. As such, manufacturers are expected to make a 
profit on the compliant vehicles they sell, and we include those 
profits in estimating technology costs.
    \432\ Importantly, the final standards, useful lives, and 
warranty periods apply only to new, MY 2027 and later heavy-duty 
vehicles. The legacy fleet is not subject to the new requirements 
and, therefore, users of prior model year vehicles will not incur 
the operating costs we estimate.
---------------------------------------------------------------------------

    We requested comment on all aspects of the cost analysis. In 
particular, we requested comment on our estimation of warranty and 
research and development costs via use of scalars applied to indirect 
cost contributors (see Section V.A.2) and our estimates of emission 
repair cost impacts (see Section V.B.3). We also requested that 
comments include supporting data and/or alternative approaches that we 
could have considered when developing estimates for the final 
rulemaking.
    In response to our requests, we received many helpful comments, 
although lack of data in conjunction with some comments made it 
challenging to evaluate the changes suggested by the commenter. After 
careful consideration of the comments we received, we have made several 
changes to the final cost analysis relative to the proposal. Those 
changes are summarized in Table V-1. Note that, throughout this 
discussion of costs, we use the term regulatory class which defines 
vehicles with similar emission standards (see Chapter 5.2.2 of the 
RIA); we use the term regulatory class for consistency with our MOVES 
model and its classification system so that our costs align with our 
inventory estimates

[[Page 4404]]

and the associated benefits discussed in Sections VI, VII and VIII.

                          Table V-1--Major Changes to the Cost Analysis Since Proposal
----------------------------------------------------------------------------------------------------------------
             Area of change                      Proposed analysis                     Final analysis
----------------------------------------------------------------------------------------------------------------
Warranty costs.........................  Warranty contributions to         Warranty costs are calculated using a
                                          indirect costs were scaled        starting point of $1,000 (2018
                                          using the ratio of proposed       dollars, $976 in 2017 dollars) per
                                          provisions (miles/age) to the     year of warranty coverage for a
                                          baseline provisions.              vehicle equipped with a heavy HDE;
                                                                            warranty costs for other regulatory
                                                                            classes were scaled by the ratio of
                                                                            the direct manufacturing costs (DMC)
                                                                            for the regulatory class to the DMC
                                                                            of the heavy HDE regulatory class.
Warranty costs.........................  Baseline warranty costs were      Baseline warranty costs are estimated
                                          estimated for the regulated       assuming that a percentage of
                                          warranty period only (i.e., the   vehicles are purchased with extended
                                          analysis assumed that no          warranties.
                                          vehicles were purchased with
                                          extended warranties).
Emission repair costs..................  Repair costs used a cost per      Repair costs use a 2021 study by the
                                          mile curve derived from a Fleet   American Transportation Research
                                          Advantage Whitepaper with         Institute (ATRI) in place of the
                                          direct manufacturing cost (DMC)   Fleet Advantage Whitepaper.
                                          ratio scalars applied to
                                          determine cost per mile values
                                          for different regulatory
                                          classes.
Fuel prices............................  Used AEO2018 fuel prices in 2017  Uses AEO2019 fuel prices for
                                          dollars.                          consistency with the final rule
                                                                            version of the MOVES model while
                                                                            continuing with 2017 dollars.
Technology piece costs.................  Exhaust aftertreatment system     EAS costs have been updated and are
                                          (EAS) costs were based on an      based on FEV teardowns as described
                                          ICCT methodology with updates     in RIA Chapter 3.
                                          by EPA.
----------------------------------------------------------------------------------------------------------------

A. Technology Package Costs

    Commenters' primary comment with respect to our proposed technology 
package costs dealt with the need to replace the emission control 
system due to the combination of the low NOX standards with 
the long warranty and useful life provisions under proposed Option 1. 
Another comment with respect to our proposed technology package costs 
dealt with the estimated warranty costs, including both the methodology 
used and the magnitude of the cost estimated by EPA. As explained in 
Sections III and IV, the final program neither imposes numeric 
NOX standards as stringent as, nor does the final rule for 
heavy HDE contain warranty and useful life provisions as long as, 
proposed Option 1. We address these comments in more detail in section 
18 of the RTC. EPA considers the concerns raised in first of these 
comments to be obviated by the final emission standards and regulatory 
useful life values, in light of which we foresee no need for a routine 
replacement of the entire emission control system to maintain in-use 
compliance as suggested by some commenters. Regarding the second, as 
discussed in more detail in Section V.A.2 and section 18 of the RTC, 
EPA has updated the warranty cost methodology, including based on 
information submitted by commenters, and this has resulted in different 
costs associated with warranty.
    Individual technology piece costs are presented in Chapter 3 of the 
RIA. The direct manufacturing costs (DMC) presented in RIA Chapter 3 
use a different dollar basis than the cost analysis, and as such, the 
DMC values presented here have been adjusted to 2017 dollars. Following 
the first year of implementation, the costs also account for a learning 
effect to represent the cost reductions expected to occur via the 
``learning by doing'' phenomenon.\433\ This provides a year-over-year 
cost for each technology package--where a technology package consists 
of the entire emission-control system--as it is applied to new engine 
sales. We then apply industry standard ``retail price equivalent'' 
(RPE) markup factors, with adjustments discussed in the rest of this 
section, to estimate indirect costs associated with each technology 
package. Both the learning effects applied to direct costs and the 
application of markup factors to estimate indirect costs are consistent 
with the cost estimation approaches used in EPA's past transportation-
related regulatory programs. The sum of the direct and indirect costs 
represents our estimate of technology costs per vehicle on a year-over-
year basis. These technology costs multiplied by estimated sales then 
represent the total technology costs associated with the final program.
---------------------------------------------------------------------------

    \433\ The ``learning by doing'' phenomenon is the process by 
which the cost to manufacture a good decreases as more of that good 
is produced, as producers of the good learn from their experience.
---------------------------------------------------------------------------

    This cost calculation approach presumes that the expected 
technologies will be purchased by original equipment manufacturers 
(OEMs) from their suppliers. So, while the DMC estimates include the 
indirect costs and profits incurred by the supplier, the indirect cost 
markups we apply cover the indirect costs incurred by OEMs to 
incorporate the new technologies into their vehicles and to cover 
profit margins typical of the heavy-duty truck industry. We discuss the 
indirect costs in more detail in Section V.A.2.
1. Direct Manufacturing Costs
    To produce a unit of output, manufacturers incur direct and 
indirect costs. Direct costs include cost of materials and labor costs 
to manufacture that unit. Indirect costs are discussed in the following 
section. The direct manufacturing costs presented here include 
individual technology costs for emission-related engine components and 
exhaust aftertreatment systems (EAS).
    Notably, for this analysis we include not only the marginal 
increased costs associated with the standards, but also the emission 
control system costs for the baseline, or no action, case.\434\ 
Throughout this discussion, we refer to baseline case costs, or 
baseline costs, which reflect our cost estimate of emission-related 
engine systems and the exhaust aftertreatment system absent impacts of 
this final rule. This inclusion of baseline system costs contrasts with 
EPA's approach in recent greenhouse gas rules or the light-duty Tier 3 
criteria pollutant rule where we estimated costs relative to a baseline 
case, which obviated the need to estimate baseline costs. We have 
included baseline costs in this analysis because the new emissions 
warranty and regulatory useful life provisions are expected to have 
some impact on not only the new technology added to comply with the 
final standards, but also on emission control technologies already 
developed and in use. The new warranty and useful life provisions will 
increase costs not only for the new technology added in response to the 
new standards, but also for the technology already in place

[[Page 4405]]

(to which the new technology is added) because the new warranty and 
useful life provisions will apply to the entire emission-control 
system, not just the new technology added in response to the new 
standards. The baseline direct manufacturing costs detailed in this 
section are intended to reflect that portion of baseline case engine 
hardware and aftertreatment systems for which new indirect costs will 
be incurred due to the new warranty and useful life provisions, even 
apart from changes in the level of emission standards.
---------------------------------------------------------------------------

    \434\ For this cost analysis, the baseline, or no action, case 
consists of MY 2019 engines and emission control systems. See also 
Section VI for more information about the emission inventory 
baseline and how that baseline is characterized.
---------------------------------------------------------------------------

    As done in the NPRM, we have estimated the baseline engine costs 
based on studies done by the International Council on Clean 
Transportation (ICCT), as discussed in more detail in Chapter 7 of the 
RIA. As discussed there, the baseline engine costs consist of 
turbocharging, fuel system, exhaust gas recirculation, etc. These costs 
represent those for technologies that will be subject to new, longer 
warranty and useful life provisions under this final rule. For costs 
associated with the action case, we have used FEV-conducted teardown-
based costs as presented in Chapter 3 of the RIA for newly added 
cylinder deactivation systems,\435\ and for the exhaust aftertreatment 
system (EAS) costs.\436\ The direct manufacturing costs for the 
baseline engine+aftertreatment and for the final program are shown for 
diesel engines in Table V-2, gasoline engines in Table V-3 and CNG 
engines in Table V-4. Costs are shown for regulatory classes included 
in the cost analysis and follow the categorization approach used in our 
MOVES model. Please refer to Chapter 6 of the RIA for a description of 
the regulatory classes and why the tables that follow include or do not 
include each regulatory class. In short, where MOVES has regulatory 
class populations and associated emission inventories, our cost 
analysis estimates costs. Note also that, throughout this section, we 
use several acronyms, including heavy-duty engine (HDE), exhaust gas 
recirculation (EGR), exhaust aftertreatment system (EAS), and 
compressed natural gas (CNG).
---------------------------------------------------------------------------

    \435\ Mamidanna, S. 2021. Heavy-Duty Engine Valvetrain 
Technology Cost Assessment. U.S. EPA Contract with FEV North 
America, Inc., Contract No. 68HERC19D0008, Task Order No. 
68HERH20F0041.Submitted to the Docket with the proposal.
    \436\ Mamidanna, S. 2021. Heavy-Duty Vehicles Aftertreatment 
Systems Cost Assessment. Submitted to the Docket with the proposal.

   Table V-2--Diesel Technology and Package Direct Manufacturing Costs per Engine by Regulatory Class for the
                                Baseline and Final Program, MY2027, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                                                                Final program
            MOVES regulatory class                        Technology              Baseline    (MY2027 increment
                                                                                                 to baseline)
----------------------------------------------------------------------------------------------------------------
Light HDE....................................  Package........................        3,699                1,957
                                               Engine hardware................        1,097                    0
                                               Closed crankcase...............           18                   37
                                               Cylinder deactivation..........            0                  196
                                               EAS............................        2,585                1,724
Medium HDE...................................  Package........................        3,808                1,817
                                               Engine hardware................        1,254                    0
                                               Closed crankcase...............           18                   37
                                               Cylinder deactivation..........            0                  147
                                               EAS............................        2,536                1,634
Heavy HDE....................................  Package........................        5,816                2,316
                                               Engine hardware................        2,037                    0
                                               Closed crankcase...............           18                   37
                                               Cylinder deactivation..........            0                  206
                                               EAS............................        3,761                2,074
Urban bus....................................  Package........................        3,884                1,850
                                               Engine hardware................        1,254                    0
                                               Closed crankcase...............           18                   37
                                               Cylinder deactivation..........            0                  147
                                               EAS............................        2,613                1,666
----------------------------------------------------------------------------------------------------------------


  Table V-3--Gasoline Technology and Package Direct Manufacturing Costs per Engine by Regulatory Class for the
                                Baseline and Final Program, MY2027, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                                                                Final program
            MOVES regulatory class                        Technology              Baseline    (MY2027 increment
                                                                                                 to baseline)
----------------------------------------------------------------------------------------------------------------
Light HDE....................................  Package........................        2,681                  688
                                               Engine hardware................          522                    0
                                               Aftertreatment.................        2,158                  664
                                               ORVR...........................            0                   24
Medium HDE...................................  Package........................        2,681                  688
                                               Engine hardware................          522                    0
                                               Aftertreatment.................        2,158                  664
                                               ORVR...........................            0                   24
Heavy HDE....................................  Package........................        2,681                  688
                                               Engine hardware................          522                    0
                                               Aftertreatment.................        2,158                  664
                                               ORVR...........................            0                   24
----------------------------------------------------------------------------------------------------------------


[[Page 4406]]


    Table V-4--CNG Technology and Package Direct Manufacturing Costs per Engine by Regulatory Class, for the
                                Baseline and Final Program, MY2027, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                                                               Final standards
            MOVES regulatory class                        Technology              Baseline    (MY2027 increment
                                                                                                 to baseline)
----------------------------------------------------------------------------------------------------------------
Heavy HDE....................................  Package........................        8,585                   25
                                               Engine hardware................          896                    0
                                               Aftertreatment.................        7,689                   25
Urban bus....................................  Package........................        6,438                   19
                                               Engine hardware................          672                    0
                                               Aftertreatment.................        5,766                   19
----------------------------------------------------------------------------------------------------------------

