37122 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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. 

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 ThreeAxle 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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1 60 FR 13216 (Dockets #92–29 and 93–69), 60 FR 

13287 (Docket #93–06), March 10, 1995. 

2Medium 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. 

3For 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). 

5Emergency 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. 

6See 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.’’ 

7 Large Truck Crash Facts 2005 (report number 

FMCSA–RI–07–046, http://www.fmcsa.dot.gov/ 

facts-research/research-technology/report/LargeTruck-Crash-Facts-2005/Large-Truck-Crash-Facts2005.pdf. 

8 DOT HS 809 569, http://www.nrd.nhtsa.dot.gov/ 

Pubs/809-569.pdf; Docket # NHTSA–2005–21462–5 

via Web site references. 

9 Docket No. NHTSA–2005–21462. 

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)). 

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. 

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

• 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. Seventysix 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. 

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 headon collisions could be reduced in 

severity, since improvement in braking 

performance could reduce impact 

speeds. 

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 costeffective 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 


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10As explained below, ‘‘typical’’ three-axle 

tractors have a GVWR less than or equal to 59,600 

pounds. 

11As explained below, ‘‘severe service’’ tractors 

refer to tractors with a GVWR over 59,600 pounds. 

12We 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. 

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. 

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. 

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 costbenefit 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-toGVWR 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

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-toGVWR 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-toGVWR 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-toGVWR 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-toGVWR 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 airbraked 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 


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37126 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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 twoaxle 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 threeaxle 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/sec2;. Each 

subsequent snub is conducted at a 

distance interval of 1 mile from the 


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37127 

13 Docket No. NHTSA–2005–21462. 

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. 

In the NPRM, NHTSA stated that it 

believed the reason that many truck 

operators had not progressed to readilyavailable, 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 highdeceleration 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 


jlentini on DSKJ8SOYB1PROD with RULES3
37128 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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. 

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 twoaxle 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. 

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 threeaxle tractors, a two-year lead time is 

adequate to meet a 25 percent reduction 

in stopping distance. No specific 

recommendations were offered for twoaxle 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, 


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37129 

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. 16 Docket # 2005–21462–20. 

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 twoaxle 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 splitcoefficient 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. 

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. 

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 °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 threeaxle 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 


jlentini on DSKJ8SOYB1PROD with RULES3
37130 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

17This regulation assigns certain g-forces within 

which cargo securement devices and systems must 

contain the vehicle’s cargo load. See 49 CFR 

393.102. 

18The issue of margin of compliance is discussed 

later in this document. 

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 noncompliant 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

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-toGVWR 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 twoaxle 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. 

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 twoaxle tractors can meet a 250-foot loadedto-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 multitrailer 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. 


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19Bendix 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. 

20 Docket # NHTSA–2005–21462–5, 6, 7. 

21See 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 

22 Docket # NHTSA–2005–21462–39, p. 25. 23 Docket # NHTSA–2005–21462–39, p. 10. 

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. 

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. 

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. 

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. 

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 


jlentini on DSKJ8SOYB1PROD with RULES3
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24 Docket # NHTSA–2005–21462–39, p. 23. 

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. 

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 singleunit 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. 

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

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. 

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 outperform 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 faderesistant 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 


jlentini on DSKJ8SOYB1PROD with RULES3
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26A 30 percent reduction from 355 feet is, in fact, 

249 feet, which the agency has rounded to an even 

250 feet. 

27 Docket # NHTSA–2005–21462–26, p. 5. 

28 Docket # NHTSA–2005–21462–35. 

29 Docket # NHTSA–2005–21462–24–0001, p. 9. 

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 Scam 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. 

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 currentlyavailable 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 twoaxle 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′′ Scam 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. 

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. 

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 


jlentini on DSKJ8SOYB1PROD with RULES3
37134 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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. 

34Memorandums of ex-parte meetings provided 

in Docket No. NHTSA–2005–21462–36. 

35 Docket # NHTSA–2005–21462–40. 

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). 

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, twoaxle, 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 threeaxle 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. 

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. 

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 lowerGVWR 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 threeaxle 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 


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36TMA comment of October 2006, docket # 

NHTSA–2005–21462–35. 

37 Docket # NHTSA–2005–21462–26. 

38 Docket # NHTSA–2005–21462–34. 

39TMA did not provide dimensions for these 

brakes, but described them as the highest available 

performance brakes. 

agency believes that it is practicable to 

require similarly-configured tractors to 

achieve similar braking performance. 

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. 

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 nonviable 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. 

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 threeaxle 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 threeaxle 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 similarlyconfigured 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. 

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 


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40TMA comments of October 12, 2006. Docket 

No. NHTSA–2005–21462–34. 

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). 

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. 

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 alldisc 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 lowerGVWR 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 threeaxle 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-toGVWR 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. 

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 


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42 Docket # NHTSA–2005–21462–26. 

43 Docket # NHTSA–2005–21462–26. 

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 twoaxle 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 twoaxle 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. 

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 twoaxle tractors. 

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 highGVWR 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 


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37138 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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 drivermodulated 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 lightlyloaded 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-toGVWR 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 lightlyloaded 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 lightlyloaded 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 


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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 


jlentini on DSKJ8SOYB1PROD with RULES3
37140 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

44See Docket No. NHTSA–2005–21462–33. 45 Docket No. NHTSA–2005–21462–36. 

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: 

• 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 passfail 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 realworld 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 highcenter-of-gravity tractor-trailer 

combinations. Second, the trailer is rearloaded, 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-ina-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 twoaxle 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 


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37141 

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. 

47 Docket #NHTSA–2005–21462–39, p. 25. 

48Hysteresis refers to friction in the foundation 

brake components. 

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. 

