# Federal Motor Vehicle Safety Standards; Air Brake Systems

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3AE9-17533

## Record

- **Collection:** Federal Register
- **Document type:** Rule
- **Published:** July 27, 2009
- **Citation:** 74 FR 37122

## Text

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 Three-Axle Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

2. Braking Performance of Two-Axle Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

3. Braking Performance of Severe Service Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

a. Definition of Severe Service Tractor and Specific Safety Benefits

b. Three-Axle Severe Service Tractors With a GVWR Under 70,000 Pounds

c. Three-Axle Severe Service Tractors With GVWR Over 70,000 Pounds

d. Severe Service Tractors With Four or More Axles

e. Two-Axle Severe Service Tractors

f. Summary of Severe Service Tractors

4. Braking Performance of Tractors With Improved Brake Systems in the Unloaded Weight Condition

5. Emergency Braking Performance of Tractors With Improved Brake Systems

a. Background Information on the Emergency Braking Performance Requirement

b. Commenters' Responses to Proposed Emergency Braking Performance Requirement

ii. Ancillary Issues Arising From Improved Brake Systems

1. Stability and Control of Tractors With Improved Brake Systems

2. Brake Issues on Tractors With Improved Brake Systems

3. Brake Balance and Trailer Compatibility Issues for Tractors With Improved Brake Systems

a. Brake Balance Between the Steer and Drive Axles

b. Tractor-Trailer Compatibility

c. Brake Balance and Trailer Compatibility Issues for Two-Axle and Severe Service Tractors

iii. Cargo Securement

iv. Testing Procedures

1. Brake Burnish Issues for Tractors With Improved Brake Systems

2. Brake Dynamometer Test Requirements

v. Stopping Distances at Reduced Initial Test Speeds

vi. Comments Regarding Foreign Trade Agreements

vii. Miscellaneous Comments

viii. Costs and Benefits of Shorter Tractor Stopping Distances

1. Estimated Benefits of a 30 Percent Reduction in Stopping Distance

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)).

1
60 FR 13216 (Dockets #92-29 and 93-69), 60 FR 13287 (Docket #93-06), March 10, 1995.

2
Medium and heavy weight vehicles are hydraulic-braked vehicles over 10,000 pounds GVWR, and all vehicles equipped with air brakes; hereinafter referred to collectively as heavy vehicles.

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.

3
For heavy truck tractors (tractors), the current stopping distance test in the loaded-to-GVWR condition is conducted with the tractor coupled to an unbraked control trailer, with weight placed over the fifth wheel of the tractor, and a 4,500 pound load on the single axle of the trailer. This test method isolates the braking performance of the tractor so that only that system's performance is evaluated. The performance of a tractor in an FMVSS No. 121 stopping distance test does not directly reflect the on-road performance of a tractor/semi-trailer combination vehicle that has braking at all wheel positions.

4
In the unloaded condition, vehicles are tested at lightly loaded vehicle weight (LLVW).

5
Emergency brake system performance is tested with a single failure in the service brake system of a part designed to contain compressed air or brake fluid.

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

6

See Traffic Safety Facts 2006—Large Trucks,
National Center for Statistics and Analysis (NCSA), report number DOT HS 810 805,
http://www.nrd.nhtsa.dot.gov/Pubs/810805.pdf.
The NCSA report uses the term “large trucks,” which in practical terms describes the same segment of the vehicle population as “heavy vehicles.”

• 385,000 large trucks were involved in traffic crashes in the U.S.

• 4,732 large trucks were involved in fatal crashes, resulting in 4,995 fatalities (12 percent of all highway fatalities reported in 2006). Seventy-five percent of the fatally injured people were occupants of another vehicle; 16 percent were truck occupants, and 8 percent were nonoccupants.

• 106,000 people were injured in crashes involving large trucks. Seventy-six percent of the injured people were occupants of another vehicle; 22 percent were truck occupants, and 2 percent were nonoccupants.

According to a report
7

published by the Analysis Division of the Federal Motor Carrier Safety Administration (FMCSA), the fatality rate for large truck crashes was 66 percent higher than the fatality rate for crashes involving only passenger vehicles (defined as a car or light truck) in 2005. When the FMCSA report considered combination trucks (
e.g.
, tractor and trailer combinations) separately, the crash fatality rate was nearly double that of passenger vehicles. Conversely, the crash fatality rate for single-unit trucks was approximately 23 percent higher than for passenger vehicles. The FMCSA data indicate that for all types of crashes involving large trucks, those involving trucks with a GVWR over 26,000 pounds have the highest rate of crash involvement.