    The direct costs are then adjusted to account for learning effects 
going forward from the first year of implementation. We describe in 
detail in Chapter 7 of the RIA the approach used to apply learning 
effects in this analysis. Learning effects were applied on a technology 
package cost basis, and MOVES-projected sales volumes were used to 
determine first-year sales and cumulative sales. The resultant direct 
manufacturing costs and how those costs decrease over time are 
presented in Section V.A.3.
2. Indirect Costs
    The indirect costs presented here are all the costs estimated to be 
incurred by manufacturers of new heavy-duty engines and vehicles 
associated with producing the unit of output that are not direct costs. 
For example, they may be related to production (such as research and 
development (R&D)), corporate operations (such as salaries, pensions, 
and health care costs for corporate staff), or selling (such as 
transportation, dealer support, and marketing). Indirect costs are 
generally recovered by allocating a share of the indirect costs to each 
unit of good sold. Although direct costs can be allocated to each unit 
of good sold, it is more challenging to account for indirect costs 
allocated to a unit of goods sold. To ensure that regulatory analyses 
capture the changes in indirect costs, markup factors (which relate 
total indirect costs to total direct costs) have been developed and 
used by EPA and other stakeholders. These factors are often referred to 
as retail price equivalent (RPE) multipliers. RPE multipliers provide, 
at an aggregate level, the relative shares of revenues, where:

Revenue = Direct Costs + Indirect Costs
Revenue/Direct Costs = 1 + Indirect Costs/Direct Costs = Retail Price 
Equivalent (RPE)

    Resulting in:

Indirect Costs = Direct Costs x (RPE-1)

    If the relationship between revenues and direct costs (i.e., RPE) 
can be shown to equal an average value over time, then an estimate of 
direct costs can be multiplied by that average value to estimate 
revenues, or total costs. Further, that difference between estimated 
revenues, or total costs, and estimated direct costs can be taken as 
the indirect costs. EPA has frequently used these multipliers \437\ to 
predict the resultant impact on costs associated with manufacturers' 
responses to regulatory requirements and we are using that approach in 
this analysis to account for most of the indirect cost contributions. 
The exception is the warranty cost as described in this section.
---------------------------------------------------------------------------

    \437\ See 75 FR 25324, 76 FR 57106, 77 FR 62624, 79 FR 23414, 81 
FR 73478, 86 FR 74434.
---------------------------------------------------------------------------

    The cost analysis estimates indirect costs by applying the RPE 
markup factor used in past rulemakings (such as those setting 
greenhouse gas standards for heavy-duty trucks).\438\ The markup 
factors are based on financial filings with the Securities and Exchange 
Commission for several engine and engine/truck manufacturers in the 
heavy-duty industry.\439\ The RPE factors for the HD truck industry are 
shown in Table V-5. Also shown in Table V-5 are the RPE factors for 
light-duty vehicle manufacturers.\440\
---------------------------------------------------------------------------

    \438\ 76 FR 57106; 81 FR 73478.
    \439\ Heavy Duty Truck Retail Price Equivalent and Indirect Cost 
Multipliers, Draft Report, July 2010.
    \440\ Rogozhin, A., et al., Using indirect cost multipliers to 
estimate the total cost of adding new technology in the automobile 
industry. International Journal of Production Economics (2009), 
doi:10.1016/j.ijpe.2009.11.031.

 Table V-5--Retail Price Equivalent Factors in the Heavy-Duty and Light-
                             Duty Industries
------------------------------------------------------------------------
                                             HD truck       LD vehicle
            Cost contributor                 industry        industry
------------------------------------------------------------------------
Direct manufacturing cost...............            1.00            1.00
Warranty................................            0.03            0.03
R&D.....................................            0.05            0.05
Other (admin, retirement, health, etc.).            0.29            0.36
Profit (cost of capital)................            0.05            0.06
RPE.....................................            1.42            1.50
------------------------------------------------------------------------

    For this analysis, EPA based indirect cost estimates for diesel and 
CNG regulatory classes on the HD Truck Industry RPE values shown in 
Table V-5.\441\ For gasoline regulatory classes, we used the LD Vehicle 
Industry values shown in Table V-5 since they more closely represent 
the cost structure of manufacturers in that industry--Ford, General 
Motors, and Stellantis.
---------------------------------------------------------------------------

    \441\ Note that the report used the term ``HD Truck'' while EPA 
generally uses the term ``HD vehicle;'' they are equivalent when 
referring to this report.
---------------------------------------------------------------------------

    Of the cost contributors listed in Table V-5, Warranty and R&D are 
the elements of indirect costs that the final rule requirements are 
expected to impact. As discussed in Section IV of this preamble, EPA is 
lengthening the required warranty period, which we expect to increase 
the contribution of warranty costs to indirect costs. EPA is also 
tightening the numeric standards and extending the regulatory useful 
life,

[[Page 4407]]

which we expect to result in increased R&D expenses as compliant 
systems are developed. All other indirect cost elements--those 
encapsulated by the ``Other'' category, including General and 
Administrative Costs, Retirement Costs, Healthcare Costs, and other 
overhead costs--as well as Profits, are expected to scale according to 
their historical levels of contribution.
    As mentioned, Warranty and R&D are the elements of indirect costs 
that are expected to be impacted. Warranty expenses are the costs that 
a business expects to or has already incurred for the repair or 
replacement of goods that it has sold. The total amount of warranty 
expense is limited by the warranty period that a business typically 
allows. After the warranty period for a product has expired, a business 
no longer incurs a warranty liability; thus, a longer warranty period 
results in a longer period of liability for a product. At the time of 
sale, a warranty liability account is adjusted to reflect the expected 
costs of any potential future warranty claims. If and when warranty 
claims are made by customers, the warranty liability account is debited 
and a warranty claims account is credited to cover warranty claim 
expenses.\442\
---------------------------------------------------------------------------

    \442\ Warranty expense is recognized in the same period as the 
sales for the products that were sold, if it is probable that an 
expense will be incurred and the company can estimate the amount of 
the expense. For more discussion of this topic, see the supporting 
material in this docket, AccountingTools.com, December 24, 2020, 
accessed January 28, 2021.
---------------------------------------------------------------------------

    In the proposed analysis, to address the expected increased 
indirect cost contributions associated with warranty (increased funding 
of the warranty liability account) due to the proposed longer warranty 
requirements, we applied scaling factors commensurate with the changes 
in proposed Option 1 or Option 2 to the number of miles included in the 
warranty period (i.e., VMT-based scaling factors). Industry commenters 
took exception to this approach, arguing that it resulted in 
underestimated costs associated with warranty. To support their 
comments, one commenter submitted data that showed costs associated 
with actual warranty claims for roughly 250,000 heavy heavy-duty 
vehicles. The following figure includes the chart from their comments, 
which are also in the public docket for this rule.
[GRAPHIC] [TIFF OMITTED] TR24JA23.002

Figure V-1 Warranty Costs Submitted as Part of the Comments From An 
Industry Association; See EPA-HQ-OAR-2019-0055-1203-A1, Page 151

    EPA considers this comment and supporting information to be 
persuasive, not only because it represents data, but also because it 
represents data from three manufacturers and over 250,000 vehicles; 
thus, we switched from a VMT-based scaling approach to a years-based 
approach to better take into account this information. However, the 
data are for heavy HDE, so it is not possible to determine an 
appropriate cost per year for light or medium HDE from the data 
directly. Also, the data represent actual warranty claims without any 
mention of the warranty claims rate (i.e., the share of engines sold 
that are making the warranty claims represented in the data). This 
latter issue makes it difficult to determine the costs that might be 
imposed on all new engines sold to cover the future warranty claims for 
the relatively smaller fraction of engines that incur warranty repair. 
In other words, if all heavy HDE purchases are helping to fund a 
warranty liability account, it is unclear if the $1,000 per year per 
engine is the right amount or if $1,000 per year is needed on only that 
percent of engines that will incur warranty repair. In the end, 
warranty costs imposed on new engine sales should be largely recouped 
by purchasers of those engines in the form of reduced emission repair 
expenses. EPA believes it is unlikely that a manufacturer would use 
their warranty program as a profit generator under the $1,000 per 
engine approach, especially in a market as competitive as the HD engine 
and vehicle industry. The possibility exists that the costs associated 
with the longer warranty

[[Page 4408]]

coverage required by this rule will (1) converge towards those of the 
better performing OEMs; and (2) drop over time via something analogous 
to the learning by doing phenomenon described earlier. If true, we have 
probably overestimated the costs estimated here as attributable to this 
rule.
    Thus, after careful consideration of these comments regarding 
warranty, and the engineering judgement of EPA subject matter experts, 
we revised our approach to estimating warranty costs, and for the final 
rule we have estimated warranty costs assuming a cost of $1,000 (2018 
dollars or $977 in 2017 dollars) per estimated number of years of 
warranty coverage for a heavy heavy-duty diesel engine or heavy-duty 
vehicle equipped with such an engine. For other regulatory (engine) 
classes, we have scaled that value by the ratio of their estimated 
baseline emission-control system direct cost to the estimated emission-
control system direct cost of the baseline heavy heavy-duty diesel 
engine. We use the baseline heavy heavy-duty diesel engine direct cost 
here because it should be consistent with the data behind the $1,000 
per year value. The resulting emission-related warranty costs per year 
for a MY 2027 HD engine are as shown in Table V-6.

                                       Table V-6--Warranty Costs per Year
                                               [2017 Dollars] \a\
----------------------------------------------------------------------------------------------------------------
         MOVES regulatory class                   Scaling approach            Diesel      Gasoline       CNG
----------------------------------------------------------------------------------------------------------------
Light HDE...............................  Base Light HDE DMC/Base Diesel           621          450  ...........
                                           Heavy HDE DMC.
Medium HDE..............................  Base Medium HDE DMC/Base Diesel          639          449  ...........
                                           Heavy HDE DMC.
Heavy HDE...............................  Base Heavy HDE DMC/Base Diesel           977          448        1,442
                                           Heavy HDE DMC.
Urban bus...............................  Base Urban bus DMC/Base Diesel           652  ...........        1,081
                                           Heavy HDE DMC.
----------------------------------------------------------------------------------------------------------------
\a\ The Base Diesel HDE DMC would be the $5,816 value shown in Table V-2.

    As noted, we have used the estimated number of years of warranty 
coverage, not the regulated number of years. In other words, a long-
haul tractor accumulating over 100,000 miles per year will reach any 
regulated warranty mileage prior to a refuse truck accumulating under 
40,000 miles per year, assuming both are in the same regulatory class 
and, therefore, have the same warranty provisions. In all cases, we 
estimate the number of years of warranty coverage by determining the 
minimum number of years to reach either the number of years, the number 
of miles, or the number of hours of operation covered by the EPA 
emissions-related warranty. We provide more detail on this in Chapter 7 
of the final RIA.
    Lastly, with respect to warranty, we have estimated that many of 
the regulated products are sold today with a warranty period longer 
than the EPA required emissions-related warranty period. In the 
proposal, we calculated baseline warranty costs only for the required 
warranty periods. In the final analysis, we calculate baseline warranty 
costs based on the warranty periods for which engines are actually 
sold. For diesel and CNG heavy HDE, we assume all are sold with 
warranties covering 250,000 miles, and for diesel and CNG medium HDE, 
we assume half are sold with warranties covering 150,000 miles. For all 
other engines and associated fuel types, we have not estimated any use 
of extended warranties in the baseline.
    We use these annual warranty costs for both the baseline and the 
final standards despite the addition of new technology associated with 
this final rule. We believe this is reasonable for two reasons: (1) The 
source data included several years of data during which there must have 
been new technology introductions, yet annual costs appear to have 
remained generally steady; and, (2) the R&D we expect to be done, 
discussed next, is expected to improve overall durability, which should 
serve to help maintain historical annual costs.
    For R&D, we have maintained the approach used in the proposal, 
although it is applied using the final useful life provisions. For 
example, for R&D on a Class 8 truck, the final standards would extend 
regulatory useful life from 10 years, 22,000 hours, or 435,000 miles, 
to 11 years, 32,000 hours, or 650,000 miles. We have applied a scaling 
factor of 1.49 (650/435) to the 0.05 R&D contribution factor for MYs 
2027 and later. We apply this same methodology to estimating R&D for 
other vehicle categories. We estimate that once the development efforts 
into longer useful life are complete, increased expenditures will 
return to their normal levels of contribution. Therefore, we have 
implemented R&D scalars for three years (2027 through 2029). In MY 2030 
and later, the R&D scaling factors are no longer applied.
    The VMT-based scaling factors applied to R&D cost contributors used 
in our cost analysis of final standards are shown in Table V-7 for 
diesel and CNG regulatory classes and in Table V-8 for gasoline 
regulatory classes.