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 twoaxle 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 offbalance 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 realworld conditions, arguing that the 

agency should not consider the issue of 

stopping distance in isolation. 

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 VRTC47 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. 

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. 

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 


jlentini on DSKJ8SOYB1PROD with RULES3
37142 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

49See http://www.itsdocs.fhwa.dot.gov/ 

JPODOCS/REPTS_TE/14349.htm. 

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 splitmu 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-toGVWR, 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 threeaxle 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 tractortrailer 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 tractortrailer 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 


jlentini on DSKJ8SOYB1PROD with RULES3
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50SAE 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. 

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. 

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. 

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 twoaxle 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 


jlentini on DSKJ8SOYB1PROD with RULES3
37144 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

51 Docket # NHTSA–2005–21462–39, p. 28. 52See 53 FR 8190. 

trailers (and converter dollies, as twoaxle 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-toGVWR 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 previouslydiscussed 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. 

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 gforces 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-tohighway 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 


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37145 

53According 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). 54FMVSS No. 121, S5.6. 

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. 

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′′ × 4′′) steer axle drum 

brakes was able to achieve 8,800 pounds 

of parking brake force, while with 

enhanced (16.5′′ × 5′′) steer axle drum 

brakes it produced only 8,000 pounds of 

force. 

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 threeaxle 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 


jlentini on DSKJ8SOYB1PROD with RULES3
37146 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

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. 

56Currently, additional brake research is 

underway on this vehicle to determine stopping 

distance and brake burnish effect interactions with 

enhanced drum brakes. 

57These requirements do not apply to the steer 

axle of tractors. 

58See S6.2.6. 

59Subsequent to this procedure, the brakes are 

burnished at a temperature between 450° and 550°. 

approximately 35 percent. The margin 

of compliance for the tests with the 

drive axles rated at 40,000 pounds 

GAWR was approximately 20 percent. 

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 twoaxle 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 singleunit 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. 

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/sec2, followed 

by a hot stop from 20 mph at a 

deceleration rate of 14 ft/sec2. 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. 

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


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37147 

60We 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. 

61See Docket No. 2005–21462–39, p. 18. 

62See Docket No. 2005–21462–39, p. 28. 

would provide data that better correlate 

with data from the actual tests, where 

the brakes have undergone similar 

lower-temperature burnishing. 

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

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/sec2

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. 

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 


jlentini on DSKJ8SOYB1PROD with RULES3
37148 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

63 Docket No. 2005–21462–39, p. 29. 

combination vehicle using all 

production equipment (tires, antilock 

braking system, air disc brakes, etc.) 

available at the present time. 

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. 

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 singleunit 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/sec2) (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/sec2) (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 


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37149 

64A 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. 

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/sec2) (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 steadystate 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 freeroll 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: 

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 antilock 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. 


jlentini on DSKJ8SOYB1PROD with RULES3
37150 Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 

65See FRIA, at VI–6. 

66See FRIA, at VI–7. We note that these figures 

in 2007 dollars discounted at 3%. 

67See FRIA, at VI–13. 

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 foreignproduced 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 propertycarrying 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


jlentini on DSKJ8SOYB1PROD with RULES3
Federal Register / Vol. 74, No. 142 / Monday, July 27, 2009 / Rules and Regulations 37151 

68See FRIA, at II–4. 

69See Docket No. NHTSA–2005–21462–26, TMA 

submission of April 14, 2006. 

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 

Low High Most 

likely 

Property 

damage ELS Monetized Low High Most likely Low High Most likely Low High Most likely 

$27 $192 $54 $169 212 $1,293 $1,271 $2,872 $1,410 ¥$141.4 $22.9 *¥$115.1 N/A $0.1 N/A 

* 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 

Low High Most 

likely 

Property 

damage ELS Monetized Low High Most likely Low High Most likely Low High Most 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

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 designrestrictive 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. 

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 twoaxle 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 underrepresented 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 


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70Test Report Nos. RAI–FM–20, RAI–MC–04, 

AND RAI–FM–21. 

71The size increases from 15′′ x 4′′ to 16.5′′ x 5′′ 

or 16.5′′ x 6′′. 

72The size increases from 16.5′′ x 7′′ to 16.5′′ x 

85⁄8′′ or 16.5′′ x 8′′. 

73We note that this figure is in 2005 dollars. 

74FRIA, V–1. 

75Figures 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. 

76FRIA, E–4. 

77FRIA, V–3. 

78Some 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 lowestcost 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). 

79FRIA, V–4. 

(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 twoaxle 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 twoaxle 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 × $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

Costs for disc brakes are estimated to 

be higher than those for enhanced Scam 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. 

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

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 twoaxle 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 


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80See FRIA, at V–5. 

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

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 twoaxle 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 stopping distance Fatalities reduced Serious injuries 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] 

30% Percent reduction in stopping distance 

Larger S-cam 

drum at all wheel 

positions 

Disc brakes at all 

wheel positions 

Front disc and 

larger rear S-cam 

drum 

Most likely 

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 


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81As 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. 

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. 

NET COST PER EQUIVALENT LIFE SAVED—Continued 

[For 30% reduction in stopping distance, in millions] 

Brake system 3 Percent 7 Percent 

Front Disc and Larger Rear S-Cam Drum .................................................................................................. NB NB 

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

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 multitrailer 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

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, 


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87The 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)). 

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. 

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 passthrough 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 


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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 costeffective, 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 


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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. 

■ In consideration of the foregoing, 

NHTSA is amending 49 CFR Part 571 as 

follows: 

PART 571—FEDERAL MOTOR 

VEHICLE SAFETY STANDARDS 

■ 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. 

■ 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: 

§ 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

Vehicle speed in miles 

per hour 

Service brake Emergency brake 

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. 


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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 

Vehicle speed in miles per hour 

Service brake Emergency brake 

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 


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