[Federal Register Volume 74, Number 142 (Monday, July 27, 2009)]
[Rules and Regulations]
[Pages 37122-37158]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E9-17533]



[[Page 37121]]

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Part III





Department of Transportation





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National Highway Traffic Safety Administration



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49 CFR Part 571



Federal Motor Vehicle Safety Standards; Air Brake Systems; Final Rule

  Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules 
and Regulations  

[[Page 37122]]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2009-0083]
RIN 2127-AJ37


Federal Motor Vehicle Safety Standards; Air Brake Systems

AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION: Final rule.

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SUMMARY: This document amends the Federal motor vehicle safety standard 
on air brake systems to improve the stopping distance performance of 
truck tractors. The rule requires the vast majority of new heavy truck 
tractors to achieve a 30 percent reduction in stopping distance 
compared to currently required levels. For these heavy truck tractors 
(approximately 99 percent of the fleet), the amended standard requires 
those vehicles to stop in not more than 250 feet when loaded to their 
gross vehicle weight rating (GVWR) and tested at a speed of 60 miles 
per hour (mph). For a small number of very heavy severe service 
tractors, the stopping distance requirement will be 310 feet under 
these same conditions. In addition, this final rule requires that all 
heavy truck tractors must stop within 235 feet when loaded to their 
``lightly loaded vehicle weight'' (LLVW).
    The purpose of these amendments is to reduce the number of 
fatalities and injuries associated with crashes involving tractor-
trailer combinations and other vehicles. In addition, we anticipate 
that this rule will prevent a substantial amount of property damage 
through averting or lessening the severity of crashes involving these 
vehicles. Once all subject heavy truck tractors on the road are 
equipped with enhanced braking systems, we estimate that annually, 
approximately 227 lives will be saved and 300 serious injuries will be 
prevented. In addition, this final rule is expected to prevent over 
$169 million in property damage annually, an amount which alone is 
expected to exceed the total cost of the rule.
    There are a number of simple and effective manufacturing solutions 
that vehicle manufacturers can use to meet the requirements of this 
final rule. These solutions include installation of enhanced drum 
brakes, air disc brakes, or hybrid disc/drum systems. We note that 
currently a number of vehicles in the commercial fleet already utilize 
these improved braking systems and already realize performance that 
would meet the requirements of the amended standard.

DATES: Effective Date: This final rule is effective November 24, 2009.
    Compliance Date: Three-axle tractors with a GVWR of 59,600 pounds 
or less must meet the reduced stopping distance requirements specified 
in this final rule by August 1, 2011. Two-axle tractors and tractors 
with a GVWR above 59,600 pounds must meet the reduced stopping distance 
requirements specified in this final rule by August 1, 2013. Voluntary 
early compliance is permitted before those dates.
    Petitions for Reconsideration: If you wish to submit a petition for 
reconsideration of this rule, your petition must be received by 
September 10, 2009.

ADDRESSES: Petitions for reconsideration should refer to the docket 
number above and be submitted to: Administrator, Room W42-300, National 
Highway Traffic Safety Administration, 1200 New Jersey Avenue, SE., 
Washington, DC 20590.
    See the SUPPLEMENTARY INFORMATION portion of this document (Section 
VI; Rulemaking Analyses and Notice) for DOT's Privacy Act Statement 
regarding documents submitted to the agency's dockets.

FOR FURTHER INFORMATION CONTACT: For non-legal issues, you may call Mr. 
Jeff Woods, Office of Crash Avoidance Standards (Telephone: 202-366-
6206) (Fax: 202-366-7002).
    For legal issues, you may call Mr. Ari Scott, Office of the Chief 
Counsel (Telephone: 202-366-2992) (Fax: 202-366-3820).
    You may send mail to both of these officials at National Highway 
Traffic Safety Administration, 1200 New Jersey Avenue, SE., Washington, 
DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary
    a. Background and Safety Problem Addressed by the Regulation
    b. Notice of Proposed Rulemaking
    c. Summary of Public Comments
    d. Requirements of the Final Rule
    e. Lead Time
    f. Specific Decisions and Differences Between the Final Rule and 
the Notice of Proposed Rulemaking
    g. Costs and Benefits
II. Background
    a. Existing Brake Technologies for Heavy Air-Braked Trucks
    b. Current Requirements of FMVSS No. 121
    c. Summary of the NPRM
    d. Summary of Public Comments on the NPRM
III. The Final Rule and Response to the Public Comments
    a. The Final Rule
    i. Summary of Requirements
    ii. Compliance Dates
    iii. Margin of Compliance
    b. Summary of NHTSA Testing and Results Conducted After 
Publication of the NPRM
    i. Testing Conducted on Three-Axle Truck Tractors
    ii. Testing Conducted on Two-Axle Truck Tractors
    iii. Testing Conducted on Severe Service Tractors
    c. Response to Public Comments
    i. Braking Performance of Heavy Truck Tractors With Improved 
Brake Systems
    1. Braking Performance of Typical Three-Axle Tractors With 
Improved Brake Systems in the Loaded-to-GVWR Condition
    2. Braking Performance of Two-Axle Tractors With Improved Brake 
Systems in the Loaded-to-GVWR Condition
    3. Braking Performance of Severe Service Tractors With Improved 
Brake Systems in the Loaded-to-GVWR Condition
    a. Definition of Severe Service Tractor and Specific Safety 
Benefits
    b. Three-Axle Severe Service Tractors With a GVWR Under 70,000 
Pounds
    c. Three-Axle Severe Service Tractors With GVWR Over 70,000 
Pounds
    d. Severe Service Tractors With Four or More Axles
    e. Two-Axle Severe Service Tractors
    f. Summary of Severe Service Tractors
    4. Braking Performance of Tractors With Improved Brake Systems 
in the Unloaded Weight Condition
    5. Emergency Braking Performance of Tractors With Improved Brake 
Systems
    a. Background Information on the Emergency Braking Performance 
Requirement
    b. Commenters' Responses to Proposed Emergency Braking 
Performance Requirement
    ii. Ancillary Issues Arising From Improved Brake Systems
    1. Stability and Control of Tractors With Improved Brake Systems
    2. Brake Issues on Tractors With Improved Brake Systems
    3. Brake Balance and Trailer Compatibility Issues for Tractors 
With Improved Brake Systems
    a. Brake Balance Between the Steer and Drive Axles
    b. Tractor-Trailer Compatibility
    c. Brake Balance and Trailer Compatibility Issues for Two-Axle 
and Severe Service Tractors
    iii. Cargo Securement
    iv. Testing Procedures
    1. Brake Burnish Issues for Tractors With Improved Brake Systems
    2. Brake Dynamometer Test Requirements
    v. Stopping Distances at Reduced Initial Test Speeds
    vi. Comments Regarding Foreign Trade Agreements
    vii. Miscellaneous Comments
    viii. Costs and Benefits of Shorter Tractor Stopping Distances
    1. Estimated Benefits of a 30 Percent Reduction in Stopping 
Distance

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    2. Cost of Improved Brake Systems
    3. Additional Costs Incurred Resulting From Improved Brake 
Systems
    4. Summary of Cost-Benefit Analysis
    ix. Lead Time
IV. Rulemaking Analyses and Notices
    a. Vehicle Safety Act
    b. Executive Order 12866 and DOT Regulatory Policies and 
Procedures
    c. Regulatory Flexibility Act
    d. Executive Order 13132 (Federalism)
    e. Executive Order 12988 (Civil Justice Reform)
    f. Executive Order 13045 (Protection of Children From 
Environmental Health and Safety Risks)
    g. Paperwork Reduction Act
    h. National Technology Transfer and Advancement Act
    i. Unfunded Mandates Reform Act
    j. National Environmental Policy Act
    k. Regulatory Identifier Number (RIN)
    l. Privacy Act
Regulatory Text

I. Executive Summary

a. Background and Safety Problem Addressed by the Regulation

    On March 10, 1995, NHTSA published three final rules \1\ as part of 
a comprehensive effort to improve the braking ability of medium and 
heavy vehicles.\2\ While the major focus of that effort was to improve 
directional stability and control through adoption of antilock brake 
system (ABS) requirements, the 1995 rules also reinstated stopping 
distance requirements for medium and heavy vehicles, replacing earlier 
requirements that had been invalidated in 1978 by the United States 
Court of Appeals for the 9th Circuit due to reliability issues (see 
PACCAR v. NHTSA, 573 F.2d 632 (9th Cir. 1978)).
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    \1\ 60 FR 13216 (Dockets 92-29 and 93-69), 60 FR 13287 
(Docket 93-06), March 10, 1995.
    \2\ Medium and heavy weight vehicles are hydraulic-braked 
vehicles over 10,000 pounds GVWR, and all vehicles equipped with air 
brakes; hereinafter referred to collectively as heavy vehicles.
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    Currently, stopping distance requirements under FMVSS No. 121, Air 
Brake Systems, vary according to vehicle type. Vehicles are tested 
under three different test conditions: (1) Loaded-to-GVWR; (2) 
unloaded; and (3) emergency braking conditions. Under the loaded-to-
GVWR condition, when stopping from 60 mph, air-braked buses must stop 
within a distance of 280 feet, air-braked single unit trucks must stop 
within 310 feet, and air-braked truck tractors must comply within 355 
feet.\3\ Under the unloaded \4\ condition at 60 mph, air-braked buses 
are required to stop within 280 feet, while single-unit trucks and 
truck tractors must stop within 335 feet. Under the emergency brake \5\ 
60 mph requirements, air-braked buses and single-unit trucks must stop 
within 613 feet, while tractors must stop within 720 feet.
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    \3\ For heavy truck tractors (tractors), the current stopping 
distance test in the loaded-to-GVWR condition is conducted with the 
tractor coupled to an unbraked control trailer, with weight placed 
over the fifth wheel of the tractor, and a 4,500 pound load on the 
single axle of the trailer. This test method isolates the braking 
performance of the tractor so that only that system's performance is 
evaluated. The performance of a tractor in an FMVSS No. 121 stopping 
distance test does not directly reflect the on-road performance of a 
tractor/semi-trailer combination vehicle that has braking at all 
wheel positions.
    \4\ In the unloaded condition, vehicles are tested at lightly 
loaded vehicle weight (LLVW).
    \5\ Emergency brake system performance is tested with a single 
failure in the service brake system of a part designed to contain 
compressed air or brake fluid.
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    Data from the agency's 2000-2002 GES database and the agency's 
2004-2006 FARS database indicate that the involvement of large trucks 
in fatal and injury-producing crashes has slightly declined, while 
vehicle-miles-traveled (VMT) has increased. However, because the number 
of registered heavy vehicles has increased, the net effect is that the 
total number of crashes remains high. According to the 2006 data: \6\
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    \6\ See Traffic Safety Facts 2006--Large Trucks, National Center 
for Statistics and Analysis (NCSA), report number DOT HS 810 805, 
http://www.nrd.nhtsa.dot.gov/Pubs/810805.pdf. The NCSA report uses 
the term ``large trucks,'' which in practical terms describes the 
same segment of the vehicle population as ``heavy vehicles.''
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     385,000 large trucks were involved in traffic crashes in 
the U.S.
     4,732 large trucks were involved in fatal crashes, 
resulting in 4,995 fatalities (12 percent of all highway fatalities 
reported in 2006). Seventy-five percent of the fatally injured people 
were occupants of another vehicle; 16 percent were truck occupants, and 
8 percent were nonoccupants.
     106,000 people were injured in crashes involving large 
trucks. Seventy-six percent of the injured people were occupants of 
another vehicle; 22 percent were truck occupants, and 2 percent were 
nonoccupants.
    According to a report \7\ published by the Analysis Division of the 
Federal Motor Carrier Safety Administration (FMCSA), the fatality rate 
for large truck crashes was 66 percent higher than the fatality rate 
for crashes involving only passenger vehicles (defined as a car or 
light truck) in 2005. When the FMCSA report considered combination 
trucks (e.g., tractor and trailer combinations) separately, the crash 
fatality rate was nearly double that of passenger vehicles. Conversely, 
the crash fatality rate for single-unit trucks was approximately 23 
percent higher than for passenger vehicles. The FMCSA data indicate 
that for all types of crashes involving large trucks, those involving 
trucks with a GVWR over 26,000 pounds have the highest rate of crash 
involvement.
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    \7\ Large Truck Crash Facts 2005 (report number FMCSA-RI-07-046, 
http://www.fmcsa.dot.gov/facts-research/research-technology/report/Large-Truck-Crash-Facts-2005/Large-Truck-Crash-Facts-2005.pdf.
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    It is expected that in most cases reductions in stopping distances 
for large trucks will result in a reduction of the impact velocity, and 
hence the severity of a crash. In some cases, reduced stopping 
distances will prevent a crash from occurring entirely (i.e., a vehicle 
with a reduced stopping distance will stop short of impacting another 
vehicle). Based on the crash data in the June 2005 NHTSA report titled 
``An Analysis of Fatal Large Truck Crashes,'' \8\ improvements in 
stopping distance will provide benefits in the following types of 
crashes: Rear-end, truck striking passenger vehicle; passenger vehicle 
turned across path of truck; and straight path, truck into passenger 
vehicle. It is estimated that these types of crashes account for 26 
percent of fatalities involving large trucks, or 655 fatalities 
annually. In addition, it is possible that some head-on collisions 
could be reduced in severity, since improvement in braking performance 
could reduce impact speeds.
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    \8\ DOT HS 809 569, http://www.nrd.nhtsa.dot.gov/Pubs/809-569.pdf; Docket  NHTSA-2005-21462-5 via Web site 
references.
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    NHTSA has been exploring the feasibility of reducing the stopping 
distance under FMVSS No. 121 for heavy air-braked vehicles by 20-30 
percent based on testing of current vehicles. We have initially focused 
on air-braked truck tractors, since the available crash data indicate 
that these vehicles are the ones most frequently involved in fatal 
truck crashes. By promulgating a more stringent requirement for air-
braked heavy tractor stopping distances, it is our intent to reduce 
fatalities and injuries relating to this class of vehicles. It is our 
belief that development of advanced air disc brakes, enhanced larger 
capacity drum brakes, and advanced ABS, offer cost-effective means to 
reduce heavy truck stopping distances and to reduce injuries and damage 
from large tractor crashes effectively.

b. Notice of Proposed Rulemaking

    On December 15, 2005, NHTSA published a Notice of Proposed 
Rulemaking (NPRM) in the Federal Register (70 FR 74270) \9\ proposing 
to amend FMVSS No. 121 so as to reduce

[[Page 37124]]

the required stopping distances for the loaded and unloaded service 
brake distances and emergency brake distances for truck tractors by 20 
to 30 percent. These amendments would apply to nearly all of the 
130,000 tractors manufactured annually. NHTSA also proposed a lead time 
of two years to implement these amendments, given that vehicles tested 
by the agency and industry were able to meet the proposed requirements 
without modifications other than the use of improved foundation brakes. 
Finally, NHTSA indicated that it was considering revising the 
dynamometer testing procedures to ensure adequate braking capability 
for trailer foundation brakes.
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    \9\ Docket No. NHTSA-2005-21462.
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    The NPRM included figures from the accompanying Preliminary 
Regulatory Impact Analysis (PRIA) indicating that enhanced brake system 
specifications would result in a range of costs and benefits based on 
the specific requirements and the choices made to reach those 
requirements. We note that in some instances, the cost estimates in the 
PRIA do not correspond to the numbers in the FRIA or those cited in the 
Final Rule. This is because NHTSA has updated its cost estimates during 
the interim period, and the FRIA uses 2007 dollars.
    The NPRM also discussed the results of testing conducted at NHTSA's 
Vehicle Research and Test Center (VRTC), as well as data from Radlinski 
and Associates provided to NHTSA. These data strongly suggested that 
with improved foundation brakes, typical three-axle tractors \10\ would 
be able to meet the proposed requirements for reduced stopping 
distance, although the Radlinski data did not include data on two-axle 
or severe service \11\ tractors. The data also indicated that some 
vehicles in service today would meet the enhanced requirements with no 
additional modifications.
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    \10\ As explained below, ``typical'' three-axle tractors have a 
GVWR less than or equal to 59,600 pounds.
    \11\ As explained below, ``severe service'' tractors refer to 
tractors with a GVWR over 59,600 pounds.
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    NHTSA requested comments on a number of subjects in the NPRM. 
Comments were requested generally on the proposal to reduce stopping 
distances 20-30 percent and on the costs of the proposal. Comments were 
also requested on a variety of specific subjects, such as the possible 
changes in dynamometer testing procedures, the application of Advanced 
ABS and Electronically Controlled Braking Systems (ECBS), and the lead 
time that would be required to implement the proposed changes. Finally, 
NHTSA requested comments on the VRTC and Radlinski testing, as well as 
information from vehicle manufacturers regarding vehicle modifications 
(other than to foundation brakes) that might be required to meet the 
proposal's enhanced braking specifications.

c. Summary of Public Comments

    Commenters brought up a variety of issues in response to the NPRM. 
Most commenters supported NHTSA's proposal to reduce the stopping 
distance requirements for heavy truck tractors. In general, safety 
organizations recommended adopting the 30 percent reduction in stopping 
distances for all heavy truck tractors. On the other hand, truck 
manufacturing groups recommended that the agency reduce the stopping 
distance requirements by 20-25 percent, and limit the scope of the 
reductions to standard three-axle tractors. In their comments, 
manufacturers cited the increased costs and complexity of upgrading to 
the stricter stopping distance requirements, as well as potential 
problems that could be encountered with upgrading the requirements for 
two-axle and severe service tractors. Many commenters also discussed 
the vehicle testing NHTSA cited in the NPRM, along with providing 
independent test and cost-benefit data.
    Other aspects of Standard No. 121 mentioned in the NPRM received 
comments as well. Several commenters recommended against making any 
changes to the emergency braking requirements in the Standard. 
Regarding brake dynamometer specifications, some commenters also 
recommended that no changes be made. Several commenters suggested that 
the brake burnish procedure could be returned to an older procedure, 
known as a ``hot burnish,'' that existed before 1993. Finally, 
attention was called to the possible ramifications of the stopping 
distance changes for issues like cargo securement and brake power at 
lower speeds.

d. Requirements of the Final Rule

    After careful consideration of the public comments on the NPRM, we 
are promulgating this final rule, which amends the requirements of 
FMVSS No. 121 by reducing the specified stopping distance for the vast 
majority of heavy truck tractors by 30 percent. For a small number of 
very heavy, severe service tractors, the stopping distance requirement 
is reduced by a smaller amount. The reduction applies to service brake 
stopping distance but does not, however, apply to emergency braking 
distances.
    For heavy trucks in the loaded-to-GVWR condition, the stopping 
distance requirements from an initial speed of 60 mph are as follows:
     A tractor with two or three axles and a GVWR of 70,000 
pounds or less must stop within 250 feet.
     A tractor with three axles and a GVWR greater than 70,000 
pounds must stop within 310 feet.
     A tractor with four or more axles and a GVWR of 85,000 
pounds or less must stop within 250 feet.
     A tractor with four or more axles and a GVWR greater than 
85,000 pounds must stop within 310 feet.\12\
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    \12\ We note that tractors with any axle with a GAWR of 29,000 
pounds or greater will continue to be excluded from FMVSS No. 121 
requirements in accordance with paragraph S3.
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    For heavy trucks in the unloaded condition, the agency is reducing 
the specified stopping distance from 60 mph by 30 percent, to a 235-
foot requirement. This requirement applies to all tractors, including 
those severe service tractors for which the loaded-to-GVWR stopping 
distance requirement has been set at 310 feet.
    Stopping distance requirements for heavy air-braked tractors are 
provided in Tables I through III (See Section III). The tables list the 
following information:
     Table I lists the requirements and details the explanation 
for stopping distance requirements in the loaded-to-GVWR condition for 
two- and three-axle tractors with a GVWR of 70,000 pounds or less, and 
tractors with four or more axles with a GVWR of 85,000 pounds or less.
     Table II lists the requirements and details the 
explanation for stopping distance requirements in the loaded-to-GVWR 
condition for three-axle tractors with a GVWR greater than 70,000 
pounds, and tractors with four or more axles and a GVWR greater than 
85,000 pounds.
     Table III lists the stopping distance requirements and 
details the explanation for all tractors in the unloaded condition.
    In addition, to reduce a possible source of test variability, the 
agency is adding a specification to the unloaded condition testing 
requirement in FMVSS No. 121 that the fuel tank is filled to 100 
percent of capacity at the beginning of testing and may not be less 
than 75 percent of capacity during any part of the testing.
    Finally, it should be noted that there were several changes 
suggested in the NPRM that we are not incorporating into this final 
rule amending FMVSS No. 121. These include:

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     There is no change in the emergency brake stopping 
distance requirement.
     There are no changes to the dynamometer test requirements.

e. Lead Time

    After carefully considering the public comments on the NPRM, the 
agency has decided to tie the lead time to the specific type of heavy 
truck in light of the anticipated challenges in making the necessary 
modifications. For the reasons discussed below, we have decided to 
provide the majority of three-axle tractors with two years lead time 
from the date of today's final rule, and we are providing two-axle and 
severe service tractors with four years lead time.
    NHTSA's test data indicate that for typical three-axle tractors 
with improved brake systems (i.e., enhanced drum brakes or air disc 
brakes), compliance with the new stopping distance requirements can be 
readily achieved. Therefore, the agency is specifying a compliance date 
that is two years from the date of publication of the final rule for 
typical three-axle tractors. ``Typical three-axle'' tractors are 
defined as having three axles and a GVWR less than or equal to 59,600 
pounds.
    Available test data also indicate that two-axle tractors with 
improved brake systems can meet a 250-foot loaded-to-GVWR stopping 
distance requirement. However, we believe additional lead time is 
needed for manufacturers to evaluate new brake systems more fully to 
ensure compatibility with existing trailers and converter dollies when 
used in multi-trailer combinations, and to minimize the risk of vehicle 
stability and control issues. With regard to severe service tractors, 
available test data and analysis indicate that the 250-foot and 310-
foot loaded-to-GVWR stopping distance requirements, depending on the 
vehicle's GVWR, are achievable. However, only limited development work 
has been performed on these vehicles, and additional lead time is 
needed for manufacturers to complete testing and validation of new 
brake systems for these vehicles. In light of these facts, NHTSA has 
decided that additional lead time is necessary for all two-axle 
tractors, and severe service tractors with a GVWR greater than 59,600 
pounds. Accordingly, for those vehicles the compliance date for today's 
final rule is four years from the date of publication.

f. Specific Decisions and Differences Between the Final Rule and the 
Notice of Proposed Rulemaking

    In the NPRM, NHTSA discussed a number of potential actions intended 
to improve vehicle safety by reducing heavy air-braked tractor stopping 
distance through amendments to FMVSS No. 121. The available data showed 
that it was both technically feasible and cost-effective to require 
improved foundation brakes on air-braked tractors that could achieve a 
20-30 percent reduction in stopping distance. The main differences 
between the NPRM and the final rule include decisions to: (1) Specify a 
30 percent reduction in stopping distance for the vast majority of 
tractors, with a smaller reduction for a small number of very heavy 
severe service tractors; (2) continue the standard's emergency braking 
requirements without change; (3) alter the stopping distance 
requirements for reduced speed tests to account for brake system 
reaction time and the available tire-road friction; and (4) extend the 
effective date for compliance by two-axle and severe service tractors. 
The rationales for these decisions are discussed briefly below, 
followed by a more complete explanation later in this document.
    In the NPRM, NHTSA proposed reducing the required stopping distance 
for heavy air-braked tractors by 20-30 percent. This range was based on 
available test results and cost analyses (described below). In the 
final rule, NHTSA is requiring a 30 percent reduction in the required 
stopping distance for the vast majority of tractors. We note that the 
agency's final regulatory impact analysis (FRIA) estimated that greater 
safety benefits would be attained with a 30-percent reduction in 
stopping distance requirements compared to the benefits estimated for a 
20-percent reduction. It estimated that more than twice as many 
benefits in fatalities and serious injuries prevented are projected for 
the 30-percent case versus the 20-percent case. The differential in 
estimated property damage reductions is even greater, with 
approximately five times the property damage prevented for the 30-
percent case versus the 20-percent case. NHTSA testing and analysis 
demonstrated that nearly all two-axle and three-axle tractors will be 
able to meet the 30 percent reduction by using improved foundation 
brakes that are readily available. For a small percentage of severe 
service tractors (estimated to be approximately one percent), namely 
three-axle tractors with a GVWR over 70,000 pounds and tractors with 
four or more axles and a GVWR over 85,000 pounds, we concluded that a 
30 percent reduction is not currently practicable. For those vehicles, 
the stopping distance is reduced by 13 percent, from the currently 
mandated level to the level of similar single-unit trucks.
    While the NPRM proposed reducing emergency brake stopping distances 
by 20-30 percent, we decided not to adopt this part of the proposal. 
Comments received from the Truck Manufacturers Association (TMA) 
indicated that in order to meet the agency's proposed emergency brake 
stopping distance requirements, manufacturers would need to modify the 
ABS algorithms to allow more drive wheel lockup. This modification 
could be detrimental to vehicle stability and control. NHTSA considered 
this, as well as the relative rarity of a crash-imminent situation 
during a brake failure, and decided to maintain the status quo.
    In the final rule, NHTSA is also altering the stopping distance 
requirement for speeds less than 60 mph from the original figures cited 
in the NPRM. Several commenters argued that the reduced stopping 
distance values in the proposed Table V of FMVSS No. 121 did not take 
into account the brake system reaction time and average deceleration. 
In the final rule, the stopping distances for speeds less than 60 mph 
have been adjusted to take these factors into consideration.
    Finally, the final rule provides additional lead time for several 
types of tractors to comply with the reduced stopping distance 
requirements. The NPRM had proposed a two-year lead time for all 
tractors to meet the reduced stopping requirements. With regards to 
typical three-axle tractors (three-axle tractors with a GVWR of 59,600 
pounds or less), the available test data showed that compliance to the 
new stopping distance requirements can be readily achieved without the 
need to make significant modifications to other vehicle systems. As 
stated above, however, the agency believes that additional lead time is 
needed for manufacturers to develop and evaluate improved braking 
systems more fully for two-axle and severe service tractors. Therefore, 
the lead time has been extended for those types of vehicles by an 
additional two years.

g. Costs and Benefits

    A 30 percent reduction in required stopping distance will realize 
significant benefits, both in terms of injuries and fatalities 
prevented, as well as in property damage prevented. The agency's 
analysis in the FRIA estimates that, with a 30 percent reduction in 
stopping distance requirements, 227 fatalities and 300 serious injuries 
will be prevented. In addition, it is estimated that a 30 percent 
reduction in stopping distance will realize significant

[[Page 37126]]

reductions in property damage. According to the FRIA, using a 3 percent 
discount rate, $205M of property damage will be prevented annually. 
Using a 7 percent discount rate, the figure is $169M.
    The range of figures in terms of net costs are based on what types 
of foundation brakes, disc brakes or enhanced drum brakes, are used to 
meet the new stopping distance requirements. The figures are derived 
based on an average annual production of about 130,000 truck tractors 
(82 percent of which are typical three-axle tractors, ten percent two-
axle tractors, and eight percent severe service tractors). Each typical 
three-axle tractor contains one steer axle and two drive axles, as do 
most severe service tractors. Each two-axle tractor contains one steer 
axle and one drive axle. Therefore, the agency estimates that in total, 
the final rule will require the upgrading of 130,000 steer axle brakes 
and 247,000 drive axle brakes. In order to compute the total cost of 
complying with the reduced stopping distance rule, the agency 
calculated the number of axles that will need to be upgraded with 
improved foundation brakes, and multiplied that number by the cost of 
the brake. The agency estimated the cost of enhanced drum brakes for 
the steer axle at $85, and for drive axles at $65. The agency estimated 
the cost of disc brakes to be $500 per axle at all wheel positions.
    Because the agency is not certain how truck manufacturers will 
choose to comply with the final rule, using the above figures, the 
agency created a range of costs of compliance. The most expensive means 
of compliance would be to use a $500 disc brake at all wheel positions, 
while the least expensive means of compliance would be to use enhanced 
drum brakes at all wheel positions. The FRIA estimates that the 
incremental cost to add disc brakes to all wheel positions would be 
$1,475 per tractor ($192M total cost), while the incremental cost to 
add enhanced drum brakes would be $211 ($27M total cost). One commenter 
(Freightliner) provided cost information, stating that the cost of disc 
brakes would be $1,627 for a three-axle tractor and $963 for a two-axle 
tractor, while the cost of drum brakes for a three-axle tractor would 
be $222. In addition, the commenter stated that development and 
manufacturing costs would need to be added, although it did not 
elaborate on what these costs would be. The agency notes that these 
figures are very similar to its own estimates.
    NHTSA testing indicated that for standard three-axle tractors, it 
is likely enhanced drum brakes at the steer axle and drive axle 
positions will enable the tractors to meet a 250-foot stopping distance 
requirement in FMVSS No. 121. For two-axle tractors and severe service 
tractors, it is likely that disc brakes would be required at all wheel 
positions. Considering that standard three-axle tractors comprise 
roughly 82 percent of all tractors, it seems likely that the total 
costs will be skewed toward the lower end of the range. In the FRIA, 
the agency estimates that the incremental average cost per tractor, 
given these assumptions, will be $413 per vehicle ($54M total). NHTSA 
notes that this figure is substantially lower than the lowest figure in 
the range of estimated savings in property damage ($169M).
    The FRIA estimates that the net cost per equivalent life saved 
(NCELS) will range from $108,000 to net benefits based on property 
damage savings alone (that is, the costs of implementing this final 
rule will be less than the costs saved in damaged property, 
irrespective of the injuries and fatalities prevented). The high figure 
($108,000 NCELS) is derived by taking the highest estimated cost figure 
and the lowest estimated property damage prevented. Conversely, the low 
figure (net benefits) is derived from using the low cost estimate and 
the high benefits estimate.