7

Large Truck Crash Facts 2005
(report number FMCSA-RI-07-046,
http://www.fmcsa.dot.gov/facts-research/research-technology/report/Large-Truck-Crash-Facts-2005/Large-Truck-Crash-Facts-2005.pdf.

It is expected that in most cases reductions in stopping distances for large trucks will result in a reduction of the impact velocity, and hence the severity of a crash. In some cases, reduced stopping distances will prevent a crash from occurring entirely (
i.e.
, a vehicle with a reduced stopping distance will stop short of impacting another vehicle). Based on the crash data in the June 2005 NHTSA report titled “An Analysis of Fatal Large Truck Crashes,”
8

improvements in stopping distance will provide benefits in the following types of crashes: Rear-end, truck striking passenger vehicle; passenger vehicle turned across path of truck; and straight path, truck into passenger vehicle. It is estimated that these types of crashes account for 26 percent of fatalities involving large trucks, or 655 fatalities annually. In addition, it is possible that some head-on collisions could be reduced in severity, since improvement in braking performance could reduce impact speeds.

8
DOT HS 809 569,
http://www.nrd.nhtsa.dot.gov/Pubs/809-569.pdf
; Docket # NHTSA-2005-21462-5 via Web site references.

NHTSA has been exploring the feasibility of reducing the stopping distance under FMVSS No. 121 for heavy air-braked vehicles by 20-30 percent based on testing of current vehicles. We have initially focused on air-braked truck tractors, since the available crash data indicate that these vehicles are the ones most frequently involved in fatal truck crashes. By promulgating a more stringent requirement for air-braked heavy tractor stopping distances, it is our intent to reduce fatalities and injuries relating to this class of vehicles. It is our belief that development of advanced air disc brakes, enhanced larger capacity drum brakes, and advanced ABS, offer cost-effective means to reduce heavy truck stopping distances and to reduce injuries and damage from large tractor crashes effectively.

b. Notice of Proposed Rulemaking

On December 15, 2005, NHTSA published a Notice of Proposed Rulemaking (NPRM) in the
Federal Register
(70 FR 74270)
9

proposing to amend FMVSS No. 121 so as to reduce

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.

9
Docket No. NHTSA-2005-21462.

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.

10
As explained below, “typical” three-axle tractors have a GVWR less than or equal to 59,600 pounds.

11
As explained below, “severe service” tractors refer to tractors with a GVWR over 59,600 pounds.

NHTSA requested comments on a number of subjects in the NPRM. Comments were requested generally on the proposal to reduce stopping distances 20-30 percent and on the costs of the proposal. Comments were also requested on a variety of specific subjects, such as the possible changes in dynamometer testing procedures, the application of Advanced ABS and Electronically Controlled Braking Systems (ECBS), and the lead time that would be required to implement the proposed changes. Finally, NHTSA requested comments on the VRTC and Radlinski testing, as well as information from vehicle manufacturers regarding vehicle modifications (other than to foundation brakes) that might be required to meet the proposal's enhanced braking specifications.

c. Summary of Public Comments

Commenters brought up a variety of issues in response to the NPRM. Most commenters supported NHTSA's proposal to reduce the stopping distance requirements for heavy truck tractors. In general, safety organizations recommended adopting the 30 percent reduction in stopping distances for all heavy truck tractors. On the other hand, truck manufacturing groups recommended that the agency reduce the stopping distance requirements by 20-25 percent, and limit the scope of the reductions to standard three-axle tractors. In their comments, manufacturers cited the increased costs and complexity of upgrading to the stricter stopping distance requirements, as well as potential problems that could be encountered with upgrading the requirements for two-axle and severe service tractors. Many commenters also discussed the vehicle testing NHTSA cited in the NPRM, along with providing independent test and cost-benefit data.