Table V-7--Scaling Factors Applied to RPE Contribution Factors To Reflect Changes in Their Contributions, Diesel
                                            & CNG Regulatory Classes
----------------------------------------------------------------------------------------------------------------
                                                                                             R&D scalars
                    Scenario                           MOVES regulatory class       ----------------------------
                                                                                       MY2027-2029     MY2030+
----------------------------------------------------------------------------------------------------------------
Baseline.......................................  Light HDE.........................            1.00         1.00
                                                 Medium HDE........................            1.00         1.00
                                                 Heavy HDE.........................            1.00         1.00
                                                 Urban Bus.........................            1.00         1.00
Final Program..................................  Light HDE.........................            2.45         1.00
                                                 Medium HDE........................            1.89         1.00
                                                 Heavy HDE.........................            1.49         1.00
                                                 Urban Bus.........................            1.49         1.00
----------------------------------------------------------------------------------------------------------------


[[Page 4409]]


    Table V-8--Scaling Factors Applied to RPE Contribution Factors To Reflect Changes in Their Contributions,
                                           Gasoline Regulatory Classes
----------------------------------------------------------------------------------------------------------------
                                                                                             R&D scalars
                    Scenario                           MOVES regulatory class       ----------------------------
                                                                                       MY2027-2029     MY2030+
----------------------------------------------------------------------------------------------------------------
Baseline.......................................  Light HDE.........................            1.00         1.00
                                                 Medium HDE........................            1.00         1.00
                                                 Heavy HDE.........................            1.00         1.00
Final Program..................................  Light HDE.........................            1.82         1.00
                                                 Medium HDE........................            1.82         1.00
                                                 Heavy HDE.........................            1.82         1.00
----------------------------------------------------------------------------------------------------------------

    Lastly, as mentioned in Section V.A.1, the markups for estimating 
indirect costs are applied to our estimates of the absolute direct 
manufacturing costs for emission-control technology shown in Table V-2, 
Table V-3 and Table V-4, not just the incremental costs associated with 
the final program (i.e., the Baseline + Final costs). Table V-9 
provides an illustrative example using a baseline technology cost of 
$5000, a final incremental cost of $1000, and an indirect cost R&D 
contribution of 0.05 with a simple scalar of 1.5 associated with a 
longer useful life period. In this case, the costs could be calculated 
according to two approaches, as shown in Table V-9. By including the 
baseline costs, we are estimating new R&D costs in the final standards, 
as illustrated by the example where including baseline costs results in 
R&D costs of $450 while excluding baseline costs results in R&D costs 
of $75.

    Table V-9--Simplified Hypothetical Example of Indirect R&D Costs
    Calculated on An Incremental vs. Absolute Technology Package Cost
    [Values are not from the analysis and are for presentation only]
------------------------------------------------------------------------
                                Using incremental
                                   costs only       Using absolute costs
------------------------------------------------------------------------
Baseline direct               $5,000..............  $5,000.
 manufacturing cost (DMC).
Direct Manufacturing Cost     $1,000..............  $5,000 + $1,000 =
 (DMC).                                              $6,000.
Indirect R&D Costs..........  $1,000 x 0.05 x 1.5   $6,000 x 0.05 x 1.5
                               = $75.                = $450.
Incremental DMC + R&D.......  $1,000 + $75 =        $6,000 + $450-$5,000
                               $1,075.               = $1,450.
------------------------------------------------------------------------

3. Technology Costs per Vehicle
    The following tables present the technology costs estimated for the 
final program on a per-vehicle basis for MY 2027. Reflected in these 
tables are learning effects on direct manufacturing costs and scaling 
effects associated with final program requirements. The sum is also 
shown and reflects the direct plus indirect cost per vehicle in the 
specific model year. Note that the indirect costs shown include 
warranty, R&D, ``other,'' and profit, the latter two which scale with 
direct costs via the indirect cost contribution factor. While direct 
costs do not change across the different vehicle types (i.e., long-haul 
versus short-haul combination), the indirect costs do vary because 
differing miles driven and operating hours between types of vehicles 
result in different warranty and useful life estimates in actual use. 
These differences impact the estimated warranty and R&D costs.
    We show costs per vehicle here, but it is important to note that 
these are costs and not prices. We are not estimating how manufacturers 
might price their products. Manufacturers may pass costs along to 
purchasers via price increases in a manner consistent with what we show 
here. However, manufacturers may also price certain products higher 
than what we show while pricing others lower--the higher-priced 
products thereby subsidizing the lower-priced products. This is true in 
any market, not just the heavy-duty highway industry. This may be 
especially true with respect to the indirect costs we have estimated 
because, for example, R&D done to improve emission durability can 
readily transfer across different engines whereas hardware added to an 
engine is uniquely tied to that engine.
    Importantly, we present costs here for MY2027 vehicles, but these 
costs continue for every model year going forward from there. 
Consistent with the learning impacts described in section V.A.2, the 
costs per vehicle decrease slightly over time, but only the increased 
R&D costs are expected to decrease significantly. Increased R&D is 
estimated to occur for three years following and including MY2027 
(i.e., MY2027-29), after which time its contribution to indirect costs 
returns to lower values as shown in Table V.4.

Table V-10--MY2027 Diesel Light HDE Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           3,699             2,332                6,031
Other Buses..............................................           3,699             2,263                5,962
School Buses.............................................           3,699             3,829                7,528
Short-Haul Single Unit Trucks............................           3,699             2,851                6,550
Transit Buses............................................           3,699             2,263                5,962
----------------------------------------------------------------------------------------------------------------

[[Page 4410]]

 
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           5,656             6,353               12,009
Other Buses..............................................           5,656             6,064               11,720
School Buses.............................................           5,656             8,830               14,485
Short-Haul Single Unit Trucks............................           5,656             8,530               14,186
Transit Buses............................................           5,656             6,064               11,720
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           1,957             4,021                5,978
Other Buses..............................................           1,957             3,800                5,757
School Buses.............................................           1,957             5,001                6,957
Short-Haul Single Unit Trucks............................           1,957             5,680                7,636
Transit Buses............................................           1,957             3,800                5,757
----------------------------------------------------------------------------------------------------------------


    Table V-11--MY2027 Diesel Medium HDE Technology Costs per Vehicle Associated With the Final Program, 2017
                                                     Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           3,808             3,774                7,582
Motor Homes..............................................           3,808             4,682                8,490
Other Buses..............................................           3,808             3,597                7,404
Refuse Trucks............................................           3,808             4,217                8,025
School Buses.............................................           3,808             4,682                8,490
Short-Haul Combination Trucks............................           3,808             2,595                6,402
Short-Haul Single Unit Trucks............................           3,808             4,682                8,490
Transit Buses............................................           3,808             3,597                7,404
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           5,625             7,572               13,197
Motor Homes..............................................           5,625             8,839               14,464
Other Buses..............................................           5,625             7,175               12,799
Refuse Trucks............................................           5,625             8,564               14,189
School Buses.............................................           5,625             8,839               14,464
Short-Haul Combination Trucks............................           5,625             4,930               10,555
Short-Haul Single Unit Trucks............................           5,625             8,839               14,464
Transit Buses............................................           5,625             7,175               12,799
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           1,817             3,798                5,615
Motor Homes..............................................           1,817             4,157                5,974
Other Buses..............................................           1,817             3,578                5,395
Refuse Trucks............................................           1,817             4,347                6,164
School Buses.............................................           1,817             4,157                5,974
Short-Haul Combination Trucks............................           1,817             2,335                4,153
Short-Haul Single Unit Trucks............................           1,817             4,157                5,974
Transit Buses............................................           1,817             3,578                5,395
----------------------------------------------------------------------------------------------------------------


Table V-12--MY2027 Diesel Heavy HDE Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks.............................           5,816             4,025                9,841
Long-Haul Single Unit Trucks.............................           5,816             7,151               12,967
Motor Homes..............................................           5,816             7,151               12,967
Other Buses..............................................           5,816             7,151               12,967
Refuse Trucks............................................           5,816             7,151               12,967
School Buses.............................................           5,816             7,151               12,967
Short-Haul Combination Trucks............................           5,816             5,658               11,473

[[Page 4411]]

 
Short-Haul Single Unit Trucks............................           5,816             7,151               12,967
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks.............................           8,132             6,535               14,667
Long-Haul Single Unit Trucks.............................           8,132            13,139               21,271
Motor Homes..............................................           8,132            13,139               21,271
Other Buses..............................................           8,132            13,139               21,271
Refuse Trucks............................................           8,132            13,139               21,271
School Buses.............................................           8,132            13,139               21,271
Short-Haul Combination Trucks............................           8,132             9,474               17,606
Short-Haul Single Unit Trucks............................           8,132            13,139               21,271
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks.............................           2,316             2,510                4,827
Long-Haul Single Unit Trucks.............................           2,316             5,988                8,304
Motor Homes..............................................           2,316             5,988                8,304
Other Buses..............................................           2,316             5,988                8,304
Refuse Trucks............................................           2,316             5,988                8,304
School Buses.............................................           2,316             5,988                8,304
Short-Haul Combination Trucks............................           2,316             3,816                6,132
Short-Haul Single Unit Trucks............................           2,316             5,988                8,304
----------------------------------------------------------------------------------------------------------------


Table V-13--MY2027 Diesel Urban Bus Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
FRM Baseline.............................................           3,884             3,238                7,122
FRM Baseline + Final Program.............................           5,734             8,901               14,635
Increased Cost of the Final Program......................           1,850             5,663                7,512
----------------------------------------------------------------------------------------------------------------


  Table V-14--MY2027 Gasoline HDE Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           2,681             1,905                4,585
Motor Homes..............................................           2,681             3,511                6,192
Other Buses..............................................           2,681             1,855                4,535
School Buses.............................................           2,681             2,989                5,670
Short-Haul Single Unit Trucks............................           2,681             2,280                4,961
Transit Buses............................................           2,681             1,855                4,535
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           3,369             3,784                7,153
Motor Homes..............................................           3,369             6,223                9,592
Other Buses..............................................           3,369             3,624                6,993
School Buses.............................................           3,369             6,223                9,592
Short-Haul Single Unit Trucks............................           3,369             4,986                8,355
Transit Buses............................................           3,369             3,624                6,993
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................             688             1,880                2,568
Motor Homes..............................................             688             2,712                3,401
Other Buses..............................................             688             1,770                2,458
School Buses.............................................             688             3,234                3,923
Short-Haul Single Unit Trucks............................             688             2,706                3,394
Transit Buses............................................             688             1,770                2,458
----------------------------------------------------------------------------------------------------------------


[[Page 4412]]


  Table V-15--MY2027 CNG Heavy HDE Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           8,585            10,556               19,141
Other Buses..............................................           8,585            10,556               19,141
Refuse Trucks............................................           8,585            10,556               19,141
School Buses.............................................           8,585            10,556               19,141
Short-Haul Combination Trucks............................           8,585             8,351               16,936
Short-Haul Single Unit Trucks............................           8,585            10,556               19,141
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................           8,610            17,988               26,598
Other Buses..............................................           8,610            17,988               26,598
Refuse Trucks............................................           8,610            17,988               26,598
School Buses.............................................           8,610            17,988               26,598
Short-Haul Combination Trucks............................           8,610            12,577               21,187
Short-Haul Single Unit Trucks............................           8,610            17,988               26,598
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks.............................              25             7,431                7,457
Other Buses..............................................              25             7,431                7,457
Refuse Trucks............................................              25             7,431                7,457
School Buses.............................................              25             7,431                7,457
Short-Haul Combination Trucks............................              25             4,225                4,251
Short-Haul Single Unit Trucks............................              25             7,431                7,457
----------------------------------------------------------------------------------------------------------------


  Table V-16--MY2027 CNG Urban Bus Technology Costs per Vehicle Associated With the Final Program, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                            Direct costs    Indirect costs    Costs per vehicle
----------------------------------------------------------------------------------------------------------------
FRM Baseline.............................................           6,438             5,367               11,806
FRM Baseline + Final Program.............................           6,457            13,490               19,948
Increased Cost of the Final Program......................              19             8,123                8,142
----------------------------------------------------------------------------------------------------------------

B. Operating Costs

    We have estimated three impacts on operating costs expected to be 
incurred by users of new MY 2027 and later heavy-duty vehicles: 
Increased diesel exhaust fluid (DEF) consumption by diesel vehicles due 
to increased DEF dose rates to enable compliance with more stringent 
NOX standards; decreased fuel costs for gasoline vehicles 
due to new onboard refueling vapor recovery systems that allow burning 
(in engine) of otherwise evaporated hydrocarbon emissions; emission 
repair impacts brought about by longer warranty and useful life 
provisions; and the potential higher emission-related repair costs for 
vehicles equipped with the new technology. For the repair impacts, we 
expect that the longer duration warranty period will result in lower 
owner/operator-incurred repair costs due to fewer repairs being paid 
for by owners/operators since more costs will be borne by the 
manufacturer, and that the longer duration useful life periods will 
result in increased emission control system durability. We have 
estimated the net effect on repair costs and describe our approach, 
along with increased DEF consumption and reduced gasoline consumption, 
in this section. Additional details on our methodology and estimates of 
operating costs are included in RIA Chapter 7.2.
1. Costs Associated With Increased Diesel Exhaust Fluid (DEF) 
Consumption in Diesel Engines
    Consistent with the approach used to estimate technology costs, we 
have estimated both baseline case DEF consumption and DEF consumption 
under the final program. For the baseline case, we estimated DEF 
consumption using the relationship between DEF dose rate and the 
reduction in NOX over the SCR catalyst. The relationship 
between DEF dose rate and NOX reduction across the SCR 
catalyst is based on methodology presented in the Technical Support 
Document to the 2012 Nonconformance Penalty rule (the NCP Technical 
Support Document, or NCP TSD).\443\ The relationship of DEF dose rate 
to NOX reduction used in that methodology considered FTP 
emissions and, as such, the DEF dose rate increased as FTP tailpipe 
emissions decreased. The DEF dose rate used in this analysis is 5.18 
percent of fuel consumed.
---------------------------------------------------------------------------

    \443\ Nonconformance Penalties for On-highway Heavy-duty Diesel 
Engines: Technical Support Document; EPA-420-R-12-014, August 2012.
---------------------------------------------------------------------------

    To estimate DEF consumption impacts under the final program, which 
involves not only the new FTP emission standards but also the new SET 
and LLC standards along with new off-cycle standards, we developed a 
new approach to estimate DEF consumption for the proposal, which we 
also applied in this final rule. For this analysis, we scaled DEF 
consumption with the NOX reductions achieved under the final 
emission standards. This was done by considering the molar mass of 
NOX, the molar mass of urea, the mass concentration of urea 
in DEF, along with the density of DEF, to estimate the

[[Page 4413]]

theoretical gallons of DEF consumed per ton of NOX reduced. 
We estimated theoretical DEF consumption per ton of NOX 
reduced at 442 gallons/ton, which we then adjusted based on testing to 
527 gallons/ton, the value used in this analysis. We describe this in 
more detail in Section 7.2.1 of the RIA.
    These two DEF consumption metrics--dose rate per gallon for an 
engine meeting the baseline emission standards and any additional DEF 
consumption per ton of NOX reduced to achieve the final 
emission standards over the final useful lives--were used to estimate 
total DEF consumption. These DEF consumption rates were then multiplied 
by DEF price per gallon, adjusted to 2017 dollars from the DEF prices 
presented in the NCP TSD, to arrive at the impacts on DEF costs for 
diesel engines. These are shown for MY2027 diesel vehicles in Table V-
17. Because these are operating costs which occur over time, we present 
them at both 3 and 7 percent discount rates.

