[Federal Register Volume 67, Number 19 (Tuesday, January 29, 2002)]
[Notices]
[Pages 4254-4257]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-2125]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-7135-1]


Official Release of the MOBILE6 Motor Vehicle Emissions Factor 
Model

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of availability.

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SUMMARY: EPA is approving and announcing the availability of the 
MOBILE6 motor vehicle emissions factor model for official use outside 
of California. MOBILE6 is the latest update to the MOBILE model for use 
by state and local governments to meet Clean Air Act requirements. 
Today's notice also starts time periods before MOBILE6 is required to 
be used in certain state implementation plan (SIP) revisions and all 
new transportation conformity analyses.
    MOBILE6 is a major revision of the MOBILE model which calculates 
air pollution emission factors from passenger cars and trucks. The new 
model is based on new and improved data and a new understanding of 
vehicle emission processes. MOBILE6 is also a more user-friendly 
version of the model which allows users to better tailor their motor 
vehicle emissions estimates to local conditions.
    EPA strongly encourages areas to use the interagency consultation 
process to examine how MOBILE6 will affect future transportation 
conformity determinations, so, if necessary, SIPs and motor vehicle 
emissions budgets can be revised with MOBILE6 or transportation plans 
and programs can be revised as appropriate prior to the end of the 
MOBILE6 conformity grace period.

DATES: EPA's approval of the MOBILE6 emissions factor model is 
effective January 29, 2002. See below for further information regarding 
how today's approval starts time periods after which MOBILE6 is 
required in new transportation conformity analyses and certain SIP and 
motor vehicle emissions budget revisions.

FOR FURTHER INFORMATION CONTACT: If you have questions on this notice, 
please send an e-mail to EPA at [email protected] or contact EPA at (734) 
214-4636 for technical model questions.

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SUPPLEMENTARY INFORMATION:

Availability of MOBILE6 and Support Materials

    Copies of the official version of the MOBILE6 model are available 
on EPA's MOBILE Web site, http://www.epa.gov/otaq/m6.htm. The MOBILE 
Web site also contains the following support materials for implementing 
the new model: a detailed MOBILE6 User's Guide; MOBILE6 training 
materials; EPA's ``Policy Guidance on the Use of MOBILE6 for SIP 
Development and Transportation Conformity'; EPA's ``Technical Guidance 
on the Use of MOBILE6 for Emission Inventory Preparation'; and a list 
of Frequently Asked Questions about MOBILE6. EPA will continue to 
update this website in the future as other MOBILE6 support materials 
are developed.
    Individuals who wish to receive EPA announcements related to the 
MOBILE model should subscribe to the EPA-MOBILENEWS e-mail listserver. 
To subscribe to the EPA-MOBILENEWS listserver, write the following in 
the body of the e-mail message: subscribe EPA-MOBILENEWS FIRSTNAME 
LASTNAME where FIRSTNAME and LASTNAME is your name (for example: John 
Smith) and send the e-mail to the EPA Listserver at 
[email protected].
    Your e-mail address will then be added to the list of subscribers 
and a confirmation message will be sent to your e-mail address. 
Whenever a message is posted to the EPA-MOBILENEWS listserver by the 
listserver owner (the Assessment and Standards Division of the EPA 
Office of Transportation and Air Quality), a copy of that message will 
be sent to every person who has subscribed.
    You can remove yourself from the list by sending another message to 
the listserver address. This message must be sent from the same e-mail 
address that you used to subscribe, and should contain the message: 
unsubscribe EPA-MOBILENEWS

Availability of Related SIP Policies

    In November 1999, EPA issued two memoranda articulating the policy 
for use of interim MOBILE5-based Tier 2 estimates and subsequent 
MOBILE6 SIP revisions. These memoranda are discussed in question 3 of 
EPA's ``Policy Guidance on the Use of MOBILE6 for SIP Development and 
Transportation Conformity.'' Copies of the memoranda are available at 
EPA's transportation conformity Web site, http://www.epa.gov/otaq/transp/traqconf.htm.