Other aspects of Standard No. 121 mentioned in the NPRM received comments as well. Several commenters recommended against making any changes to the emergency braking requirements in the Standard. Regarding brake dynamometer specifications, some commenters also recommended that no changes be made. Several commenters suggested that the brake burnish procedure could be returned to an older procedure, known as a “hot burnish,” that existed before 1993. Finally, attention was called to the possible ramifications of the stopping distance changes for issues like cargo securement and brake power at lower speeds.

d. Requirements of the Final Rule

After careful consideration of the public comments on the NPRM, we are promulgating this final rule, which amends the requirements of FMVSS No. 121 by reducing the specified stopping distance for the vast majority of heavy truck tractors by 30 percent. For a small number of very heavy, severe service tractors, the stopping distance requirement is reduced by a smaller amount. The reduction applies to service brake stopping distance but does not, however, apply to emergency braking distances.

For heavy trucks in the loaded-to-GVWR condition, the stopping distance requirements from an initial speed of 60 mph are as follows:

• A tractor with two or three axles and a GVWR of 70,000 pounds or less must stop within 250 feet.

• A tractor with three axles and a GVWR greater than 70,000 pounds must stop within 310 feet.

• A tractor with four or more axles and a GVWR of 85,000 pounds or less must stop within 250 feet.

• A tractor with four or more axles and a GVWR greater than 85,000 pounds must stop within 310 feet.
12

12
We note that tractors with any axle with a GAWR of 29,000 pounds or greater will continue to be excluded from FMVSS No. 121 requirements in accordance with paragraph S3.

For heavy trucks in the unloaded condition, the agency is reducing the specified stopping distance from 60 mph by 30 percent, to a 235-foot requirement. This requirement applies to all tractors, including those severe service tractors for which the loaded-to-GVWR stopping distance requirement has been set at 310 feet.

Stopping distance requirements for heavy air-braked tractors are provided in Tables I through III (
See
Section III). The tables list the following information:

• Table I lists the requirements and details the explanation for stopping distance requirements in the loaded-to-GVWR condition for two- and three-axle tractors with a GVWR of 70,000 pounds or less, and tractors with four or more axles with a GVWR of 85,000 pounds or less.

• Table II lists the requirements and details the explanation for stopping distance requirements in the loaded-to-GVWR condition for three-axle tractors with a GVWR greater than 70,000 pounds, and tractors with four or more axles and a GVWR greater than 85,000 pounds.

• Table III lists the stopping distance requirements and details the explanation for all tractors in the unloaded condition.

In addition, to reduce a possible source of test variability, the agency is adding a specification to the unloaded condition testing requirement in FMVSS No. 121 that the fuel tank is filled to 100 percent of capacity at the beginning of testing and may not be less than 75 percent of capacity during any part of the testing.

Finally, it should be noted that there were several changes suggested in the NPRM that we are not incorporating into this final rule amending FMVSS No. 121. These include:

• There is no change in the emergency brake stopping distance requirement.

• There are no changes to the dynamometer test requirements.

e. Lead Time

After carefully considering the public comments on the NPRM, the agency has decided to tie the lead time to the specific type of heavy truck in light of the anticipated challenges in making the necessary modifications. For the reasons discussed below, we have decided to provide the majority of three-axle tractors with two years lead time from the date of today's final rule, and we are providing two-axle and severe service tractors with four years lead time.

NHTSA's test data indicate that for typical three-axle tractors with improved brake systems (
i.e.,
enhanced drum brakes or air disc brakes), compliance with the new stopping distance requirements can be readily achieved. Therefore, the agency is specifying a compliance date that is two years from the date of publication of the final rule for typical three-axle tractors. “Typical three-axle” tractors are defined as having three axles and a GVWR less than or equal to 59,600 pounds.

Available test data also indicate that two-axle tractors with improved brake systems can meet a 250-foot loaded-to-GVWR stopping distance requirement. However, we believe additional lead time is needed for manufacturers to evaluate new brake systems more fully to ensure compatibility with existing trailers and converter dollies when used in multi-trailer combinations, and to minimize the risk of vehicle stability and control issues. With regard to severe service tractors, available test data and analysis indicate that the 250-foot and 310-foot loaded-to-GVWR stopping distance requirements, depending on the vehicle's GVWR, are achievable. However, only limited development work has been performed on these vehicles, and additional lead time is needed for manufacturers to complete testing and validation of new brake systems for these vehicles. In light of these facts, NHTSA has decided that additional lead time is necessary for all two-axle tractors, and severe service tractors with a GVWR greater than 59,600 pounds. Accordingly, for those vehicles the compliance date for today's final rule is four years from the date of publication.