                       Table V-17--MY2027 Lifetime DEF Costs per Diesel Vehicle Associated With Final NOX Standards, 2017 Dollars
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                         3% Discount rate                                7% Discount rate
                                                         -----------------------------------------------------------------------------------------------
                                                           Light HDE  Medium HDE   Heavy HDE   Urban bus   Light HDE  Medium HDE   Heavy HDE   Urban bus
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                      FRM Baseline
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........      34,009  ..........  ..........  ..........      25,768  ..........
Long-Haul Single Unit Trucks............................       3,759       5,686       6,823  ..........       2,937       4,443       5,331  ..........
Motor Homes.............................................  ..........       1,489       1,764  ..........  ..........       1,068       1,265  ..........
Other Buses.............................................       9,118      11,285      11,688  ..........       6,695       8,286       8,582  ..........
Refuse Trucks...........................................  ..........       8,435       8,787  ..........  ..........       6,317       6,581  ..........
School Buses............................................       2,331       3,030       3,187  ..........       1,712       2,225       2,340  ..........
Short-Haul Combination Trucks...........................  ..........      16,323      17,154  ..........  ..........      12,735      13,384  ..........
Short-Haul Single Unit Trucks...........................       2,733       4,144       4,975  ..........       2,100       3,184       3,823  ..........
Transit Buses...........................................       9,192      11,254  ..........      11,742       6,750       8,263  ..........       8,622
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              FRM Baseline + Final Program
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........      37,621  ..........  ..........  ..........      28,580  ..........
Long-Haul Single Unit Trucks............................       4,011       6,215       7,916  ..........       3,136       4,865       6,200  ..........
Motor Homes.............................................  ..........       1,617       2,016  ..........  ..........       1,162       1,450  ..........
Other Buses.............................................       9,805      12,277      13,594  ..........       7,209       9,040      10,011  ..........
Refuse Trucks...........................................  ..........       9,182      10,246  ..........  ..........       6,895       7,696  ..........
School Buses............................................       2,501       3,293       3,671  ..........       1,839       2,424       2,702  ..........
Short-Haul Combination Trucks...........................  ..........      17,575      19,378  ..........  ..........      13,727      15,154  ..........
Short-Haul Single Unit Trucks...........................       2,949       4,573       5,864  ..........       2,268       3,522       4,517  ..........
Transit Buses...........................................       9,867      12,149  ..........      13,410       7,253       8,945  ..........       9,863
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Increased Cost of the Final Program
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........       3,612  ..........  ..........  ..........       2,812  ..........
Long-Haul Single Unit Trucks............................         252         529       1,094  ..........         199         422         869  ..........
Motor Homes.............................................  ..........         128         253  ..........  ..........          94         185  ..........
Other Buses.............................................         687         992       1,906  ..........         514         754       1,428  ..........
Refuse Trucks...........................................  ..........         747       1,459  ..........  ..........         579       1,115  ..........
School Buses............................................         170         263         484  ..........         127         199         362  ..........
Short-Haul Combination Trucks...........................  ..........       1,251       2,224  ..........  ..........         992       1,771  ..........
Short-Haul Single Unit Trucks...........................         216         429         889  ..........         168         337         694  ..........
Transit Buses...........................................         675         896  ..........       1,669         504         681  ..........       1,241
--------------------------------------------------------------------------------------------------------------------------------------------------------

2. Costs Associated With Changes in Fuel Consumption on Gasoline 
Engines
    We have estimated a decrease in fuel costs, i.e., fuel savings, 
associated with the final ORVR requirements on gasoline engines. Due to 
the ORVR systems, evaporative emissions that would otherwise be emitted 
into the atmosphere will be trapped and subsequently burned in the 
engine. We describe the approach taken to estimate these impacts in 
Chapter 7.2.2 of the RIA. These newly captured evaporative emissions 
are converted to gallons and then multiplied by AEO 2019 reference case 
gasoline prices (converted to 2017 dollars) to arrive at the monetized 
impacts. These impacts are shown in Table V-18. In the aggregate, we 
estimate that the ORVR requirements in the final program will result in 
an annual reduction of approximately 0.3 million (calendar year 2027) 
to 4.9 million (calendar year 2045) gallons of gasoline, representing 
roughly 0.1 percent of gasoline consumption from impacted vehicles.

[[Page 4414]]



   Table V-18--MY2027 Lifetime Fuel Costs per Gasoline Vehicle Associated With ORVR Requirements, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                   3% Discount rate                    7% Discount rate
                                         -----------------------------------------------------------------------
                                           Light HDE  Medium HDE   Heavy HDE   Light HDE  Medium HDE   Heavy HDE
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............     120,876     150,530     192,727      94,841     118,108     151,216
Motor Homes.............................      30,329      38,339      48,887      21,905      27,691      35,309
Other Buses.............................     273,223  ..........  ..........     201,982  ..........  ..........
School Buses............................      69,242  ..........  ..........      51,188  ..........  ..........
Short-Haul Single Unit Trucks...........      86,494     109,427     139,754      66,791      84,501     107,918
Transit Buses...........................     269,797  ..........  ..........     199,449  ..........  ..........
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............     120,744     150,349     192,470      94,739     117,969     151,019
Motor Homes.............................      30,271      38,260      48,781      21,864      27,635      35,233
Other Buses.............................     272,656  ..........  ..........     201,570  ..........  ..........
School Buses............................      69,110  ..........  ..........      51,092  ..........  ..........
Short-Haul Single Unit Trucks...........      86,397     109,292     139,566      66,717      84,399     107,777
Transit Buses...........................     269,245  ..........  ..........     199,047  ..........  ..........
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............        -132        -181        -257        -102        -139        -197
Motor Homes.............................         -58         -79        -106         -41         -56         -75
Other Buses.............................        -567  ..........  ..........        -412  ..........  ..........
School Buses............................        -132  ..........  ..........         -96  ..........  ..........
Short-Haul Single Unit Trucks...........         -97        -135        -187         -74        -102        -141
Transit Buses...........................        -552  ..........  ..........        -402  ..........  ..........
----------------------------------------------------------------------------------------------------------------

3. Emission-Related Repair Cost Impacts Associated With the Final 
Program
    The final extended warranty and useful life requirements will have 
an impact on emission-related repair costs incurred by truck owners. 
Researchers have noted the relationships among quality, reliability, 
and warranty for a variety of goods.\444\ Wu,\445\ for instance, 
examines how analyzing warranty data can provide ``early warnings'' on 
product problems that can then be used for design modifications. 
Guajardo et al. describe one of the motives for warranties to be 
``incentives for the seller to improve product quality''; specifically 
for light-duty vehicles, they find that buyers consider warranties to 
substitute for product quality, and to complement service quality.\446\ 
Murthy and Jack, for new products, and Saidi-Mehrabad et al. for 
second-hand products, consider the role of warranties in improving a 
buyer's confidence in quality of the good.447 448
---------------------------------------------------------------------------

    \444\ Thomas, M., and S. Rao (1999). ``Warranty Economic 
Decision Models: A Summary and Some Suggested Directions for Future 
Research.'' Operations Research 47(6):807-820.
    \445\ Wu, S (2012). Warranty Data Analysis: A Review. Quality 
and Reliability Engineering International 28: 795-805.
    \446\ Guajardo, J., M Cohen, and S. Netessine (2016). ``Service 
Competition and Product Quality in the U.S. Automobile Industry.'' 
Management Science 62(7):1860-1877. The other rationales are 
protection for consumers against failures, provision of product 
quality information to consumers, and a means to distinguish 
consumers according to their risk preferences.
    \447\ Murthy, D., and N. Jack (2009). ``Warranty and 
Maintenance,'' Chapter 18 in Handbook of Maintenance Management and 
Engineering, Mohamed Ben-Daya et al., editors. London: Springer.
    \448\ Saidi-Mehrabad, M., R. Noorossana, and M. Shafiee (2010). 
``Modeling and analysis of effective ways for improving the 
reliability of second-hand products sold with warranty.'' 
International Journal of Advanced Manufacturing Technology 46: 253-
265.
---------------------------------------------------------------------------

    On the one hand, we expect owner-incurred emission repair costs to 
decrease due to the final program because the longer emission warranty 
requirements will result in more repair costs covered by the OEMs. 
Further, we expect improved serviceability in an effort by OEMs to 
decrease the repair costs that they will incur. We also expect that the 
longer useful life periods in the final standards will result in more 
durable parts to ensure regulatory compliance over the longer 
timeframe. On the other hand, we also expect that the more costly 
emission control systems required by the final program may result in 
higher repair costs which might increase owner-incurred costs outside 
the warranty and/or useful life periods.
    As discussed in Section V.A.2, we have estimated increased OEM 
costs associated with increased warranty liability (i.e., longer 
warranty periods), and for more durable parts resulting from the longer 
useful life periods. These costs are accounted for via increased 
warranty costs and increased research and development (R&D) costs. We 
also included additional aftertreatment costs in the direct 
manufacturing costs to address the increased useful life requirements 
(e.g., larger catalyst volume; see Chapters 2 and 3 of the RIA for 
detailed discussions). We estimate that the new useful life and 
warranty provisions will help to reduce emission repair costs during 
the emission warranty and regulatory useful life periods, and possibly 
beyond.
    In the proposal, to estimate impacts on emission repair costs, we 
began with an emission repair cost curve derived from an industry white 
paper.\449\ Some commenters took exception to the approach we took, 
preferring instead that we use what they consider to be a more 
established repair and maintenance cost estimate from the American 
Transportation Research

[[Page 4415]]

Institute.\450\ After careful consideration of the ATRI data, we 
derived a cost per mile value for repair and maintenance based on the 
10 years of data gathered and presented. We chose to use the ATRI data 
in place of the data used in the proposal because it constituted 10 
years of data from an annually prepared study compared to the one year 
of data behind the study used in the proposal.
---------------------------------------------------------------------------

    \449\ See ``Mitigating Rising Maintenance & Repair Costs for 
Class-8 Truck Fleets, Effective Data & Strategies to Leverage Newer 
Trucks to Reduce M&R Costs,'' Fleet Advantage Whitepaper Series, 
2018.
    \450\ ``An Analysis of the Operational Costs of Trucking: 2021 
Update,'' American Transportation Research Institute, November 2021.
---------------------------------------------------------------------------

    Because the ATRI data represent heavy HD combination vehicles it 
was necessary for us to scale the ATRI values for applicability to HD 
vehicles with different sized engines having different emission-control 
system costs. We have done this in the same way as was discussed 
earlier for scaling of warranty cost (see Table V-6). Given that future 
engines and vehicles will be equipped with new, more costly technology, 
it is possible that the repair costs for vehicles under the final 
program will be higher than the repair costs in the baseline. We have 
included such an increase for the period beyond useful life. This is 
perhaps conservative because it seems reasonable to assume that the R&D 
used to improve durability during the useful life period would also 
improve durability beyond it. Nonetheless, we also think it is 
reasonable to include an increase in repair costs, relative to the 
baseline case, because the period beyond useful life is of marginally 
less concern to manufacturers.\451\ Lastly, since our warranty and 
useful life provisions pertain to emissions-related systems and their 
repair, we adjusted the ATRI values by 10.8 percent to arrive at an 
emission-related repair cost. The 10.8 percent value was similarly used 
in the proposal and was derived by EPA using data in the Fleet 
Advantage Whitepaper. Table V-19 shows how we have scaled the repair 
and maintenance costs derived from the ATRI study.
---------------------------------------------------------------------------

    \451\ This is not meant to suggest that manufacturers no longer 
care about their products beyond their regulatory useful life, but 
rather to reflect the expectation that regulatory pressures--i.e., 
regulatory compliance during the useful life--tend to focus 
manufacturer resources.
---------------------------------------------------------------------------

    Importantly, during the warranty period, there are no emission-
related repair costs incurred by owner/operators since those will be 
covered under warranty.