II. Background

a. Existing Brake Technologies for Heavy Air-Braked Trucks

    The relevant brake technologies at issue in this rulemaking can be 
divided into two categories, S-cam drum brakes (drum brakes) and air 
disc brakes (disc brakes).
    The most common type of foundation brake used in air brake systems 
for heavy vehicles is the S-cam brake. This is a leading/trailing type 
of brake with fixed pivot type shoes. Upon brake application, air 
pressure enters the brake chamber causing the diaphragm to push the 
pressure plate, which in turn applies a force to the end of the brake 
slack adjuster. This force creates a torque on the camshaft, and 
rotates the camshaft to which the S-cam is attached. The camshaft head, 
which is S-shaped, forces the brake shoes against the surface of the 
brake drum to create the retardation force for braking. Enhanced S-cam 
drum brakes are essentially larger and wider versions of standard S-cam 
drum brakes. On the steer axle, for example, the diameter of the brake 
drum is 16.5 inches versus 15 inches for the standard steer axle drum, 
and this produces more braking torque. Typically the enhanced steer 
axle drum brake lining is 5 inches wide instead of the standard steer 
axle brake lining width of 4 inches. On the drive axles, both standard 
and enhanced S-cam drum brakes use a 16.5 inch diameter drum, while the 
standard lining width is 7 inches versus 8 or 8.625 inches for the 
enhanced drum brake. The increased width of the lining and brake drum 
provides greater thermal capacity, so that enhanced S-cam drum brakes 
operate cooler, contributing to longer life, and they are also less 
prone to fade during high-speed stops.
    Air disc brakes are also used on commercial vehicles, but are still 
used in relatively small numbers in the U.S. A disc brake is basically 
a C-clamp with the retardation force applied by friction pads that 
squeeze the brake rotor mounted between them. All air disc brake 
systems are composed of a rotor, brake linings, a caliper, an adjusting 
mechanism, and an air brake chamber, among other parts, and there are 
many different designs to accomplish their function. Disc brakes offer 
a number of favorable performance characteristics including linear 
torque output and high resistance to fade, although they are 
substantially more expensive than drum brakes.

b. Current Requirements of FMVSS No. 121

    Under the current FMVSS No. 121 requirements, most truck tractors 
are required to stop within 355 feet, when tested at 60 mph in the 
loaded-to-GVWR condition while pulling an unbraked control trailer. 
Standard No. 121 also requires that truck tractors stop within 335 
feet, when tested at 60 mph in the unloaded condition. Finally, the 
standard requires an emergency brake stopping distance of 720 feet, 
when tested at 60 mph in the unloaded condition. Currently, the 
standard does not specify different requirements for different vehicles 
based on their number of axles or on their GVWR, except that vehicles 
with a GAWR (gross axle weight rating) of 29,000 pounds or more are 
exempt from the standard, as are certain vehicles with a GVWR greater 
than 120,000 pounds.
    Before testing, brakes are burnished according to the procedure 
specified in paragraph S6.1.8 of the standard. The tractor is coupled 
to an unbraked control trailer and loaded so that the combined weight 
of the tractor and trailer equals the GVWR of the tractor. 
Thermocouples are installed in the brake linings to measure the brake 
temperatures. The burnish consists of 500 snubs (reductions in speed) 
from 40 mph to 20 mph using the service brakes at a deceleration rate 
of 10 ft/sec\2\;. Each subsequent snub is conducted at a distance 
interval of 1 mile from the

[[Page 37127]]

point of the beginning of the previous snub.

c. Summary of the NPRM

    On December 15, 2005, NHTSA published an NPRM in the Federal 
Register (70 FR 74270) \13\ proposing to amend FMVSS No. 121 to reduce 
the required stopping distance for the loaded and unloaded service 
brake conditions and emergency brake conditions for heavy truck 
tractors by 20 to 30 percent. NHTSA proposed a lead time of two years 
to implement this requirement, given that vehicles tested by the agency 
and private industry were able to meet the proposed requirements 
without modifications other than improved foundation brakes. In 
addition, NHTSA suggested that it was considering revising dynamometer 
testing procedures to ensure adequate braking capability for trailer 
foundation brakes.
---------------------------------------------------------------------------

    \13\ Docket No. NHTSA-2005-21462.
---------------------------------------------------------------------------

    In the NPRM, NHTSA stated that it believed the reason that many 
truck operators had not progressed to readily-available, more advanced 
brake systems was because truck operators did not have this cost 
savings information available. Further, the proposal stated that truck 
operators are cost-sensitive in terms of the initial purchase price of 
the vehicle and are reluctant to add different types and sizes of brake 
components to their specifications. The agency noted that the proposed 
requirements would result in net cost savings for truck operators if 
the savings resulting from decreased property damage are taken into 
consideration.
    NHTSA also provided data from its Vehicle Research and Test Center 
(VRTC) to compare the performance of air-braked tractors and trailers 
equipped with a variety of brake system configurations. These data 
indicated that the tested vehicles would be able to comply with a 20-30 
percent reduction in the stopping distance requirements with 
modifications only to the foundation brake systems. Testing was also 
conducted on heavy trucks with a failed primary reservoir in order to 
generate data on emergency stopping distances; the results indicated 
that the same modifications that improved service brake stopping 
distances also improved emergency braking stopping distances.
    Industry data provided by Radlinski and Associates (Radlinski), 
commissioned by two brake lining manufacturers, were also cited in the 
NPRM. These data related to standard three-axle tractors equipped with 
enhanced, larger-capacity S-cam drum brakes at all axle positions. 
These data indicated that the tractors were able to meet the 30 percent 
reduced stopping distance requirement without disc brakes, and the 
braking performance in these tests exceeded that of NHTSA's own tests 
at the VRTC, in some cases even when disc brakes were applied at all 
positions.
    In the NPRM, NHTSA requested comments on a variety of topics to 
further the agency's understanding of the ramifications of various 
measures for improving braking systems. As a preliminary matter, 
comments were solicited on the safety need for improved braking 
distances. Comments were also requested on the implications of 
improving stopping distances by 20 percent and 30 percent, including 
necessary lead time, needed vehicle modifications, and issues regarding 
brake balance. The agency also sought comments on the Radlinski data, 
as well as information on developments in electronically-controlled 
braking systems (ECBS) and advanced ABS, and how these systems could 
benefit heavy vehicle safety.

d. Summary of Public Comments on the NPRM

    NHTSA received 27 comments on the December 2005 NPRM, from heavy 
vehicle manufacturers (International Truck and Engine Corporation 
(International); Freightliner LLC (Freightliner)), brake suppliers 
(Arvin Meritor; Meritor WABCO (Meritor); WABCO Vehicle Control Systems 
(WABCO); Honeywell Bremsbelag GmbH (Honeywell); Bendix Commercial 
Systems/Spicer Foundation Brake (Bendix); Haldex Brake Products 
Corporation (Haldex); Brake Pro), industry organizations and 
associations (Truck Manufacturers Association (TMA); Heavy Duty Brake 
Manufacturers Council (HDBMC); American Trucking Associations (ATA); 
Owner Operators Independent Drivers Association (OOIDA); National 
Automobile Dealers Association (NADA)), automobile safety advocates 
(Insurance Institute for Highway Safety (IIHS); Advocates for Highway 
and Auto Safety (Advocates)), a foreign government (People's Republic 
of China), and concerned organizations and individuals (John W. Klegey; 
Automotive Safety Office (ASO); Roger L. Adkins; Graham Lower; Timothy 
Larrimore; Anonymous; University of Washington; Roger Sauder). All of 
the comments on the NPRM can be reviewed in Docket No. NHTSA-2005-
21462. Commenters expressed a range of views, with vehicle 
manufacturers, brake suppliers, and trade associations generally 
supporting the NPRM. Advocacy groups generally recommended that the 
agency adopt a standard at the stricter end of the range (toward 30 
percent) for all tractors, while most of the trucking industry comments 
recommended that NHTSA reduce the stopping distances by 20-25 percent 
(instead of 20-30 percent), and only for typical three-axle tractors. 
As part of its comments, TMA provided a crash data analysis indicating 
that typical three-axle tractors comprise 82 percent of tractor 
production and are involved in 91 percent of fatal crashes involving 
tractors.
    The following overview of the public comments reflects the key 
issues raised by the commenters, including the safety and cost benefits 
of reducing stopping distances, recommended percentages for reducing 
stopping distances, as well as issues of technical feasibility and 
stability that arise from increasing brake torque. Other issues were 
raised as well, including reduced stopping distances in the unloaded 
vehicle condition, emergency brake stopping distances, maintenance 
issues, recommended dynamometer testing changes, and brake burnish 
procedures. Comments were also received in response to NHTSA's 
questions about the validity and applicability of the Radlinski testing 
data, the impact of ECBS and advanced ABS, and on the margin of 
compliance for testing in accordance with FMVSS No. 121. A few 
commenters recommended that the government undertake additional, 
cooperative studies with industry in order to gather data for two-axle 
and severe service tractors. Finally, comments were provided on the 
implications of reduced stopping distance for reduced test speed 
stopping distance testing and for issues of cargo securement under 
high-deceleration conditions.
    Although the agency also requested comments on trailer stopping 
distance test data and efforts to improve the braking performance of 
single-unit trucks, few comments were received regarding those issues. 
Likewise, only a small number of comments addressed the agency's 
requests for information about the costs of improved braking systems, 
as well as any increase in weight. The issues raised in the public 
comments are discussed in further detail and addressed below in Section 
III, The Final Rule and Response to Public Comments.
General Need To Reduce Stopping Distance Performance for Tractors
    Support for NHTSA's proposal to reduce the stopping distance 
performance of heavy truck tractors was

[[Page 37128]]

nearly universal. Highway safety advocacy organizations, such as 
Advocates and IIHS, supported the largest reduction of stopping 
distances within the range proposed by NHTSA (i.e., a 30 percent 
reduction from the current requirements of FMVSS No. 121 for all 
tractors). Most of the trucking industry comments favored a 25 percent 
reduction in stopping distances, but those commenters recommended 
limiting the new requirements to standard three-axle tractors, which 
account for over 80 percent of tractor production. It should be noted 
that some industry commenters suggested reducing stopping distances by 
only 20 percent, the lowest reduction proposed by NHTSA.
Comments on the Proposal To Reduce Service Brake Stopping Distance 
Performance by 20-30 Percent in the Loaded-to-GVWR Condition
    The majority of commenters fell into two groups, those who 
supported 30 percent reductions in stopping distances for all tractors, 
and those who supported less stringent requirements. Most trucking 
industry comments (from truck manufacturers and brake suppliers) urged 
25 percent reductions for standard three-axle tractors only. In making 
these recommendations, the trucking industry commenters argued that 
data had not been provided for two-axle and severe service tractors, 
and that operational problems (e.g., brake balance, stability, and 
steering pull) could occur if brake output is increased for those 
tractors. Specifically, TMA suggested that amending FMVSS No. 121 to 
require heavy trucks to stop within shorter distances may force 
manufacturers to implement designs that could cause poorer real-world 
stopping performance and instability. On this point, TMA stated that 
one of the reasons current production tractors are equipped with low-
power steer axle brakes is for low-level brake applications, and that 
tractors designed only to achieve maximum straight-line decelerations 
when fully loaded may not perform well during normal brake 
applications.
    In contrast, other commenters, including some brake suppliers 
(Bendix and Wabco) as well as Advocates and IIHS, supported a 30 
percent reduction in stopping distance for all tractors. These 
commenters cited the agency's safety benefit analysis as justifying the 
cost of the improvement. Advocates also argued that there are other 
benefits associated with the use of disc brakes, including greater 
resistance to fading.\14\ Bendix stated that more powerful brakes, both 
disc and enhanced drum, are currently available and being used on the 
road with no significant operational problems.
---------------------------------------------------------------------------

    \14\ ``Brake Fade'' is a term used to describe a temporary 
decrease in torque output of a brake when exposed to certain 
conditions, such as high heat.
---------------------------------------------------------------------------

Comments on the Proposal To Reduce Service Brake Stopping Distance 
Performance by 20-30 Percent in the Lightly Loaded Condition
    Few comments were received on this topic. However, TMA stated that 
currently, standard three-axle unloaded tractors start to experience 
rear wheel slip during brake applications of approximately 30 psi or 
more.
Comments on the Proposal To Reduce Emergency Braking Stopping Distance 
by 20-30 Percent
    Comments from the trucking industry opposed the proposed reduction 
in emergency braking stopping distance. Many commenters stated that 
NHTSA had not provided any crash data or any other rationale to justify 
why any such reduction is necessary. These commenters also stated that 
the occurrence of a crash-imminent situation at the same time as a 
primary or secondary brake system failure is likely to be extremely 
rare.
Comments on the Proposed Two-Year Lead Time
    Trucking industry commenters and NADA argued that, for standard 
three-axle tractors, a two-year lead time is adequate to meet a 25 
percent reduction in stopping distance. No specific recommendations 
were offered for two-axle or severe service tractors, although ATA 
suggested a two-stage implementation strategy for standard three-axle 
tractors and all other tractors. These commenters also stated that if 
the agency decides on a 30 percent reduction in stopping distance, 
longer lead times would be required for brake system development and 
evaluation.
    Haldex and other commenters also recommended that the stopping 
distance reduction be timed as to not coincide with the 2010 effective 
date for new engine emission standards, set to become effective by the 
Environmental Protection Agency.
Vehicle Modifications Necessary To Meet Proposed Reductions in Stopping 
Distance
    Commenters from the trucking and brake industry stated that the 
largest percentage of improvements in stopping distance would be 
achieved by using more powerful steer axle brakes; either enhanced drum 
brakes (larger in width and/or diameter than standard drum brakes) or 
disc brakes. Most commenters added that more powerful brakes on the 
drive axles would further contribute to braking performance. 
Freightliner indicated that 97 percent of its fleet would require brake 
improvements to meet a 25 percent stopping distance reduction.
    Commenters from the trucking industry suggested, but provided 
little specific information on, other modifications to the vehicle that 
may be necessary to achieve the improved braking performance. These 
modifications include chassis structural analysis, redesign, and 
validation. TMA stated that packaging larger steer axle brakes could 
result in steering problems. On the other hand, brake suppliers 
suggested that these issues could be resolved.
    For two-axle tractors, several commenters stated that instability 
could prove to be a problem. Accordingly, TMA stated that for two-axle 
tractors with a short wheelbase, the following modifications would be 
necessary to allow the tractor to comply with a 30 percent reduction in 
the FMVSS No. 121 test: (1) Steer axle brakes would need to be 
enhanced; and (2) drive axle brake torque would need to be reduced to 
prevent wheel lockup (a condition which would prove hazardous during 
normal road braking situations). TMA indicated that these problems 
could be mitigated by added electronic stability systems, but that such 
systems could increase stopping distance and dramatically increase 
cost.
Margin of Compliance Issues
    Commenters on this issue stated that tractor manufacturers target a 
10 percent margin of compliance to account for test conditions and 
vehicle variability. Haldex stated that with a 10 percent margin of 
compliance on a 25 percent reduction in stopping distance, 
manufacturers would strive to achieve a total reduction in stopping 
distance of 35 percent.
Cost and Weight of Improved Braking Systems
    Few commenters provided information on the issues of cost and 
weight of improved braking systems in response to NHTSA's request. 
Freightliner provided cost information on improved foundation brakes, 
but without supporting data. According to Freightliner's figures, 
installing enhanced drum brakes on a three-axle tractor would add $222 
to the cost,

[[Page 37129]]

while adding disc brakes would cost an additional $1,627; the cost of 
adding disc brakes to a two-axle tractor would be $963. TMA commented 
that for two-axle and severe service tractors, NHTSA did not provide a 
cost analysis, and it argued that increasing stopping performance would 
result in cessation of production of certain vehicles manufactured in 
low volumes because manufacturers would not be able to amortize the 
manufacturing/engineering costs, which would in turn limit market 
choice.
    With regard to weight, Bendix stated that, currently, the heaviest 
drum brake weighs 32 lbs. more than the lightest disc brake, while the 
heaviest disc brake weighs 134 lbs. more than the lightest drum brake. 
WABCO stated that its disc brakes are equivalent in weight to high 
performance drum brakes.
Brake Balance Issues With Existing Trailers
    Commenters provided relatively little information on the issue of 
brake balance with existing trailers. Truck manufacturers stated that 
brake balance information will need to be further evaluated. Some brake 
manufacturers provided comments as well. For example, Bendix stated 
that its tests of disc-braked tractors had shown no objectionable brake 
balance issues. ArvinMeritor, however, stated that if stopping distance 
were reduced by more than 25 percent, drive axle torque would need to 
be increased, which would cause disruptive issues with the existing 
trailer fleet.
Braking Performance of Single-Unit Trucks
    Commenters provided relatively little information regarding single-
unit trucks. Haldex and Bendix suggested that further testing needs to 
be done, and that the government should work with industry to develop 
test data on the subject. Bendix stated that currently, single-unit 
trucks have a higher center of gravity than tractors, and that their 
stopping distances are about 15 percent shorter than tractors.
Developments in Advanced ABS and ECBS Systems and Their Effects on 
Stopping Distance Performance
    Several brake suppliers provided comments on the state of advanced 
ABS and ECBS on stopping distance performance. Specifically, WABCO 
stated that currently, ABS systems installed on tractors uses modified 
individual regulation (MIR), which reduces yaw movement \15\ on split-
coefficient road surfaces. According to the commenter, with larger 
foundation brakes, this system should not require significant 
modification, and it could help alleviate potential problems with 
larger brakes. Bendix also stated that electronic stability programs 
for rollover prevention and yaw stability are available on a variety of 
truck tractors.
---------------------------------------------------------------------------

    \15\ Yaw movement refers to vehicle rotation producing lateral 
sliding, due to tires on one side of the road producing more 
friction than tires on the other side.
---------------------------------------------------------------------------

    Haldex stated that ECBS may improve stopping distance by reducing 
the interval it takes between the time when the vehicle operator 
depresses the brake pedal to the time when brake forces are actually 
generated. However, Haldex also stated that because FMVSS No. 121 
requires redundant brake control systems, ECBS is not a viable option 
for heavy vehicles at this time. Haldex, like a number of other 
commenters, stated that advanced ABS does not reduce stopping distance.
Dynamometer Testing Requirements
    Truck manufacturers and brake suppliers both recommended that there 
be no changes to the FMVSS No. 121 dynamometer requirements. Some brake 
manufacturers, such as Haldex and HDBMC, stated that current 
dynamometer testing procedures in FMVSS No. 121 impose no appreciable 
limitations on the useable brake torque, and expressed concern that 
changes in dynamometer requirements could have the effect of limiting 
their options.
    Arvin Meritor and Bendix stated that they were planning on 
conducting further dynamometer testing, and would present the results 
to NHTSA. However, NHTSA has not received any additional information on 
this issue.
Brake Burnish Issues
    A comment by HDBMC stated that in order to achieve a reduction in 
stopping distance, higher torque front brakes would be required on 
truck tractors. According to the commenter, the higher torque front 
brakes would do more of the work during burnish, thus lowering the rear 
brake temperatures and reducing the conditioning of the rear brakes. 
HDBMC stated that coupled with the trend toward wider rear brake 
configurations, this will result in lower temperatures for rear brakes, 
and the critical temperature needed to properly condition the rear 
brakes would not be achieved. In order to address this issue, HDBMC 
recommended the agency reinstate the FMVSS No. 121 burnish procedure 
that existed prior to 1993. HDBMC also stated that because the 
specification for rear-axle burnishing was reduced when the standard 
was amended in 1993,\16\ parking brake performance has been negatively 
affected, and this problem would be expected to worsen under the 
agency's reduced stopping distance proposal.
---------------------------------------------------------------------------

    \16\ Docket  2005-21462-20.
---------------------------------------------------------------------------

    Arvin Meritor also commented on the burnish issue, requesting that 
an optional burnish procedure be added to the FMVSS No. 121 dynamometer 
test. The commenter's recommended procedure calls for six optional 
stops, using 100 PSI pressure from a starting speed of 60 mph, at the 
conclusion of the 350 [deg]F brake burnish.
Comments on Tractor Stopping Distance Data
    Comments from manufacturers raised two objections to the stopping 
distance data provided by NHTSA. To begin with, several commenters 
stated that the agency's proposal was non-specific, because it 
specified a range of potential stopping distance reductions, rather 
than a pinpoint proposal. Further, commenters stated that NHTSA 
performed testing only on typical three-axle tractors. For example, TMA 
stated that the absence of data on two-axle and severe service tractors 
should preclude the agency from issuing a rulemaking on those types of 
tractors at this time. TMA and Bendix provided their own testing data 
from tractors with enhanced foundation brakes, which in general showed 
significant improvements in performance.
    With regards to the Radlinski testing data referred to in the NPRM, 
few commenters provided specific comments. Instead, most commenters 
simply noted that the data were limited to standard three-axle 
tractors. Bendix added that it believes the Radlinski test data is 
representative of improvements that can be achieved.
    A cooperative testing system for tractor stopping distance was 
recommended by a variety of commenters, including International, 
Freightliner, HDBMC, and Arvin Meritor. In addition, the TMA 
recommended the agency initiate a test program for two-axle and severe 
service tractors.
In-Use Truck Brake System Maintenance
    Several commenters (truck manufacturers and brake suppliers) 
commented on the need for better servicing and maintenance of truck 
brakes, noting that in-service brakes frequently fall short of the 
standards set for brakes sold with new vehicles. Brake

[[Page 37130]]

Pro stated that the vast majority (85 percent) of trucks, tractor-
trailers, and trailers in North America have had some form of brake 
system component maintenance work or replacement work done on them, and 
would no longer necessarily meet the new vehicle stopping distance 
standards. TMA stated that 45 percent of trucks involved in crashes 
where brakes were the primary avoidance system had non-compliant 
brakes.
Reduced Test Speed Stopping Distance Requirements
    HDBMC and Bendix argued that brake system reaction time is not 
taken into account in the NPRM's proposed tables in the reduced speed 
test requirements. They argued that this resulted in unrealistic 
stopping distances. Both commenters provided recommendations for 
adjusting the lower test speed stopping distances to account for brake 
system reaction time.
Cargo Securement
    OOIDA commented that if tractors with improved brake systems are 
able to achieve higher deceleration rates, this could affect the safety 
of cargo securement systems, and they provided information on the 
Federal Motor Carrier Safety Administration's (FMCSA's) recent 
regulatory changes in this area.\17\
---------------------------------------------------------------------------

    \17\ This regulation assigns certain g-forces within which cargo 
securement devices and systems must contain the vehicle's cargo 
load. See 49 CFR 393.102.
---------------------------------------------------------------------------

III. The Final Rule and Response to Public Comments

a. The Final Rule

i. Summary of Requirements
    In light of the estimated benefits, in terms of lives saved and 
property damage avoided, we are upgrading the brake performance 
requirements of FMVSS No. 121 for air-braked tractors. The requirements 
of this regulation have been drafted so as to advance the safety and 
braking performance of truck tractors without imposing overly high 
costs on the trucking industry or requiring technical advances beyond 
what are available in the commercial market today. In overview, the 
final rule specifies 30 percent decreases in required stopping distance 
for the vast majority of air-braked tractors. The rule also sets 
somewhat less stringent requirements for a small percentage of truck 
tractors in light of practicability concerns.
    Specifically, the upgrade to FMVSS No. 121 set forth in this final 
rule specifies a 30 percent reduction in stopping distance that is 
expected to apply to approximately 99 percent of air-braked tractors. 
The reduction lowers the maximum stopping distance from the current 
distance of 355 feet to 250 feet when tractors are tested in the 
loaded-to-GVWR condition from 60 mph. For three-axle tractors with a 
GVWR of over 70,000 pounds, and four (or more) axle tractors with a 
GVWR of over 85,000 pounds, the stopping distance requirement in the 
loaded-to-GVWR condition is being set at 310 feet.
    The decision to adopt a 250-foot stopping distance is based on the 
agency's analysis of the potential safety benefits that may be achieved 
by using enhanced braking technology and the costs and feasibility of 
upgrading the requirements to the new level. NHTSA research 
demonstrated that for most tractors--including standard three-axle 
tractors which comprise over 80 percent of the commercial fleet--the 
upgrade could be achieved at relatively low cost and with minimal 
impact to tractor design specifications. Specifically, research 
demonstrated that relatively low-cost enhanced drum brakes would be 
adequate to achieve stopping distances within 250 feet, with a margin 
of compliance of 10 percent.\18\ For most of the remaining tractors, 
including two-axle and most severe service tractors, NHTSA concluded 
that the upgraded requirements were also attainable, although more 
powerful disc brakes and other design changes may need to be 
implemented in order to stop within the required limits without 
detrimental effects on stability or brake balance.
---------------------------------------------------------------------------

    \18\ The issue of margin of compliance is discussed later in 
this document.
---------------------------------------------------------------------------

    For a small number of severe service tractors with three axles and 
a GVWR of 70,000 pounds or more, or equipped with four or more axles 
and a GVWR of 85,000 pounds or more, the agency is setting a 310-foot 
requirement (similar to the current loaded-to-GVWR requirement for air-
braked single-unit trucks). This is due to the fact that even when 
fitted with current disc brakes at all wheel positions, it has been 
demonstrated that these vehicles cannot achieve 30 percent reductions 
in stopping distance.
    For all tractors, the stopping distance requirement in the lightly-
loaded test condition is set at 235 feet, as it was determined that 
with improved foundation brakes, this requirement is well within the 
capabilities of all heavy truck manufacturers to achieve.
    The required improvement in stopping distance performance is 
limited to service brakes, and does not include emergency braking. 
Several commenters argued persuasively that improvements to emergency 
braking performance could have deleterious effects on lateral stability 
and control, due to modifications to the ABS algorithms that would be 
required to meet the emergency braking requirements. Further, there are 
no data to show that tractors operating in the bobtail condition (i.e., 
with no trailer attached) and experiencing an emergency braking 
situation are contributing to the heavy truck crash problem.
ii. Compliance Dates
    There are two compliance dates on which the new stopping distance 
requirements become mandatory. For standard three-axle tractors, the 
new stopping distance requirements become mandatory on August 1, 2011. 
``Standard three-axle tractor'' refers to typical three-axle tractors 
that have a steer axle GAWR less than or equal to 14,600 pounds and a 
combined drive axle GAWR less than or equal to 45,000 pounds, for a 
total GVWR equal to or less than 59,600 pounds. The agency's test data 
show that, for these tractors, compliance with the new stopping 
distance requirements can be readily achieved.
    The compliance date for all two-axle tractors, as well as severe 
service tractors with a GVWR greater than 59,600 pounds, is August 1, 
2013. NHTSA's test data indicate that two-axle tractors can meet a 250-
foot loaded-to-GVWR stopping distance requirement with improved brake 
systems. However, additional lead time is needed for manufacturers to 
more fully evaluate new brake systems to ensure compatibility with 
existing trailers and converter dollies when used in multi-trailer 
combinations. Further, more time is needed to minimize the risk of 
vehicle stability and control issues. With regard to severe service 
tractors, the available test data and analysis indicate that the 
respective 250-foot and 310-foot stopping distance requirements can be 
met by improved brake systems. However, as only limited development 
work has been performed, these vehicles require additional lead time to 
ensure complete testing and validation of new brake systems.
iii. Margin of Compliance
    Manufacturers need to ensure that all of their vehicles meet a test 
requirement established by a Federal safety standard. To account for 
variability, including vehicle-to-vehicle variability, they typically 
design vehicles with a margin of compliance.