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

In the NPRM, NHTSA discussed a number of potential actions intended to improve vehicle safety by reducing heavy air-braked tractor stopping distance through amendments to FMVSS No. 121. The available data showed that it was both technically feasible and cost-effective to require improved foundation brakes on air-braked tractors that could achieve a 20-30 percent reduction in stopping distance. The main differences between the NPRM and the final rule include decisions to: (1) Specify a 30 percent reduction in stopping distance for the vast majority of tractors, with a smaller reduction for a small number of very heavy severe service tractors; (2) continue the standard's emergency braking requirements without change; (3) alter the stopping distance requirements for reduced speed tests to account for brake system reaction time and the available tire-road friction; and (4) extend the effective date for compliance by two-axle and severe service tractors. The rationales for these decisions are discussed briefly below, followed by a more complete explanation later in this document.

In the NPRM, NHTSA proposed reducing the required stopping distance for heavy air-braked tractors by 20-30 percent. This range was based on available test results and cost analyses (described below). In the final rule, NHTSA is requiring a 30 percent reduction in the required stopping distance for the vast majority of tractors. We note that the agency's final regulatory impact analysis (FRIA) estimated that greater safety benefits would be attained with a 30-percent reduction in stopping distance requirements compared to the benefits estimated for a 20-percent reduction. It estimated that more than twice as many benefits in fatalities and serious injuries prevented are projected for the 30-percent case versus the 20-percent case. The differential in estimated property damage reductions is even greater, with approximately five times the property damage prevented for the 30-percent case versus the 20-percent case. NHTSA testing and analysis demonstrated that nearly all two-axle and three-axle tractors will be able to meet the 30 percent reduction by using improved foundation brakes that are readily available. For a small percentage of severe service tractors (estimated to be approximately one percent), namely three-axle tractors with a GVWR over 70,000 pounds and tractors with four or more axles and a GVWR over 85,000 pounds, we concluded that a 30 percent reduction is not currently practicable. For those vehicles, the stopping distance is reduced by 13 percent, from the currently mandated level to the level of similar single-unit trucks.

While the NPRM proposed reducing emergency brake stopping distances by 20-30 percent, we decided not to adopt this part of the proposal. Comments received from the Truck Manufacturers Association (TMA) indicated that in order to meet the agency's proposed emergency brake stopping distance requirements, manufacturers would need to modify the ABS algorithms to allow more drive wheel lockup. This modification could be detrimental to vehicle stability and control. NHTSA considered this, as well as the relative rarity of a crash-imminent situation during a brake failure, and decided to maintain the status quo.

In the final rule, NHTSA is also altering the stopping distance requirement for speeds less than 60 mph from the original figures cited in the NPRM. Several commenters argued that the reduced stopping distance values in the proposed Table V of FMVSS No. 121 did not take into account the brake system reaction time and average deceleration. In the final rule, the stopping distances for speeds less than 60 mph have been adjusted to take these factors into consideration.

Finally, the final rule provides additional lead time for several types of tractors to comply with the reduced stopping distance requirements. The NPRM had proposed a two-year lead time for all tractors to meet the reduced stopping requirements. With regards to typical three-axle tractors (three-axle tractors with a GVWR of 59,600 pounds or less), the available test data showed that compliance to the new stopping distance requirements can be readily achieved without the need to make significant modifications to other vehicle systems. As stated above, however, the agency believes that additional lead time is needed for manufacturers to develop and evaluate improved braking systems more fully for two-axle and severe service tractors. Therefore, the lead time has been extended for those types of vehicles by an additional two years.

g. Costs and Benefits

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

reductions in property damage. According to the FRIA, using a 3 percent discount rate, $205M of property damage will be prevented annually. Using a 7 percent discount rate, the figure is $169M.