                      Table V-19--Scaling Approach Used in Estimating Baseline Emission-Related Repair Costs per Mile, 2017 Cents *
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                  Repair & maintenance         Emission-related repair
                                                                                             ------------------------------      (10.8% of repair &
           MOVES  regulatory class                           Scaling approach                                                       maintenance)
                                                                                               Diesel   Gasoline     CNG   -----------------------------
                                                                                                                             Diesel   Gasoline     CNG
--------------------------------------------------------------------------------------------------------------------------------------------------------
Light HDE...................................  Base Light HDE DMC/Base Diesel Heavy HDE DMC..      10.1      7.28  ........      1.09      0.79  ........
Medium HDE..................................  Base Medium HDE DMC/Base Diesel Heavy HDE DMC.      10.3      7.28  ........      1.12      0.79  ........
Heavy HDE...................................  Base Heavy HDE DMC/Base Diesel Heavy HDE DMC..      15.8      7.28      23.2      1.71      0.79      2.52
Urban bus...................................  Base Urban bus DMC/Base Diesel Heavy HDE DMC..      9.80  ........      16.2      1.06  ........      1.75
--------------------------------------------------------------------------------------------------------------------------------------------------------
* The Base Diesel Heavy HDE DMC would be the $5,816 value shown in Table V-2; shown is scaling of baseline emission-repair costs per mile although we
  also scaled emission-repair cost per hour and applied those values for most vocational vehicles; this is detailed in Chapter 7.2.3 of the final RIA.

    We present more details in Chapter 7 of the RIA behind the 
emission-repair cost values we are using, the scaling used and the 10.8 
percent emission-related repair adjustment factor and how it was 
derived. As done for warranty costs, we have used estimated ages for 
when warranty and useful life are reached, using the required miles, 
ages and hours along with the estimated miles driven and hours of 
operation for each specific type of vehicle. This means that warranty 
and useful life ages are reached in different years for different 
vehicles, even if they belong to the same service class and have the 
same regulatory warranty and useful life periods. For example, we 
expect warranty and useful life ages to be attained at different points 
in time by a long-haul combination truck driving over 100,000 miles per 
year or over 2,000 hours per year and a refuse truck driven around 
40,000 miles per year or operating less than 1,000 hours per year. The 
resultant MY2027 lifetime emission-related repair costs are shown in 
Table V-20 for diesel HD vehicles, in Table V-21 for gasoline HD 
vehicles, and in Table V-22 for CNG HD vehicles. Since these costs 
occur over time, we present them using both a 3 percent and a 7 percent 
discount rate. Note that these costs assume that all emission-related 
repair costs are paid by manufacturers during the warranty period, and 
beyond the warranty period the emission-related repair costs are 
incurred by owners/operators.

                               Table V-20--MY2027 Lifetime Emission-Related Repair Costs per Diesel Vehicle, 2017 Dollars
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                         3% Discount rate                                7% Discount rate
                                                         -----------------------------------------------------------------------------------------------
                                                           Light HDE  Medium HDE   Heavy HDE   Urban bus   Light HDE  Medium HDE   Heavy HDE   Urban bus
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                      FRM Baseline
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........      22,041  ..........  ..........  ..........      16,138  ..........
Long-Haul Single Unit Trucks............................       3,208       2,493       3,060  ..........       2,440       1,790       2,109  ..........
Motor Homes.............................................  ..........         613         936  ..........  ..........         394         602  ..........
Other Buses.............................................       4,292       3,668       4,719  ..........       3,083       2,499       3,074  ..........
Refuse Trucks...........................................  ..........       2,222       3,110  ..........  ..........       1,506       2,065  ..........
School Buses............................................       1,148       1,050       1,604  ..........         771         684       1,045  ..........
Short-Haul Combination Trucks...........................  ..........       6,635       8,088  ..........  ..........       5,003       5,823  ..........
Short-Haul Single Unit Trucks...........................       1,799       1,292       1,973  ..........       1,318         876       1,338  ..........

[[Page 4416]]

 
Transit Buses...........................................       4,242       3,625  ..........       3,941       3,047       2,469  ..........       2,732
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              FRM Baseline + Final Program
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........      25,070  ..........  ..........  ..........      17,497  ..........
Long-Haul Single Unit Trucks............................       2,284       1,531       1,524  ..........       1,509         956         906  ..........
Motor Homes.............................................  ..........         480         728  ..........  ..........         272         415  ..........
Other Buses.............................................       4,090       3,261       3,454  ..........       2,598       1,978       1,979  ..........
Refuse Trucks...........................................  ..........       1,408       2,038  ..........  ..........         819       1,180  ..........
School Buses............................................         667         772       1,174  ..........         378         439         673  ..........
Short-Haul Combination Trucks...........................  ..........       7,029       6,436  ..........  ..........       4,960       4,225  ..........
Short-Haul Single Unit Trucks...........................         764         721       1,115  ..........         451         421         655  ..........
Transit Buses...........................................       4,042       3,224  ..........       2,394       2,567       1,955  ..........       1,370
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Increased Cost of the Final Program
--------------------------------------------------------------------------------------------------------------------------------------------------------
Long-Haul Combination Trucks............................  ..........  ..........       3,028  ..........  ..........  ..........       1,359  ..........
Long-Haul Single Unit Trucks............................        -924        -962      -1,536  ..........        -931        -834      -1,203  ..........
Motor Homes.............................................  ..........        -132        -207  ..........  ..........        -122        -187  ..........
Other Buses.............................................        -203        -406      -1,265  ..........        -486        -520      -1,095  ..........
Refuse Trucks...........................................  ..........        -814      -1,072  ..........  ..........        -687        -885  ..........
School Buses............................................        -481        -278        -430  ..........        -393        -245        -372  ..........
Short-Haul Combination Trucks...........................  ..........         394      -1,651  ..........  ..........         -43      -1,598  ..........
Short-Haul Single Unit Trucks...........................      -1,035        -570        -857  ..........        -867        -455        -684  ..........
Transit Buses...........................................        -200        -402  ..........      -1,547        -480        -514  ..........      -1,362
--------------------------------------------------------------------------------------------------------------------------------------------------------


          Table V-21--MY2027 Lifetime Emission-Related Repair Costs per Gasoline Vehicle, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                   3% Discount rate                    7% Discount rate
                                         -----------------------------------------------------------------------
                                           Light HDE  Medium HDE   Heavy HDE   Light HDE  Medium HDE   Heavy HDE
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............       2,324       2,324       2,324       1,768       1,768       1,768
Motor Homes.............................         431         431         431         278         278         278
Other Buses.............................       3,111  ..........  ..........       2,234  ..........  ..........
School Buses............................         832  ..........  ..........         559  ..........  ..........
Short-Haul Single Unit Trucks...........       1,304       1,304       1,304         955         955         955
Transit Buses...........................       3,074  ..........  ..........       2,208  ..........  ..........
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............       1,831       1,831       1,831       1,271       1,271       1,271
Motor Homes.............................         275         275         275         156         156         156
Other Buses.............................       2,898  ..........  ..........       1,917  ..........  ..........
School Buses............................         442  ..........  ..........         252  ..........  ..........
Short-Haul Single Unit Trucks...........         764         764         764         483         483         483
Transit Buses...........................       2,865  ..........  ..........       1,895  ..........  ..........
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks............        -493        -493        -493        -497        -497        -497
Motor Homes.............................        -156        -156        -156        -122        -122        -122
Other Buses.............................        -212  ..........  ..........        -317  ..........  ..........
School Buses............................        -390  ..........  ..........        -306  ..........  ..........
Short-Haul Single Unit Trucks...........        -540        -540        -540        -471        -471        -471
Transit Buses...........................        -210  ..........  ..........        -313  ..........  ..........
----------------------------------------------------------------------------------------------------------------


[[Page 4417]]


             Table V-22--MY2027 Lifetime Emission-Related Repair Costs per CNG Vehicle, 2017 Dollars
----------------------------------------------------------------------------------------------------------------
                                                                     3% Discount rate        7% Discount rate
                                                                 -----------------------------------------------
                                                                   Heavy HDE   Urban bus   Heavy HDE   Urban bus
----------------------------------------------------------------------------------------------------------------
                                                  FRM Baseline
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks....................................       4,517  ..........       3,113  ..........
Other Buses.....................................................       6,966  ..........       4,537  ..........
Refuse Trucks...................................................       4,590  ..........       3,048  ..........
School Buses....................................................       2,368  ..........       1,542  ..........
Short-Haul Combination Trucks...................................      11,938  ..........       8,595  ..........
Short-Haul Single Unit Trucks...................................       2,912  ..........       1,975  ..........
Transit Buses...................................................  ..........       6,532  ..........       4,529
----------------------------------------------------------------------------------------------------------------
                                          FRM Baseline + Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks....................................       1,720  ..........       1,029  ..........
Other Buses.....................................................       3,807  ..........       2,194  ..........
Refuse Trucks...................................................       2,260  ..........       1,317  ..........
School Buses....................................................       1,294  ..........         746  ..........
Short-Haul Combination Trucks...................................       7,723  ..........       5,143  ..........
Short-Haul Single Unit Trucks...................................       1,248  ..........         737  ..........
Transit Buses...................................................  ..........       2,822  ..........       1,626
----------------------------------------------------------------------------------------------------------------
                                       Increased Cost of the Final Program
----------------------------------------------------------------------------------------------------------------
Long-Haul Single Unit Trucks....................................      -2,797  ..........      -2,084  ..........
Other Buses.....................................................      -3,158  ..........      -2,344  ..........
Refuse Trucks...................................................      -2,330  ..........      -1,732  ..........
School Buses....................................................      -1,074  ..........        -797  ..........
Short-Haul Combination Trucks...................................      -4,215  ..........      -3,452  ..........
Short-Haul Single Unit Trucks...................................      -1,664  ..........      -1,238  ..........
Transit Buses...................................................  ..........      -3,710  ..........      -2,903
----------------------------------------------------------------------------------------------------------------

C. Program Costs

    Using the cost elements outlined in Sections V.A and V.B, we have 
estimated the costs associated with the final program. Costs are 
presented in more detail in Chapter 7 of the RIA. As noted earlier, 
costs are presented in 2017 dollars in undiscounted annual values along 
with present values (PV) and equivalent annualized values (EAV) at both 
3 and 7 percent discount rates with values discounted to the 2027 
calendar year.

Table V-23--Total Technology & Operating Cost Impacts of the Final Program Relative to the Baseline Case, All Regulatory Classes and All Fuels, Billions
                                                                   of 2017 Dollars \a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Direct   Indirect               Other                Total    Emission                          Total
            Calendar year               tech    warranty   Indirect   indirect   Indirect    tech     repair     Urea    Fuel cost   operating   Program
                                        cost      cost     R&D cost     cost      profit     cost      cost      cost                  cost       cost
--------------------------------------------------------------------------------------------------------------------------------------------------------
2027................................      1.1        2.1       0.21       0.34      0.058      3.8       0.00     0.06     -0.0004       0.057       3.9
2028................................      1.1        2.1       0.20       0.32      0.055      3.7      -0.05     0.12     -0.0008        0.07       3.8
2029................................      1.0        2.1       0.19       0.31      0.053      3.7      -0.30     0.18     -0.0013       -0.12       3.6
2030................................      1.0        2.1      0.051       0.30      0.052      3.5      -0.43     0.25     -0.0017       -0.19       3.4
2031................................      1.0        2.2      0.050       0.30      0.051      3.6      -0.50     0.33     -0.0022       -0.17       3.4
2032................................     0.99        2.2      0.049       0.29      0.050      3.6      -0.57     0.41     -0.0027       -0.16       3.4
2033................................     0.98        2.2      0.049       0.29      0.050      3.6      -0.61     0.47     -0.0034       -0.14       3.5
2034................................     0.98        2.3      0.049       0.29      0.049      3.6      -0.64     0.53     -0.0041       -0.11       3.5
2035................................     0.96        2.3      0.048       0.28      0.049      3.7      -0.66     0.58     -0.0048       -0.08       3.6
2036................................     0.95        2.3      0.048       0.28      0.048      3.7      -0.66     0.63     -0.0054       -0.04       3.6
2037................................     0.95        2.4      0.048       0.28      0.048      3.7      -0.60     0.68     -0.0060        0.07       3.8
2038................................     0.95        2.4      0.048       0.28      0.048      3.7      -0.54     0.72     -0.0066        0.17       3.9
2039................................     0.95        2.5      0.047       0.28      0.048      3.8      -0.49     0.76     -0.0072        0.27       4.0
2040................................     0.95        2.5      0.047       0.28      0.048      3.8      -0.45     0.80     -0.0078        0.34       4.2
2041................................     0.95        2.5      0.047       0.28      0.048      3.9      -0.41     0.84     -0.0083        0.41       4.3
2042................................     0.95        2.6      0.047       0.28      0.048      3.9      -0.39     0.87     -0.0088        0.47       4.4
2043................................     0.95        2.6      0.047       0.28      0.048      3.9      -0.37     0.91     -0.0093        0.53       4.5
2044................................     0.95        2.7      0.048       0.28      0.048      4.0      -0.35     0.94     -0.0097        0.57       4.6
2045................................     0.95        2.7      0.048       0.28      0.048      4.1      -0.34     0.97      -0.010        0.62       4.7
PV, 3%..............................       14         33        1.1        4.2       0.72       53       -6.2      7.7      -0.069         1.4        55
PV, 7%..............................       10         24       0.90        3.0       0.52       38       -4.3      4.9      -0.043        0.60        39
EAV, 3%.............................      1.0        2.3      0.078       0.29      0.050      3.7      -0.43     0.54     -0.0048       0.099       3.8

[[Page 4418]]

 
EAV, 7%.............................      1.0        2.3      0.087       0.29      0.051      3.7      -0.42     0.48     -0.0042       0.058       3.8
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Values show 2 significant digits; negative cost values denote savings; calendar year values are undiscounted, present values are discounted to 2027;
  Program Cost is the sum of Total Tech Cost and Total Operating Cost. Note also that the Information Collection Request costs addressed in Section XII
  would fall within the ``Other'' indirect costs shown here.