[[Page 37131]]

    With regard to stopping distance, the comments stated that the 
traditional industry compliance margin is 10 percent.\19\ We note that 
this does not necessarily mean that manufacturers do not sometimes 
certify vehicles with a smaller margin of compliance. However, they do 
need to take whatever steps are necessary to ensure that each vehicle 
they certify complies with applicable requirements.
---------------------------------------------------------------------------

    \19\ Bendix stated, for example, that the traditional industry 
compliance margin is 10 percent. Docket  NHTSA-2005-21462-
24, p. 5. TMA referred to ``a requisite 10 percent compliance 
margin.'' Docket  NHTSA-2005-21462-34.
---------------------------------------------------------------------------

    We believe that calculations of 10 percent compliance margins are 
useful for analytical and discussion purposes in considering what 
stopping distance requirements are appropriate and practicable.
    We note that in this document, in many cases we have cited a ten 
percent margin of compliance from the average stopping distance that a 
vehicle test has demonstrated in testing despite the fact that a 
vehicle is required to meet the requirement in only one of six stops. 
However, since there is generally little variability in the distance 
achieved among multiple stops due largely to the incorporation of anti-
lock braking systems, it generally doesn't make much difference whether 
we look at the average or best stop distance.

b. Summary of NHTSA Testing and Results Conducted After Publication of 
the NPRM

i. Testing Conducted on Three-Axle Truck Tractors
    Available test data demonstrate that typical three-axle tractors 
can meet a requirement with a 30 percent reduction in stopping distance 
using only enhanced drum brakes, the least expensive type of improved 
foundation brake available. NHTSA used the same definition for a 
``typical three-axle tractor'' as TMA and HDBMC, which is a 6x4 
configuration (three axles with six wheel positions; a non-driven steer 
axle and two rear drive axles) with a GVWR below 59,600 pounds, a steer 
axle with a GAWR equal or less than 14,600 pounds, and tandem drive 
axles rated equal or less than 45,000 pounds total capacity. According 
to the test data from the Radlinski \20\ reports (7 tests), typical 
three-axle tractors with enhanced S-cam drum brakes at all wheel 
positions achieved the target 30 percent reduction in stopping 
distance, with margins of compliance (based on a 250-foot stopping 
distance requirement) ranging from 12 to 18 percent. This is superior 
to the ten percent threshold used by most manufacturers.
---------------------------------------------------------------------------

    \20\ Docket  NHTSA-2005-21462-5, 6, 7.
---------------------------------------------------------------------------

    NHTSA also conducted testing at its Vehicle Research Test Center 
(VRTC), using a variety of foundation brake systems.\21\ The VRTC tests 
of two tractors showed that with disc brakes at all wheel positions, 
both tractors could meet the 30 percent target with compliance margins 
between six and 13 percent, while one of these tractors could meet the 
30 percent target using a hybrid (disc/drum) configuration with disc 
brakes on the steer axle and standard drive axle drum brakes (16.5'' 
diameter drum x 7'' wide brake linings) with a six percent margin of 
compliance.
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    \21\ See Class 8 Truck Tractor Braking Performance Improvement 
Study, available at: http://www.nhtsa.dot.gov/staticfiles/DOT/NHTSA/NRD/Multimedia/PDFs/VRTC/ca/capubs/DOTHS809700.pdf
---------------------------------------------------------------------------

    The above tests show that disc brakes provide an alternative means 
to achieve compliance with a 30 percent reduction in the stopping 
distance requirement. All of the all-disc braked examples could meet or 
exceed the ten percent margin of compliance with one exception (one 
VRTC test). Moreover, the agency is confident that the performance of 
that one example could readily be improved by increasing the torque 
output of that disc brake (or switching to newer, readily-available, 
and more powerful disc brakes).
    Results for the hybrid combination of disc brakes on the steer axle 
and standard drum brakes on the drive axle were mixed, with one tractor 
meeting the 30 percent reduction in stopping distance with a six 
percent margin, even though the performance would be expected to match 
or exceed the performance of a tractor with enhanced drum brakes at all 
wheel positions (which, as the Radlinski testing showed, was able to 
meet the 30 percent reduction with margins over ten percent). Also, the 
agency did not test any hybrid configurations using enhanced drum 
brakes (standard 16.5'' x 7'' drive axle brakes were used in the 
agency's hybrid tests). Based on these results, one conclusion that can 
be drawn regarding cost is enhanced drive axle S-cam drum brakes will 
be necessary, at a minimum, whether used on the steer or drive axles of 
a standard three-axle tractor, because the available data show that 
standard drum brakes (15'' x 4'' steer, 16.5'' x 7'' drive) have not 
been able to achieve the necessary performance to meet the requirements 
in this final rule.
ii. Testing Conducted on Two-Axle Truck Tractors
    NHTSA's testing after publication of the NPRM indicated that a 
Sterling 4x2 tractor is capable of complying with a 250-foot stopping 
distance with enhanced foundation brakes.\22\ In the VRTC testing, the 
test tractor was purchased new and was originally equipped with larger 
steer axle S-cam drum brakes of 16.5'' diameter by 5'' lining width, 
and standard S-cam drum brakes (16.5'' x 7'') on the drive axle. In the 
as-received state (approximately 1,000 miles of normal road use, half 
of the time in the bobtail condition and half of the time towing a 48-
foot flatbed trailer), the average stopping distance (based on six 
stops) was 241 feet from 60 mph at GVWR plus 4,500 pounds of weight on 
the single axle, unbraked control trailer as specified in FMVSS No. 
121. However, when the foundation brakes were replaced with all new 
components and subjected to a complete FMVSS No. 121 burnish, the 
average stopping distance increased to 332 feet. Further investigation 
of this problem indicated that the replacement brake linings generated 
less torque than the original linings. This is discussed in further 
detail in the brake burnish section below.
---------------------------------------------------------------------------

    \22\ Docket  NHTSA-2005-21462-39, p. 25.
---------------------------------------------------------------------------

    The same VRTC test tractor was also tested with disc brakes. The 
first configuration of the VRTC testing was a hybrid brake system test. 
In this test, the tractor was equipped with disc brakes on the steer 
axle and the standard S-cam drum brakes on the drive axle (hybrid brake 
configuration), and again subjected to an FMVSS No. 121 burnish. The 
average loaded-to-GVWR stopping distance was 223 feet, meeting the 
proposed 250-foot stopping distance requirement with a margin of 
compliance of 11 percent. In the final configuration, the tractor was 
equipped with disc brakes on both the steer axle and drive axle. Here, 
the average loaded-to-GVWR stopping distance was 200 feet, a 20 percent 
margin of compliance.
iii. Testing Conducted on Severe Service Tractors
    After publication of the NPRM, the agency conducted additional 
testing on a severe service truck judged to have similar service 
braking characteristics as a tractor of similar size and weight 
dimensions.\23\ The test truck was a three-axle Peterbilt Model 357 
with a steer axle GAWR of 18,000 pounds and tandem drive axle GAWR of 
44,000 pounds. The total GVWR was 62,000

[[Page 37132]]

pounds, and the wheelbase was 275 inches. The vehicle was purchased as 
a chassis-cab and manufactured as a single-unit truck, and a load frame 
was attached to the frame rails for test loading purposes. Although a 
single-unit truck differs in many ways from a truck tractor, based on 
our testing we found that the single-unit truck was likely to 
experience similar, if more severe, dynamic load transfer onto its 
steer axle than if it had been tested as a tractor, thereby rendering 
it a reasonable surrogate for a severe service tractor in this context.
---------------------------------------------------------------------------

    \23\ Docket  NHTSA-2005-21462-39, p. 10.
---------------------------------------------------------------------------

    The substantive difference in braking performance for this vehicle 
in the truck versus tractor configuration would be apparent in 
emergency braking performance, for which the truck configuration would 
likely need to utilize spring brake modulation to meet the stopping 
distance requirement at GVWR (this is because there is no equivalent 
test requirement for tractors, since emergency braking requirements 
only apply in the unloaded condition), and there are also differences 
in parking brake performance requirements for single-unit trucks and 
tractors. However, neither of these brake system differences were 
factors during the normal service brake tests for the Peterbilt truck.
    The truck used in the VRTC testing was tested with a variety of 
brake configurations in order to determine its stopping distance 
performance. The truck was originally manufactured with enhanced 16.5'' 
x 6'' S-cam drum brakes on the steer axle, and standard 16.5'' x 7'' S-
cam drum brakes on the drive axles. It was also equipped with a 6S/6M 
ABS system that should provide the highest braking efficiency because 
the braking forces are modulated individually at each wheel position. 
With the OEM S-cam drum brakes, the average loaded-to-GVWR, 60 mph 
stopping distance was 280 feet, which would not meet the enhanced 250 
feet stopping distance requirement. In a hybrid configuration with disc 
brakes on the steer axle and standard S-cam drum brakes on the drive 
axles, the average stopping distance was 251 feet. With disc brakes at 
all wheel positions, the average stopping distance was 224 feet, 
meeting the target reduced stopping distance with a better than 10 
percent margin of compliance.
    Another test condition that was evaluated for the severe service 
Peterbilt truck was to up-load the vehicle to a GVWR of 76,000 pounds 
and conduct 60 mph stops using all disc brakes. The average stopping 
distance for six stops was 254 feet and the minimum stopping distance 
out of the six stops was 251 feet. The standard deviation of all six 
stops was 3.2 feet, indicating that there was very little stop-to-stop 
variability, and thus this vehicle achieved very repeatable performance 
with disc brakes.\24\
---------------------------------------------------------------------------

    \24\ Docket  NHTSA-2005-21462-39, p. 23.
---------------------------------------------------------------------------

    In July 2006, the VRTC also ran simulation testing based on the 
results of the Peterbilt truck testing to determine braking performance 
at 80,000 pounds GVWR.\25\ This study used the Truck Sim vehicle 
dynamics modeling software with which the VRTC staff has extensive 
experience, including validation of many modules (such as foundation 
brakes and ABS control systems) used in the program. This simulation 
study determined that with the same all-disc brake configuration, but 
with the GVWR increased to 80,000 pounds, a heavy truck's estimated 
stopping distance would be 280 feet. By increasing the brake torque on 
the steer axle (using type 30 brake chambers in place of type 24 
chambers), the estimated stopping distance decreased to 262 feet at 
80,000 pounds GVWR. Additional parametric studies (by modeling further 
increases in brake torque at all wheel positions) showed that if brake 
torque could be increased sufficiently to utilize all available tire-
road friction, stopping distances as low as 227 feet could be achieved 
(meeting the 30 percent target with a nine percent margin of 
compliance). However, the agency is not aware that there are any 
available disc brakes currently capable of generating the requisite 
torque and that would also be able to be packaged within the available 
wheel envelope. Based upon this analysis, the agency has concluded that 
the 30 percent reduction in stopping distance may not be feasible for 
heavy truck tractors above 80,000 pounds GVWR.
---------------------------------------------------------------------------

    \25\ VRTC/R&D--Vehicle Modeling Research to Estimate Stopping 
Distances for 80,000-lb GVWR Trucks and Tractors Using Current Brake 
Technologies. Docket  NHTSA-2005-21462-39, p. 15.
---------------------------------------------------------------------------

c. Response to Public Comments

i. Straight-Line Braking Performance of Tractors With Improved Brake 
Systems
    In this section, we discuss data and arguments relating to the 
performance of tractors with improved braking systems. The purpose of 
this section is to address whether various tractor configurations are 
capable of meeting the proposed performance requirements of FMVSS No. 
121 with improved braking systems. In addition, we provide additional 
insight on what kind of improved brakes will be necessary for various 
tractor configurations to meet the requirements of the standard, and 
provide further refinement of our cost estimates. This portion of the 
final rule deals only with straight-line braking performance. Issues of 
stability, control, brake balance, burnish, and other issues are dealt 
with later in the rule.
1. Braking Performance of Typical Three-Axle Tractors With Improved 
Brake Systems in the Loaded-to-GVWR Condition
    In the NPRM, the agency proposed to amend the standard's fully-
loaded service brake stopping distance, at 60 mph, from the currently-
required 355 feet to a new, reduced distance in the range of 284 feet 
(20 percent reduction) to 249 feet (30 percent reduction). The agency 
requested comments on the proposed reductions in the required stopping 
distance.
    A number of commenters supported the agency's decision to reduce 
the stopping distance for typical three-axle tractors by 30 percent. 
Advocates and IIHS supported the 30 percent reduction proposal over the 
20 percent reduction proposal, citing the significantly higher 
estimated benefits in terms of the number of injuries, fatalities, and 
property damage prevented. Advocates also suggested that the agency 
should mandate the use of disc brakes in addition to the reduced 
stopping distances, arguing that under actual service conditions, disc 
brakes will out-perform hybrid systems and drum brakes because disc 
brakes are relatively immune to fade from either water or heat. IIHS 
also stated that an additional benefit of the reduced stopping distance 
would be encouraging the use of disc brake systems, citing similar 
fade-resistant attributes of disc brakes.
    One brake manufacturer, Bendix, commented that it supported a 30 
percent reduction in stopping distance for three-axle tractors, and 
submitted test data to support the feasibility of this requirement. 
Eight tests with disc brakes at all wheel positions showed that all of 
the tractors tested could meet the 30 percent target with compliance 
margins between 21 percent and 18 percent. Data on one hybrid three-
axle tractor showed that the 30 percent target was met with an eight 
percent margin of compliance. Finally, one all drum brake equipped 
tractor (drum brake sizes were not specified) met the 30 percent target 
with a 14 percent margin of compliance.
    The TMA recommended that the stopping distance for three-axle 
tractors be reduced by a maximum of 25 percent, a position shared by 
International, Haldex, and NADA. TMA supplied test results for three-
axle

[[Page 37133]]

tractors as well. For three-axle tractors equipped with all disc brakes 
(8 tests), the 30 percent target in stopping distance reduction was met 
with margins of compliance ranging from 10-20 percent. In hybrid 
configurations with disc brakes on the steer axle and enhanced drum 
brakes on the drive axles (eight tests) and in all enhanced S-cam drum 
configurations (eight tests), the margins of compliance ranged from two 
to 20 percent.
    In its comments, ArvinMeritor stated that for typical three-axle 
tractors to achieve tractor stopping distance reductions greater than 
25 percent, an increase in drive axle torque would be needed. Based on 
the vehicle testing conducted by NHTSA (see above, section III, B), the 
agency agrees with this comment, and recognizes that improved drive 
axle foundation brakes will be part of meeting a requirement that 
reduces stopping distance by 30 percent.
    For the final rule, the agency has decided to reduce the stopping 
distance for typical three-axle tractors in the loaded-to-GVWR 
condition, at 60 mph, from the currently-required 355 feet to 250 
feet.\26\ In arriving at this requirement, the agency reviewed the 
available test data of typical three-axle tractors with improved brake 
systems. That data showed that a 30 percent reduction is possible using 
a variety of enhanced brake systems. In addition, to ensure that the 
amended standard is practicable, the agency considered the margin of 
compliance that truck manufacturers typically would use during 
compliance to ensure that all similar production tractors would comply 
with the requirement, which specifies a target stopping distance of 225 
feet.
---------------------------------------------------------------------------

    \26\ A 30 percent reduction from 355 feet is, in fact, 249 feet, 
which the agency has rounded to an even 250 feet.
---------------------------------------------------------------------------

    Given the totality of the data provided by TMA and Bendix, NHTSA 
believes the test data demonstrate that for typical three-axle tractors 
a 30 percent reduction in stopping distance is readily achievable. In 
most cases a 10 percent margin of compliance was met or exceeded. Both 
NHTSA and commenters'data are consistent with the agency's position 
that a 30 percent reduction is feasible. For example, some tests 
demonstrate that typical three-axle tractors with enhanced drum brakes 
at all wheel positions are readily capable of attaining 30 percent 
reductions with more than a 10 percent margin of compliance, although 
the upper range (lowest performing) of the data from TMA on at least 
one tractor with enhanced drum brakes showed that the margin of 
compliance was approximately five percent.
    NHTSA does not agree with the recommendation from Advocates that it 
mandate disc brakes for use in all heavy truck tractors. NHTSA has not 
mandated the use of disc brakes because these presumed safety benefits 
have not been quantified, and no data to this extent was provided by 
Advocates. Further, we have no information as to what the net benefit 
of any safety benefit unique to disc brakes would be, and how it would 
compare to the increased costs of disc brakes.
    The agency believes that the available data demonstrate that 30 
percent reductions in stopping distance are readily achievable on 
typical three-axle tractors. A ten percent margin of compliance has 
been demonstrated for the majority of tractors using disc brakes and 
enhanced drum brakes (the exact percentage for margin of compliance 
cannot be determined for some of the data for which only ranges in 
performance for several tests were indicated). Therefore, the agency 
concludes that it is practicable to achieve 30 percent reductions in 
stopping distance when currently-available improved foundation brakes 
are applied to typical three-axle tractors. We also note that many 
tests demonstrate that enhanced drum brakes on the steer and drive 
axles were sufficient for many standard three-axle tractors to meet the 
30 percent reduction, allowing the lowest-cost option to be used for 
the vast majority of heavy truck tractors.
2. Braking Performance of Two-Axle Tractors With Improved Brake Systems 
in the Loaded-to-GVWR Condition
    NHTSA proposed in the NPRM to reduce the stopping distance for all 
truck tractors, which includes two-axle tractors. As discussed below, 
based on agency testing and comments received, the agency concludes 
that all two-axle tractors can meet the 30 percent reduction in 
stopping distance requirements with improved braking systems. Although 
the agency did not include test data on two-axle tractors when the NPRM 
was published, since that time, the agency has completed a foundation 
brake study at the VRTC on a typical two-axle tractor. In addition, 
testing data from the TMA and Bendix also indicate that two-axle 
tractors are capable of meeting a 30 percent reduction in stopping 
distance with a ten percent margin of compliance if equipped with disc 
brakes.
    While industry commenters generally did not support reducing 
stopping distance for two-axle tractors, TMA data submitted in response 
to the NPRM indicated that for regular service two-axle tractors (i.e., 
with a drive axle GAWR below 23,000 pounds), the 250-foot stopping 
distance requirement could be met using disc brakes.\27\ TMA tested 
two-axle tractors in hybrid brake configurations and an all-disc 
configuration. The first hybrid configuration (one test; disc brakes on 
the steer axle and standard 16.5'' x 7'' S-cam drum brakes on the drive 
axle) was able to meet the 250-foot requirement with a margin of 
compliance of approximately 12 percent. A second hybrid configuration 
(two tests; with disc brakes on the steer axle and enhanced 16.5'' x 
8.625'' S-cam drum brakes on the drive axle) indicated that both test 
vehicles met the 250 foot requirement, one with a margin of 
approximately 15 percent, and the other with a margin of only two 
percent. Finally, an all-disc configuration (one test) met the proposed 
30 reduction with a 22 percent margin of compliance.
---------------------------------------------------------------------------

    \27\ Docket  NHTSA-2005-21462-26, p. 5.
---------------------------------------------------------------------------

    TMA also provided supplemental comments in October 2006,\28\ with 
additional data on the performance of two-axle tractors with improved 
foundation brakes. Two tractors with disc brakes at all wheel positions 
indicated that the best of six stops ranged from 206 to 213 feet in the 
loaded-to-GVWR condition from 60 mph, indicating margins of compliance 
well over ten percent. A third tractor with a hybrid disc/drum 
configuration was able to stop in 221 feet, giving it a 12 percent 
margin of compliance. A fourth tractor with enhanced S-cam drum brakes 
at all wheel positions had a shortest stop of approximately 248 feet, 
and thus a marginal compliance with a 30 percent stopping distance 
reduction. Three tractors tested, when tested with standard drum 
brakes, could not meet a 250-foot stopping distance.
---------------------------------------------------------------------------

    \28\ Docket  NHTSA-2005-21462-35.
---------------------------------------------------------------------------

    Bendix also provided data indicating that two-axle tractors could 
meet the 30 percent stopping distance reduction.\29\ Bendix provided 
test data on the disc/drum hybrid configuration (two tests; and the 
drive axle drum brake sizes were not specified). In those tests, the 
average stopping distances for both tractors would meet the proposed 
250-foot requirement with a margin of compliance of 12 percent for one 
vehicle and nine percent for the other. Using the best of six stops for 
the poorer performing vehicle (225 feet, rather than the average 
stopping distance of 228 feet), the margin of compliance

[[Page 37134]]

increases to 10 percent. Bendix test data on all-disc brake two-axle 
tractors (two tests) indicated that both vehicles would meet a 250-foot 
stopping distance requirement and that the margins of compliance were 
19 and 14 percent based on the average of six stops in each test. The 
GAWRs for all two-axle tractor tests were 22,999 pounds or less on the 
drive axle and 12,000 pounds or less on the steer axle (i.e., they were 
not severe service two-axle tractors).
---------------------------------------------------------------------------

    \29\ Docket  NHTSA-2005-21462-24-0001, p. 9.
---------------------------------------------------------------------------

    Finally, in its original comments, TMA stated that drive axle brake 
torque would need to be reduced to prevent wheel lockup (a condition 
which would prove hazardous during normal road braking situations). 
However, we believe ABS, which has been required on all new truck 
tractors manufactured on or after March 1, 1997, prevents wheel lockup. 
Hence, this comment is not persuasive.
    Based on the testing data accumulated by NHTSA and provided by the 
commenters, the agency has concluded that meeting a 30 percent 
reduction in stopping distance is achievable for currently-produced 
two-axle tractors with at least a 10 percent margin of compliance with 
all-disc configurations. To a lesser extent, the hybrid disc/drum 
configurations (some of which had good margins of compliance, and some 
of which had poor margins) may also be able to achieve the 30 percent 
reduction in stopping distance.
3. Braking Performance of Severe Service Tractors With Improved Brake 
Systems in the Loaded-to-GVWR Condition
a. Definition of Severe Service Tractor and Specific Safety Benefits
    With the exception of certain vehicles with extremely high GVWRs or 
GAWRs that are excluded from the requirements of Standard No. 121, the 
reduced stopping distance requirements proposed in the NPRM were to 
apply to all severe service tractors. For purposes of this document, 
NHTSA is using TMA's definition of a three-axle severe service tractor, 
as a three-axle tractor having a steer axle GAWR greater than 14,600 
pounds and tandem drive axles with a total GAWR greater than 45,000 
pounds. In addition, severe service tractors include those tractors 
with twin steer axles, auxiliary axles (e.g., lift axles), and/or 
tridem drive axles. Chassis configurations include 6x4, 8x4, 8x6, 10x6, 
and 14x4 layouts. Based on comments from TMA and Freightliner, the GVWR 
of severe service tractors is greater than 59,600 pounds and can exceed 
100,000 pounds. The commenters explained that severe service tractors 
are used in special purpose applications such as oil field service, 
extreme heavy hauling, transporting earth moving equipment, and 
logging. The commenters further stated that operation is both on-road 
and off-road, and in some cases, on-road use is at relatively low 
speeds with the tractor-trailer combinations being accompanied by 
escort vehicles.
    Freightliner \30\ stated that severe service tractors comprise 
approximately seven percent of tractor production and are involved in 
5.6 percent of fatal tractor crashes, according to the UMTRI report on 
Class 8 tractors involved in fatal crashes (included with TMA's 
comments).\31\ To the extent possible, the agency compares fatal crash 
involvement rates of vehicle types based upon fatalities per 100 
million vehicle miles traveled (VMT) (see Section II of the NPRM). As 
described in the NPRM, tractors have a lower overall crash rate per 100 
million VMT compared to light vehicles (passenger cars, light trucks, 
and SUVs), but are over-represented in fatal crashes. The UMTRI report 
submitted by TMA \32\ did not analyze tractor crash data for the three 
types of tractors studied (typical three-axle, two-axle, and severe 
service tractors) based upon VMT exposure, and the agency is not aware 
such VMT exposure data being available from the known crash data 
sources. Based upon the comments received, it appears that the on-road 
mileage exposure for severe service tractors is lower than for typical 
three-axle or two-axle tractors.\33\ Nonetheless, the 5.6 percent 
fatality involvement rate does not indicate that severe service 
tractors are underrepresented in fatal crashes to an extent that the 
agency should consider excluding them from this final rule. Given the 
potential safety benefits, we believe the deciding factor in 
determining the loaded-to-GVWR stopping distance requirements for 
severe service tractors under this final rule should be dependent on 
the best performance that can be achieved using the available improved 
brake systems.
---------------------------------------------------------------------------

    \30\ Docket  NHTSA-2005-21462-25.
    \31\ Docket  NHTSA-2005-21462-26.
    \32\ Docket No. NHTSA-2005-21462-26; see attachment, p. 16.
    \33\ Docket  NHTSA-2005-21462-26, p. 11.
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    In its comments, TMA delineated several broad categories of severe 
service tractors that the agency believes comprise highly relevant 
categories. The first is three-axle severe service tractors with GVWRs 
ranging from approximately 60,000-70,000 pounds. These tractors have a 
steer axle GAWR in the 13,000-14,500-pound range and tandem drive axles 
rated in the approximate range of 46,000-55,000 pounds (as depicted in 
Figure 5 in TMA's April 2006 comments, which shows a three-axle tractor 
towing double trailers.) The second category of severe service tractors 
described by TMA are three-axle severe service tractors with GVWRs 
above 70,000 pounds. Finally, there are severe service tractors in 8x4, 
8x6, 10x6, 14x4, and other configurations. This group of vehicles is 
used in special purpose or extreme heavy haul applications (as depicted 
in Figure 6 of TMA's comments, which shows a 10x6, twin-steer tractor 
with tridem drive axles.) Based upon the information provided to the 
agency in several ex parte meetings that have been held since the 
publication of the NPRM,\34\ the typical weight ratings for the 10x6 
tractor photographed would be 14,500 pounds GAWR for each steer axle 
and 20,000 pounds for each drive axle, yielding a GVWR of 89,000 
pounds. This tractor would not be excluded from FMVSS No. 121 based on 
its axle ratings. Other unusual tractor configurations would also tend 
to have high GVWRs over 70,000 pounds and still be subject to FMVSS No. 
121.
---------------------------------------------------------------------------

    \34\ Memorandums of ex-parte meetings provided in Docket No. 
NHTSA-2005-21462-36.
---------------------------------------------------------------------------

b. Three-Axle Severe Service Tractors With a GVWR Under 70,000 Pounds
    Based on the agency's testing, as well as test data provided by the 
commenters, NHTSA believes that severe service three-axle tractors with 
a GVWR under 70,000 pounds can meet a 250-foot stopping distance 
requirement using enhanced foundation brake systems. VRTC test results 
and commenter data lead the agency to believe that three-axle severe 
service tractors with a GVWR between 60,000 and 70,000 pounds are 
capable of meeting the 30 percent reduction in stopping distance using 
available enhanced braking systems.
    NHTSA's testing indicated that lower-GVWR three-axle severe service 
tractors will be able to meet a 250-foot stopping distance requirement. 
Here, NHTSA refers to the Peterbilt truck, tested by the VRTC, which is 
very similar to three-axle severe service tractors of the 60,000-70,000 
pounds GVWR category. As stated above, the VRTC testing used a single-
unit truck with comparable braking performance to a severe-service 
three-axle truck tractor. This tractor, when equipped with disc brakes 
and tested at a GVWR of 62,000 pounds, was able to meet the 250-foot 
stopping distance requirement with a 10 percent margin of 
compliance.\35\ Therefore, the

[[Page 37135]]

agency believes that it is practicable to require similarly-configured 
tractors to achieve similar braking performance.
---------------------------------------------------------------------------

    \35\ Docket  NHTSA-2005-21462-40.
---------------------------------------------------------------------------