The range of figures in terms of net costs are based on what types of foundation brakes, disc brakes or enhanced drum brakes, are used to meet the new stopping distance requirements. The figures are derived based on an average annual production of about 130,000 truck tractors (82 percent of which are typical three-axle tractors, ten percent two-axle tractors, and eight percent severe service tractors). Each typical three-axle tractor contains one steer axle and two drive axles, as do most severe service tractors. Each two-axle tractor contains one steer axle and one drive axle. Therefore, the agency estimates that in total, the final rule will require the upgrading of 130,000 steer axle brakes and 247,000 drive axle brakes. In order to compute the total cost of complying with the reduced stopping distance rule, the agency calculated the number of axles that will need to be upgraded with improved foundation brakes, and multiplied that number by the cost of the brake. The agency estimated the cost of enhanced drum brakes for the steer axle at $85, and for drive axles at $65. The agency estimated the cost of disc brakes to be $500 per axle at all wheel positions.

Because the agency is not certain how truck manufacturers will choose to comply with the final rule, using the above figures, the agency created a range of costs of compliance. The most expensive means of compliance would be to use a $500 disc brake at all wheel positions, while the least expensive means of compliance would be to use enhanced drum brakes at all wheel positions. The FRIA estimates that the incremental cost to add disc brakes to all wheel positions would be $1,475 per tractor ($192M total cost), while the incremental cost to add enhanced drum brakes would be $211 ($27M total cost). One commenter (Freightliner) provided cost information, stating that the cost of disc brakes would be $1,627 for a three-axle tractor and $963 for a two-axle tractor, while the cost of drum brakes for a three-axle tractor would be $222. In addition, the commenter stated that development and manufacturing costs would need to be added, although it did not elaborate on what these costs would be. The agency notes that these figures are very similar to its own estimates.

NHTSA testing indicated that for standard three-axle tractors, it is likely enhanced drum brakes at the steer axle and drive axle positions will enable the tractors to meet a 250-foot stopping distance requirement in FMVSS No. 121. For two-axle tractors and severe service tractors, it is likely that disc brakes would be required at all wheel positions. Considering that standard three-axle tractors comprise roughly 82 percent of all tractors, it seems likely that the total costs will be skewed toward the lower end of the range. In the FRIA, the agency estimates that the incremental average cost per tractor, given these assumptions, will be $413 per vehicle ($54M total). NHTSA notes that this figure is substantially lower than the lowest figure in the range of estimated savings in property damage ($169M).

The FRIA estimates that the net cost per equivalent life saved (NCELS) will range from $108,000 to net benefits based on property damage savings alone (that is, the costs of implementing this final rule will be less than the costs saved in damaged property, irrespective of the injuries and fatalities prevented). The high figure ($108,000 NCELS) is derived by taking the highest estimated cost figure and the lowest estimated property damage prevented. Conversely, the low figure (net benefits) is derived from using the low cost estimate and the high benefits estimate.

II. Background

a. Existing Brake Technologies for Heavy Air-Braked Trucks

The relevant brake technologies at issue in this rulemaking can be divided into two categories, S-cam drum brakes (drum brakes) and air disc brakes (disc brakes).

The most common type of foundation brake used in air brake systems for heavy vehicles is the S-cam brake. This is a leading/trailing type of brake with fixed pivot type shoes. Upon brake application, air pressure enters the brake chamber causing the diaphragm to push the pressure plate, which in turn applies a force to the end of the brake slack adjuster. This force creates a torque on the camshaft, and rotates the camshaft to which the S-cam is attached. The camshaft head, which is S-shaped, forces the brake shoes against the surface of the brake drum to create the retardation force for braking. Enhanced S-cam drum brakes are essentially larger and wider versions of standard S-cam drum brakes. On the steer axle, for example, the diameter of the brake drum is 16.5 inches versus 15 inches for the standard steer axle drum, and this produces more braking torque. Typically the enhanced steer axle drum brake lining is 5 inches wide instead of the standard steer axle brake lining width of 4 inches. On the drive axles, both standard and enhanced S-cam drum brakes use a 16.5 inch diameter drum, while the standard lining width is 7 inches versus 8 or 8.625 inches for the enhanced drum brake. The increased width of the lining and brake drum provides greater thermal capacity, so that enhanced S-cam drum brakes operate cooler, contributing to longer life, and they are also less prone to fade during high-speed stops.