VI. Estimated Emissions Reductions From the Final Program

    The final program, which is described in detail in Sections III and 
IV, is expected to reduce emissions from highway heavy-duty engines in 
several ways. We project the final emission standards for heavy-duty CI 
engines will reduce tailpipe emissions of NOX; the 
combination of the final low-load test cycle and off-cycle test 
procedure for CI engines will help to ensure that the reductions in 
tailpipe emissions are achieved in-use, not only under high-speed, on-
highway conditions, but also under low-load and idle conditions. We 
also project reduced tailpipe emissions of NOX, CO, PM, 
VOCs, and associated air toxics from the final emission standards for 
heavy-duty SI engines, particularly under cold-start and high-load 
operating conditions. The longer emission warranty and regulatory 
useful life requirements for heavy-duty CI and SI engines in the final 
rule will help maintain the expected emission reductions for all 
pollutants, including primary exhaust PM2.5, throughout the 
useful life of the engine. The onboard refueling vapor recovery 
requirements for heavy-duty SI engines in the final rule will reduce 
VOCs and associated air toxics. See RIA Chapter 5.3 for details on 
projected emission reductions of each pollutant.
    Section VI.A provides an overview of the methods used to estimate 
emission reductions from our final program. All the projected emission 
reductions from the final program are outlined in Section VI.B, with 
more details provided in the RIA Chapter 5. Section VI.C presents 
projected emission reductions from the final program by engine 
operations and processes (e.g., medium-to-high load or low-load engine 
operations).

A. Emission Inventory Methodology

    To estimate the emission reductions from the final program, we used 
the current public version of EPA's Motor Vehicle Emission Simulator 
(MOVES) model, MOVES3. MOVES3 includes all the model updates previously 
made for the version of the MOVES model used for the NPRM analysis 
(``MOVES CTI NPRM''), as well as other more recent updates. Detailed 
descriptions of the underlying data and analyses that informed the 
model updates are discussed in Chapter 5.2 of the RIA and documented in 
peer-reviewed technical reports referenced in the RIA. Inputs developed 
to model the national emission inventories for the final program are 
also discussed in Chapter 5.2.2 of the RIA.

B. Estimated Emission Reductions From the Final Program

    As discussed in Sections III and IV, the final program includes 
new, more stringent numeric emission standards, as well as longer 
regulatory useful life and emissions warranty periods compared to 
today's standards. Our estimates of the emission impacts of the final 
program in calendar years 2030, 2040, and 2045 are presented in Table 
VI-1. As shown in Table VI-1, we estimate that the final program will 
reduce NOX emissions from highway heavy-duty vehicles by 48 
percent nationwide in 2045. We also estimate an eight percent reduction 
in primary exhaust PM2.5 from highway heavy-duty vehicles. 
VOC emissions from heavy-duty vehicles will be 23 percent lower. 
Emissions of CO from heavy-duty vehicles are estimated to decrease by 
18 percent. Reductions in heavy-duty vehicle emissions of other 
pollutants, including air toxics, range from an estimated reduction of 
about 28 percent for benzene to about seven percent change in 
acetaldehyde. RIA Chapter 5.5.2 includes additional details on the 
emission reductions by vehicle fuel type; Chapter 5.5.4 provides our 
estimates of criteria pollutant emissions reductions for calendar years 
2027 through 2045.
    As the final program is implemented, emission reductions are 
expected to increase over time as the fleet turns over to new, 
compliant engines. We estimate no change in CO2 emissions 
from the final program, based on data in our feasibility and cost 
analyses of the final program (see Section III for more 
discussion).\452\
---------------------------------------------------------------------------

    \452\ This estimate includes the assumption that vehicle sales 
will not change in response to the final rule. See Section X for 
further discussion on vehicle sales impacts of this final rule.

  Table VI-1--Annual Emission Reductions From Heavy-Duty Vehicles in Calendar Years (CY) 2030, 2040, and 2045--
           Emissions With Final Program in Place Relative to the Heavy-Duty Vehicle Emissions Baseline
----------------------------------------------------------------------------------------------------------------
                                             CY2030                    CY2040                    CY2045
                                   -----------------------------------------------------------------------------
             Pollutant                US short                  US short                  US short
                                        tons     % reduction      tons     % reduction      tons     % reduction
----------------------------------------------------------------------------------------------------------------
NOX...............................      139,677           14      398,864           44      453,239           48
VOC...............................        5,018            5       17,139           20       20,758           23
Primary Exhaust PM2.5.............          115            1          491            7          566            8
CO................................       43,978            3      208,935           16      260,750           18
Acetaldehyde......................           36            2          124            6          145            7
Benzene...........................           40            4          177           23          221           28
Formaldehyde......................           29            1          112            7          134            8

[[Page 4419]]

 
Naphthalene.......................            2            1            7           13            9           16
----------------------------------------------------------------------------------------------------------------

C. Estimated Emission Reductions by Engine Operations and Processes

    Looking more closely at the NOX emission inventory from 
highway heavy-duty vehicles, our analysis shows that the final 
standards will reduce emissions across several engine operations and 
processes, with the greatest reductions attributable to medium-to-high 
load engine operations, low-load engine operations, and age effects 
(Table VI-2). Emission reductions attributable to medium-to-high load 
engine operations are based on changes in the new numeric emissions 
standards compared to existing standards and corresponding test 
procedures, as described in preamble Section III. Emission reductions 
attributable to the age effects category are based on longer useful 
life and warranty periods in the final rule, which are described in 
preamble Section IV.
    Table 5-13 in Chapter 5.2.2 of the RIA shows that tampering and 
mal-maintenance significantly increases emissions from current heavy 
heavy-duty engines (e.g., we estimate a 500 percent increase in 
NOX emissions for heavy heavy-duty vehicles due to 
NOX aftertreatment malfunction). Absent the final rule, 
these substantial increases in emissions from tampering and mal-
maintenance could potentially have large impact on the HD 
NOX inventory. However, the longer regulatory useful life 
and emission-related warranty requirements in the final rule will 
ensure that more stringent standards are met for a longer period of 
time while the engines are in use. Specifically, we estimate 18 percent 
fewer NOX emissions in 2045 due to the longer useful life 
and warranty periods reducing the likelihood of tampering and mal-
maintenance after the current useful life periods of heavy-duty CI 
engines.453 454 We note that these estimates of emissions 
impacts from tampering and mal-maintenance of heavy-duty engines 
reflect currently available data and may not fully reflect the extent 
of emissions impacts from tampering or mal-maintenance; thus, 
additional data on the emissions impacts of heavy-duty tampering and 
mal-maintenance may show that there would be additional emissions 
reductions from the final rule.
---------------------------------------------------------------------------

    \453\ See Chapter 5.2.2 of the RIA for a discussion of how we 
calculate the emission rates due to the final useful life and 
warranty periods for Light, Medium, and Heavy heavy-duty engines.
    \454\ Although we anticipate emission benefits from the 
lengthened warranty and useful life periods from gasoline and NG-
fueled vehicles, they were not included in the analysis done for the 
final rule (see RIA Chapter 5.2 for details).
---------------------------------------------------------------------------

    Further, due to insufficient data, we are currently unable to 
quantify the impacts of other provisions to improve maintenance and 
serviceability of emission controls systems (e.g., updated maintenance 
intervals, requiring manufacturers to provide more information on how 
to diagnose and repair emission control systems, as described in 
preamble Section IV). We expect the final provisions to improve 
maintenance and serviceability will reduce incentives to tamper with 
the emission control systems on MY 2027 and later engines, which would 
avoid large increases in emissions that would impact the reductions 
projected from the final rule. For example, we estimate a greater than 
3000 percent increase in NOX emissions for heavy heavy-duty 
vehicles due to malfunction of the NOX emissions 
aftertreatment on a MY 2027 and later heavy heavy-duty vehicle. As 
such, the maintenance and serviceability provisions combined with the 
longer useful life and warranty periods will provide a comprehensive 
approach to ensure that the new, much more stringent emissions 
standards are met during in use operations.
    Table VI-2 compares NOX emissions in 2045 from different 
engine operations and processes with and without the final standards. A 
graphical comparison of NOX emissions by process is included 
in RIA Chapter 5.5.3.

                       Table VI-2--Heavy-Duty NOX Emission Reductions by Process in CY2045
                                                    [US tons]
----------------------------------------------------------------------------------------------------------------
                                        Emission inventory                     Percent       Emission inventory
     Engine operation or process       contribution without      Tons      reduction from     contribution with
                                         final program (%)     reduced        baseline        final program (%)
----------------------------------------------------------------------------------------------------------------
Medium- to High-Load.................                    36      217,708                64                    24
Low-Load.............................                    30      177,967                63                    21
Aging................................                    22       35,750                18                    34
Extended Idle & APU..................                     2       11,692                63                     1
Starts...............................                     5       10,122                23                     7
Historical Fleet (MY 2010 to 2026)...                     6            0                 0                    12
----------------------------------------------------------------------------------------------------------------

VII. Air Quality Impacts of the Final Rule

    As discussed in Section VI, we project the standards in the final 
rule will result in meaningful reductions in emissions of 
NOX, VOC, CO and PM2.5. When feasible, we conduct 
full-scale photochemical air quality modeling to accurately project 
levels of criteria and air toxic pollutants, because the atmospheric 
chemistry related to ambient concentrations of PM2.5, ozone,

[[Page 4420]]

and air toxics is very complex. Air quality modeling was performed for 
the proposed rule and demonstrated improvements in concentrations of 
air pollutants. Given the similar structure of the proposed and final 
programs, the geographic distribution of emissions reductions and 
modeled improvements in air quality are consistent and demonstrate that 
the final rule will lead to substantial improvements in air 
quality.\455\
---------------------------------------------------------------------------

    \455\ Additional detail on the air quality modeling inventory 
used in the proposed rule, along with the final rule emission 
reductions, can be found in Chapter 5 of the RIA.
---------------------------------------------------------------------------

    Specifically, we expect this rule will decrease ambient 
concentrations of air pollutants, including significant improvements in 
ozone concentrations in 2045 as demonstrated in the air quality 
modeling analysis. We also expect reductions in ambient 
PM2.5, NO2 and CO due to this rule. Although the 
spatial resolution of the air quality modeling is not sufficient to 
quantify it, this rule's emission reductions will also reduce air 
pollution in close proximity to major roadways, where concentrations of 
many air pollutants are elevated and where people of color and people 
with low income are disproportionately exposed.
    The emission reductions provided by the final standards will be 
important in helping areas attain the NAAQS and prevent future 
nonattainment. In addition, the final standards are expected to result 
in improvements in nitrogen deposition and visibility. Additional 
information and maps showing expected changes in ambient concentrations 
of air pollutants in 2045 are included in the proposal, Chapter 6 of 
the RIA and in the Air Quality Modeling Technical Support Document from 
the proposed rule.456 457
---------------------------------------------------------------------------

    \456\ USEPA (2021) Technical Support Document: Air Quality 
Modeling for the HD 2027 Proposal. EPA-HQ-OAR-2019-0055. October 
2021.
    \457\ Section VII of the proposed rule preamble, 87 FR 17414 
(March 28, 2022).
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    The proposed rule air quality modeling analysis consisted of a base 
case, reference scenario, and control scenario. The ``base'' case 
represents 2016 air quality. The ``reference'' scenario represents 
projected 2045 air quality without the proposed rule and the 
``control'' scenario represents projected 2045 emissions with the 
proposed rule. Air quality modeling was done for the future year 2045 
when the program will be fully implemented and when most of the 
regulated fleet will have turned over.

A. Ozone

    The scenario modeled for the proposed rule reduced 8-hour ozone 
design values significantly in 2045. Ozone design values decreased by 
more than 2 ppb in over 150 counties, and over 200 additional modeled 
counties are projected to have decreases in ozone design values of 
between 1 and 2 ppb in 2045. Our modeling projections indicate that 
some counties will have design values above the level of the 2015 NAAQS 
in 2045, and the rule will help those counties, as well as other 
counties, in reducing ozone concentrations. Table VII-1 shows the 
average projected change in 2045 8-hour ozone design values due to the 
modeled scenario. Counties within 10 percent of the level of the NAAQS 
are intended to reflect counties that, although not violating the 
standard, would also be affected by changes in ambient levels of ozone 
as they work to ensure long-term attainment or maintenance of the ozone 
NAAQS. The projected changes in design values, summarized in Table VII-
1, indicate in different ways the overall improvement in ozone air 
quality due to emission reductions from the modeled scenario.