I. What Is MOBILE6?

    MOBILE is an EPA emissions factor model for estimating pollution 
from on-road motor vehicles in states outside of California. MOBILE 
calculates emissions of volatile organic compounds (VOCs), nitrogen 
oxides (NOX) and carbon monoxide (CO) from passenger cars, 
motorcycles, buses, and light-duty and heavy-duty trucks. The model 
accounts for the emission impacts of factors such as changes in vehicle 
emission standards, changes in vehicle populations and activity, and 
variation in local conditions such as temperature, humidity, fuel 
quality, and air quality programs.
    MOBILE is used to calculate current and future inventories of motor 
vehicle emissions at the national and local level. These inventories 
are used to make decisions about air pollution policies and programs at 
the local, state and national level. Inventories based on MOBILE are 
also used to meet the federal Clean Air Act's state implementation plan 
(SIP) and transportation conformity requirements.
    MOBILE6 is the first major update of the MOBILE model since 1993. 
The MOBILE model was first developed in 1978. It has been updated many 
times to reflect changes in the vehicle fleet and fuels, to incorporate 
EPA's growing understanding of vehicle emissions, and to cover new 
emissions regulations and modeling needs. Although some minor updates 
were made in 1996 with the release of MOBILE5b, MOBILE6 is the first 
major revision to MOBILE since MOBILE5a was released in 1993.
    EPA produced 48 technical reports explaining the data and analysis 
behind the MOBILE6 estimates and the methods in the model. State and 
local governments, industry, academia, and the general public were 
previously offered an opportunity to comment on MOBILE6 technical 
reports, which are currently posted on EPA's MOBILE6 Web site http://www.epa.gov/otaq/m6.htm.
    MOBILE6 provides many more options for users to incorporate local 
inputs than were possible in MOBILE5a or MOBILE5b. These new options 
are provided for implementers to use if desired, and MOBILE6 defaults 
are appropriate when local information is not available for MOBILE6 
purposes. Users now have the option to adapt MOBILE to local conditions 
and model special situations that are not reflected in the model's 
defaults. MOBILE6 also has an updated structure that allows users to 
create result files with emissions by hour of the day, and to segregate 
start and running emissions. The new output uses standard database 
formats to allow users to easily post-process their results. These 
features will be useful for entering the emissions data into air 
quality models and other tools that make use of motor vehicle emission 
inventories. For further information regarding operating MOBILE6, 
please refer to the MOBILE6 User's Guide and EPA's ``Technical Guidance 
on the Use of MOBILE6 for Emission Inventory Preparation.'' Please see 
Availability of MOBILE6 and Support Materials for how to obtain these 
documents.

II. SIP Policy for MOBILE6

    EPA has articulated its policy regarding the use of MOBILE6 in SIP 
development in its ``Policy Guidance on the Use of MOBILE6 for SIP 
Development and Transportation Conformity.'' Today's notice highlights 
certain aspects of the guidance, but state and local governments should 
refer to the guidance for more detailed information on how and when to 
use MOBILE6 in attainment and maintenance SIPs, inventory updates, and 
other SIP submission requirements. See Availability of Related SIP 
Policies to obtain the MOBILE6 policy guidance.
    Although MOBILE6 should be used in SIP development as expeditiously 
as possible, EPA also recognizes the time and level of effort that 
States have already undertaken in SIP development with MOBILE5. States 
that have already submitted SIPs or will submit SIPs shortly after 
EPA's approval of MOBILE6 are not required to revise these SIPs simply 
because a new motor vehicle emissions model is now available. States 
can choose to use MOBILE6 in these SIPs, for example, if it is 
determined that future conformity determinations would be ensured 
through such a SIP revision. However, EPA does not believe that a 
State's use of MOBILE5 should be an obstacle to EPA approval for SIPs 
that have been or will soon be submitted, assuming that such SIPs are 
otherwise approvable and significant SIP work has already occurred 
(e.g., attainment modeling for an attainment SIP has already been 
completed with MOBILE5). It would be unreasonable to require States to 
revise these SIPs with MOBILE6 since significant work has already 
occurred, and EPA intends to act on these SIPs in a timely manner.
    States should use MOBILE6 where SIP development is in its initial 
stages or hasn't progressed far enough along that switching to MOBILE6 
would create a significantly adverse impact on State resources. For 
example, SIPs that will be submitted later in 2002 should be based on 
MOBILE6 since there is