    TMA's supplemental comments include data that enhance NHTSA's 
confidence in the practicability of this requirement. The data indicate 
that for lower GVWR three-axle severe service tractors, a 250-foot 
stopping distance and a ten percent margin of compliance can be 
achieved for three-axle, all-disc braked tractors of 62,000 and 66,000 
pounds GVWR.\36\ Both VRTC and TMA test data show that three-axle 
severe service tractors under 70,000 pounds GVWR are capable of meeting 
the reduced stopping distance with improved foundation brakes and can 
also achieve a 10 percent margin of compliance.
---------------------------------------------------------------------------

    \36\ TMA comment of October 2006, docket  NHTSA-2005-
21462-35.
---------------------------------------------------------------------------

    In its original comments,\37\ TMA also stated that building a 
severe service tractor with improved brakes would result in production 
of a vehicle that is not commercially viable. TMA argued that such a 
vehicle would have far too aggressive brake linings, which would result 
in chatter and frequent failures of various brake components. TMA 
stated that this would be a commercially non-viable product. NHTSA 
notes that in its later comments submitted on October 2006, TMA tested 
a severe service tractor with disc brakes that was able to meet the 
proposed reduced stopping distance, and the organization did not 
further discuss these problems. NHTSA also notes that when equipped 
with modern enhanced braking systems, similarly-configured vehicles can 
meet the proposed requirements without the problems that TMA foresaw in 
its April 2006 comments. Therefore, the agency believes that the 
problems TMA described are obviated by the use of disc brakes.
---------------------------------------------------------------------------

    \37\ Docket  NHTSA-2005-21462-26.
---------------------------------------------------------------------------

    In October 2006, TMA submitted supplemental comments that included 
additional information on severe service tractor stopping distance 
performance. The TMA testing included six drum and six disc brake 
configurations, performed on vehicles with three different drive axle 
GAWRs. TMA stated that the disc brakes used in these tests were 
prototype models that had not been fully tested for production (as 
dynamometer and other test data were not yet available). The agency 
assumes that these would be the largest practical disc brakes that 
would work within the available wheel and suspension envelope.
    TMA's test results are discussed below, but the result we believe 
to be most noteworthy is that the TMA testing indicated that the 
proposed 30 percent reduction in stopping distance could be achieved 
using disc brakes. To summarize the TMA test results, when tested at a 
steer axle weight of 20,000 pounds and a tandem drive axle weight of 
46,000 pounds, yielding a GVWR of 66,000 pounds, the baseline all-drum 
brake configuration (it was not specified whether the drum brakes were 
standard or larger sized) had a stopping distance of 262 feet. Testing 
of a hybrid configuration using the prototype disc brakes on the steer 
axle yielded a stopping distance of 229 feet, thus meeting the target 
with an eight percent margin of compliance. Finally, when tested with 
disc brakes at all wheel positions; the stopping distance was 223 feet, 
yielding an 11 percent margin of compliance. We note that the data for 
the all-disc brake test are consistent with the performance obtained by 
VRTC in its tests of the Peterbilt truck with a 62,000 pounds GVWR.
c. Three-Axle Severe Service Tractors With GVWR Over 70,000 Pounds
    In contrast to three-axle tractors with a GVWR between 59,600-
70,000 pounds, agency testing and commenters' data indicate that it is 
not practicable at this time for higher-GVWR three-axle severe service 
tractors to meet a 250-foot stopping distance requirement. In making 
this determination, the agency carefully considered its own data, as 
well as the data on high-GVWR three-axle truck tractors provided by the 
TMA in its comments. Nonetheless, NHTSA believes that improvements in 
stopping distance for these vehicles should be pursued, albeit at a 
level less than a 30 percent reduction. TMA's supplemental comments 
indicate that tractors with very high GVWRs (with regard to three-axle 
tractors, these have single axle weight ratings of 26,000 pounds or 
more, or tandem axle weight ratings of 52,000 pounds or more) make up 
less than one percent of annual tractor production.
    The agency believes that severe service tractors over 70,000-pound 
GVWR can meet the stopping distance requirements for similar vehicles 
that are configured as single-unit trucks rather than tractors, because 
similarly-configured single unit trucks are currently being 
manufactured in compliance with FMVSS No. 121. As the service brake 
stopping distance requirement for single-unit trucks is 310 feet in the 
loaded-to-GVWR condition, the agency believes that specifying this 
standard on severe service tractors of similar weight is a practicable 
alternative to a 30 percent reduction in stopping distance.
    TMA provided simulation test data for hybrid and all-disc 
foundation brake configurations of three-axle severe service tractors 
with a GVWR over 70,000 pounds.\38\ The data that TMA used in its 
comments were based upon unspecified simulations, presumably similar to 
the Truck Sim work performed by VRTC. A footnote in the supplemental 
TMA submission indicates that one all-drum brake configuration at 
72,000 pounds GVWR was verified by actual vehicle testing. The 
simulation results for a 72,000-pound GVWR tractor (20,000-pound steer 
axle load and 52,000-pound tandem drive axle load) estimated that the 
hybrid configuration would achieve a 248-foot stopping distance (within 
the 30 percent reduction target, but with little margin of compliance). 
When equipped with disc brakes at all wheel positions, the stopping 
distance was estimated at 242 feet, which would meet a 30 percent 
reduction in stopping distance with a three percent margin of 
compliance. The configuration with drum brakes \39\ at all wheel 
positions was road tested at 72,000 pounds GVWR and had a stopping 
distance of 285 feet, above the 250-foot limit. TMA also stated that it 
is unclear what technologies would be needed to achieve high levels of 
braking performance improvements for tractors in this weight category.
---------------------------------------------------------------------------

    \38\ Docket  NHTSA-2005-21462-34.
    \39\ TMA did not provide dimensions for these brakes, but 
described them as the highest available performance brakes.
---------------------------------------------------------------------------

    In addition, TMA simulated a test condition with a tractor at 
78,000 pounds GVWR, with a 20,000-pound steer axle load and a 58,000-
pound tandem drive axle load. This tractor was not able to meet a 250-
foot stopping distance with any brake combination, although it must be 
noted that a vehicle with a 58,000-pound tandem rating (29,000-pound 
GAWR per axle) is exempt from FMVSS No. 121 under Section 3, 
Applicability, paragraph (b). The stopping distance simulation results 
for this vehicle were 307 feet for the drum/drum configuration, 268 
feet for the hybrid configuration, and 261 feet for the all-disc 
configuration. Despite the fact that the specific vehicle tested here 
would not be subject to the requirements of FMVSS No. 121, it does 
represent the upper edge of the GVWR range regulated under the FMVSS 
No. 121 requirements, and therefore the agency believes the TMA data 
are useful in setting stopping distance

[[Page 37136]]

requirements for severe service tractors as part of this final rule.
    In its October 2006 comments, TMA presented testing that indicated 
trucks with a GVWR over 70,000 pounds are incapable of meeting a 250-
foot stopping distance requirement. In one example, a 72,000-pound GVWR 
tractor equipped with all disc brakes only achieved a three percent 
margin of compliance, which the agency does not consider to be enough 
for manufacturers to reliably build tractors with assured compliance to 
FMVSS No. 121. Similarly, a 78,000-pound GVWR three-axle tractor 
equipped with all disc brakes stopped in 261 feet, thus it did not meet 
a 250-foot stopping distance requirement. Because all-disc brake 
configurations generally produce the best available braking 
performance, it is not clear what advancements could be used to bring 
trucks of this weight within a 250-foot stopping distance. The agency 
therefore concludes that three-axle tractors with a GVWR greater than 
70,000 pounds should be provided with a longer stopping distance 
requirement.
    The agency has considered all of the available data and comments 
regarding severe service tractors to determine appropriate loaded-to-
GVWR stopping distance requirements for these vehicles. The agency 
agrees with TMA that, based on all available information, foundation 
brakes that could provide loaded-to-GVWR stopping distance performance 
in the 250-foot range at 60 mph are not available for three-axle severe 
service tractors with a GVWR over 70,000 pounds. There are little or no 
test data available for tractors with a GVWR over 70,000 fitted with 
the largest available disc brakes to demonstrate that they would be 
able to meet a 30 percent reduction in stopping distance. In making 
this statement, the agency notes the TMA supplemental comments, which 
discuss the lack of extensive testing of prototype disc brakes.\40\ 
Therefore, the agency does not believe it is practicable at this time 
to require three-axle severe service tractors over 70,000 pounds GVWR 
to meet the 30 percent reduction in stopping distance.
---------------------------------------------------------------------------

    \40\ TMA comments of October 12, 2006. Docket No. NHTSA-2005-
21462-34.
---------------------------------------------------------------------------

    However, for three-axle tractors with a GVWR over 70,000 pounds, a 
310-foot stopping distance requirement is an achievable goal. This 
represents a 13 percent reduction in stopping distance from the current 
355-foot requirement. Based upon this requirement, and assuming a 10 
percent margin of compliance, the 78,000-pound GVWR three-axle tractor, 
discussed in the TMA comments of October 2006, could meet the 
requirement with an adequate margin of compliance in a hybrid or all-
disc brake configuration. Further, the 72,000-pound GVWR three-axle 
tractor would achieve an eight percent margin of compliance with an 
all-drum brake configuration. In that case, either slight improvements 
in the drum brakes or the installation of disc brakes on the steer axle 
would allow the tractor to achieve a ten percent margin of compliance. 
The agency believes that in both cases safety benefits will be obtained 
because of these improvements, but whether these benefits would be the 
same or smaller than for typical (non-severe service) three-axle 
tractors is unknown. We also note that for vehicles with a drive axle 
GAWR of 29,000 pounds or more, FMVSS No. 121 is not applicable, so that 
typically three-axle tractors with a GVWR of 78,000 pounds or more will 
be exempt from this requirement.
    As previously discussed, the tests at VRTC of a severe service 
truck (used as a surrogate severe service tractor), loaded to a GVWR of 
76,000 pounds and equipped with all disc brakes, had an average 
stopping distance of 254 feet. This represents an 18 percent margin of 
compliance to the 310-foot stopping distance requirement implemented 
under this final rule.

d. Severe Service Tractors With Four or More Axles

    For severe service tractors with more than three axles, there is a 
similar distinction to be made between lower-GVWR tractors and higher-
GVWR tractors. While the NPRM proposed reducing the stopping distance 
for all tractors uniformly, commenters and agency testing have 
indicated that a distinction should be made, similar to the distinction 
within severe service three-axle tractors. With regard to severe 
service tractors with four or more axles, we believe there are some 
tractor configurations that, even though they are in the severe service 
category, can comply with a 250-foot stopping distance requirement when 
most or all of the brakes are upgraded to disc brakes. A small 
percentage of these tractors, however, will not be able to currently 
comply with this requirement, and thus necessitate a different 
approach.
    Some extra-axle tractors are based on, and perform very similarly 
to, severe service three-axle truck tractors. One example of this is a 
severe service three-axle tractor that has an auxiliary axle installed 
by either the truck manufacturer or by a vehicle alterer. The agency 
believes that its testing of a single-unit truck at VRTC provides a 
basis for determining the scope of this final rule with regard to 
similarly configured tractors. Using the VRTC three-axle Peterbilt 
truck as a guideline, which had GAWRs of 18,000 pounds for the steer 
axle, 44,000 pounds for the tandem drive axles, and a total GVWR of 
62,000 pounds, we considered the installation of a lift axle placed in 
front of the drive axles with a GAWR of 20,000 pounds. We note that 
this is on the upper end of axle weight ratings for lift axles; many 
lower GAWR ratings for lift axles are also available. The GVWR would 
now be increased to 82,000 pounds, and although the agency has no full 
vehicle test data, the loaded-to-GVWR service braking performance of 
the tractor would not be expected to decrease substantially from the 
performance in the original three-axle configuration (this vehicle was 
tested with three axles at 62,000 pounds GVWR and was able to stop in 
224 feet when equipped with disc brakes at all wheel positions). We 
make this assumption because of the auxiliary brake requirements FMVSS 
No. 121, which mandate high levels of fade resistance and stopping 
power requirements.
    Although the agency does not have data on the dynamic load 
increases on lift axles under hard braking, we expect load transfer 
increases (if any) to be minimal. This assumption is based on prior 
analyses that show the greatest load transfer to be on the steer axle, 
while drive axles (and trailer axles in the case of combination vehicle 
tests) typically have small decreases in vertical load under hard 
braking.\41\ Thus, it would not be expected that lift axle foundation 
brakes would need to be substantially increased in size to provide the 
needed retardation force to meet the new stopping distance 
requirements.
---------------------------------------------------------------------------

    \41\ Docket No. 21462-2005-33 (see slide 8 of TMA's presentation 
for typical load transfer of a tractor-trailer combination vehicle 
during hard braking).
---------------------------------------------------------------------------

    TMA provided data that confirmed NHTSA's belief that lower-GVWR 
severe service tractors with four or more axles are capable of meeting 
a 250-foot stopping distance requirement, even when using drum brakes 
on the drive axles. We note that the TMA supplemental data, supplied in 
October 2006, for the 66,000-pound GVWR three-axle severe service 
tractor showed that this tractor was able to achieve a stopping 
distance of 229 feet in a hybrid configuration (disc brakes on steer 
axle only), and its drive axles were rated at 23,000 pounds GAWR each. 
Therefore, adequately performing drum brakes that

[[Page 37137]]

are typically installed on auxiliary axles should be available for a 
20,000-pound auxiliary axle; in other words, it is not expected that 
disc brakes would be needed on the auxiliary axles in order to achieve 
satisfactory performance.
    Next, we turn to TMA comment that dynamic load transfer to the 
steer axle may be an issue for some severe service tractors with four 
or more axles, such as the twin-steer example described above with a 
GVWR above 85,000 pounds. Using a 20,000-pound steer axle GAWR as an 
example, the agency believes there is not an adequate installation 
envelope to install a large enough disc brake to be able to meet a 250-
foot stopping distance requirement for these vehicles. There are a 
number of constraints on the installation envelope that limit the 
diameter of the disc rotor and caliper assembly that can be fit within 
the inside diameter of the wheel rim, including: (1) The articulation 
of the spindle and foundation brakes needed for adequate steering cut; 
(2) vertical clearance with chassis components during dynamic steer 
axle loading (compression during hard braking); and (3) the size of the 
wheels. The agency agrees with TMA that, based on all available 
information, foundation brakes that could provide loaded-to-GVWR 
stopping distance performance in the 250-foot range are not available 
for these tractors. Further, NHTSA is not aware of sufficient test data 
available for such tractors fitted with the largest disc brakes to 
confirm this (noted in the TMA supplemental comments citing tests of 
prototype disc brakes that have not been tested extensively). Because 
of these inherent limitations of the steer axle brakes, the agency has 
decided to adopt requirements for stopping distance of tractors with 
four or more axles and a GVWR greater than 85,000 pounds of 310 feet 
(rather than 250 feet) along the lines of the requirements for single-
unit trucks of this size. The agency believes, for the same reasons as 
discussed above, that tractor-trailers can achieve similar service 
braking performance as similar single-unit trucks.

e. Two-Axle Severe Service Tractors

    We also respond to TMA's April 2006 comments regarding what it 
identified as a distinct class of severe service two-axle tractors, 
which TMA defined as a two-axle truck tractor having a drive axle GAWR 
of 23,000 pounds or more. Based on our review of the commenters' data, 
the agency does not believe that the commenters have provided 
sufficient information to justify allowing these tractors to be subject 
to a less rigorous stopping distance requirement than other two-axle 
tractors, and that the proposed specifications for improved stopping 
distances are practicable.
    Commenters' test data show that two-axle truck tractors with a 
higher GVWR have similar braking performance to other two-axle 
tractors. TMA provided test data for one severe service two-axle 
tractor with standard 16.5'' x 5'' S-cam drum brakes on the steer axle 
and standard 16.5'' x 7'' S-cam drum brakes on the drive axle.\42\ The 
stopping distance for this tractor was approximately 315 feet, so this 
brake configuration would not meet a 250-foot stopping distance 
requirement. However, this test result does not make it necessary to 
exclude severe service tractors from the improved stopping distance 
requirement entirely.
---------------------------------------------------------------------------

    \42\ Docket  NHTSA-2005-21462-26.
---------------------------------------------------------------------------

    First, we note that the two-axle tractor cited by TMA is not a 
typical severe service tractor because it does not have a GVWR in 
excess of 59,600 pounds, thereby putting it outside the standard 
definition of a severe service tractor.
    Second, of particular significance is the fact that this test 
result does not show how this vehicle would perform with upgraded 
brakes, specifically disc brakes. Disc brakes are the type of brakes 
that have been demonstrated to typically provide the shortest stopping 
distance. Therefore, the agency declines to use the TMA data on this 
``severe service two-axle tractor'' in formulating the requirements of 
this final rule.
    We do not have test data for this specific configuration of vehicle 
equipped with disc brakes. However, considering that the achieved 
stopping distance of the severe service two-axle tractor is roughly 
equivalent to what many other two-axle tractors can achieve when 
equipped with standard S-cam drum brakes at all wheel positions,\43\ 
NHTSA believes that ``severe service two-axle'' tractors will be able 
to achieve similar enhancements using enhanced S-cam drum brakes or 
disc brakes in lieu of standard S-cam drum brakes. Therefore, the 
agency is not specifying a longer stopping distance for these vehicles. 
However, for reasons discussed below, the agency is providing a longer 
lead time for all two-axle tractors.
---------------------------------------------------------------------------

    \43\ Docket  NHTSA-2005-21462-26.
---------------------------------------------------------------------------

f. Summary of Severe Service Tractors

    Based upon the above analysis, the agency is setting the loaded-to-
GVWR stopping distance requirements for severe service tractors as 
follows:
     A tractor with three axles and a GVWR of 70,000 pounds or 
less must stop within 250 feet.
     A tractor with three axles and a GVWR greater than 70,000 
pounds must stop within 310 feet.
     A tractor with four or more axles and a GVWR of 85,000 
pounds or less must stop within 250 feet.
     A tractor with four or more axles and a GVWR greater than 
85,000 pounds must stop within 310 feet.

Further, the agency does not recognize a class of two-axle severe 
service tractors, and notes that all two-axle tractors are required to 
meet a 250-foot stopping distance requirement.
    The agency believes that these requirements will enhance vehicle 
safety by ensuring that the vast majority of tractors (estimated to be 
approximately 99 percent of annual tractor production) will meet a 
requirement with a 30 percent reduction in stopping distance. The 
remaining one percent of tractors, which are high-GVWR severe service 
tractors, will be required to meet a requirement with a 13 percent 
reduction in stopping distance, which is equal to the current required 
stopping distance performance for single-unit trucks. Finally, those 
tractors with any axle with GAWR of 29,000 pounds or greater will 
continue to be excluded from the FMVSS No. 121 requirements.
4. Braking Performance of Tractors With Improved Brake Systems in the 
Unloaded Weight Condition
    In the NPRM, the agency proposed to reduce the existing FMVSS No. 
121 unloaded weight stopping distance for heavy truck tractors from 335 
feet by 20 percent (i.e., to 268 feet) to 30 percent (i.e., to 235 
feet). Testing in the unloaded weight condition (also known as lightly-
loaded vehicle weight or LLVW) is performed without any trailer 
attached to the tractor (i.e., bobtail condition), plus up to an 
additional 500 pounds allowed for the test driver and vehicle 
instrumentation. In addition, up to 1,000 pounds is allowed for a roll 
bar structure. The tractor is required to meet the unloaded stopping 
distance requirement for at least one out of six test stops.
    One potential issue that arises when reducing stopping distance in 
the lightly-loaded condition is the issue of wheel lockup, as there is 
far less available tire-road friction than in the loaded-to-GVWR 
condition. Requirements in FMVSS No. 121, S5.3.1, paragraphs (a) 
through (d), specify allowances for wheel lockup during either a 
service brake stopping distance test in the loaded or unloaded

[[Page 37138]]

condition, and applies to trucks, tractors, and buses. At speeds above 
20 mph, wheel lockup on certain axles is only permitted to be momentary 
(less than one second), while unlimited wheel lockup on auxiliary axles 
is permitted. At speeds below 20 mph, unlimited wheel lockup is 
permitted on any wheel. These wheel lockup provisions were necessary 
before ABS was mandated, to ensure that the test driver could bring the 
vehicle to a stop without loss of control due to unlimited wheel 
lockup. In the case of a tractor in the unloaded condition, the drive 
axle wheels are very easy to lock up, as there is little vertical load 
on them. Prior to the advent of ABS, some tractors were equipped with 
bobtail proportioning valves to reduce the brake pressure to the drive 
axles in the unloaded condition and make it easier to stop the vehicle 
within the required distance (using more steer axle brake power, where 
a substantial vertical load exists), and also to improve the on-road 
drivability of bobtail tractors.
    However, since March 1, 1997, all tractors have been required to be 
equipped with ABS on at least one steer axle and one drive axle, which 
has virtually eliminated wheel lockup in tractors. While the relevant 
FMVSS No. 121 requirement states that only one rear axle of a tractor 
needs to be equipped with ABS, most tractors also indirectly control 
the wheels on the other rear axle in the case of tandem drive axles, or 
they employ direct ABS control of both tandem drive axles. In the case 
of a severe service truck or tractor with non-liftable auxiliary axles 
mounted rearward of the tandem drive axles, an auxiliary ABS system may 
be necessary on those auxiliary axles to meet the wheel lockup 
provisions in S5.3.1, but trucks and tractors with liftable auxiliary 
axles typically do not need to have ABS on those axles. In addition, 
the braking-in-a-curve test in S5.3.6 was included in FMVSS No. 121 to 
ensure that the ABS provides adequate vehicle control and stability 
when in a curve on slippery pavement and subjected to a full-treadle 
brake application. The braking-in-a-curve test ensures that the ABS is 
regulating the braking forces at the wheels to keep the tires rolling, 
so they can generate the lateral forces required for maintaining the 
curve, and the vehicle does not plow out of the curve during braking.
    In addition, ABS systems can help greatly decrease the stopping 
distances for lightly-loaded tractors. Since the addition of these ABS 
requirements, conducting braking tests on trucks and buses in the 
unloaded condition has been greatly simplified. Rather than requiring 
the driver to modulate the brake treadle to try to achieve the required 
stopping distance while staying within the wheel lockup provisions in 
S5.3.1, the test driver can make a full treadle brake application at 
the initiation of the stop and the ABS ensures that the wheel lockup 
provisions are met. The result is much greater braking efficiency and 
shorter stopping distances compared to driver-modulated stops. This is 
evident by reviewing the VRTC test data for tractors tested in the 
unloaded condition. Compared to the FMVSS No. 121 requirement of 
stopping within 335 feet (unloaded condition), typical bobtail tractor 
stopping distances for tractors with improved foundation brake systems 
are approximately 180 feet, or 46 percent lower than the current 335-
foot requirement. As an example, VRTC tests of the tractors equipped 
with hybrid disc/drum brakes and all-disc brakes resulted in unloaded 
stopping distances ranging from 176 to 183 feet (six tests), meeting a 
target stopping distance of 235 feet (a 30 percent reduction from the 
current stopping distance requirement) with margins of compliance 
ranging from 25 to 22 percent.
    It is likely that even current standard drum brakes have the 
necessary torque to permit a substantial reduction in tractor stopping 
distance in the lightly-loaded condition. VRTC tests of the 6x4 severe 
service truck (used as a surrogate example of a severe service tractor) 
with all disc brakes (224-foot loaded-to-GVWR stopping distance) 
stopped in the lightly-loaded condition in 172 feet, meeting a target 
distance of 235 feet with a 27 percent margin of compliance. Even when 
tested with brake configurations that did worse in the loaded-to-GVWR 
test condition (all drum brakes and disc/drum brake hybrid 
configurations), the unloaded stopping distances were 172 feet and 178 
feet. This indicates that stopping performance in the unloaded 
condition for this severe service vehicle was not significantly 
sensitive to the configuration of the foundation brakes, since any 
combination of foundation brakes could fully utilize the available 
tire-road friction of the vehicle in its light weight condition. 
Further, it demonstrates that the ABS system (6S/6M on this vehicle) 
delivered good efficiency in keeping the braking force near the peak of 
available tire-road friction.
    Very few comments were received on the agency's proposal to reduce 
the stopping distance in the lightly-loaded condition by 20-30 percent. 
No test data were submitted on stopping performance of tractors 
equipped with improved braking systems tested in the lightly-loaded 
condition. Several commenters made recommendations. TMA and 
ArvinMeritor recommended 25 percent reductions in lightly-loaded 
stopping distances, and IIHS recommended a 30 percent reduction, but no 
data were provided to support these recommendations. TMA stated that 
currently under unloaded conditions, tractors experience some wheel 
slip at brake applications of 30 psi, and that if the steer axle brake 
is improved to meet a 30 percent reduction in stopping distance, rear 
wheel slip might be experienced at as little as 20 psi. However, 
considering that TMA is recommending a 25 percent decrease in stopping 
distance in the unloaded condition, we believe the shorter stopping 
distance achieved more than compensates for the slight increase in ABS 
activations under these conditions.
    Based on the available data, the agency believes that a longer 
lightly-loaded stopping distance is not necessary for the highest-GVWR 
severe service tractors. Those vehicles have been provided with some 
relief (310-foot loaded-to-GVWR stopping distance requirement, as 
opposed to 250 feet) for tests in the loaded condition because of the 
torque-generating limitations of foundation brakes. However, the agency 
does not believe that any relief is needed for these tractors when 
tested in the lightly-loaded condition. The definition of a ``truck 
tractor'' in 49 CFR 571.3 specifies that it is ``primarily for drawing 
other motor vehicles and not so constructed as to carry a load other 
than a part of the weight of the vehicle and the load so drawn.'' 
Therefore, tractors in the lightly-loaded condition have extremely 
light load weights relative to their GVWR since they do not have any 
load-carrying capability outside of trailer towing. Tractors in the 
lightly-loaded condition, including the heaviest GVWR severe service 
tractors, can therefore achieve braking performance similar to each 
other.
    In this final rule, the agency is setting the heavy truck stopping 
distance requirement in the lightly-loaded condition at 235 feet, a 30 
percent reduction from the existing FMVSS No. 121 requirement. The 
available test data, while limited in terms of the number of tests 
conducted, indicate that margins of compliance of 20 percent or more 
can readily be attained. Severe service tractors that have lift axles 
would be expected to perform similarly, as the lift axles would be in 
the raised position during this test. To the agency's knowledge, severe 
service tractors