           Table VII-1--Average Change in Projected 8-Hour Ozone Design Values in 2045 Due to the Rule
----------------------------------------------------------------------------------------------------------------
                                                                                                  Population-
                                                 Number of        2045        Average change    weighted average
        Projected design value category           counties   Population \a\   in 2045 design    change in design
                                                                                value (ppb)       value (ppb)
----------------------------------------------------------------------------------------------------------------
all modeled counties..........................          457     246,949,949             -1.87              -2.23
counties with 2016 base year design values              118     125,319,158             -2.12              -2.43
 above the level of the 2015 8-hour ozone
 standard.....................................
counties with 2016 base year design values              245      93,417,097             -1.83              -2.10
 within 10% of the 2015 8-hour ozone standard.
counties with 2045 reference design values               15      37,758,488             -2.26              -3.03
 above the level of the 2015 8-hour ozone
 standard.....................................
counties with 2045 reference design values               56      39,302,665             -1.78              -2.02
 within 10% of the 2015 8-hour ozone standard.
counties with 2045 control design values above           10      27,930,138             -2.36              -3.34
 the level of the 2015 8-hour ozone standard..
counties with 2045 control design values                 42      31,395,617             -1.69              -1.77
 within 10% of the 2015 8-hour ozone standard.
----------------------------------------------------------------------------------------------------------------
\a\ Population numbers based on Woods & Poole data. Woods & Poole Economics, Inc. (2015). Complete Demographic
  Database. Washington, DC. http://www.woodsandpoole.com/index.php.

B. Particulate Matter

    The scenario modeled for the proposed rule reduced 24-hour and 
annual PM2.5 design values in 2045. Annual PM2.5 
design values in the majority of modeled counties decreased by between 
0.01 and 0.05 [mu]g/m\3\ and by greater than 0.05 [mu]g/m\3\ in over 75 
additional counties. 24-hour PM2.5 design values decreased 
by between 0.15 and 0.5 [mu]g/m\3\ in over 150 counties and by greater 
than 0.5 [mu]g/m\3\ in 5 additional counties. Our modeling projections 
indicate that some counties will have design values above the level of 
the 2012 PM2.5 NAAQS in 2045 and the rule will help those 
counties, as well as other counties, in reducing PM2.5 
concentrations. Table VII-2 and Table VII-3 present the average 
projected changes in 2045 annual and 24-hour PM2.5 design 
values. Counties within 10 percent of the level of the NAAQS are 
intended to reflect counties that, although not violating the 
standards, would also be affected by changes in ambient levels of 
PM2.5 as they work to ensure long-term attainment or 
maintenance of the annual and/or 24-hour PM2.5 NAAQS. The 
projected changes in PM2.5 design values, summarized in 
Table VII-2 and Table VII-3, indicate in different ways the overall 
improvement in PM2.5 air quality due to the emission 
reductions resulting from the modeled scenario. We expect this rule's 
reductions in directly emitted PM2.5 will also contribute to 
reductions in PM2.5 concentrations near roadways, although 
our air quality modeling is not of sufficient resolution to capture 
that impact.

[[Page 4421]]



           Table VII-2--Average Change in Projected Annual PM2.5 Design Values in 2045 Due to the Rule
----------------------------------------------------------------------------------------------------------------
                                                                                                  Population-
                                                 Number of        2045        Average change    weighted average
        Projected design value category           counties   Population \a\   in 2045 design    change in design
                                                                               value (ug/m3)     value (ug/m3)
----------------------------------------------------------------------------------------------------------------
all modeled counties..........................          568     273,604,437             -0.04              -0.04
counties with 2016 base year design values               17      26,726,354             -0.09              -0.05
 above the level of the 2012 annual PM2.5
 standard.....................................
counties with 2016 base year design values                5       4,009,527             -0.06              -0.06
 within 10% of the 2012 annual PM2.5 standard.
counties with 2045 reference design values               12      25,015,974             -0.10              -0.05
 above the level of the 2012 annual PM2.5
 standard.....................................
counties with 2045 reference design values                6       1,721,445             -0.06              -0.06
 within 10% of the 2012 annual PM2.5 standard.
counties with 2045 control design values above           10      23,320,070             -0.10              -0.05
 the level of the 2012 annual PM2.5 standard..
counties with 2045 control design values                  8       3,417,349             -0.08              -0.09
 within 10% of the 2012 annual PM2.5 standard.
----------------------------------------------------------------------------------------------------------------
\a\ Population numbers based on Woods & Poole data. Woods & Poole Economics, Inc. (2015). Complete Demographic
  Database. Washington, DC. http://www.woodsandpoole.com/index.php.


          Table VII-3--Average Change in Projected 24-Hour PM2.5 Design Values in 2045 Due to the Rule
----------------------------------------------------------------------------------------------------------------
                                                                                                  Population-
                                                 Number of        2045        Average change    weighted average
        Projected design value category           counties   Population \a\   in 2045 design    change in design
                                                                               value (ug/m3)     value (ug/m3)
----------------------------------------------------------------------------------------------------------------
all modeled counties..........................          568     272,852,777             -0.12              -0.17
counties with 2016 base year design values               33      28,394,253             -0.40              -0.67
 above the level of the 2006 daily PM2.5
 standard.....................................
counties with 2016 base year design values               15      13,937,416             -0.18              -0.27
 within 10% of the 2006 daily PM2.5 standard..
counties with 2045 reference design values               29      14,447,443             -0.38              -0.55
 above the level of the 2006 daily PM2.5
 standard.....................................
counties with 2045 reference design values               12      22,900,297             -0.30              -0.59
 within 10% of the 2006 daily PM2.5 standard..
counties with 2045 control design values above           29      14,447,443             -0.38              -0.55
 the level of the 2006 daily PM2.5 standard...
counties with 2045 control design values                 10      19,766,216             -0.26              -0.60
 within 10% of the 2006 daily PM2.5 standard..
----------------------------------------------------------------------------------------------------------------
\a\ Population numbers based on Woods & Poole data. Woods & Poole Economics, Inc. (2015). Complete Demographic
  Database. Washington, DC. http://www.woodsandpoole.com/index.php.

C. Nitrogen Dioxide

    The scenario modeled for the proposed rule decreased annual 
NO2 concentrations in most urban areas and along major 
roadways by more than 0.3 ppb and decreased annual NO2 
concentrations by between 0.01 and 0.1 ppb across much of the rest of 
the country in 2045. The emissions reductions in the modeled scenario 
will also likely decrease 1-hour NO2 concentrations and help 
any potential nonattainment areas attain and maintenance areas maintain 
the NO2 standard.\458\ We expect this rule will also 
contribute to reductions in NO2 concentrations near 
roadways, although our air quality modeling is not of sufficient 
resolution to capture that impact. Section 6.4.4 of the RIA contains 
more detail on the impacts of the rule on NO2 
concentrations.
---------------------------------------------------------------------------

    \458\ As noted in Section II, there are currently no 
nonattainment areas for the NO2 NAAQS.
---------------------------------------------------------------------------

D. Carbon Monoxide

    The scenario modeled for the proposed rule decreased annual CO 
concentrations by more than 0.5 ppb in many urban areas and decreased 
annual CO concentrations by between 0.02 and 0.5 ppb across much of the 
rest of the country in 2045. The emissions reductions in the modeled 
scenario will also likely decrease 1-hour and 8-hour CO concentrations 
and help any potential nonattainment areas attain and maintenance areas 
maintain the CO standard.\459\ Section 6.4.5 of the RIA contains more 
detail on the impacts of the rule on CO concentrations.
---------------------------------------------------------------------------

    \459\ As noted in Section II, there are currently no 
nonattainment areas for the CO NAAQS.
---------------------------------------------------------------------------

E. Air Toxics

    In general, the scenario modeled for the proposed rule had 
relatively little impact on national average ambient concentrations of 
the modeled air toxics in 2045. The modeled scenario had smaller 
impacts on air toxic pollutants dominated by primary emissions (or a 
decay product of a directly emitted pollutant), and relatively larger 
impacts on air toxics that primarily result from photochemical 
transformation, in this case due to the projected large reductions in 
NOX emissions. Specifically, in 2045, our modeling projects 
that ambient benzene and naphthalene concentrations will decrease by 
less than 0.001 ug/m3 across the country. Acetaldehyde 
concentrations will increase slightly across most of the country, while 
formaldehyde will generally have small decreases in most areas and some 
small increases in urban areas. Section 6.4.6 of the RIA contains more 
detail on the impacts of the modeled scenario on air toxics 
concentrations.

F. Visibility

    Air quality modeling was used to project visibility conditions in 
145 Mandatory Class I Federal areas across the United States. The 
results show that the modeled scenario improved visibility in these 
areas.\460\ The average visibility at all modeled Mandatory Class I 
Federal areas on the 20 percent most impaired days is projected to 
improve by 0.04 deciviews, or 0.37 percent, in 2045 due to the rule. 
Section 6.4.7 of the RIA contains more detail on the visibility portion 
of the air quality modeling.
---------------------------------------------------------------------------

    \460\ The level of visibility impairment in an area is based on 
the light-extinction coefficient and a unitless visibility index, 
called a ``deciview'', which is used in the valuation of visibility. 
The deciview metric provides a scale for perceived visual changes 
over the entire range of conditions, from clear to hazy. Under many 
scenic conditions, the average person can generally perceive a 
change of one deciview. The higher the deciview value, the worse the 
visibility. Thus, an improvement in visibility is a decrease in 
deciview value.
---------------------------------------------------------------------------

G. Nitrogen Deposition

    The scenario modeled for the proposed rule projected substantial 
decreases in nitrogen deposition in 2045. The modeled scenario resulted 
in annual decreases of greater than 4 percent in some areas and greater 
than

[[Page 4422]]

1 percent over much of the rest of the country. For maps of deposition 
impacts, and additional information on these impacts, see Section 6.4.8 
of the RIA.

H. Environmental Justice

    EPA's 2016 ``Technical Guidance for Assessing Environmental Justice 
in Regulatory Analysis'' provides recommendations on conducting the 
highest quality analysis feasible, recognizing that data limitations, 
time and resource constraints, and analytic challenges will vary by 
media and regulatory context.\461\ When assessing the potential for 
disproportionately high and adverse health or environmental impacts of 
regulatory actions on people of color, low-income populations, Tribes, 
and/or indigenous peoples, the EPA strives to answer three broad 
questions: (1) Is there evidence of potential environmental justice 
(EJ) concerns in the baseline (the state of the world absent the 
regulatory action)? Assessing the baseline will allow the EPA to 
determine whether pre-existing disparities are associated with the 
pollutant(s) under consideration (e.g., if the effects of the 
pollutant(s) are more concentrated in some population groups). (2) Is 
there evidence of potential EJ concerns for the regulatory option(s) 
under consideration? Specifically, how are the pollutant(s) and its 
effects distributed for the regulatory options under consideration? 
And, (3) do the regulatory option(s) under consideration exacerbate or 
mitigate EJ concerns relative to the baseline? It is not always 
possible to quantitatively assess these questions.
---------------------------------------------------------------------------

    \461\ ``Technical Guidance for Assessing Environmental Justice 
in Regulatory Analysis.'' Epa.gov, Environmental Protection Agency, 
https://www.epa.gov/sites/production/files/2016-06/documents/ejtg_5_6_16_v5.1.pdf. (June 2016).
---------------------------------------------------------------------------

    EPA's 2016 Technical Guidance does not prescribe or recommend a 
specific approach or methodology for conducting an environmental 
justice analysis, though a key consideration is consistency with the 
assumptions underlying other parts of the regulatory analysis when 
evaluating the baseline and regulatory options. Where applicable and 
practicable, the Agency endeavors to conduct such an analysis.\462\ EPA 
is committed to conducting environmental justice analysis for 
rulemakings based on a framework similar to what is outlined in EPA's 
Technical Guidance, in addition to investigating ways to further weave 
environmental justice into the fabric of the rulemaking process.
---------------------------------------------------------------------------

    \462\ As described in this section, EPA evaluated environmental 
justice for this rule as recommended by the EPA 2016 Technical 
Guidance. However, it is EPA's assessment of the relevant statutory 
factors in CAA section 202(a)(3)(A) that justify the final emission 
standards. See section I.D. for further discussion of the statutory 
authority for this rule.
---------------------------------------------------------------------------

    There is evidence that communities with EJ concerns are 
disproportionately impacted by the emissions sources controlled in this 
final rule.\463\ Numerous studies have found that environmental hazards 
such as air pollution are more prevalent in areas where people of color 
and low-income populations represent a higher fraction of the 
population compared with the general population.464 465 466 
Consistent with this evidence, a recent study found that most 
anthropogenic sources of PM2.5, including industrial sources 
and light- and heavy-duty vehicle sources, disproportionately affect 
people of color.\467\ In addition, compared to non-Hispanic Whites, 
some other racial groups experience greater levels of health problems 
during some life stages. For example, in 2018-2020, about 12 percent of 
non-Hispanic Black; 9 percent of non-Hispanic American Indian/Alaska 
Native; and 7 percent of Hispanic children were estimated to currently 
have asthma, compared with 6 percent of non-Hispanic White 
children.\468\ Nationally, on average, non-Hispanic Black and Non-
Hispanic American Indian or Alaska Native people also have lower than 
average life expectancy based on 2019 data, the latest year for which 
CDC estimates are available.\469\
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    \463\ Mohai, P.; Pellow, D.; Roberts Timmons, J. (2009) 
Environmental justice. Annual Reviews 34: 405-430. https://doi.org/10.1146/annurev-environ-082508-094348.
    \464\ Rowangould, G.M. (2013) A census of the near-roadway 
population: public health and environmental justice considerations. 
Trans Res D 25: 59-67. http://dx.doi.org/10.1016/j.trd.2013.08.003.
    \465\ Marshall, J.D., Swor, K.R.; Nguyen, N.P. (2014) 
Prioritizing environmental justice and equality: diesel emissions in 
Southern California. Environ Sci Technol 48: 4063-4068. https://doi.org/10.1021/es405167f.
    \466\ Marshall, J.D. (2008) Environmental inequality: air 
pollution exposures in California's South Coast Air Basin. Atmos 
Environ 21: 5499-5503. https://doi.org/10.1016/j.atmosenv.2008.02.005.
    \467\ C.W. Tessum, D.A. Paolella, S.E. Chambliss, J.S. Apte, 
J.D. Hill, J.D. Marshall, PM2.5 polluters 
disproportionately and systemically affect people of color in the 
United States. Sci. Adv. 7, eabf4491 (2021).
    \468\ http://www.cdc.gov/asthma/most_recent_data.htm.
    \469\ Arias, E. Xu, J. (2022) United States Life Tables, 2019. 
National Vital Statistics Report, Volume 70, Number 19. [Online at 
https://www.cdc.gov/nchs/data/nvsr/nvsr70/nvsr70-19.pdf].
---------------------------------------------------------------------------