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adequate time to incorporate the new model's results. MOBILE6 should be 
incorporated into these SIPs since MOBILE6's emissions estimates are 
based on the best information currently available, as required by Clean 
Air Act section 172(c)(3) and 40 CFR 51.112(a)(1).
    In addition, SIPs that EPA has already approved are not required to 
be revised in most areas now that EPA has approved MOBILE6. As 
discussed below, there are exceptions for certain nonattainment and 
maintenance areas that have included interim MOBILE5-based estimates of 
the federal Tier 2 vehicle and fuel standards (65 FR 6698).
    In November of 1999, EPA issued two memoranda \1\ to articulate its 
policy regarding States that incorporated MOBILE5-based interim Tier 2 
standard benefits into their SIPs and motor vehicle emissions budgets 
(``budgets''). Although these memoranda primarily targeted certain 
serious and severe ozone nonattainment areas, EPA has implemented this 
policy in all other areas that have made use of federal Tier 2 benefits 
in air quality plans from EPA's April 2000 MOBILE5 guidance, ``MOBILE5 
Information Sheet #8: Tier 2 Benefits Using MOBILE5.''
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    \1\ November 3, 1999 EPA memorandum entitled, ``Guidance on 
Motor Vehicle Emissions Budgets in One-Hour Ozone Attainment 
Demonstrations,'' and November 8, 1999 EPA memorandum entitled, ``1-
Hour Ozone Attainment Demonstrations and Tier 2/Sulfur Rulemaking.'' 
Please see Availability of Related SIP Policies for how to obtain 
these memoranda.
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    All States whose attainment demonstrations or maintenance plans 
include interim estimates of the Tier 2 standards have committed to 
revise and resubmit their budgets within either 1 or 2 years of the 
final release of MOBILE6 in order to gain SIP approval. States that 
committed to revise their budgets within 2 years after MOBILE6 is 
released also committed that conformity will not be determined during 
the second year unless there are adequate SIP budgets in place that 
were developed using MOBILE6. The effective date of today's Federal 
Register notice will constitute the start of the 1 or 2-year time 
periods for these SIP revisions. SIP revisions are due by January 29, 
2003, for States that committed to revise budgets within one year of 
MOBILE6's release. SIP revisions are due by January 29, 2004, for 
States that committed to revise budgets within two years of MOBILE6's 
release.

III. Transportation Conformity Policy for MOBILE6

    Transportation conformity is a Clean Air Act requirement to ensure 
that federally supported highway and transit activities are consistent 
with (``conform to'') the SIP. Conformity to a SIP means that a 
transportation activity will not cause or contribute to new air 
pollution violations; worsen existing violations; or delay timely 
attainment of federal air quality standards.
    The transportation conformity rule (40 CFR part 93) requires that 
conformity analyses be based on the latest motor vehicle emissions 
model approved by EPA. Section 176(c)(1) of the Clean Air Act states 
that ``. . . [t]he determination of conformity shall be based on the 
most recent estimates of emissions, and such estimates shall be 
determined from the most recent population, employment, travel, and 
congestion estimates. . . .'' When we approve a new emissions model 
such as MOBILE6, a grace period is established before the model is 
required for conformity analyses. The conformity rule provides for a 
grace period for new emissions models of between 3-24 months.
    EPA articulated its intentions for establishing the length of a 
conformity grace period in the preamble to the 1993 transportation 
conformity rule (58 FR 62211):

    EPA and [the Department of Transportation (DOT)] will consider 
extending the grace period if the effects of the new emissions model 
are so significant that previous SIP demonstrations of what emission 
levels are consistent with attainment would be substantially 
affected. In such cases, States should have an opportunity to revise 
their SIPs before MPOs must use the model's new emissions factors.