[[Page 37139]]

equipped with improved brake systems that have non-liftable auxiliary 
axles, or tridem drive axles, have not been tested, but are expected to 
perform similarly or with only slightly longer stopping distances 
(e.g., due to driveline and axle interactions on a tridem drive system, 
or slightly lower tire traction due to aggressive off-road tread 
patterns). However, due to the large margins of compliance already 
achieved, the agency believes that the 235-foot requirement is 
practicable for tractors that might have slightly longer stopping 
distances than the typical examples tested.
    One minor issue that the agency is addressing is the lack of a fuel 
tank fill specification in FMVSS No. 121. Vehicle curb weight is 
measured with all fluid levels and reservoirs (e.g., antifreeze, 
windshield washer fluid) at the recommended levels (i.e., filled to 
capacity or other designated fill levels). The agency reviewed FMVSS 
No. 121 for a specification on the vehicle's fuel tank fill level 
during road tests and found that this is not addressed. In contrast, 
FMVSS No. 135, Light Vehicle Brake Systems, specifies under the vehicle 
test conditions in paragraph S6.3.2 that the fuel tank shall be filled 
to 100 percent of capacity at the beginning of testing and that it may 
not be less than 75 percent of capacity during any part of the testing.
    The agency is adding a similar requirement to FMVSS No. 121 in this 
final rule. The lack of a fuel tank fill specification adds a possible 
source of test variability, such as when testing in the lightly-loaded 
condition where the additional weight of the fuel may be advantageous, 
in that it may increase the tractor test weight and thus provide 
additional tire friction at the drive axles. Therefore, by specifying 
that the fuel tank(s) must remain at least 75 percent full during all 
portions of the brake testing, test variability is reduced. Test 
severity is not increased as a result of providing this specification. 
We note that for the loaded-to-GVWR tests, this specification permits 
up to 25 percent of the fuel to be used over the course of testing 
without continually adding ballast or refueling the vehicle.
5. Emergency Braking Performance of Tractors With Improved Brake 
Systems
a. Background Information on the Emergency Braking Performance 
Requirement
    In the NPRM, the agency proposed to reduce the emergency braking 
stopping distance in FMVSS No. 121 by 20 percent to 30 percent, from 
the current 720 feet to a value between 580 feet and 504 feet. However, 
in light of concerns raised in the comments, NHTSA has decided against 
adoption of any change in the standard's emergency brake stopping 
distance performance requirements.
    The emergency brake system requirements in FMVSS No. 121 are tested 
by inducing a single failure in the service brake system of a part 
designed to contain compressed air, excluding specific components 
(i.e., a common valve, manifold, brake fluid housing, or brake chamber 
housing).
    Test data from VRTC tests of tractors in the emergency braking mode 
were provided in Table II of the NPRM. These tests were conducted with 
failed primary systems, and, therefore, the data represent the 
performance of tractors stopping using only the steer axle brakes. The 
longest stops measured were with standard, 15'' x 4'' S-cam drum brakes 
(636 feet for one tractor and 432 feet for the other tractor). As steer 
axle brake improvements were made, emergency stopping distance also 
improved. The best stops were with disc brakes on the steer axle (four 
tests), which ranged from 276 to 303 feet, demonstrating very good 
margins of compliance against the 720-foot FMVSS No. 121 requirement. 
Thus, the agency's proposed requirements of 504 feet to 580 feet for 
emergency brake stopping distance appeared to be achievable with 
improved brake systems.
b. Commenters' Responses to Proposed Emergency Braking Performance 
Requirement
    Several commenters (Bendix, ArvinMeritor, International) 
recommended that the agency leave the standard's emergency brake 
stopping distance requirements unchanged. Bendix argued that increasing 
the torque output on foundation brakes would have a corresponding 
decrease in emergency brake stopping distance, but only if the improved 
brakes are used in the emergency stopping test. Thus, a tractor that 
has had its steer axle brake improved to meet a 30 percent reduction in 
stopping distance would exhibit no enhancement in emergency braking 
performance if the front brake circuit (secondary air system) were 
disabled. This would potentially cause the vehicle to fail that portion 
of the emergency brake stopping distance test, even with improved 
foundation brakes. Bendix stated that the agency has not provided 
evidence of a need for improved emergency braking system performance in 
its analysis. ArvinMeritor commented that emergency braking performance 
in the failed secondary air system test (i.e., using only the drive 
axle brakes, which have a very low weight when measured in the unloaded 
condition) is already limited by tire-road adhesion today, thus making 
further improvements impossible due to wheel lockup.
    In its comments, TMA stated that the emergency braking performance 
of tractors with improved brake systems could lead to more aggressive 
lockup of wheels on the drive axle(s) during emergency braking. 
According to TMA, increased use of ABS could cause the emergency 
braking performance with improved drive axle brakes to be worse than 
with current foundation brakes. TMA stated that truck manufacturers 
would need to modify the ABS algorithms to allow more drive wheel 
lockup to meet the agency's proposed emergency brake stopping distance 
requirements, and that this would be detrimental to vehicle stability 
and control. Further, TMA commented that the likelihood of a crash-
imminent situation occurring at the same time as a failure in either 
the primary or secondary air systems is immeasurably small.
    Although somewhat counterintuitive, the agency acknowledges that 
the failed secondary system braking performance of tractors might be 
negatively impacted by improved brake systems, as suggested by the 
commenters. Accordingly, we have decided that not to make any changes 
in the emergency brake system stopping distance requirements at this 
time. Maintaining the status quo for emergency brake stopping 
requirements is not expected to have any negative effect on achieving 
the estimated safety benefits of the overall heavy truck stopping 
distance rulemaking, because tractors operating in bobtail mode and 
experiencing an emergency braking situation are not significant 
contributors to the crash problem that has been identified.
ii. Ancillary Issues Arising From Improved Brake Systems
1. Stability and Control of Tractors With Improved Brake Systems
    Several commenters (TMA, HDBMC, ATA) brought up a number of issues 
relating to the stability and control of tractors that arise from 
installation of improved brake systems pursuant to the agency's 
proposal to improve heavy truck stopping distance performance 
requirements by 30 percent. These issues included potential problems 
with lateral stability (especially in two-axle, short wheelbase 
tractors), excessive steering wheel pull, and excessive steer axle 
suspension jounce (compression). Commenters stated that these problems

[[Page 37140]]

would be expected to apply to all tractors, but commenters expressed 
their opinion that such problems would likely be especially acute in 
two-axle tractors, particularly in those with a shorter wheelbase.
    In a meeting held with NHTSA on March 29, 2006, representatives of 
TMA, HDBMC, and ATA discussed several issues involving tractors with 
improved brake systems that were included in presentation materials 
available for review in the DOT docket.\44\ One issue raised in that 
presentation involved computer simulations provided by TMA which were 
conducted by Freightliner of two tractors in a braking-in-a-curve 
maneuver (see Slide 10). In that maneuver, the tractor with more 
powerful foundation brakes (a hybrid configuration of front disc brakes 
and rear drum brakes) experienced a jackknife loss-of-control, while 
the tractor with standard drum brakes remained stable. According to 
TMA's comments, this indicated that installing more powerful foundation 
brakes to improve performance in the straight-line stopping distance 
test could have the unintended consequence of inducing stability 
problems in some on-road driving situations. Thus, TMA raised concerns 
about the stability and control of short-wheelbase two-axle tractors 
when more powerful foundation brakes are applied. Although not depicted 
in the presentation slides, the following were the test conditions for 
the above scenario, as described by TMA at the meeting:
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    \44\ See Docket No. NHTSA-2005-21462-33.
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     The curve has a radius of 500 feet and was a high-friction 
dry surface (0.9 peak coefficient of friction).
     The entry speed of the tractor was 48 mph.
     The tractor was connected to a tandem-axle trailer, and 
the trailer was rear-loaded to 34,000 pounds weight on the trailer 
axles.
     The trailer was unbraked.
     A full-treadle brake application was used.
    While the maneuver described by TMA has some similarities to the 
FMVSS No. 121 stability and control test requirement that is used as a 
pass-fail measure to assess the performance of a tractor's ABS (see 
S5.3.6.1), the agency does not believe that the TMA test is appropriate 
for assessing the vehicle's stability, due to vital differences in the 
test procedures, as explained below. In the FMVSS No. 121 test, the 
road surface is wetted and slippery (0.5 peak coefficient of friction 
as opposed to 0.9), and the entry speed is typically between 30 and 34 
mph, as opposed to 48 mph. The loading condition of the trailer in the 
FMVSS test is also different. Although an unbraked FMVSS No. 121 
control trailer is used, in the FMVSS test, the trailer is front loaded 
(i.e., loaded over the kingpin at the front of the trailer) in order to 
load the tractor to its GVWR. In contrast, in the TMA test, the trailer 
was rear loaded, which puts the majority of the weight on the unbraked 
trailer axles rather than the tractor's drive axles. This maneuver 
deprives the drive axles of braking traction, and constitutes a worst-
case braking scenario.
    At the March 29, 2006 meeting, the agency questioned whether TMA's 
simulation is representative of a real-world driving situation. As 
explained below, the simulation appeared to the agency to be a 
combination of several worst-case scenarios, the first of which 
involves the high entry speed of the tractor that, for this curve, 
approaches the rollover threshold of some high-center-of-gravity 
tractor-trailer combinations. Second, the trailer is rear-loaded, which 
is not a safe operating practice. (In general, trailers should not be 
rear-loaded because the tractor drive axles will be too light during 
braking and/or acceleration.) Third, the trailer brake system was 
deactivated. Finally, the test assumes a full-brake application which, 
on the highway, represents a panic braking situation. As a result, the 
agency is not convinced by TMA's comment that improving the steer axle 
brakes will have a negative impact on lateral stability.
    The agency has further reason to doubt TMA's assertion that lateral 
stability will be negatively impacted by improving the tractor's 
foundation brakes. In its comments, TMA referred to a Society of 
Automotive Engineers (SAE) technical paper, A Study of Jackknife 
Stability of Class VIII Vehicles with Multiple Trailers with ABS Disc/
Drum Brakes (SAE 2004-01-1741). TMA stated that this study, consisting 
of vehicle simulation modeling to evaluate the stability of two-axle 
tractors towing double trailers, found that two-axle tractors with more 
aggressive brakes either jackknifed or ran off the road under various 
combinations of conditions. However, based upon the agency's review, 
that study seems to indicate that more powerful foundation brakes were 
not a cause of the jackknifing, but rather that the cause was a lack of 
tractor ABS. In analyzing this SAE report, the agency notes that only 
when the tractor ABS was disabled did instability occur, and it 
occurred regardless of whether the tractor was equipped with S-cam drum 
brakes or disc brakes. However, the type of instability exhibited 
varied depending upon the types of foundation brakes installed on the 
tractor; specifically, tractors with all drum brakes went into a 
jackknife (oversteer), while the tractors with disc brakes tended to 
plow out of the curve (understeer).
    The only benefit of less powerful brakes indicated by the tractor 
simulations with inoperative ABS was that the lane departure occurred 
sooner in the maneuver when the tractor was equipped with disc brakes. 
We do not believe that this argument justifies a requirement that would 
result in installation of weaker foundation brakes. Instead, we believe 
that this study is more indicative of the importance to fleets in 
maintaining ABS on tractors, trailers, and converter dollies. It is 
also important to note TMA's comment that 4 to 16 percent of tractors 
and 8 to 26 percent of trailers in service have non-functioning ABS or 
ABS warning lamps. While this rulemaking does not relate to in-service 
maintenance issues (issues which generally fall under FMCSA's 
jurisdiction), proper maintenance is very important.
    The agency conducted an additional investigation to determine the 
validity of the TMA testing regarding lateral instability. To further 
investigate suggestions regarding the potential for increased lateral 
instability, the agency held a meeting with the TMA at the VRTC in East 
Liberty, Ohio, on July 11, 2006.\45\ At that meeting, the agency 
presented results of several braking-in-a-curve simulations performed 
at VRTC using its Truck Sim vehicle dynamics modeling software to 
estimate the scope of potential vehicle instability problems for two-
axle tractors. In a high-friction (i.e., 0.9 coefficient of friction, 
or mu), 500-foot radius curve braking test with a rear-loaded, unbraked 
trailer, a two-axle tractor with a very short wheelbase of 130 inches 
experienced a jackknife condition. Two other tractors with short 
wheelbases (142 and 148 inches) were marginally stable, meaning they 
were not under full control, but did stay within the 12-foot-wide lane. 
For comparison purposes, we note that a three-axle tractor with a 190-
inch wheelbase remained stable during this maneuver. The agency also 
performed slippery-surface (low friction) tests at 45 mph, and found 
that a short-wheelbase tractor (148 inches) spun out both with standard 
drum brakes and with disc brakes. This test also caused a standard 
three-axle tractor (with drum brakes) to spin out. For a final 
comparison, we

[[Page 37141]]

note that during a previous track test, even a high-performance sports 
car spun out during this maneuver at 45 mph. Again, these results 
demonstrated to the agency that the TMA test was too rigorous for any 
typical vehicle to be able to navigate the curve.
---------------------------------------------------------------------------

    \45\ Docket No. NHTSA-2005-21462-36.
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    Further, we note that in its supplemental comments from October 
2006, TMA submitted information about tests on four two-axle tractors 
that showed substantially fewer problems of lateral instability than 
had been suggested earlier. The results of these tests showed that two-
axle tractors are capable of maintaining a high degree of lateral 
stability when equipped with improved foundation brakes. TMA 
acknowledged that these vehicles did not exhibit controllability or 
handling problems. Nonetheless, TMA suggested in its supplemental 
comments that due to the relatively large amount of testing and 
validation required for issues such as brake lining, brake chamber 
sizes, slack adjuster lengths, tire properties, ABS algorithms, and 
potentially electronic stability control (ESC) systems, additional lead 
time for two-axle tractors may be required.
    In the end, after considering all of the available information on 
stability and control that affects shorter wheelbase, two-axle 
tractors, the agency has decided that an allowance for longer stopping 
distances is unnecessary. Only under the most severe conditions was 
instability found to be an issue, and rarely did it correlate with the 
improved braking systems. Nonetheless, the agency is aware that there 
is a greater need for additional design efforts and validation on two-
axle tractors, so in this final rule, we are providing more lead time 
for manufacturers to achieve compliance with the new stopping distance 
requirements for these tractors, thereby providing manufacturers with 
more time to identify and remedy potential problems. (The issue of the 
compliance date is addressed in further detail below in Section III, c, 
viii.)
2. Brake Balance Issues on Tractors With Improved Brake Systems
    Because the main factor in generating the additional brake torque 
to achieve a reduced stopping distance is the addition of more powerful 
steer axle brakes, the effects of more powerful steer axle brakes are 
raised by this rulemaking. These issues involve the balance of braking 
power generated by different tires, as well as concern that the new 
designs could engender off-balance brake systems. Two issues raised 
included the difference in brake torque generated by the steer and 
drive axles, and the potential for increased steering wheel pull 
resulting from more powerful steer axle brakes. The agency addresses 
each of those concerns below.
    Several commenters asserted that the mandate to decrease stopping 
distance would necessitate less powerful drive axle brakes on two-axle 
tractors, because dynamic loading would cause the weight on the drive 
axle to be substantially less during hard braking.\46\ Freightliner 
commented that because 31 percent of the rear axle load will transfer 
to the steer axle during hard braking, two-axle tractors will require 
less powerful drive axle brakes than they currently have. While 
Freightliner did not provide a rationale for this in its comment, it is 
presumed that this would be to improve brake balance at maximum 
braking, without having to cycle the ABS on the drive axle. Similarly, 
ATA commented that it may be necessary to reduce drive axle brake power 
on two-axle tractors to compensate for the weight transfer to the steer 
axle. In its original comments, TMA also argued that decreasing the 
drive axle torque by 20 percent would be necessary to prevent ABS 
activation, which could result in even longer stopping distances. All 
of these commenters argued that the combination of much more powerful 
steer axle brakes and less powerful drive axle brakes would result in a 
vehicle that would perform poorly under real-world conditions, arguing 
that the agency should not consider the issue of stopping distance in 
isolation.
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    \46\ ``Dynamic Loading'' refers to the temporary redistribution 
of downward force during a hard braking incident. During rapid 
deceleration, proportionally more weight is borne by the front of 
the tractor (the steer axle) and less is borne by the rear (the 
drive axle and the trailer axle). In two-axle tractors, where 
proportionally more weight is borne by the steer axle than in other 
designs, the concern is that during hard braking, too little weight 
will be borne by the drive axles, and the available tire-road 
friction will not be high enough to allow them to utilize all of the 
available brake torque. In these situations, the ABS would be 
activated, lessening those brakes' effectiveness.
---------------------------------------------------------------------------

    The agency's test data, however, do not fit with these statements. 
The agency's data indicate that a reduction in drive axle torque would 
not be necessary to improve stopping distances in hard-braking 
situations. Test data from VRTC \47\ tests on a two-axle tractor showed 
that after installing more powerful steer axle disc brakes, installing 
more powerful drive axle brakes only served to shorten overall stopping 
distance. The agency also notes that this improvement occurred without 
stability or control problems when tested both in the lightly-loaded 
and loaded-to-GVWR conditions as specified in the FMVSS No. 121 
braking-in-a-curve test. In nearly every test, whether using two-axle, 
three-axle, or severe service tractors, the tractors that achieved the 
shortest stopping distances were those equipped with more powerful disc 
brakes at all wheel positions. In all tests, the ABS was found to 
perform very efficiently in limiting wheel lockup and allowing tractors 
with improved braking systems to maintain good stability in both 
straight line and braking-in-a-curve tests.
---------------------------------------------------------------------------

    \47\ Docket NHTSA-2005-21462-39, p. 25.
---------------------------------------------------------------------------

    On a related topic, TMA also commented that more powerful steer 
axle brakes could contribute to instability through steering wheel 
pull. Steering wheel pull can occur when the steer axle brake on one 
side of the vehicle is able to produce more braking power than the 
brake on the other side. This is an issue that affects all tractors 
with enhanced steer axle brakes, not just two-axle tractors. TMA stated 
that on ``split-mu surfaces,'' i.e., ones where one side of the road 
has less friction than the other (such as transitional surfaces, or 
when one side of the road is wet), imbalances in steer axle brakes are 
magnified and drivers must provide sufficiently more frequent and 
aggressive steering wheel input to keep the vehicle on its intended 
path. TMA argued that if the power of the steer axle brakes were 
increased, the potential effects of side-to-side imbalance would also 
increase.
    The agency believes that disc brakes, in general, will provide 
better steer axle brake balance than current standard drum brakes do. 
This is because for any given air pressure, the torque output of drum 
brakes can vary by 30 percent due to hysteresis,\48\ lining variations, 
brake adjustment, and drum condition (e.g., eccentricity and being out-
of-round). In comparison, for any given air pressure, disc brakes 
typically do not have variations in torque output exceeding 10 percent. 
Thus, in a tractor with two disc brakes on the steer axle under 
braking, there would typically be less steering wheel pull during 
braking, as compared to a tractor using drum brakes. However, the 
agency is aware that if a manufacturer chose to upgrade the steer 
brakes to enhanced S-cam drum brakes, there is a potential for more 
steering wheel pull than with standard S-cam drum brakes.
---------------------------------------------------------------------------

    \48\ Hysteresis refers to friction in the foundation brake 
components.
---------------------------------------------------------------------------

    Steering wheel pull on split-mu road surfaces is a potential 
problem with any type of brake (although most significantly with 
enhanced drum brakes), but there are various steps that

[[Page 37142]]

manufacturers can take to ameliorate the problem. One approach is to 
utilize a modified individual wheel ABS control strategy to reduce the 
pressure to both steer axle brakes in the event the wheel on the low-
friction surface approaches lockup. In its comments, Meritor Wabco 
stated that most of today's antilock systems use Modified Individual 
Regulation (MIR) on the steer axle to reduce the yaw moment produced 
when different levels of torque are generated by the steer axle brakes, 
a situation that typically occurs during braking on split-mu surfaces. 
According to the commenter, after a short amount of time, the pressure 
can be adjusted to match the friction at each wheel. This action can 
result in steering wheel pull, but it is added incrementally, so it 
does not surprise the driver. This method of ABS control ensures that 
the driver is able to easily control the vehicle during the maneuver, 
and it also produces a shorter stopping distance by taking advantage of 
the higher braking forces generated by the wheel on the high friction 
surface. Thus, the agency believes that the potential for additional 
steering wheel pull is small, and when combined with advancements in 
ABS and the use of disc brakes, we have decided that this is not a 
reason to adopt a less stringent stopping distance requirement.
3. Brake Balance and Trailer Compatibility Issues for Tractors With 
Improved Brake Systems
a. Brake Balance Between the Steer and Drive Axles
    ``Brake balance'' refers to the concept that brakes on the steer 
axle and drive axle(s) should provide approximately equal shares of the 
retardation force in response to the dynamic loads placed on them 
during hard braking. Currently, the drive axle brakes of many tractors 
produce a large percentage of the total brake torque during heavy 
braking, as steer axle brakes are designed for long life. When 
addressing the issue of good brake balance on a tractor that is loaded 
to its GVWR and subjected to a full treadle brake application, the 
agency must take into account that the vertical load on the steer axle 
can increase by up to 50 percent or more. It is therefore expected that 
manufacturers will meet the reduced stopping distance requirements in 
this rulemaking primarily by improving the brake torque of steer axle 
brakes, thus allowing good brake balance during hard braking 
applications.
    The agency notes that a bobtail tractor (i.e., with no trailer) 
will generally have poor brake balance. This is because the drive axles 
have a very low vertical loading, while the steer axle is typically 
closer to its rated capacity. In that case, a tractor is reliant on its 
ABS to prevent drive axle wheel lockup during moderate and hard brake 
applications. This rulemaking will not have a substantial effect on the 
brake balance of tractors operated in the bobtail condition.
    Achieving the desired loaded-to-GVWR, limit-of-performance stopping 
distance reduction, as well as brake balance, will generally require 
upgrades to both the steer and drive axles of a truck tractor. The 
benefits of this rulemaking will primarily be achieved by increasing 
the steer axle brake power on tractors. As previously discussed, small 
improvements are also likely to be needed on tractor drive axles, as 
test data show there were no tractors complying with 30 percent 
reductions in stopping distance, with good margins of compliance, using 
standard-sized 16.5'' x 7'' drive axle S-cam drum brakes. Agency 
testing has shown that increasing the drive axle brake power allows 
better utilization of the available tire friction and reduces brake 
fade during a single high-speed stop and also during repetitive stops 
at all speeds.
    Several organizations commented on the issue of brake balance 
between the steer and drive axles. HDMBC stated that improvements in 
brake torque will mainly be on the steer axles of tractors, and this 
will result in the steer axle doing a larger share of combination 
braking work that could affect brake wear balance. However, HDBMC did 
not recommend that NHTSA take any particular regulatory action in light 
of this. Haldex stated that more evaluation will be needed to determine 
the effects of improved braking systems on brake balance.
    The agency agrees that the majority of improvements in tractor 
braking performance will be gained by significant increases in steer 
axle brake torque. The agency believes that this will result in 
improvements in the tractor's brake balance during maximum effort 
braking, as under current conditions, standard steer axle brakes do not 
have the same power as drive axle brakes. The agency also believes that 
modest increases in tractor drive axle brake torque will be necessary 
for most tractors, but we do not think that this will cause significant 
brake balance issues, as some commenters argued. In reaching this 
conclusion, the agency notes that the available test data show that one 
of the best-performing three-axle tractors (used in the Radlinski 
tests) was a tractor currently used in regular fleet service, so we 
presume that this vehicle exhibited acceptable brake balance in terms 
of both performance and maintenance costs. We also note that the 
enhanced drive axle drum brakes on this tractor (16.5'' x 8.625'') were 
primarily designed for long service life. This is achieved by operating 
at lower temperatures during low-pressure braking, thereby reducing 
lining wear that is temperature-sensitive.
    In its comments, ArvinMeritor argued that reductions in stopping 
distance of over 25 percent would adversely impact brake balance and 
would likely result in significant dissatisfaction on the part of end 
users. ArvinMeritor stated that these concerns specifically include 
brake lining life reductions, brake drum durability problems, more 
frequent maintenance, and reduced vehicle uptime as a result of these 
issues. ArvinMeritor also stated that tractor-trailer compatibility 
will be a significant issue if the standard were to require stopping 
distance to be reduced by more than 25 percent from current levels. The 
commenter claimed that the mixing of new truck tractors with either new 
or old trailers would represent a real and disruptive issue for the 
trucking industry, although it failed to state why it would cause 
disruption.
    Without any supporting data for ArvinMeritor's comment, the agency 
cannot accept its above-stated position, particularly given the 
substantial evidence in the record that tractor-trailer compatibility 
will not be negatively affected by the improved foundation brake 
systems on new truck tractors. Although the agency is not aware of any 
published reports on the compatibility issue of tractors with improved 
brake systems being used with the existing trailer fleet, we note that 
the tests conducted by Radlinski (using a three-axle tractor with 
enhanced S-cam drum brakes on both the steer and drive axles) were with 
a production vehicle used in regular fleet service. Those tests were 
conducted in 2003, and tractors such as the one tested have been in use 
since at least that time, with no indications of brake balance or 
trailer compatibility problems of which the agency is aware. Further, 
in 2004, the agency (in concert with other government agencies and 
private industry partners under cooperative agreement contract) 
completed field tests of 50 Volvo three-axle tractors equipped with 
disc brakes in regular fleet service.\49\ The disc brakes were one 
component of several crash avoidance enhancement systems installed on 
these tractors. No compatibility or brake

[[Page 37143]]

balance issues were found among these vehicles during extensive 
operation with trailers equipped with standard, 16.5'' x 7'' S-cam drum 
brakes. Brake lining wear rates on the tractors were lower than those 
of standard drum brake components, and similar to the wear rates of 
extended life (enhanced) S-cam drum brakes.
---------------------------------------------------------------------------

    \49\ See http://www.itsdocs.fhwa.dot.gov/JPODOCS/REPTS_TE/14349.htm.
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b. Tractor-Trailer Compatibility
    ``Tractor-trailer compatibility'' is closely related to brake 
balance and has a similar definition. Traditionally, that term has been 
defined to mean equal truck tractor drive axle brake operating 
conditions and life relative to trailer axle brake operating conditions 
and life. The compatibility issue is important for end-users of 
tractor-trailers, as they desire even wear on trailer and tractor drive 
axle brakes. One commenter, ArvinMeritor, stated that typically, 
tractor-trailer compatibility does not include steer axle brakes, due 
to comparatively lower torque output and resulting longer life compared 
to the other brakes in the combination. The agency understands that 
under the current stopping distance requirements, typical steer axle 
drum brakes (15'' x 4'') have comparatively low torque output and long 
life compared to brakes at other wheel positions.
    Several commenters argued that the majority of braking takes place 
at pressures between 10 psi and 15 psi, as opposed to full treadle 
brake applications. HDMBC commented that at these pressures, balanced 
brake wear is expected between the truck tractor and trailer by the end 
user. HDBMC stated that further evaluation may be needed in light of 
the increased percentage of braking contributed by the truck tractor.
    Similarly, many commenters discussed how the improved stopping 
distance requirements in the agency's proposal would require the 
tractor to take on an increased percentage of the total braking of the 
truck tractor/trailer combination. Haldex and HDBMC both raised this 
issue, although neither recommended that NHTSA take any particular 
regulatory action in light of this issue. HDBMC stated that its purpose 
in commenting on this issue was to highlight the impact that reduced 
stopping distance requirements will have on maintenance costs and end-
user acceptance of new vehicles, while Haldex merely stated that brake 
balance will require more evaluation.
    ATA commented that tractor-trailer compatibility should not be an 
issue if stopping distance were reduced by only 20 percent. However, 
ATA did not comment on potential compatibility issues for a 30 percent 
reduction. ATA stated that in the case of two-axle and severe service 
tractors, there could be operational or safety issues associated with 
the reduced stopping distance proposal, and, therefore, a delay in the 
implementation of new requirements for those vehicles would be needed 
to overcome these issues.
    ArvinMeritor relayed significant concerns regarding tractor-trailer 
compatibility in its comments. ArvinMeritor stated that reductions in 
stopping distance of up to 25 percent can be achieved without 
sacrificing brake balance or tractor-trailer compatibility. It stated 
that this is because that level of reduced stopping distance can be 
achieved by only increasing steer axle brake torque. However, it stated 
that for reductions of over 25 percent, increases in tractor drive axle 
torque will be necessary, and that this will adversely impact brake 
compatibility and result in more frequent brake maintenance and reduced 
vehicle uptime. Arvin Meritor stated that it does not have enough 
information on the compatibility of tractors with air disc brakes when 
operated with the existing trailer fleet to provide more specific 
comments.
    NHTSA does have testing information on disc brakes, and after 
evaluating that data, the agency believes that disc brakes installed on 
a typical three-axle tractor's drive axles would not have detrimental 
brake balance issues during braking. Dynamometer testing was performed 
at VRTC on two brands of 16.5'' x 7'' S-cam drum brakes and two brands 
of air disc brakes (one 16.93'' rotor diameter x 1.77'' rotor 
thickness, the other 16.90'' x 1.77'') \50\ to quantify such 
characteristics. In one comparison of an S-cam drum brake to a disc 
brake, similar torque outputs were produced when each brake was stopped 
on the dynamometer from an initial speed of 30 mph. However, when 
stopped from a high speed of 70 mph, the S-cam drum brake lost 42 
percent of its maximum effectiveness while the disc brake lost only 24 
percent of its maximum effectiveness. Such a disc brake, when installed 
on a typical tractor drive axle, would not be expected to have 
detrimental brake balance issues under normal, low-pressure braking 
because the torque output is similar to the drum brake. In addition, it 
provides much shorter stopping distance when under hard braking from 
highway speeds because of reduced brake fade.
---------------------------------------------------------------------------

    \50\ SAE Technical Report, Comparison of Heavy Truck Foundation 
Brake Performance Measured with an Inertia Brake Dynamometer and 
Analyses of Brake Output Responses to Dynamic Pressure Inputs (SAE 
Report No. 2005-01-3611, Hoover and Zagorski, Transportation 
Research Center, Inc.). Available from SAE, and the report is 
available for review at NHTSA's Technical Reference Division.
---------------------------------------------------------------------------