    In addition, as discussed in Section II.B.7 of this document, 
concentrations of many air pollutants are elevated near high-traffic 
roadways, and populations who live, work, or go to school near high-
traffic roadways experience higher rates of numerous adverse health 
effects, compared to populations far away from major roads.
    EPA's analysis of environmental justice includes an examination of 
the populations living in close proximity to truck routes and to major 
roads more generally. This analysis, described in Section VII.H.1 of 
this document, finds that there is substantial evidence that people who 
live or attend school near major roadways are more likely to be people 
of color, Hispanic ethnicity, and/or low socioeconomic status. This 
final rule will reduce emissions that contribute to NO2 and 
other near-roadway pollution, improving air quality for the 72 million 
people who live near major truck routes and are already overburdened by 
air pollution from diesel emissions.
    Heavy-duty vehicles also contribute to regional concentrations of 
ozone and PM2.5. As described in Section VII.H.2 of this 
document, EPA used the air quality modeling data described in this 
Section VII to conduct a demographic analysis of human exposure to 
future air quality in scenarios with and without the rule in place. 
Although the spatial resolution of the air quality modeling is not 
sufficient to capture very local heterogeneity of human exposures, 
particularly the pollution concentration gradients near roads, the 
analysis does allow estimates of demographic trends at a national 
scale. The analysis indicates that the largest predicted improvements 
in both ozone and PM2.5 are estimated to occur in areas with 
the worst baseline air quality, and that a larger number of people of 
color are projected to reside in these areas.
1. Demographic Analysis of the Near-Road Population
    We conducted an analysis of the populations living in close 
proximity to truck freight routes as identified in USDOT's FAF4.\470\ 
FAF4 is a model from the USDOT's Bureau of Transportation Statistics 
(BTS) and Federal Highway Administration (FHWA), which provides data 
associated with freight movement in the United States.\471\ Relative to 
the rest of

[[Page 4423]]

the population, people living near FAF4 truck routes are more likely to 
be people of color and have lower incomes than the general population. 
People living near FAF4 truck routes are also more likely to live in 
metropolitan areas. Even controlling for region of the country, county 
characteristics, population density, and household structure, race, 
ethnicity, and income are significant determinants of whether someone 
lives near a FAF4 truck route. We note that we did not analyze the 
population living near warehousing, distribution centers, 
transshipment, ot intermodal freight facilities.
---------------------------------------------------------------------------

    \470\ U.S. EPA (2021). Estimation of Population Size and 
Demographic Characteristics among People Living Near Truck Routes in 
the Conterminous United States. Memorandum to the Docket.
    \471\ FAF4 includes data from the 2012 Commodity Flow Survey 
(CFS), the Census Bureau on international trade, as well as data 
associated with construction, agriculture, utilities, warehouses, 
and other industries. FAF4 estimates the modal choices for moving 
goods by trucks, trains, boats, and other types of freight modes. It 
includes traffic assignments, including truck flows on a network of 
truck routes. https://ops.fhwa.dot.gov/freight/freight_analysis/faf/
.
---------------------------------------------------------------------------

    We additionally analyzed national databases that allowed us to 
evaluate whether homes and schools were located near a major road and 
whether disparities in exposure may be occurring in these environments. 
Until 2009, the U.S. Census Bureau's American Housing Survey (AHS) 
included descriptive statistics of over 70,000 housing units across the 
nation and asked about transportation infrastructure near respondents' 
homes every two years.472 473 We also analyzed the U.S. 
Department of Education's Common Core of Data (CCD), which includes 
enrollment and location information for schools across the United 
States.\474\
---------------------------------------------------------------------------

    \472\ U.S. Department of Housing and Urban Development, & U.S. 
Census Bureau. (n.d.). Age of other residential buildings within 300 
feet. In American Housing Survey for the United States: 2009 (pp. A-
1). Retrieved from https://www.census.gov/programs-surveys/ahs/data/2009/ahs-2009-summary-tables0/h150-09.html.
    \473\ The 2013 AHS again included the ``etrans'' question about 
highways, airports, and railroads within half a block of the housing 
unit but has not maintained the question since then.
    \474\ http://nces.ed.gov/ccd/.
---------------------------------------------------------------------------

    In analyzing the 2009 AHS, we focused on whether a housing unit was 
located within 300 feet of a ``4-or-more lane highway, railroad, or 
airport'' (this distance was used in the AHS analysis).\475\ We 
analyzed whether there were differences between households in such 
locations compared with those in locations farther from these 
transportation facilities.\476\ We included other variables, such as 
land use category, region of country, and housing type. We found that 
homes with a non-White householder were 22-34 percent more likely to be 
located within 300 feet of these large transportation facilities than 
homes with White householders. Homes with a Hispanic householder were 
17-33 percent more likely to be located within 300 feet of these large 
transportation facilities than homes with non-Hispanic householders. 
Households near large transportation facilities were, on average, lower 
in income and educational attainment and more likely to be a rental 
property and located in an urban area compared with households more 
distant from transportation facilities.
---------------------------------------------------------------------------

    \475\ This variable primarily represents roadway proximity. 
According to the Central Intelligence Agency's World Factbook, in 
2010, the United States had 6,506,204 km of roadways, 224,792 km of 
railways, and 15,079 airports. Highways thus represent the 
overwhelming majority of transportation facilities described by this 
factor in the AHS.
    \476\ Bailey, C. (2011) Demographic and Social Patterns in 
Housing Units Near Large Highways and other Transportation Sources. 
Memorandum to docket.
---------------------------------------------------------------------------

    In examining schools near major roadways, we used the CCD from the 
U.S. Department of Education, which includes information on all public 
elementary and secondary schools and school districts nationwide.\477\ 
To determine school proximities to major roadways, we used a geographic 
information system (GIS) to map each school and roadways based on the 
U.S. Census's TIGER roadway file.\478\ We estimated that about 10 
million students attend schools within 200 meters of major roads, about 
20 percent of the total number of public school students in the United 
States.\479\ About 800,000 students attend public schools within 200 
meters of primary roads, or about 2 percent of the total. We found that 
students of color were overrepresented at schools within 200 meters of 
primary roadways, and schools within 200 meters of primary roadways had 
a disproportionate population of students eligible for free or reduced-
price lunches.\480\ Black students represent 22 percent of students at 
schools located within 200 meters of a primary road, compared to 17 
percent of students in all U.S. schools. Hispanic students represent 30 
percent of students at schools located within 200 meters of a primary 
road, compared to 22 percent of students in all U.S. schools.
---------------------------------------------------------------------------

    \477\ http://nces.ed.gov/ccd/.
    \478\ Pedde, M.; Bailey, C. (2011) Identification of Schools 
within 200 Meters of U.S. Primary and Secondary Roads. Memorandum to 
the docket.
    \479\ Here, ``major roads'' refer to those TIGER classifies as 
either ``Primary'' or ``Secondary.'' The Census Bureau describes 
primary roads as ``generally divided limited-access highways within 
the Federal interstate system or under state management.'' Secondary 
roads are ``main arteries, usually in the U.S. highway, state 
highway, or county highway system.''
    \480\ For this analysis we analyzed a 200-meter distance based 
on the understanding that roadways generally influence air quality 
within a few hundred meters from the vicinity of heavily traveled 
roadways or along corridors with significant trucking traffic. See 
U.S. EPA, 2014. Near Roadway Air Pollution and Health: Frequently 
Asked Questions. EPA-420-F-14-044.
---------------------------------------------------------------------------

    We also reviewed existing scholarly literature examining the 
potential for disproportionate exposure among people of color and 
people with low socioeconomic status (SES). Numerous studies evaluating 
the demographics and socioeconomic status of populations or schools 
near roadways have found that they include a greater percentage of 
residents of color, as well as lower SES populations (as indicated by 
variables such as median household income). Locations in these studies 
include Los Angeles, CA; Seattle, WA; Wayne County, MI; Orange County, 
FL; the State of California generally; and 
nationally.481 482 483 484 485 486 487 Such disparities may 
be due to multiple factors.488 489 490 491 492
---------------------------------------------------------------------------

    \481\ Marshall, J.D. (2008) Environmental inequality: air 
pollution exposures in California's South Coast Air Basin.
    \482\ Su, J.G.; Larson, T.; Gould, T.; Cohen, M.; Buzzelli, M. 
(2010) Transboundary air pollution and environmental justice: 
Vancouver and Seattle compared. GeoJournal 57: 595-608. doi:10.1007/
s10708-009-9269-6.
    \483\ Chakraborty, J.; Zandbergen, P.A. (2007) Children at risk: 
measuring racial/ethnic disparities in potential exposure to air 
pollution at school and home. J Epidemiol Community Health 61: 1074-
1079. doi:10.1136/jech.2006.054130.
    \484\ Green, R.S.; Smorodinsky, S.; Kim, J.J.; McLaughlin, R.; 
Ostro, B. (20042004) Proximity of California public schools to busy 
roads. Environ Health Perspect 112: 61-66. doi:10.1289/ehp.6566.
    \485\ Wu, Y.; Batterman, S.A. (2006) Proximity of schools in 
Detroit, Michigan to automobile and truck traffic. J Exposure Sci & 
Environ Epidemiol. doi:10.1038/sj.jes.7500484.
    \486\ Su, J.G.; Jerrett, M.; de Nazelle, A.; Wolch, J. (2011) 
Does exposure to air pollution in urban parks have socioeconomic, 
racial, or ethnic gradients? Environ Res 111: 319-328.
    \487\ Jones, M.R.; Diez-Roux, A.; Hajat, A.; et al. (2014) Race/
ethnicity, residential segregation, and exposure to ambient air 
pollution: The Multi-Ethnic Study of Atherosclerosis (MESA). Am J 
Public Health 104: 2130-2137. [Online at: https://doi.org/10.2105/AJPH.2014.302135].
    \488\ Depro, B.; Timmins, C. (2008) Mobility and environmental 
equity: do housing choices determine exposure to air pollution? Duke 
University Working Paper.
    \489\ Rothstein, R. The Color of Law: A Forgotten History of How 
Our Government Segregated America. New York: Liveright, 2018.
    \490\ Lane, H.J.; Morello-Frosch, R.; Marshall, J.D.; Apte, J.S. 
(2022) Historical redlining is associated with present-day air 
pollution disparities in US Cities. Environ Sci & Technol Letters 9: 
345-350. DOI: [Online at: https://doi.org/10.1021/acs.estlett.1c01012].
    \491\ Ware, L. (2021) Plessy's legacy: the government's role in 
the development and perpetuation of segregated neighborhoods. RSF: 
The Russel Sage Foundation Journal of the Social Sciences, 7:92-109. 
DOI: DOI: 10.7758/RSF.2021.7.1.06.
    \492\ Archer, D.N. (2020) ``White Men's Roads through Black 
Men's Homes'': advancing racial equity through highway 
reconstruction. Vanderbilt Law Rev 73: 1259.
---------------------------------------------------------------------------

    People with low SES often live in neighborhoods with multiple 
stressors

[[Page 4424]]

and health risk factors, including reduced health insurance coverage 
rates, higher smoking and drug use rates, limited access to fresh food, 
visible neighborhood violence, and elevated rates of obesity and some 
diseases such as asthma, diabetes, and ischemic heart disease. Although 
questions remain, several studies find stronger associations between 
air pollution and health in locations with such chronic neighborhood 
stress, suggesting that populations in these areas may be more 
susceptible to the effects of air pollution.493 494 495 496
---------------------------------------------------------------------------

    \493\ Clougherty, J.E.; Kubzansky, L.D. (2009) A framework for 
examining social stress and susceptibility to air pollution in 
respiratory health. Environ Health Perspect 117: 1351-1358. 
Doi:10.1289/ehp.0900612.
    \494\ Clougherty, J.E.; Levy, J.I.; Kubzansky, L.D.; Ryan, P.B.; 
Franco Suglia, S.; Jacobson Canner, M.; Wright, R.J. (2007) 
Synergistic effects of traffic-related air pollution and exposure to 
violence on urban asthma etiology. Environ Health Perspect 115: 
1140-1146. doi:10.1289/ehp.9863.
    \495\ Finkelstein, M.M.; Jerrett, M.; DeLuca, P.; Finkelstein, 
N.; Verma, D.K.; Chapman, K.; Sears, M.R. (2003) Relation between 
income, air pollution and mortality: a cohort study. Canadian Med 
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    Several publications report nationwide analyses that compare the 
demographic patterns of people who do or do not live near major 
roadways.497 498 499 500 501 502 Three of these studies 
found that people living near major roadways are more likely to be 
people of color or low in SES.503 504 505 They also found 
that the outcomes of their analyses varied between regions