In consultation with the DOT, EPA considers many factors in 
establishing the length of the grace period, including the degree of 
change in emissions models and the effects of the new model on the 
transportation planning process (40 CFR 93.111).
    Upon consideration of all of these factors, EPA is establishing a 
2-year grace period, which begins today and ends on January 29, 2004, 
before MOBILE6 is required for new conformity analyses in most cases. 
During this grace period, areas should use the interagency consultation 
process to examine how MOBILE6 will impact their future conformity 
determinations.
    However, the grace period will be shorter than 2 years for a given 
pollutant if an area revises its SIP and budgets with MOBILE6 and such 
budgets become applicable for conformity purposes prior to the end of 
the 2-year grace period. For example, if an area revises a previously 
submitted (but not approved) MOBILE5-based ozone SIP with MOBILE6 and 
EPA finds the revised MOBILE6 budgets adequate for conformity, such 
budgets would apply for conformity on the effective date of the Federal 
Register notice announcing EPA's adequacy finding. In this example, if 
an area was in nonattainment for ozone and CO, the MOBILE6 grace period 
would end for ozone once EPA found the new MOBILE6-based ozone SIP 
budgets adequate, but MOBILE5 could continue to be used for CO 
conformity determinations until the end of the general MOBILE6 grace 
period.
    During the grace period, areas can use an approved version of 
MOBILE5 \2\ for conformity determinations or choose to use MOBILE6 on a 
faster time frame. When the grace period ends on January 29, 2004, 
MOBILE6 will become the only approved motor vehicle emissions model for 
new transportation conformity analyses outside of California. In 
general, this means that all new VOC, NOX, and CO conformity 
analyses started after the end of the 2-year grace period must be based 
on MOBILE6, even if the SIP is based on an earlier version of the 
MOBILE model. As discussed above, the grace period for new conformity 
analyses would be shorter for a given pollutant if an area revised its 
SIP and budgets with MOBILE6 for such pollutant and such budgets became 
applicable for conformity purposes prior to the end of the 2-year grace 
period. EPA strongly encourages areas to use the consultation process 
to examine how MOBILE6 will affect future conformity determinations, 
so, if necessary, SIPs and budgets can be revised with MOBILE6 or 
transportation plans and programs can be revised as appropriate prior 
to the end of the grace period.
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    \2\ Please refer to EPA's Office of Transportation and Air 
Quality's August 11, 1997 memorandum entitled, ``Summary of Comments 
on and Guidance for Use of MOBILE5b,'' which describes our policy on 
when MOBILE5a or 5b can be used in conformity determinations.
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    For consistency purposes, EPA encourages areas that have 
incorporated interim MOBILE5-based Tier 2 estimates into their SIPs to 
continue to use MOBILE5 (instead of MOBILE6) for conformity analyses 
until new MOBILE6 budgets are submitted and found adequate (unless the 
grace period ends before this occurs). These areas have committed to 
submit SIP revisions within 1-2 years of MOBILE6's release, therefore 
conformity budgets based on MOBILE6 should be in place by the end of 
the grace period.
    Finally, the conformity rule provides some flexibility for analyses 
that are started before or during the grace period. Regional conformity 
analyses

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that began before the end of the grace period may continue to rely on 
an approved version of MOBILE5. Conformity determinations for 
transportation projects may also be based on an approved version of 
MOBILE5 if the regional analysis was begun before the end of the grace 
period, and if the final environmental document for the project is 
issued no more than three years after the issuance of the draft 
environmental document (see 40 CFR 93.111(c)). The interagency 
consultation process should be used if it is unclear whether a MOBILE5-
based analysis was begun before the end of the grace period.

    Dated: January 23, 2002.
Margo Tsirigotis Oge,
Director, Office of Transportation and Air Quality, United States 
Environmental Protection Agency.
[FR Doc. 02-2125 Filed 1-28-02; 8:45 am]
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