    There is also the possibility that the drive axle can be equipped 
with an enhanced S-cam drum brake instead of an air disc brake, as it 
would be in a hybrid or all-drum brake configuration. While the agency 
has not completed sufficient testing of enhanced drive/trailer axle S-
cam drum brakes (either 16.5'' x 8'' or 16.5'' x 8.625'') under its 
dynamometer test program at VRTC to determine the reasons for improved 
torque generation, it is likely that the wider brake drum has increased 
thermal capacity. This is because the total friction between the lining 
and the drum would take place spread out over a larger area. Therefore, 
during a single, 60 mph stop, experience has shown that there would be 
less fade than for a standard 16.5'' x 7'' axle brake. The agency may 
conduct future dynamometer testing at VRTC to determine in further 
detail the characteristics of the enhanced S-cam tractor drive axle 
drum brake. Currently, however, the agency refers back to the use of 
the in-service truck tractor used in the Radlinski tests (which used 
enhanced drum brakes) as evidence of the lack of significant brake 
balance issues using enhanced S-cam drive axle drum brakes.
c. Brake Balance and Trailer Compatibility Issues for Two-Axle and 
Severe Service Tractors
    NHTSA does not believe that two-axle or severe service tractors 
will have problems with regard to brake balance and trailer 
compatibility.
    There were no comments regarding tractor-trailer compatibility for 
two-axle tractors, although Freightliner expressed concern that two-
axle tractors may suffer from tractor-trailer compatibility problems of 
reduced balance when used with existing trailer brakes. The agency is 
aware of little data on the brake balance and trailer compatibility 
issues for two-axle tractors with improved brake systems, and most of 
the comments on two-axle tractors were concerns with stability and 
control rather than issues of balance between steer and drive or 
tractor and trailer brakes. NHTSA is aware that some two-axle tractors 
are already being equipped with larger 16.5'' x 5'' steer axle S-cam 
brakes, and presumably these brakes are providing satisfactory brake 
balance trailer compatibility in fleet service. While test data cited 
above shows that two-axle tractors can attain the reduced stopping 
distances using disc brakes on the steer and drive axles, that data did 
not consider compatibility with existing

[[Page 37144]]

trailers (and converter dollies, as two-axle tractors are often used in 
double- or triple-trailer combinations).
    Given the lack of data or other evidence of a problem, we think 
that Freightliner's arguments in this context involve speculative 
concerns; consequently, the agency currently has no reason to believe 
that two-axle tractors with improved brake systems will have 
compatibility issues. Nonetheless, considering the complexity of brake 
system interactions and the current lack of available data (as well as 
for many other reasons, discussed at length below), the agency has 
decided to provide longer lead time for the requirements of this final 
rule for two-axle and severe service tractors so as to provide four 
years of lead time. This will provide truck manufacturers time to 
develop designs that do not have problems in this area.
    The agency similarly received few comments regarding trailer 
compatibility for severe service tractors. However, both TMA and 
Freightliner stated that some heavier severe service tractors are 
limited to low speeds when fully loaded, and if such a tractor were 
required to comply with shorter stopping distances from 60 mph, the 
brakes would be over-designed (i.e., be too powerful for their typical 
usages). At highway speeds with light loads, this could result in 
excessive wheel lockup.
    The agency has already partially addressed this issue by providing 
a longer, 310-foot stopping distance requirement for high-GVWR severe 
service tractors. We understand that many of the severe service 
tractors that require escort vehicles and low speeds when loaded to 
GVWR fall into this category, or have a GAWR over 29,000 pounds, and 
thus are excluded from FMVSS No. 121 entirely. In addition, because the 
overall brake balance problem for the widely-varying loading condition 
already exists for these vehicles, we believe that installation of 
improved brake systems on severe service tractors would have only an 
incremental (and minimal) effect on brake balance and trailer 
compatibility.
iii. Cargo Securement
    A comment from OOIDA stated concern that the proposed requirement 
of shorter stopping distances would increase the g-forces acting upon a 
truck's load to the point where such forces exceed the conditions 
specified in standards for cargo securement under Federal Motor Carrier 
Safety Administration (FMCSA) regulations. Under the relevant 
provisions of FMCSA's cargo securement requirements, 49 CFR 
393.102(a)(1) provides that tiedown assemblies (including chains, wire 
rope, steel strapping, synthetic webbing, and cordage) and other 
attachment or fastening devices must be designed, installed, and 
maintained to ensure that the maximum forces acting on the devices do 
not exceed the manufacturer's breaking strength under a 0.8g 
deceleration in the forward direction. These requirements were adopted 
in a September 27, 2002 final rule (67 FR 61212) and became effective 
on January 1, 2004. The purpose of this FMCSA requirement is to reduce 
crashes caused by incidents of shifting and falling cargo.
    In response to OOIDA's comment, the agency reviewed deceleration 
rates from tractor tests with improved brake systems to determine 
whether the cargo securement limits had been reached. Agency testing 
indicated that under FMVSS No. 121 testing in the loaded-to-GVWR 
condition with an unbraked control trailer, deceleration rates of 
approximately 0.65g were typical. However, as noted by Freightliner in 
its comments, such a tractor is capable of higher deceleration rates 
when operating with a normal load on a braked trailer. Freightliner 
stated that tests of such a combination vehicle showed that it was able 
to stop in 187 feet from a speed of 60 mph, but did not provide 
deceleration data for this test.
    After reviewing the previously-discussed data from VRTC, NHTSA 
believes that trailers will not exceed FCMSA's cargo securement 
requirement. The agency analyzed stopping data for a two-axle tractor 
equipped with disc brakes at all wheel positions, towing a 53-foot van 
trailer which was also equipped with disc brakes. The tractor and 
trailer had normal ABS control of all wheels, and had the shortest 
measured stopping distance of all tractor-trailer combination tests at 
VRTC. In the test, the tractor steer axle was loaded to 11,000 pounds; 
its drive axle was loaded to 22,700 pounds, and the tandem trailer 
axles were loaded to 34,000 pounds (loaded-to-highway weight). This 
combination stopped from 60 mph in a distance of 186 feet. NHTSA 
reviewed the deceleration rate during the stop and notes that 
deceleration was fairly constant at approximately 0.8g once steady-
state deceleration was achieved (approximately 0.6 seconds after the 
full treadle application).\51\ We do note that there were momentary 
spikes of higher and lower deceleration (typical for data traces of 
this type), with the highest peak at 0.89g for a very short duration. 
However, the accelerometer was mounted on the tractor frame, and it is 
NHTSA's belief that the acceleration peaks were anomalies likely due to 
vibration, as it would not possible for a massive object such as a 
loaded tractor or trailer to have acceleration rate changes indicated 
by the peaks. Therefore, the agency has concluded that the highest 
deceleration rate by a tractor with improved brakes was slightly below 
0.8g, thus remaining under the deceleration specified by FMCSA's cargo 
securement requirement.
---------------------------------------------------------------------------

    \51\ Docket  NHTSA-2005-21462-39, p. 28.
---------------------------------------------------------------------------

    The agency also reviewed deceleration data for the VRTC test 
tractor in the unloaded condition, and we arrived at similar 
conclusions. The unloaded stopping distance for this tractor-trailer 
combination was 191 feet (a longer stopping distance than 187 feet, and 
thus producing even less g-forces on deceleration), which indicates 
that both in the loaded and unloaded condition the limits of tire 
adhesion have been reached. The slightly longer stopping distance in 
the unloaded condition is likely due to additional cycling of the ABS 
on both the tractor and trailer compared to the loaded-to-highway 
weight testing.
iv. Testing Procedures
1. Brake Burnish Issues for Tractors With Improved Brake Systems
    As discussed in this section, brake burnishing is the process of 
wearing in the friction components of foundation brakes (brake linings 
and brake drums or disc rotors), which is necessary to allow the 
friction surfaces to reach a close-to-normal operating condition prior 
to conducting stopping distance and grade-holding tests. Currently, in 
FMVSS No. 121, the burnish procedure is specified in S6.1.8. This 
procedure involves subjecting a tractor to a series of 500 brake 
``snubs'' (i.e., applications of the brake) from an initial speed of 40 
mph to a final speed of 20 mph. Virtually all heavy vehicles (trucks, 
tractors, and buses) use this burnish procedure. Prior to September 1, 
1993, vehicle manufacturers were able to use an alternate burnish 
procedure, which conducted the snubs from higher initial speeds.\52\ 
The primary difference between these two procedures is the temperature 
at which the brake operates during the burnish. The current procedure 
is frequently referred to as a ``cold burnish,'' because the brake 
temperatures typically reach only 300-400 degrees Fahrenheit (F), 
whereas the

[[Page 37145]]

old procedure is known as a ``hot burnish,'' as the temperatures 
typically reached 500 degrees F or more. The reason the agency changed 
from the hot to cold burnish procedure is that when heavy vehicles are 
operated on the road under normal conditions, the brakes may never 
reach the same temperatures that are reached under the hot burnish 
procedure. Therefore, the real world brake performance may have been 
lower than that tested under FMVSS No. 121 before September 1993.
---------------------------------------------------------------------------

    \52\ See 53 FR 8190.
---------------------------------------------------------------------------

    In the March 14, 1988 final rule establishing the brake burnish 
procedures, NHTSA stated that given ``consistent research findings 
about the temperatures to which drum brakes are subjected during normal 
driving, the agency concludes that a burnish that subjects drum brakes 
to significantly higher temperatures cannot be said to be 
representative of normal driving conditions. By allowing the drum 
brakes to be heated to temperatures well in excess of those encountered 
during normal driving, the burnish procedures would ideally condition 
the drum brakes. However, the agency is more interested in the braking 
capability of vehicles when the brakes are in the condition they are 
most likely to be when used on the roads than in the maximum braking 
capability of a braking system if the brakes are ideally conditioned.'' 
See 53 FR 8194.
    Several commenters recommended that changes to the burnish 
procedure be made in relation to the agency's overall efforts to 
achieve a reduction in stopping distances for truck tractors. 
Specifically, comments on this issue were raised by HDBMC, which 
recommended changes to the current burnish procedure that would allow 
the brake linings to be burnished at higher temperatures than the 
current burnish procedure produces (essentially a return to the pre-
1993 requirements). While the agency has considered the comments 
relating to burnish procedure, it has decided not to make any changes 
to that procedure in this rulemaking, for the reasons that follow.
    HDBMC recommended in its comments that NHTSA reinstate an optional 
temperature in FMVSS No. 121, as permitted prior to September 1, 1993, 
to use the hot burnish procedure. HDBMC stated that in order to achieve 
the proposed reduction in stopping distance, many tractors will be 
equipped with higher torque steer axle brakes. In addition, the 
commenter stated that there tractors will also likely be equipped with 
wider rear axle brakes (arguing that because NHTSA is mandating a 30-
percent reduction in stopping distance, most vehicles will be using 
wider drive axle drum brakes or disc brakes). As a result, the 
commenter reasoned that steer axle brakes will do more of the work 
during burnish, thus lowering the temperature on the drive axle brakes. 
If wider drive axle drum brakes are used, HDBMC continued, this will 
result in further lowering of the drive axle brake temperatures. These 
lower temperatures could result in insufficient brake burnishing on the 
drive axle brakes. If this were the case, higher friction brake linings 
on the drive axle brakes may be required, likely resulting in higher 
maintenance costs and less end-user satisfaction.\53\ Further, HDBMC 
indicated that the decreased lining contact on the drive axles may 
negatively impact parking brake drawbar pull performance. HDBMC 
provided an example where a tractor with standard (15'' x 4'') steer 
axle drum brakes was able to achieve 8,800 pounds of parking brake 
force, while with enhanced (16.5'' x 5'') steer axle drum brakes it 
produced only 8,000 pounds of force.
---------------------------------------------------------------------------

    \53\ According to comments by TMA, aggressive high friction 
brake linings designed to meet strict performance criteria can 
produce unsatisfactory results when used in real-world applications. 
For example, in one scenario, TMA suggested that overly aggressive 
brake linings could glaze over under normal use conditions. This 
could lead to brake chatter and the subsequent failure of numerous 
components. TMA Comment from April 14, 2006, available at NHTSA-
2005-21462-34).
---------------------------------------------------------------------------

    According to HDBMC, therefore, if NHTSA required the improved 
stopping distances without altering the burnish procedure to provide 
better burnishing, vehicle manufacturers would have to provide highly 
unsatisfactory brake linings in order to meet the standard, which would 
be unfit then for on-road use. Therefore, HDBMC suggests that the 
burnish procedure be altered.
    As discussed in the rulemaking cited above concerning burnish, the 
agency believes it is appropriate to test the braking capability of 
vehicles when the brakes are in the condition they are most likely to 
be when used on the roads. For this reason, we do not believe it would 
be appropriate to modify the burnish procedure so that it is less 
reflective of the conditioning experienced by brakes in the real world. 
However, we have analyzed whether the proposed reduced stopping 
distance requirements, coupled with the ``cold burnish'' procedure, 
would result in the problems suggested by HDBMC. For reasons discussed 
below, we believe these problems will not occur.
    NHTSA has reviewed the agency's data from the Radlinski testing in 
order to consider this issue. This test used the current cold burnish 
procedure in preparation for testing a typical three-axle tractor with 
enhanced S-cam drum brakes at all wheel positions, and that vehicle 
achieved a 30-percent reduction in stopping distance with a good margin 
of compliance. Based on the review of all of the test data for this 
vehicle, as well as the simple fact that the vehicle was able to 
achieve the required stopping distances using the cold burnish 
procedure, the agency concluded that the current procedure adequately 
conditioned the foundation brakes in preparation for conducting the 
remainder of the FMVSS No. 121 test sequence.
    A review of the three-axle tractor tests conducted by Radlinski 
provides insight into the brake lining condition and temperatures of 
improved braking systems during and after the cold burnish procedure. 
Comparing two tests using the same brake lining (Spicer EES 420 linings 
on the steer and drive axles, with ArvinMeritor cast iron drums) at two 
drive axle GAWRs (34,000 and 40,000 pounds) showed that the lining 
contact patterns on the drive axle brakes (the percentage of the lining 
surface that is in full contact with the brake drum) after burnish 
appeared to be slightly better at the higher 40,000-pound GAWR. Steer 
axle burnish contact patterns for the two test conditions were 
approximately the same. Drive axle lining temperatures for the two test 
conditions throughout the burnish showed slightly higher temperatures 
for the 40,000-pound GAWR test (average approximately 400 degrees F) 
than for the 36,000-pound GAWR test (average approximately 380 degrees 
F), with the highest temperatures occurring at the end of the burnish 
sequence. Steer axle burnish temperatures were approximately the same 
for both test conditions and averaged around 280 degrees F.
    Parking brake force was also adequate using the current burnish 
procedure. The average parking brake force (forward and rearward 
drawbar pulls, four tests with one-quarter wheel revolution per test, 
with parking brakes on the forward drive axle only) slightly favored 
the lower drive axle GAWRs. Although lining contact patterns were about 
the same for the front drive axle (which is not the one equipped with 
the parking brakes), overall, the tests at the higher GAWR had slightly 
more lining contact among both drive axles, which is consistent with 
the slightly higher burnish temperatures. Parking brake performance 
measured by the drawbar method \54\ showed that with the tests 
conducted at 36,000 pounds GAWR, the margin of compliance was

[[Page 37146]]

approximately 35 percent. The margin of compliance for the tests with 
the drive axles rated at 40,000 pounds GAWR was approximately 20 
percent.
---------------------------------------------------------------------------

    \54\ FMVSS No. 121, S5.6.
---------------------------------------------------------------------------

    During the loaded-to-GVWR service brake stops from 60 mph, the 
tests with the drive axles at 36,000 pounds GAWR and Type 20 brake 
chambers on the steer axle showed that steer axle brake temperatures 
were typically 30 to 40 degrees F lower than the drive axle lining 
temperatures (that averaged around 180 degrees F) during the first half 
of the stop. However, the steer axle temperatures during the second 
half of the stop increased to approximately the same temperatures as 
the drive axle brakes. When tested with Type 24 brake chambers on the 
steer axle, temperature trends during the stop were similar, except 
that the steer axle brakes were approximately 20 degrees F hotter than 
for the tests with Type 20 steer axle brake chambers. In both cases, 
the steer axle brake temperatures increased more than the drive axle 
temperatures over the duration of the stops.
    The agency has concluded from reviewing the brake temperatures 
during the burnish, and the brake temperatures and stopping distance 
data during the loaded-to-GVWR tests, that under the various 
combinations of drive axle GAWRs, brake chamber sizes, and slack 
adjusters that were reviewed, the vehicle appeared to perform optimally 
in all regards. The parking brake drawbar test margins of compliance 
were also good, with the tests at the lower GAWR having slightly better 
compliance margins. In sum, the test results revealed that the current 
burnish procedure provided adequate burnishing for tractors with 
improved braking systems to meet both service brake stopping distance 
requirements as well as parking brake requirements.
    The agency also recognizes that the results from tests conducted by 
Radlinski may not be as applicable to two-axle or severe service 
tractors. However, agency stopping distance testing on these tractors 
indicated that installation of disc brakes generally would be required 
in order to meet the improved stopping distance requirements. Agency 
tests with disc brakes showed that there were no apparent brake burnish 
problems, and disc brakes are generally less sensitive to the burnish 
procedure because of the geometry of the linings and rotors. Disc 
brakes' linings and rotors are manufactured with flat friction surfaces 
that mate well when assembled on the vehicle. Thus, there is little 
wear-in necessary to achieve full lining to rotor contact, and the 
brakes readily achieve full torque-generating capability under the 
existing FMVSS No. 121 burnish procedure.
    VRTC testing of two-axle and severe service tractors demonstrated 
that these vehicles are able to achieve the required stopping distances 
using the cold burnish procedure. VRTC tests on a two-axle tractor with 
a 148-inch wheelbase, using all disc brakes, yielded a 200-foot 
stopping distance and good parking brake performance. Tests on the same 
tractor with a hybrid braking system yielded a 223-foot stopping 
distance.\55\ Preliminary tests of the three-axle severe service 
surrogate tractor (i.e., a single-unit truck) with a hybrid brake 
configuration (disc brakes on the steer axle and standard 16.5'' x 7'' 
drum brakes on the drive axles) showed mixed results. After the burnish 
procedure, the drive axle brakes showed less contact area after 
burnishing than when the truck was tested with drum brakes on the steer 
axle, supporting HDBMC's argument. However, the test results for the 
hybrid configuration showed higher parking brake drawbar forces on the 
drive axles when compared to tests of the all-drum brake vehicle that 
had more drive axle lining contact area after burnish.\56\ Based on the 
test results, it is evident that the current FMVSS No. 121 brake 
burnish procedure provides adequate burnishing to conduct the required 
tests for stopping distance and parking brake pull.
---------------------------------------------------------------------------

    \55\ VRTC testing of the two-axle tractor with all drum brakes 
revealed problems with replacement brake linings, but the agency has 
yet to determine how much of the problem is due to burnish procedure 
versus lining properties. This test yielded two different stopping 
distances (241 feet versus 332 feet) with original and replacement 
brake linings. When the replacement linings were machined to better 
match the curvature of the drums, they achieved similar stopping 
distances, leading NHTSA to believe that the cause is related to the 
lining properties, and not the burnish procedure. Regardless, 
neither lining was able to achieve a 30 percent reduction in 
stopping distance with a 10 percent margin of compliance.
    \56\ Currently, additional brake research is underway on this 
vehicle to determine stopping distance and brake burnish effect 
interactions with enhanced drum brakes.
---------------------------------------------------------------------------

    In summary, based upon available data, NHTSA has decided to 
maintain its prior rulemaking decision amending FMVSS No. 121 to 
require the use of the cold burnish procedure. The agency is not aware 
of an actual problem with the burnish procedure for typical three-axle 
tractors. The agency's testing revealed that all types of tractors were 
able to meet the required stopping distances using the existing cold 
burnish procedure. Furthermore, there is no evidence that the current 
burnish procedure is not indicative of real-world braking conditions. 
Therefore, we see no need to make any changes to the burnish 
requirements of FMVSS No. 121.
2. Brake Dynamometer Test Requirements
    In the NPRM, the agency requested recommendations on potential 
modifications to the brake dynamometer requirements of FMVSS No. 121. 
These requirements test brake retardation force, power, and recovery 
under strict conditions. The agency received a variety of responses to 
this request. The majority of commenters stated that they recommend no 
changes to the dynamometer requirements. However, NHTSA received one 
comment (ArvinMeritor), suggesting the addition of an optional 
dynamometer procedure. For the reasons discussed below, the agency has 
considered the comments, and has decided that no action is necessary or 
appropriate at this time.
    Currently, the requirements of paragraph S5.4.2, Brake power, apply 
to all foundation brakes for all air-braked vehicles covered under 
FMVSS No. 121. Under the standard, after burnishing, the fade portion 
of the test specifies ten consecutive snubs from 50 to 15 mph at a 
deceleration rate of 9 ft/sec\2\, followed by a hot stop from 20 mph at 
a deceleration rate of 14 ft/sec\2\. After the hot stop, 20 brake 
recovery stops from 30 mph at a deceleration rate of 12 ft/sec \2\ at 
one minute intervals are made.\57\ Brake pressure limits are placed on 
the fade and recovery requirements, while the hot stop does not have an 
upper air pressure limitation.
---------------------------------------------------------------------------

    \57\ These requirements do not apply to the steer axle of 
tractors.
---------------------------------------------------------------------------

    ArvinMeritor requested that NHTSA modify the dynamometer test 
procedure to allow the option of conducting a series of six 60 mph 100 
psi stops at the conclusion of the 350 degree F dynamometer 
burnish.\58\ ArvinMeritor stated that it believes the torque data 
obtained from these stops would be closer to the brake torques obtained 
during the vehicle stopping distance test and, therefore, would provide 
a more accurate stopping distance calculation. Currently, it states, 
because the temperatures in the dynamometer tests significantly exceed 
those generated during the stopping distance tests, the dynamometer 
performance data do not always correlate directly with the actual 
vehicle test results. According to ArvinMeritor, the optional stops, 
conducted before the brakes are burnished at the high temperatures,\59\

[[Page 37147]]

would provide data that better correlate with data from the actual 
tests, where the brakes have undergone similar lower-temperature 
burnishing.
---------------------------------------------------------------------------

    \58\ See S6.2.6.
    \59\ Subsequent to this procedure, the brakes are burnished at a 
temperature between 450[deg] and 550[deg].
---------------------------------------------------------------------------

    While there is some cause to believe that allowing an additional 
six stops from 60 mph would provide useful information for modeling 
purposes, as ArvinMeritor asserts, NHTSA does not have enough 
information to adopt this recommendation. ArvinMeritor did not describe 
what the test conditions would be for these optional stops (such as the 
initial brake temperature or intervals between stops), but we assume 
they would be conducted with an initial brake temperature between 150 
and 200 degrees F, with a cool-down to that initial temperature between 
stops. If so, the optional stops would probably not have much influence 
on the remainder of the dynamometer test requirements, since those 
stops occur in much higher temperature ranges. However, such stops 
could have an influence on the brake retardation force requirements in 
S5.4.1, if the 60 mph optional stops resulted in additional higher 
temperature burnishing beyond the required burnish procedure. The 
agency would need more information on the potential benefits and 
ramifications of this procedure prior to amending the standard to 
specify a manufacturer option in this area.
    Two commenters (HDBMC and Haldex) recommended that there be no 
changes made to the current dynamometer requirements. Both stated that 
the current requirements do not limit the amount of steer axle brake 
torque. (Haldex also mentioned that there is no limit in drive axle 
brake torque.) As the increases in stopping distance will largely be 
achieved through increasing steer axle brake torque, both commenters 
stated that this aspect of the requirements should not be changed. A 
third commenter (Bendix) stated that it is conducting dynamometer 
testing and would be willing to provide this information to NHTSA on a 
confidential basis upon completion of its testing program, although 
this information has not been received.
    TMA commented that the agency could not make any changes to the 
dynamometer requirements without first issuing a separate NPRM, as no 
specific changes to these requirements were proposed in the NPRM for 
this rule. TMA stated that if the agency did go through with a separate 
rulemaking to modify the dynamometer requirements, it would likely need 
to have a different effective date than the one mandated in this final 
rule. In that case, according to TMA, the effect would be to undo all 
the work TMA member companies will need to do to respond to the current 
final rule, since designs will have been tailored to meet the 
currently-proposed requirements. TMA stated that any component change 
can greatly influence performance of the braking system, and as a 
result, TMA members require a 10-year stability period between 
rulemakings that affect brake system design in order to amortize 
development and investment costs. While this comment does not 
substantively address the issue of possible changes to the dynamometer 
requirements, the agency has taken TMA's concerns into consideration.
    Based on the comments received and our assessment of this issue, 
the agency has decided not to modify the dynamometer test requirements. 
TMA's concerns notwithstanding, the agency believes that, if necessary, 
it would be better to consider revisions to the dynamometer 
requirements in a future rulemaking effort separate from the current 
tractor stopping distance rulemaking.
v. Stopping Distances at Reduced Initial Test Speeds
    HDBMC and Bendix commented that in the NPRM, the 20 percent and 30 
percent stopping distance reduction values in Table II of FMVSS No. 121 
for test speeds below 60 mph did not take into account the brake system 
reaction time and average deceleration. Thus, under the agency's 
proposed stopping distance requirements for a 30 percent reduction in 
stopping distance from an initial speed of 20 mph, the commenters 
stated that an average deceleration as high as 0.95 g would be 
necessary (with an allowance for a 10 percent margin of compliance in 
stopping distance). According to the commenters, this deceleration rate 
is not achievable with existing truck braking and tire technology.
    The agency has reviewed the tables of stopping distances provided 
by HDBMC and Bendix in their respective comments. In the case of HDBMC, 
it did not indicate what equations or methods it used to derive their 
recommended tables. For example, the agency could not determine what 
was occurring during the brake system reaction time (for 0.36, 0.45, 
and 0.54 second reaction times). Bendix provided similar 
recommendations but again it did not describe how its recommended 
tables of stopping distance were derived. The agency believes that 
because both commenters recommended stopping distances at reduced test 
speeds that are much longer than what the agency had proposed, the 
commenters' recommendations are not accounting for the buildup in 
deceleration that the agency's data indicate does occur during the 
initial brake pressure increase during typical stopping distance tests 
using a full treadle valve brake application. Nevertheless, after 
consideration of this issue the agency is providing the following 
analysis and revised stopping distance stables for tests conducted at 
reduced test speeds.\60\
---------------------------------------------------------------------------

    \60\ We note that the neither the notice of proposed rulemaking, 
nor the previous rulemaking on this issue (53 FR 8190), contained 
detailed information on how the stopping distances for reduced 
initial test speeds were derived.
---------------------------------------------------------------------------

    For this analysis, we are using the stopping distance equation that 
was derived by researchers at the VRTC. The equation is as follows:

St = (\1/2\ Vo tr) + ((\1/2\) 
Vo\2\;/af)--((1/24) af 
tr\2\;)

Where:
St = Total stopping distance in feet
Vo = Initial Speed in ft/sec
tr = Air pressure rise time in seconds
af = Steady state deceleration in ft/sec[sup2]

    The complete derivation of this equation is included in the 
docket.\61\ For the final rule, we selected an air pressure rise time 
of 0.45 seconds that is equal to the brake actuation timing requirement 
in S5.3.3. This requirement specifies that for a truck (including a 
truck-tractor), the air pressure in the brake chambers must reach at 
least 60 psi within 0.45 seconds.
---------------------------------------------------------------------------

    \61\ See Docket No. 2005-21462-39, p. 18.
---------------------------------------------------------------------------

    The agency reviewed three test plots of deceleration versus time 
for tractor tests it conducted at VRTC to determine if the plot 
characteristics matched the stopping distance equation and the pressure 
rise time selected for this final rule. The three plots are included in 
the docket.\62\ The first plot is for the Sterling 4x2 tractor equipped 
with disc brakes at all wheel positions and coupled to a braked 53-foot 
van trailer with tandem axles also equipped with disc brakes. The 
vehicle was loaded to typical highway weight (i.e., steer axle 11,000 
pounds; drive axle 22,700 pounds, tandem trailer axles 34,000 pounds) 
that is slightly below the GVWR for each vehicle. This combination 
represents the best-performing unit that was tested at VRTC, and it had 
a 60 mph stopping distance of 186 feet. As the plot shows, the steady-
state deceleration was slightly less than 0.8g for the duration of the 
stop. The 0.8g deceleration was reached within approximately 0.5 
seconds from the point of brake application. This deceleration and 
stopping distance are believed to be the best obtainable for a tractor-
trailer

[[Page 37148]]

combination vehicle using all production equipment (tires, antilock 
braking system, air disc brakes, etc.) available at the present time.
---------------------------------------------------------------------------

    \62\ See Docket No. 2005-21462-39, p. 28.
---------------------------------------------------------------------------

    The next two plots included from VRTC tests are for tractors that 
achieved a stopping distance of approximately 250 feet. These were used 
to determine the steady-state deceleration required to achieve this 
stopping distance. The second plot \63\ is for a Volvo 6x4 tractor 
equipped with disc brakes on the steer axle and S-cam drum brakes on 
the drive axles, and it was coupled to an unbraked control trailer. The 
tractor was loaded to GVWR and was also braking the extra 4,500 pounds 
on the control trailer axle. The stopping distance for this vehicle 
from 60 mph was 249 feet and the steady state deceleration was 
approximately 0.45g. The plot shows that this tractor achieved the 
0.45g deceleration rate at approximately 0.4 seconds.
---------------------------------------------------------------------------

    \63\ Docket No. 2005-21462-39, p. 29.
---------------------------------------------------------------------------

    The third plot is for a Peterbilt 6x4 tractor equipped with 
enhanced S-cam drum brakes on the steer axle and standard S-cam drum 
brakes on the drive axles, loaded to GVWR with an unbraked control 
trailer. The 60-mph stopping distance was 250 feet, and the 
deceleration varied slightly from approximately 0.48g at the midpoint 
of the stop to approximately 0.56g near the end of the stop. The 
deceleration during the stop was not exactly stead state since the 
deceleration rate increased towards the end of the stop. The rate at 
0.45 seconds was approximately 0.36g.
    The plots for the second and third tests, the Volvo and Peterbilt 
tractors respectively, demonstrate that for a 250-foot stopping 
distance requirement, deceleration rates in the range of 0.45g to 0.56g 
would be achieved by actual vehicles. It appears that the Volvo had a 
slightly faster application timing, and thus had a lower steady-state 
deceleration rate than the Peterbilt while attaining approximately the 
same stopping distance.
    Using the VRTC equation for stopping distance, we derived the 
following three tables of stopping distance for three requirements in 
this final rule: (1) Standard service tractors loaded to GVWR plus 
4,500 pounds on the unbraked control trailer axle; (2) severe service 
tractors loaded to GVWR plus 4,500 pounds on the unbraked control 
trailer axle; and (3) all tractors tested in the lightly-loaded vehicle 
condition. Note that the table for severe service tractors contains the 
same values currently in FMVSS No. 121 for single-unit trucks loaded to 
GVWR, but we are reproducing this table here to show the estimated 
deceleration levels with a 0.45-second pressure rise time.