Air disc brakes are also used on commercial vehicles, but are still used in relatively small numbers in the U.S. A disc brake is basically a C-clamp with the retardation force applied by friction pads that squeeze the brake rotor mounted between them. All air disc brake systems are composed of a rotor, brake linings, a caliper, an adjusting mechanism, and an air brake chamber, among other parts, and there are many different designs to accomplish their function. Disc brakes offer a number of favorable performance characteristics including linear torque output and high resistance to fade, although they are substantially more expensive than drum brakes.

b. Current Requirements of FMVSS No. 121

Under the current FMVSS No. 121 requirements, most truck tractors are required to stop within 355 feet, when tested at 60 mph in the loaded-to-GVWR condition while pulling an unbraked control trailer. Standard No. 121 also requires that truck tractors stop within 335 feet, when tested at 60 mph in the unloaded condition. Finally, the standard requires an emergency brake stopping distance of 720 feet, when tested at 60 mph in the unloaded condition. Currently, the standard does not specify different requirements for different vehicles based on their number of axles or on their GVWR, except that vehicles with a GAWR (gross axle weight rating) of 29,000 pounds or more are exempt from the standard, as are certain vehicles with a GVWR greater than 120,000 pounds.

Before testing, brakes are burnished according to the procedure specified in paragraph S6.1.8 of the standard. The tractor is coupled to an unbraked control trailer and loaded so that the combined weight of the tractor and trailer equals the GVWR of the tractor. Thermocouples are installed in the brake linings to measure the brake temperatures. The burnish consists of 500 snubs (reductions in speed) from 40 mph to 20 mph using the service brakes at a deceleration rate of 10 ft/sec
2
;. Each subsequent snub is conducted at a distance interval of 1 mile from the

point of the beginning of the previous snub.

c. Summary of the NPRM

On December 15, 2005, NHTSA published an NPRM in the
Federal Register
(70 FR 74270)
13

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

13
Docket No. NHTSA-2005-21462.

In the NPRM, NHTSA stated that it believed the reason that many truck operators had not progressed to readily-available, more advanced brake systems was because truck operators did not have this cost savings information available. Further, the proposal stated that truck operators are cost-sensitive in terms of the initial purchase price of the vehicle and are reluctant to add different types and sizes of brake components to their specifications. The agency noted that the proposed requirements would result in net cost savings for truck operators if the savings resulting from decreased property damage are taken into consideration.

NHTSA also provided data from its Vehicle Research and Test Center (VRTC) to compare the performance of air-braked tractors and trailers equipped with a variety of brake system configurations. These data indicated that the tested vehicles would be able to comply with a 20-30 percent reduction in the stopping distance requirements with modifications only to the foundation brake systems. Testing was also conducted on heavy trucks with a failed primary reservoir in order to generate data on emergency stopping distances; the results indicated that the same modifications that improved service brake stopping distances also improved emergency braking stopping distances.

Industry data provided by Radlinski and Associates (Radlinski), commissioned by two brake lining manufacturers, were also cited in the NPRM. These data related to standard three-axle tractors equipped with enhanced, larger-capacity S-cam drum brakes at all axle positions. These data indicated that the tractors were able to meet the 30 percent reduced stopping distance requirement without disc brakes, and the braking performance in these tests exceeded that of NHTSA's own tests at the VRTC, in some cases even when disc brakes were applied at all positions.

In the NPRM, NHTSA requested comments on a variety of topics to further the agency's understanding of the ramifications of various measures for improving braking systems. As a preliminary matter, comments were solicited on the safety need for improved braking distances. Comments were also requested on the implications of improving stopping distances by 20 percent and 30 percent, including necessary lead time, needed vehicle modifications, and issues regarding brake balance. The agency also sought comments on the Radlinski data, as well as information on developments in electronically-controlled braking systems (ECBS) and advanced ABS, and how these systems could benefit heavy vehicle safety.