 Table I--Stopping Distance Calculations for Two- and Three-Axle Tractors With a GVWR of 70,000 Pounds or Less,
   and Tractors With Four or More Axles and a GVWR of 85,000 Pounds of Less, in the Loaded-to-GVWR Condition.
                                  (Brake System Reaction Time is 0.45 Seconds)
----------------------------------------------------------------------------------------------------------------
            Initial vehicle speed                       Steady-state deceleration             Stopping distance
----------------------------------------------------------------------------------------------------------------
        (mph)                 (ft/sec)             (ft/sec\2\)               (g's)                  (ft)
----------------------------------------------------------------------------------------------------------------
                20                   29.3                  18.00                   0.56                     30
                25                   36.7                  18.00                   0.56                     45
                30                   44.0                  17.50                   0.54                     65
                35                   51.3                  17.00                   0.53                     89
                40                   58.7                  17.00                   0.53                    114
                45                   66.0                  16.80                   0.52                    144
                50                   73.3                  16.80                   0.52                    176
                55                   80.7                  16.80                   0.52                    212
                60                   88.0                  16.80                   0.52                    250
----------------------------------------------------------------------------------------------------------------


  Table II--Stopping Distance Calculations for Three-Axle Tractors With a GVWR Greater Than 70,000 Pounds, and
 Tractors With Four or More Axles and a GVWR Greater Than 85,000 Pounds, in the Loaded-to-GVWR Condition. (Brake
                                      System Reaction Time of 0.45 Seconds)
----------------------------------------------------------------------------------------------------------------
            Initial vehicle speed                       Steady-state deceleration             Stopping distance
----------------------------------------------------------------------------------------------------------------
        (mph)                 (ft/sec)             (ft/sec\2\)               (g's)                  (ft)
----------------------------------------------------------------------------------------------------------------
                20                   29.3                  15.00                   0.47                     35
                25                   36.7                  14.65                   0.45                     54
                30                   44.0                  14.15                   0.44                     78
                35                   51.3                  13.90                   0.43                    106
                40                   58.7                  13.75                   0.43                    138
                45                   66.0                  13.60                   0.42                    175
                50                   73.3                  13.45                   0.42                    216
                55                   80.7                  13.40                   0.42                    261
                60                   88.0                  13.35                   0.41                    310
----------------------------------------------------------------------------------------------------------------


[[Page 37149]]


Table III--Stopping Distance Calculation for All Tractors in the Unloaded Condition. (Brake System Reaction Time
                                                of 0.45 Seconds.)
----------------------------------------------------------------------------------------------------------------
            Initial vehicle speed                       Steady-state deceleration             Stopping distance
----------------------------------------------------------------------------------------------------------------
        (mph)                 (ft/sec)             (ft/sec\2\)               (g's)                  (ft)
----------------------------------------------------------------------------------------------------------------
                20                   29.3                  19.80                   0.61                     28
                25                   36.7                  19.40                   0.60                     43
                30                   44.0                  18.80                   0.58                     61
                35                   51.3                  18.10                   0.56                     84
                40                   58.7                  18.10                   0.56                    108
                45                   66.0                  17.95                   0.56                    136
                50                   73.3                  17.95                   0.56                    166
                55                   80.7                  17.95                   0.56                    199
                60                   88.0                  17.95                   0.56                    235
----------------------------------------------------------------------------------------------------------------

    We compared the calculated values for the 60 mph, 250-foot stopping 
distance requirements in Table I for a typical tractor to those test 
vehicles described above, in order to determine if the actual and 
calculated decelerations are similar. The calculated steady-state 
deceleration from the table with an initial test speed of 60 mph is 
0.56g of deceleration, and this compares to 0.45g for the Volvo (that 
had a quicker response time, and thus slightly lower steady-state 
deceleration than the Peterbilt), and 0.48 to 0.52g for the Peterbilt 
(which had a slower response time, and thus a slightly higher steady-
state deceleration than the Volvo). These values are similar to the 
0.52g calculated in Table I, and therefore the agency believes the 
equation used to calculate the stopping distances is valid. We did not 
perform similar analyses for stopping distances conducted at other 
initial test speeds, because we did not conduct any testing at reduced 
test speeds. Only tests from an initial speed of 60 mph were conducted 
at VRTC.
    We do not understand the basis for the concerns raised by HDBMC and 
Bendix in their comments about the proposed stopping distances 
requiring abnormally high deceleration levels. As shown in the tables 
of calculated stopping distances, the maximum required deceleration for 
an unloaded tractor at an initial speed of 20 mph is 0.61g. Even with a 
ten percent added margin of compliance, the actual performance would 
not appear to need to be greater than 0.67g. As described above, for 
the tests on the Sterling tractor operated with a braked van trailer, 
deceleration of almost 0.8g was attained at highway weight. Our tests 
of unloaded tractors indicated that nearly similar stopping distance 
performance was attained in the bobtail mode, an in each case a margin 
of compliance substantially greater than 10 percent was achieved when 
the vehicle was tested from an initial speed of 60 mph. It appears to 
us that HDBMC and Bendix could be using a method such as a free-roll 
during pressure rise that would assume no braking during the initial 
pressure rise. However, these commenters did not provide enough detail 
in the comments for the agency to thoroughly evaluate their claims. In 
any event, for the reasons discussed above, we believe that the new 
stopping distance calculations for the lower initial test speeds 
properly take into account brake actuation periods, and do not require 
excessive rates of deceleration.
vi. Comments Regarding Foreign Trade Agreements
    A comment from the government of the People's Republic of China 
requested that Chinese manufacturers be given a longer transitional 
period for implementation of improved stopping distance requirements, 
citing the Agreement on Technical Barriers to Trade.\64\ China cited 
clause 12.3 of the Agreement, which reads:
---------------------------------------------------------------------------

    \64\ A summary of the treaty on the Web site of the World Trade 
Organization reads, ``[t]his agreement will extend and clarify the 
Agreement on Technical Barriers to Trade reached in the Tokyo Round. 
It seeks to ensure that technical negotiations and standards, as 
well as testing and certification procedures, do not create 
unnecessary obstacles to trade. However, it recognizes that 
countries have the right to establish protection, at levels they 
consider appropriate, for example for human, animal or plant life or 
health or the environment, and should not be prevented from taking 
measures necessary to ensure those levels of protection are met. The 
agreement therefore encourages countries to use international 
standards where these are appropriate, but it does not require them 
to change their levels of protection as a result of 
standardization.'' Available at http://www.wto.org/english/docs_e/legal_e/ursum_e.htm#dAgreement.

    Members shall, in the preparation and application of technical 
regulations, standards, and conformity assessment procedures, take 
account of the special development, financial and trade needs of 
developing country Members, with a view to ensuring that such 
technical regulations, standards and conformity assessment 
procedures do not create unnecessary obstacles to exports from 
---------------------------------------------------------------------------
developing country Members.

    In its comment, China quoted the agency in stating in the NPRM that 
``improvements in truck tractor stopping distance performance may 
involve more than simply increasing the power of foundation brakes, as 
changes might be required to suspensions and frames, etc., to handle 
the higher braking torque without decreasing vehicle durability and 
safety.'' Further, China noted that the requirements of the Chinese 
National Standards on truck stopping distance (GB7258-2004 and GB12676-
1999) are significantly less stringent than the stopping distances 
proposed by NHTSA. Finally, China cited the fact that disc brakes--
along with larger capacity drum brakes, electrically controlled braking 
systems, and anti-lock braking systems--were only starting to be used 
on a limited number of vehicles in China. All of these factors, China 
stated, should be taken into consideration in a decision whether to 
give Chinese manufacturers a longer transitional period for 
implementation of the improved stopping distance requirements.
    We have carefully considered China's comments. In responding, we 
begin by noting that, in the U.S., the applicable FMVSSs are the same 
regardless of where a motor vehicle or item of motor vehicle equipment 
is manufactured. Therefore, any extension of lead time would not be 
limited to Chinese manufacturers but would be available to all 
manufacturers irrespective of where they manufacture truck tractors for 
the U.S. market. While we carefully consider the issue of necessary 
lead time in establishing and amending FMVSSs, we also recognize that 
extending lead time can also result in the delay of safety benefits.
    We note that while China highlighted substantial differences 
between the Chinese and proposed U.S.

[[Page 37150]]

requirements regarding stopping distance requirements for heavy truck 
tractors, it did not provide specific information explaining why 
particular Chinese manufacturers would need additional time to comply 
with the new stopping distance requirements. There are many other 
substantial differences in vehicle safety regulation between the two 
countries, and we believe that a manufacturer building vehicles 
otherwise compliant to the U.S. FMVSSs would likely be capable of 
making the relatively minor modifications in brake design required by 
the upgraded performance requirements in this final rule, consistent 
with the lead time provided in this final rule.
    With specific regard to extended lead time, we note that as 
discussed above, the agency is providing longer lead time, relative to 
that proposed in the NPRM, of four years for two-axle and severe 
service tractors. This relates to the additional design and testing 
work that must be done on these tractors to ensure that they can meet 
the improved stopping distances while maintaining good stability and 
control of the vehicles at issue. Therefore, Chinese manufacturers, 
like other manufacturers, will have longer time to undertake the design 
and testing necessary to meet the improved standards for these classes 
of truck tractors.
    However, we believe that two years is adequate lead time for 
manufacturers to design standard three-axle tractors that can meet the 
improved stopping distance requirements. We note that standard three-
axle tractors that already comply with the 30 percent reduction in 
required stopping distance are being manufactured and used on public 
roads in this country already. NHTSA has determined that these tractors 
can be improved to meet the enhanced requirements with relatively 
little design work, as compared to other classes of heavy truck 
tractors. We also believe that extending the lead time for these 
vehicles would inappropriately delay the safety benefits of this final 
rule.
vii. Miscellaneous Comments
    Several commenters expressed concerns regarding the current state 
of heavy truck tractor maintenance. Brake Pro, Haldex, and HDBMC all 
commented that current vehicle maintenance procedures in many cases do 
not maintain braking systems at the same level as original equipment. 
Brake Pro added that aftermarket and foreign-produced brake lining 
material may be less efficient than materials included as original 
equipment. While these may be valid concerns, they are outside the 
scope of this rulemaking. This rulemaking addresses only new vehicles 
and the equipment sold on new vehicles; it does not apply to 
maintenance procedures once the vehicles are sold to end users.
    In-service performance requirements for brake systems on commercial 
vehicles are covered under the Federal Motor Carrier Safety 
Administration's (FMCSA's) Federal Motor Carrier Safety Regulations 
(FMCSRs), as cited in the Code of Federal Regulations at Title 49, Part 
393, Section 52, Brake Performance. That regulation sets service and 
emergency brake stopping distance requirements for various categories 
of passenger- and property-carrying commercial motor vehicles from an 
initial speed of 20 mph. It also includes minimum vehicle deceleration 
requirements for service brake systems. While it may be appropriate to 
set new standards for tractors that will be required to comply with 
shorter stopping distance requirements, it is not clear how that would 
be done at the present time, given the influences of trailer braking 
and operating weight versions the FMVSS No. 121 testing that is 
performed at full GVWR using an unbraked control trailer. Presumably, 
additional research or study would need to be conducted to derive 
proposed revisions to the FMCSRs. However, that work has not yet been 
performed.
    A comment from an individual (Mr. John Kegley) requested that the 
new rule mandate that all Class 8 trucks have engine or exhaust brakes. 
Similarly, a comment from Mr. Timothy Larrimore suggested that the 
regulation should mandate that all trucks have four axles. Based on the 
data presented above, it is our belief that modifying the stopping 
distance requirements is the best way to achieve safety benefits, while 
still permitting manufacturers to use their own discretion in how they 
meet those requirements. We are not adopting these commenters' 
suggestions.
    Finally, a comment from Mr. Roger Sauder suggested that instead of 
mandating new stopping distance requirements, the agency should focus 
on informing the public about proper driving techniques in the presence 
of large vehicles. We are not adopting this suggestion. We note that 
currently, such public education projects are already in place. 
Further, the data presented above indicate that reducing the stopping 
distance of heavy trucks will result in a substantial reduction in 
injuries and property damage prevented.
viii. Costs and Benefits of Shorter Tractor Stopping Distances
1. Estimated Benefits of a 30 Percent Reduction in Stopping Distance
    In the Final Regulatory Impact Analysis (FRIA), the agency 
estimates that substantially greater safety benefits will be attained 
with a 30 percent reduction in required stopping distance compared to 
the benefits for a 20 percent reduction. For the 30 percent reduction 
scenario, the agency estimates that 227 fatalities and 300 serious 
injuries (AIS 3-5) will be prevented by improving the stopping distance 
requirement. For the 20 percent reduction scenario, the agency 
estimates that only 91 fatalities and 127 serious injuries would be 
prevented.\65\ The differential in estimated reduced property damage is 
even greater, with approximately five times the property damage 
prevented for the 30 percent case versus the 20 percent case ($205 
million compared to $39 million).\66\ In estimating the numbers of 
property damage-only (PDO) vehicle involvements, crashes, and injuries, 
figures were derived from the agency's 2004-2006 GES database and the 
number of fatalities was determined from the agency's 2004-2006 FARS 
database. A more detailed comparison between the two alternatives, 
using a 7% discount rate, is laid out in the table below: \67\
---------------------------------------------------------------------------

    \65\ See FRIA, at VI-6.
    \66\ See FRIA, at VI-7. We note that these figures in 2007 
dollars discounted at 3%.
    \67\ See FRIA, at VI-13.

[[Page 37151]]



                      Annual Costs and Benefits in Millions of 2007 Dollars Discounted at 7% for 30% Reduction in Stopping Distance
--------------------------------------------------------------------------------------------------------------------------------------------------------
     Costs (in millions)           Benefits (in millions)              Net benefit                     Net cost                     Cost per ELS
--------------------------------------------------------------------------------------------------------------------------------------------------------
                       Most    Property                                             Most                            Most                          Most
   Low       High     likely    damage      ELS    Monetized     Low      High     likely      Low       High      likely      Low      High     likely
--------------------------------------------------------------------------------------------------------------------------------------------------------
     $27      $192       $54      $169       212     $1,293    $1,271    $2,872    $1,410    -$141.4     $22.9       \*\-       N/A      $0.1       N/A
                                                                                                                   $115.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
* The PDO benefits were greater than the costs, which resulted in a negative number.


                      Annual Costs and Benefits in Millions of 2007 Dollars Discounted at 7% for 20% Reduction in Stopping Distance
--------------------------------------------------------------------------------------------------------------------------------------------------------
      Costs (in millions)            Benefits (in millions)              Net benefit                    Net cost                    Cost per ELS
--------------------------------------------------------------------------------------------------------------------------------------------------------
                         Most    Property                                             Most                          Most                          Most
   Low        High      likely    damage      ELS    Monetized     Low      High     likely      Low      High     likely      Low      High     likely
--------------------------------------------------------------------------------------------------------------------------------------------------------
     $19       $134        $48       $32        87       $531      $426    $1,082      $512    -$12.9    $101.6     $15.4       N/A      $1.1      $0.2
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The FRIA estimates there are 864 fatalities, 15,614 non-fatal 
injuries and 17,621 PDO crashes occurring annually in which the front 
of a braked truck tractor strikes another vehicle. It is estimated that 
reducing the stopping distance of truck tractors will reduce the 
following subsets of those crashes: (1) Rear-end, truck striking 
passenger vehicle (4 percent of total passenger car occupant 
fatalities); (2) passenger vehicle turned across path of truck (8 
percent); and (3) straight path, truck into passenger vehicle 
(generally side-impact crashes at roadway junctions; 14 percent). The 
total percentage of all passenger vehicle occupant fatalities for these 
crash types was 26 percent. In addition, it is possible that some of 
the head-on collisions could be reduced in severity, since improvements 
in the braking capability of large trucks could reduce impact 
speeds.\68\
---------------------------------------------------------------------------

    \68\ See FRIA, at II-4.
---------------------------------------------------------------------------

    The reduction in required stopping distance also produces 
substantial benefits in property damage reduction. Using a three 
percent discount rate, the agency believes that $205 million of 
property damage will be prevented annually (present value of property 
damage savings over the lifetime of these vehicles) with the 30 percent 
required reduction in stopping distance. Using a seven percent discount 
rate, the resulting figure is $169 million in property damage 
prevented.
    Some commenters (Advocates, IIHS) stated that the agency should 
mandate not only the 30 percent reduction in required stopping 
distance, but also mandate the use of disc brakes in truck tractors. 
These commenters also stated that disc brakes have certain 
characteristics (namely resistance to fading at high temperatures) 
which would provide additional benefits that enhanced S-cam drum brakes 
would not, even if they provided equivalent torque in the FMVSS No. 121 
testing requirements. Accordingly, the commenters argued that these 
benefits should be factored into the cost-benefit analysis.
    NHTSA, however, does not have data on the benefits of disc brakes 
beyond the benefits of similar-performing drum brakes. We note that 
FMVSS No. 121 is a performance-based standard, and any type of 
foundation brake that can meet the stopping distance and other 
requirements of the standard are permitted. Thus, it is not design-
restrictive with respect to the type of foundation brake used to meet 
the requirements.
    In a comment, Freightliner and TMA suggested that two-axle tractors 
present less of a need to reduce stopping distances than standard 
three-axle tractors do. Freightliner and TMA stated that two-axle 
tractors represent 10 percent of air-braked tractors produced annually, 
but are only involved in 3.4 percent of fatal crashes involving 
tractors. Because of this low fatality rate, the commenters claim, 
these vehicles should not be included in the agency's rulemaking to 
require shorter stopping distances. International also commented that 
it believes two-axle tractors should be excluded from the rulemaking. 
Although International did not cite the fatality involvement rates in 
its comments, it stated that it was an active participant in the 
preparation of TMA's comments.
    TMA included in its comments a report on Class 8 truck tractor 
crash statistics performed by the University of Michigan Transportation 
Research Institute (UMTRI) using its Trucks Involved in Fatal Accidents 
database for the years 1999 through 2003.\69\ This submission presented 
an alternative data set, which purportedly showed that the proportion 
of fatalities from these types of accidents is only 21.2 percent. The 
agency notes, however, that the UMTRI study was restricted to Class 8 
(heavy truck tractors with a GVWR greater than 33,000 pounds) vehicle 
crashes, which would account for the slight disparity between the 
figures cited by TMA and NHTSA.
---------------------------------------------------------------------------

    \69\ See Docket No. NHTSA-2005-21462-26, TMA submission of April 
14, 2006.
---------------------------------------------------------------------------

    Table 7 of the UMTRI report shows the type of road (interstate, 
U.S. route, State route, county road, etc.) on which the Class 8 
tractor fatal involvements occurred, as well as the tractor type. The 
data indicate that two and three-axle tractors have similar crash 
rates, and that they occur on different types of roads in similar 
frequencies. According to this submission, two-axle tractor crash data 
regarding road type for Class 8 tractors were quite similar to those 
for typical three-axle tractors. Only slightly fewer fatal crashes 
occurred among two-axle tractors on interstates (29 percent) compared 
to three-axle tractor fatal crashed occurring on interstates (34 
percents). Crashes among the two vehicle configurations were nearly the 
same for U.S. and State routes, and slightly higher for two-axle 
tractor crashes on county roads (seven percent) versus typical three-
axle tractors (five percent).
    The agency does not agree with TMA that two-axle tractors are 
under-represented in fatal crashes to a degree that would warrant their 
being excluded from this final rule. Table 3 of the UMTRI report 
indicated that there were 724 Class 3 through 7 tractors in the sample 
(most if not all of these would be two-axle Class 7 tractors with a 
GVWR between 26,001 and 33,000 pounds, and would be in the lower 
combination weight applications such as beverage delivery), compared to 
the 534 crashes of Class 8 two-axle tractors

[[Page 37152]]

(GVWR greater than 33,000 pounds) in the sample that was used in its 
analysis. Thus, more than half of the two-axle tractors involved in 
fatal crashes are missing from UMTRI's analysis because they were not 
Class 8 tractors (the report states that only Class 8 tractors were 
used in the analysis). Therefore, we believe that the data indicate 
that two-axle tractors are represented in fatal crashes to a similar 
extent as three-axle tractors.
2. Cost of Improved Brake Systems
    Because the agency does not know the specific methods that truck 
manufacturers would use to upgrade tractor brake systems to meet the 
new requirements, in developing the NPRM the agency used an array of 
foundation brake upgrades to estimate the increased costs for the brake 
system improvements. The highest cost of complying with shorter 
stopping distance requirements would be realized if all tractors were 
equipped with disc brakes rather than the current S-cam drum brakes, 
and the lowest cost would be realized if all tractors could meet the 
new requirements if they were equipped with enhanced (larger) S-cam 
drum brakes. Both methods have been demonstrated to provide sufficient 
improvements in braking performance for typical three-axle tractors, 
while agency testing and data completed after the publication of the 
NPRM show that the disc brake approach would be required to meet the 30 
percent reduction in required stopping distance for certain less common 
configurations of tractors (i.e., severe service and two-axle 
tractors).
    In quantifying the costs to comply with the reduced stopping 
distance requirements, in the FRIA, the agency used as a basis the 
costs of installing improved brake systems on new truck tractors. NHTSA 
also determined that currently, approximately ten percent of tractors 
have enhanced S-cam drum brakes installed on the steer axle, and three 
percent of tractors have enhanced S-cam drum brakes installed on the 
drive axles. Therefore, in determining the costs of upgrading to 
improved brake systems, we calculated the costs of upgrading 90 percent 
of all steer axles and 97 percent of all drive axles. Commenters also 
indicated that approximately 82 percent of all tractors are typical 
three-axle tractors (similar to the tractors from the Radlinski and 
VRTC tests). TMA and Freightliner stated that typical three-axle 
tractors comprise 82 percent of annual tractor production and ATA 
stated that such tractors comprise 81 percent of production. 
Freightliner commented that two-axle tractors comprise ten percent of 
tractor production, and severe service tractors comprise seven percent 
(although there may be a rounding error as Freightliner's statements on 
total production for the three types of tractors add to 99 percent).
    With regard to standard three-axle tractors, based on the VRTC test 
report and the three test reports \70\ from Federal Mogul and Motion 
Control Industries, the 30 percent reduction in required stopping 
distance could be met by using larger S-cam drum brakes or disc brakes 
at all wheel positions on tractors. The agency believes that the cost 
to install larger drum brakes would be much lower than the cost to 
install air disc brakes, although we do not have specific cost 
information on the various modifications to truck tractor braking 
systems. In the PRIA, the agency estimated that the cost for larger S-
cam drum brakes is $75 for the steer axle \71\ and $50 for each drive 
axle \72\ to meet the 30 percent reduction requirement. For typical 
three-axle tractors, which make up about 82 percent of annual 
production, we estimated $175 ($75steer + 2 x 
$50drive = $175) for larger drum brakes. In its comments 
regarding the PRIA, Freightliner stated that larger drum brakes at all 
wheel positions would be $222. However, that manufacturer did not break 
costs associated with steer and drive axles. Due to limited data, for 
purposes of our cost estimates in the FRIA, we assumed that the cost 
for larger S-cam drum brakes is $85 for the steer axle and $65 for each 
drive axle ($215 for typical three-axle tractors).\73\ Although the 
estimated $215 is lower than Freightliner's $222 cost (about three 
percent lower), we would expect that when larger quantities of brakes 
are produced the cost will be lower than the current $222.\74\ The 
agency estimates that if manufacturers were to install enhanced drum 
brakes at all wheel positions, the total cost of this rulemaking would 
be $27 million ($211 \75\ per vehicle).\76\
---------------------------------------------------------------------------

    \70\ Test Report Nos. RAI-FM-20, RAI-MC-04, AND RAI-FM-21.
    \71\ The size increases from 15'' x 4'' to 16.5'' x 5'' or 
16.5'' x 6''.
    \72\ The size increases from 16.5'' x 7'' to 16.5'' x 8\5/8\'' 
or 16.5'' x 8''.
    \73\ We note that this figure is in 2005 dollars.
    \74\ FRIA, V-1.
    \75\ Figures for the estimated incremental cost per vehicle take 
into consideration the fact that 10 percent of tractors currently in 
production are equipped with larger drum brakes at the steer axle, 
and 3 percent are equipped with larger drum brakes at the drive 
axle. See FRIA [V-2]. Further, we note that this figure is in 2007 
dollars.
    \76\ FRIA, E-4.
---------------------------------------------------------------------------

    Costs for disc brakes are estimated to be higher than those for 
enhanced S-cam drum brakes.\77\ The agency does not have specific cost 
information on disc brakes, but assumes, based on the current average 
pricing of disc brakes, that the cost would be $500 per axle (either 
steer or drive axles). If all affected vehicles are equipped with disc 
brakes to meet the requirement, the agency estimates that the 
associated incremental cost would be about $192M (or $1,475 per truck 
tractor, considering that approximately 82 percent of truck tractors 
have three axles) to fit disc brakes at each wheel position of the 
130,000 truck tractors manufactured each year.\78\ Freightliner also 
provided comments on the cost of disc brakes, indicating that the 
incremental costs of upgrading to disc brakes on all axles would be 
$1,627 for three-axle tractors and $963 for two-axle tractors. These 
figures are not significantly different from those used in the FRIA, 
and again we would expect that if larger quantities of brakes are 
produced the cost would be lower than the current $500 per axle, as 
suggested by the IIHS in its comments.
---------------------------------------------------------------------------

    \77\ FRIA, V-3.
    \78\ Some of the typical three-axle tractors may need disc 
brakes on the steer axle only, and many of these tractors may be 
able to comply by upgrading to enhanced drum brakes (the lowest-cost 
option). Thus it is unlikely that the total cost to implement the 
requirements would be close to the high-end cost estimate in the 
FRIA (which was to install disc brakes on all tractors).
---------------------------------------------------------------------------

    In its analysis, the agency also considered the cost of installing 
hybrid brake systems on all truck tractors. If all applicable vehicles 
are equipped with front disc and rear larger S-cam drum brakes, the 
associated cost of the rulemaking would be about $80M (or $613 per 
vehicle).\79\
---------------------------------------------------------------------------

    \79\ FRIA, V-4.
---------------------------------------------------------------------------

    Finally, in the FRIA, the agency provides a best estimate of the 
incremental cost. This scenario assumes that for typical three-axle 
tractors, manufacturers would comply with the reduced stopping distance 
requirements through use of the least costly means available, i.e., the 
use of enhanced drum brakes at all wheel positions. For two-axle and 
severe service tractors, which make up approximately 18 percent of all 
tractors, manufacturers would need to use disc brakes at all wheel 
positions. The total cost of these improvements, which consist of 
upgrading standard three-axle tractors to enhanced S-cam drum brake 
configurations and upgrading two-axle and severe service tractors to 
all-disc brake configurations, would be an average cost of $413 per 
vehicle, or about $55.4 million total

[[Page 37153]]

annual costs. However, we also note that a small number of commercial 
truck tractors (approximately three percent, all of which are standard 
three-axle tractors) already comply with the 30 percent reduction in 
required stopping distance. Subtracting the cost of those vehicles from 
the total implementation cost of the rule yields a total incremental 
cost of $53.7 million.\80\
---------------------------------------------------------------------------

    \80\ See FRIA, at V-5.
---------------------------------------------------------------------------

3. Additional Costs Incurred Resulting From Improved Brake Systems
    The NPRM also asked for information on tractor components other 
than the foundation brakes (e.g., frames and suspension) that may need 
to be modified to meet shorter stopping distance requirements of 20-30 
percent. Specifically, the agency was seeking to identify additional 
costs or weight penalties that might be required to meet the new 
stopping distance requirements. While numerous commenters discussed 
potential additional costs that could result from the use of improved 
brake systems in truck tractors, relatively little specific information 
was supplied on vehicle modifications that may be required to equip 
tractors with more powerful foundation brakes. TMA cited chassis 
structural analysis, design, and validation, but did not elaborate on 
the costs or scope of these issues. TMA also stated that more powerful 
brakes may require tuning with regard to brake noise, vibration, and 
modifications to the ABS. Freightliner stated that if two-axle tractors 
are fitted with disc brakes, electronic stability control systems may 
be needed to reduce instability during hard braking events. Haldex 
stated that routine vehicle modifications (e.g., tires, suspensions, 
chassis structure) would be most effectively addressed by the vehicle 
manufacturers.
    On the issue of weight penalties for improved brake systems, Bendix 
provided data on drum brake weights versus disc brake weights. It 
stated that the heaviest drum brakes weigh more than the lightest disc 
brakes, while the heaviest disc brakes weigh more than the lightest 
drum brakes. It stated that for a three-axle tractor equipped with all 
disc brakes, total vehicle weight could increase by 212 pounds, or 
could decrease by 134 pounds, compared to an all drum braked tractor, 
depending on which disc or drum brakes are used for comparison. 
ArvinMeritor stated in its comments that the new brakes will weigh 
more, although it did not provide a specific value. WABCO, on the other 
hand, stated that the weight of a disc brake is equivalent to the 
weight of high performance drum brakes.
    After evaluating all comments and available data, we estimate that 
the improved brakes may add a small amount of weight to the vehicle, 
resulting in slight additional fuel consumption and possible loss of 
revenue by displacing cargo-carrying capability, but that those costs 
cannot be determined from the available data. Overall, however, we 
believe those costs to be very small.
4. Summary of Costs and Benefits Estimates
    The FRIA calculates cost and benefits ratios for larger drum brake, 
disc brake, and hybrid disc/drum brake tractor configurations. As part 
of this analysis, the agency estimated Net Cost per Equivalent Life 
Saved (NCELS) for such scenarios. A wide range of estimates are 
provided because of the uncertainty in knowing in advance exactly which 
brake system improvements will be employed to meet the new 
requirements. The agency's estimates of costs and benefits are 
summarized in tables presented below. We note, for reasons discussed 
earlier, that while manufacturers can meet the upgraded requirements 
with larger drum brakes for a significant majority of tractors, it is 
likely that disc brakes will be needed for two-axle and severe axle 
tractors (comprising approximately 18 percent of tractors).

                    Estimated Annual Safety Benefits
------------------------------------------------------------------------
  Percent reduction in                               Serious injuries
   stopping distance        Fatalities reduced            reduced
------------------------------------------------------------------------
               30%                      227                      300
------------------------------------------------------------------------


                        Property Damage Prevented
                              [In millions]
------------------------------------------------------------------------
  Percent reduction in
   stopping distance           3% Discount              7% Discount
------------------------------------------------------------------------
               30%                     $205                     $169
------------------------------------------------------------------------


                                                Incremental Costs
                                                 [2007 Dollars]
----------------------------------------------------------------------------------------------------------------
                                      Larger S-cam drum    Disc brakes at     Front disc and
  30% Percent reduction in stopping      at all wheel        all wheel      larger rear S-cam     Most likely
              distance                    positions          positions             drum           combination
----------------------------------------------------------------------------------------------------------------
Total Cost..........................               $27M              $192M               $80M               $54M
Cost Per Vehicle....................                211              1,475                613                413
----------------------------------------------------------------------------------------------------------------


                   Net Cost per Equivalent Life Saved
          [For 30% reduction in stopping distance, in millions]
------------------------------------------------------------------------
           Brake system                 3 Percent          7 Percent
------------------------------------------------------------------------
Larger S-Cam Brake................                 NB                 NB
All Disc Brake....................                 NB             $0.108

[[Page 37154]]

 
Front Disc and Larger Rear S-Cam                   NB                 NB
 Drum.............................
Most Likely Combination...........                 NB                 NB
------------------------------------------------------------------------
 NB = Net Benefits (Property damage benefits exceed the costs).

ix. Lead Time
    NHTSA is specifying differing compliance dates for typical three-
axle tractors on the one hand, and two-axle and severe service tractors 
on the other. The agency has described the available test data for 
typical three-axle tractors with improved brake systems, showing that 
compliance with the new stopping distance requirements can be readily 
achieved. Therefore, the agency is requiring a compliance date that is 
about two years from the date of publication of this final rule for 
typical three-axle tractors (i.e., three-axle truck tractors with a 
GVWR less than or equal to 59,600 pounds).\81\
---------------------------------------------------------------------------

    \81\ As stated above, ``typical three-axle tractors'' have a 
steer axle GAWR less than or equal to 14,600 pounds and a combined 
drive axle GAWR less than or equal to 45,000 pounds. Summing these 
GAWRs yields a GVWR that is equal to or less than 59,600 pounds.
---------------------------------------------------------------------------

    The lead time for all two-axle tractors, and severe service 
tractors with a GVWR greater than 59,600 pounds, is approximately four 
years from the date of publication of this final rule. As previously 
described, available test data indicate that two-axle tractors can meet 
a 250-foot loaded-to-GVWR stopping distance requirement with improved 
brake systems. However, additional lead time is needed to more fully 
evaluate new brake systems to ensure compatibility with existing 
trailers and converter dollies when used in multi-trailer combinations, 
and to minimize the risk of vehicle stability and control issues, 
particularly on shorter wheelbase two-axle tractors. For severe service 
tractors, the agency described the available test data and analyses 
indicating that vehicle improvements are available that would make the 
new 250-foot and 310-foot loaded-to-GVWR stopping distance requirements 
attainable. However, only limited development work relevant to reduced 
stopping distance has been performed on these vehicles to date. As 
several commenters indicated, additional lead time is needed for 
complete testing and validation of new brake systems for these vehicles 
to ensure that full compliance can be achieved, without compromising 
control, stability, and comfort elements important to end users.

IV. Rulemaking Analyses and Notices

a. Vehicle Safety Act

    Under 49 U.S.C. Chapter 301, Motor Vehicle Safety (49 U.S.C. 30101 
et seq.), the Secretary of Transportation is responsible for 
prescribing motor vehicle safety standards that are practicable, meet 
the need for motor vehicle safety, and are stated in objective 
terms.\82\ These motor vehicle safety standards set the minimum level 
of performance for a motor vehicle or motor vehicle equipment to be 
considered safe.\83\ When prescribing such standards, the Secretary 
must consider all relevant, available motor vehicle safety 
information.\84\ The Secretary also must consider whether a proposed 
standard is reasonable, practicable, and appropriate for the type of 
motor vehicle or motor vehicle equipment for which it is prescribed and 
the extent to which the standard will further the statutory purpose of 
reducing traffic accidents and associated deaths.\85\ The 
responsibility for promulgation of Federal motor vehicle safety 
standards has been delegated to NHTSA.\86\
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    \82\ 49 U.S.C. 30111(a).
    \83\ 49 U.S.C. 30102(a)(9).
    \84\ 49 U.S.C. 30111(b).
    \85\ Id.
    \86\ 49 U.S.C. 105 and 322; delegation of authority at 49 CFR 
1.50.
---------------------------------------------------------------------------

    Based upon the agency's research, the agency determined that a 
substantial number of fatalities and injuries result annually from 
collisions between combination trucks (i.e., tractor trailers) and 
light vehicles. The agency further determined that a 30 percent 
reduction in heavy truck tractor stopping distance is both 
technologically and financially achievable and could prevent a 
substantial number of these identified fatalities and injuries. In 
developing this final rule amending the relevant requirements of FMVSS 
No. 121 to reduce heavy truck stopping distance, the agency carefully 
considered the statutory requirements of 49 U.S.C. Chapter 301.
    First, this final rule reflects the agency's careful consideration 
and analysis of all issues raised in public comments on the agency's 
December 2005 notice of proposed rulemaking. In responding to the 
issues raised in the comments, the agency considered all relevant motor 
vehicle safety information. In preparing this document, the agency 
carefully evaluated relevant, available research, testing results, and 
other information related to various air brake technologies. In sum, 
this document reflects our consideration of all relevant, available 
motor vehicle safety information.
    Second, to ensure that the heavy truck stopping distance 
requirements remain practicable, the agency evaluated the potential 
impacts of the proposed requirements in light of the cost, 
availability, and suitability of various air brake systems, consistent 
with our safety objectives and the requirements of the Safety Act. As 
explained in detail in the FRIA, this final rule adopts a 30 percent 
reduction in stopping distance for the overwhelming majority of 
tractors, which corresponds to the most stringent of the requirements 
proposed in the NPRM. (For the remaining one percent (mostly severe 
service tractors with high GVWRs), the final rule adopts a requirement 
for a 13 percent reduction in stopping distance beyond the standard's 
existing levels.) Our analysis of the available data and public 
comments shows that it is practicable for the subject vehicles to 
achieve the newly required reduction in stopping distance using 
available technology. In sum, we believe that this final rule is 
practicable and will increase the benefits of FMVSS No. 121, including 
prevention of deaths and injuries associated with many types of crashes 
involving heavy truck tractors.
    Third, the regulatory text following this preamble is stated in 
objective terms in order to specify precisely what performance is 
required and how performance will be tested to ensure compliance with 
the standard. Specifically, this final rule modifies the performance 
requirements specified in Table 2 of Standard No. 121, without 
substantively altering the standard's test procedures. The standard's 
test procedures continue to delineate carefully how testing will be 
conducted,

[[Page 37155]]

including applicable brake burnish and dynamometer procedures. The 
agency continues to believe that this test procedure is sufficiently 
objective and will not result in any uncertainty as to whether a given 
vehicle satisfies the requirements of the FMVSS No. 121.
    Fourth, we believe that this final rule will meet the need for 
motor vehicle safety by making certain modifications that will reduce 
heavy truck stopping distances, thereby permitting the driver to 
potentially avert crash-related fatalities and injuries.
    Finally, we believe that this final rule is reasonable and 
appropriate for motor vehicles subject to the applicable requirements. 
As discussed elsewhere in this notice, the modifications to the 
standard resulting from this final rule will further the agency's 
efforts to prevent the injuries, fatalities, and property damage 
associated with crashes involving heavy truck tractors and other 
vehicles. NHTSA has determined that enhanced foundation brakes used to 
meet the requirements of this final rule offer an effective means to 
prevent (or mitigate the severity of) many of these crashes. 
Accordingly, we believe that this final rule is appropriate for covered 
vehicles that are or will become subject to these provisions of FMVSS 
No. 121 because it furthers the agency's objective of preventing deaths 
and serious injuries.

b. Executive Order 12866 and DOT Regulatory Policies and Procedures

    Executive Order 12866, ``Regulatory Planning and Review'' (58 FR 
51735, October 4, 1993), provides for making determinations whether a 
regulatory action is ``significant'' and therefore subject to OMB 
review and to the requirements of the Executive Order. The Order 
defines a ``significant regulatory action'' as one that is likely to 
result in a rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or Tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations of recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    We have considered the impact of this action under Executive Order 
12866 and the Department of Transportation's regulatory policies and 
procedures. Given that the estimated costs of this final rule could 
exceed $100 million, this action has been determined to be economically 
significant under the Executive Order and accordingly has been reviewed 
by the Office of Management and Budget. Further, this rulemaking action 
has been determined to be ``significant'' under the Department of 
Transportation's Regulatory Policies and Procedures (44 FR 11034; 
February 26, 1979).
    As discussed above, there are a number of simple and effective 
manufacturing solutions that vehicle manufacturers can use to meet the 
requirements of this final rule. These solutions include installation 
of enhanced drum brakes, air disc brakes, or hybrid disc/drum systems. 
The costs will vary depending on which solution is selected. We believe 
the most likely low cost scenario would be for a significant majority 
of tractors to use enhanced drum brakes, with about 18 percent needing 
to use more expensive disc brakes. Under this scenario, annual costs 
would be about $50 million. If disc brakes were used for all tractors, 
annual costs would be $178 million.
    Once all subject heavy truck tractors on the road are equipped with 
enhanced braking systems, we estimate that annually, approximately 258 
lives will be saved and 284 serious injuries will be prevented. In 
addition, this final rule is expected to prevent over $140 million in 
property damage annually, an amount which alone is expected to exceed 
the total cost of the rule.
    The agency has prepared and placed in the docket a Final Regulatory 
Impact Analysis.

c. Regulatory Flexibility Act

    Pursuant to the Regulatory Flexibility Act (5 U.S.C. 601 et seq., 
as amended by the Small Business Regulatory Enforcement Fairness Act 
(SBREFA) of 1996), whenever an agency publishes a notice of rulemaking 
for any proposed or final rule, it must either prepare and make 
available for public comment a regulatory flexibility analysis that 
describes the effect of the rule on small entities (i.e., small 
businesses, small organizations, and small governmental jurisdictions) 
\87\ or certify that the rule will not have a significant economic 
impact on a substantial number of small entities. In order to make such 
a certification, the agency must conduct a threshold analysis. The 
results of that analysis must be included in a statement that 
accompanies the certification and provides the factual basis for making 
it.
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    \87\ The Small Business Administration's regulations at 13 CFR 
Part 121 define a small business, in part, as a business entity 
``which operates primarily within the United States.'' (13 CFR 
121.105(a)).
---------------------------------------------------------------------------

    NHTSA has considered the effects of this final rule under the 
Regulatory Flexibility Act. I certify that this final rule will not 
have a significant economic impact on a substantial number of small 
entities. The basis for this certification is that the vast majority of 
truck tractors manufactured in the United States are produced by five 
vehicle manufacturers, none of which is a small business. The remaining 
volume of heavy truck tractors (about 1 percent) is produced by final-
stage manufacturers, which may be small businesses. However, it is our 
understanding that these final-stage manufacturers rarely make 
modifications to the tractor's braking system; instead, they rely upon 
the pass-through certification provided by chassis manufacturers. 
Accordingly, we do not believe that this final rule will have a 
significant economic impact on truck tractor manufacturers that are 
classified as small businesses.
    Regarding the impacts on brake manufacturers, we are aware of six 
original equipment air brake manufacturers. However, none of them is 
classified as a small business. In any event, due to the fact that the 
rule will generally necessitate installation of more advanced (and 
higher priced) drum and disc brakes, we anticipate that the final rule 
will result in a positive economic impact upon brake manufacturers 
regardless of business size.

d. Executive Order 13132 (Federalism)

    NHTSA has examined today's final rule pursuant to Executive Order 
13132 (64 FR 43255, August 10, 1999) and concluded that no additional 
consultation with States, local governments, or their representatives 
is mandated beyond the rulemaking process. The agency has concluded 
that the rule does not have federalism implications, because the rule 
does not have ``substantial direct effects on the States, on the 
relationship between the national government and the States, or on the 
distribution of power and the responsibilities among the various levels 
of government.''
    Further, no consultation is needed to discuss the preemptive effect 
of today's rule. NHTSA's safety standards can have preemptive effect in 
at least two ways. First, the National Traffic and Motor Vehicle Safety 
Act contains an

[[Page 37156]]

express preemption provision: ``When a motor vehicle safety standard is 
in effect under this chapter, a State or a political subdivision of a 
State may prescribe or continue in effect a standard applicable to the 
same aspect of performance of a motor vehicle or motor vehicle 
equipment only if the standard is identical to the standard prescribed 
under this chapter.'' 49 U.S.C. 30103(b)(1). It is this statutory 
command that unavoidably preempts State legislative and administrative 
law, not today's rulemaking, so consultation would be unnecessary.
    Second, the Supreme Court has recognized that State requirements 
imposed on motor vehicle manufacturers, including sanctions imposed by 
State tort law, can stand as an obstacle to the accomplishment and 
execution of a NHTSA safety standard. When such a conflict is 
discerned, the Supremacy Clause of the Constitution makes the State 
requirements unenforceable. See Geier v. American Honda Motor Co., 529 
U.S. 861 (2000). NHTSA does not currently foresee any potential State 
requirements that might conflict with today's final rule. Without any 
conflict, there could not be any implied preemption.

e. Executive Order 12988 (Civil Justice Reform)

    With respect to the review of the promulgation of a new regulation, 
section 3(b) of Executive Order 12988, ``Civil Justice Reform'' (61 FR 
4729, February 7, 1996) requires that Executive agencies make every 
reasonable effort to ensure that the regulation: (1) Clearly specifies 
the preemptive effect; (2) clearly specifies the effect on existing 
Federal law or regulation; (3) provides a clear legal standard for 
affected conduct, while promoting simplification and burden reduction; 
(4) clearly specifies the retroactive effect, if any; (5) adequately 
defines key terms; and (6) addresses other important issues affecting 
clarity and general draftsmanship under any guidelines issued by the 
Attorney General. This document is consistent with that requirement.
    Pursuant to this Order, NHTSA notes as follows. The preemptive 
effect of this rule is discussed above. NHTSA notes further that there 
is no requirement that individuals submit a petition for 
reconsideration or pursue other administrative proceeding before they 
may file suit in court.

f. Executive Order 13045 (Protection of Children From Environmental 
Health and Safety Risks)

    Executive Order 13045, ``Protection of Children from Environmental 
Health and Safety Risks'' (62 FR 19855, April 23, 1997), applies to any 
rule that: (1) Is determined to be ``economically significant'' as 
defined under Executive Order 12866, and (2) concerns an environmental, 
health, or safety risk that the agency has reason to believe may have a 
disproportionate effect on children. If the regulatory action meets 
both criteria, the agency must evaluate the environmental health or 
safety effects of the planned rule on children, and explain why the 
planned regulation is preferable to other potentially effective and 
reasonably feasible alternatives considered by the agency.
    Although this final rule is an economically significant regulatory 
action under Executive Order 12866, the problems associated with 
crashes involving heavy trucks and other vehicles equally impact all 
persons riding in a vehicle, regardless of age. Consequently, this 
final rule does not involve decisions based upon health and safety 
risks that disproportionately affect children, as would necessitate 
further analysis under Executive Order 13045.

g. Paperwork Reduction Act

    Under the Paperwork Reduction Act of 1995 (PRA), a person is not 
required to respond to a collection of information by a Federal agency 
unless the collection displays a valid OMB control number. There are 
not any information collection requirements associated with this final 
rule.

h. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), Public Law 104-113, (15 U.S.C. 272) directs the 
agency to evaluate and use voluntary consensus standards in its 
regulatory activities unless doing so would be inconsistent with 
applicable law or is otherwise impractical. Voluntary consensus 
standards are technical standards (e.g., materials specifications, test 
methods, sampling procedures, and business practices) that are 
developed or adopted by voluntary consensus standards bodies, such as 
the Society of Automotive Engineers. The NTTAA directs us to provide 
Congress (through OMB) with explanations when we decide not to use 
available and applicable voluntary consensus standards. The NTTAA does 
not apply to symbols.
    There are no voluntary consensus standards related to heavy truck 
stopping distance available at this time. However, NHTSA will consider 
any such standards as they become available.

i. Unfunded Mandates Reform Act

    Section 202 of the Unfunded Mandates Reform Act of 1995 (UMRA) 
requires Federal agencies to prepare a written assessment of the costs, 
benefits, and other effects of proposed or final rules that include a 
Federal mandate likely to result in the expenditure by State, local, or 
Tribal governments, in the aggregate, or by the private sector, of more 
than $100 million annually (adjusted for inflation with base year of 
1995 (so currently about $118 million in 2004 dollars)). Before 
promulgating a NHTSA rule for which a written statement is needed, 
section 205 of the UMRA generally requires the agency to identify and 
consider a reasonable number of regulatory alternatives and adopt the 
least costly, most cost-effective, or least burdensome alternative that 
achieves the objectives of the rule. The provisions of section 205 do 
not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows the agency to adopt an alternative other than the 
least costly, most cost-effective, or least burdensome alternative if 
the agency publishes with the final rule an explanation of why that 
alternative was not adopted.
    As discussed in that notice, this final rule amending FMVSS No. 121 
is not expected to result in the expenditure by State, local, or Tribal 
governments, in the aggregate, of more than $118 million annually, but 
it may result in an expenditure of that magnitude by vehicle 
manufacturers and/or their suppliers. In the final rule, NHTSA has 
adopted a performance requirement for most heavy truck tractors to 
reduce stopping distance by 30 percent from the standard's previous 
levels (with approximately one percent of heavy truck tractors with an 
extremely high GVWR which will be required to achieve a stopping 
distance 13 percent below previous levels); we believe that this 
approach is consistent with safety, and it should provide a number of 
choices regarding the means used for compliance (e.g., enhanced drum 
brakes, all-disc brakes, or hybrid drum/disc brakes), thereby offering 
flexibility to minimize costs of compliance with the standard. As noted 
previously, the agency has prepared a detailed economic assessment in 
the FRIA. In

[[Page 37157]]

that assessment, the agency analyzed the cost-benefit analysis of both 
a 20 percent and a 30 percent reduction in required stopping distance. 
Although the 30 percent requirement does cost more to implement, the 
benefits estimated in the 30 percent reduction scenario far outweighed 
those identified in the 20 percent reduction scenario.

j. National Environmental Policy Act

    NHTSA has analyzed this rulemaking action for the purposes of the 
National Environmental Policy Act. The agency has determined that 
implementation of this action will not have any significant impact on 
the quality of the human environment.

k. Regulatory Identifier Number (RIN)

    The Department of Transportation assigns a regulation identifier 
number (RIN) to each regulatory action listed in the Unified Agenda of 
Federal Regulations. The Regulatory Information Service Center 
publishes the Unified Agenda in April and October of each year. You may 
use the RIN contained in the heading at the beginning of this document 
to find this action in the Unified Agenda.

l. Privacy Act

    Please note that anyone is able to search the electronic form of 
all comments received into any of our dockets by the name of the 
individual submitting the comment (or signing the comment, if submitted 
on behalf of an association, business, labor union, etc.). You may 
review DOT's complete Privacy Act Statement in the Federal Register 
published on April 11, 2000 (Volume 65, Number 70; Pages 19477-78), or 
you may visit http://docketsinfo.dot.gov/.

List of Subjects in 49 CFR Part 571

    Standard No. 121, Air-brake systems.

0
In consideration of the foregoing, NHTSA is amending 49 CFR Part 571 as 
follows:

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

0
1. The authority citation for Part 571 of Title 49 continues to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166; 
delegation of authority at 49 CFR 1.50.


0
2. Section 571.121 is amended by revising S5, adding S6.1.18, revising 
Table II, and adding Table IIa after Table II to read as follows:


Sec.  571.121  Standard No. 121; Air brake systems.

* * * * *
    S5. Requirements. Each vehicle shall meet the following 
requirements under the conditions specified in S6. However, at the 
option of the manufacturer, the following vehicles may meet the 
stopping distance requirements specified in Table IIa instead of Table 
II: Three-axle tractors with a GVWR of 59,600 pounds or less that are 
manufactured before August 1, 2011; two-axle tractors that are 
manufactured before August 1, 2013, and tractors with a GVWR above 
59,600 pounds that are manufactured before August 1, 2013.
* * * * *
    S6.1.18 Fuel tank loading.
    The fuel tank(s) is (are) filled to 100 percent of rated capacity 
at the beginning of testing and is (are) not less than 75 percent of 
rated capacity during any part of the testing.
* * * * *

                                                           Table II--Stopping Distance in Feet
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                  Service brake                                      Emergency brake
                                                 -------------------------------------------------------------------------------------------------------
         Vehicle speed in miles per hour            PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9
                                                 -------------------------------------------------------------------------------------------------------
                                                      (1)          (2)          (3)          (4)          (5)          (6)          (7)          (8)
--------------------------------------------------------------------------------------------------------------------------------------------------------
20..............................................           32           35           30           35           38           28           83           85
25..............................................           49           54           45           54           59           43          123          131
30..............................................           70           78           65           78           84           61          170          186
35..............................................           96          106           89          106          114           84          225          250
40..............................................          125          138          114          138          149          108          288          325
45..............................................          158          175          144          175          189          136          358          409
50..............................................          195          216          176          216          233          166          435          504
55..............................................          236          261          212          261          281          199          520          608
60..............................................          280          310          250          310          335          235          613          720
--------------------------------------------------------------------------------------------------------------------------------------------------------
Note:
(1) Loaded and Unloaded Buses.
(2) Loaded Single-Unit Trucks.
(3) Loaded Tractors with Three Axles and a GVWR of 70,000 lbs. or less; or with Four of More Axles and a GVWR of 85,000 lbs. or less. Tested with an
  Unbraked Control Trailer.
(4) Loaded Tractors with Three Axles and a GVWR greater than 70,000 lbs.; or with Four or More Axles and a GVWR greater than 85,000 lbs. Tested with an
  Unbraked Control Trailer.
(5) Unloaded Single-Unit Trucks.
(6) Unloaded Tractors (Bobtail).
(7) All Vehicles except Tractors, Loaded and Unloaded.
(8) Unloaded Tractors.


[[Page 37158]]


 Table IIa--Stopping Distance in Feet: Optional Requirements for: (1) Three-Axle Tractors With a GVWR of 59,600
Pounds or Less Manufactured Before August 1, 2011; (2) Two-Axle Tractors Manufactured Before August 1, 2013; and
             (3) Tractors With a GVWR of More Than 59,600 Pounds Manufactured Before August 1, 2013
----------------------------------------------------------------------------------------------------------------
                                                       Service brake                         Emergency brake
                                   -----------------------------------------------------------------------------
  Vehicle speed in miles per hour     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9     PFC  0.9
                                   -----------------------------------------------------------------------------
                                        (1)          (2)          (3)          (4)          (5)          (6)
----------------------------------------------------------------------------------------------------------------
20................................           32           35           38           40           83           85
25................................           49           54           59           62          123          131
30................................           70           78           84           89          170          186
35................................           96          106          114          121          225          250
40................................          125          138          149          158          288          325
45................................          158          175          189          200          358          409
50................................          195          216          233          247          435          504
55................................          236          261          281          299          520          608
60................................          280          310          335          355          613          720
----------------------------------------------------------------------------------------------------------------
Note: (1) Loaded and unloaded buses; (2) Loaded single unit trucks; (3) Unloaded truck tractors and single unit
  trucks; (4) Loaded truck tractors tested with an unbraked control trailer; (5) All vehicles except truck
  tractors; (6) Unloaded truck tractors.

* * * * *

    Issued: July 20, 2009.
Ronald L. Medford,
Acting Deputy Administrator.
[FR Doc. E9-17533 Filed 7-24-09; 8:45 am]
BILLING CODE 4910-59-P