d. Summary of Public Comments on the NPRM

NHTSA received 27 comments on the December 2005 NPRM, from heavy vehicle manufacturers (International Truck and Engine Corporation (International); Freightliner LLC (Freightliner)), brake suppliers (Arvin Meritor; Meritor WABCO (Meritor); WABCO Vehicle Control Systems (WABCO); Honeywell Bremsbelag GmbH (Honeywell); Bendix Commercial Systems/Spicer Foundation Brake (Bendix); Haldex Brake Products Corporation (Haldex); Brake Pro), industry organizations and associations (Truck Manufacturers Association (TMA); Heavy Duty Brake Manufacturers Council (HDBMC); American Trucking Associations (ATA); Owner Operators Independent Drivers Association (OOIDA); National Automobile Dealers Association (NADA)), automobile safety advocates (Insurance Institute for Highway Safety (IIHS); Advocates for Highway and Auto Safety (Advocates)), a foreign government (People's Republic of China), and concerned organizations and individuals (John W. Klegey; Automotive Safety Office (ASO); Roger L. Adkins; Graham Lower; Timothy Larrimore; Anonymous; University of Washington; Roger Sauder). All of the comments on the NPRM can be reviewed in Docket No. NHTSA-2005-21462. Commenters expressed a range of views, with vehicle manufacturers, brake suppliers, and trade associations generally supporting the NPRM. Advocacy groups generally recommended that the agency adopt a standard at the stricter end of the range (toward 30 percent) for all tractors, while most of the trucking industry comments recommended that NHTSA reduce the stopping distances by 20-25 percent (instead of 20-30 percent), and only for typical three-axle tractors. As part of its comments, TMA provided a crash data analysis indicating that typical three-axle tractors comprise 82 percent of tractor production and are involved in 91 percent of fatal crashes involving tractors.

The following overview of the public comments reflects the key issues raised by the commenters, including the safety and cost benefits of reducing stopping distances, recommended percentages for reducing stopping distances, as well as issues of technical feasibility and stability that arise from increasing brake torque. Other issues were raised as well, including reduced stopping distances in the unloaded vehicle condition, emergency brake stopping distances, maintenance issues, recommended dynamometer testing changes, and brake burnish procedures. Comments were also received in response to NHTSA's questions about the validity and applicability of the Radlinski testing data, the impact of ECBS and advanced ABS, and on the margin of compliance for testing in accordance with FMVSS No. 121. A few commenters recommended that the government undertake additional, cooperative studies with industry in order to gather data for two-axle and severe service tractors. Finally, comments were provided on the implications of reduced stopping distance for reduced test speed stopping distance testing and for issues of cargo securement under high-deceleration conditions.

Although the agency also requested comments on trailer stopping distance test data and efforts to improve the braking performance of single-unit trucks, few comments were received regarding those issues. Likewise, only a small number of comments addressed the agency's requests for information about the costs of improved braking systems, as well as any increase in weight. The issues raised in the public comments are discussed in further detail and addressed below in Section III,
The Final Rule and Response to Public Comments.

General Need To Reduce Stopping Distance Performance for Tractors

Support for NHTSA's proposal to reduce the stopping distance performance of heavy truck tractors was

nearly universal. Highway safety advocacy organizations, such as Advocates and IIHS, supported the largest reduction of stopping distances within the range proposed by NHTSA (
i.e.,
a 30 percent reduction from the current requirements of FMVSS No. 121 for all tractors). Most of the trucking industry comments favored a 25 percent reduction in stopping distances, but those commenters recommended limiting the new requirements to standard three-axle tractors, which account for over 80 percent of tractor production. It should be noted that some industry commenters suggested reducing stopping distances by only 20 percent, the lowest reduction proposed by NHTSA.

Comments on the Proposal To Reduce Service Brake Stopping Distance Performance by 20-30 Percent in the Loaded-to-GVWR Condition

The majority of commenters fell into two groups, those who supported 30 percent reductions in stopping distances for all tractors, and those who supported less stringent requirements. Most trucking industry comments (from truck manufacturers and brake suppliers) urged 25 percent reductions for standard three-axle tractors only. In making these recommendations, the trucking industry commenters argued that data had not been provided for two-axle and severe service tractors, and that operational problems (
e.g.,
brake balance, stability, and steering pull) could occur if brake output is increased for those tractors. Specifically, TMA suggested that amending FMVSS No. 121 to require heavy trucks to stop within shorter distances may force manufacturers to implement designs that could cause poorer real-world stopping performance and instability. On this point, TMA stated that one of the reasons current production tractors are equipped with low-power steer axle brakes is for low-level brake applications, and that tractors designed only to achieve maximum straight-line decelerations when fully loaded may not perform well during normal brake applications.

In contrast, other commenters, including some brake suppliers (Bendix and Wabco) as well as Advocates and IIHS, supported a 30 percent reduction in stopping distance for all tractors. These commenters cited the agency's safety benefit analysis as justifying the cost of the improvement. Advocates also argued that there are other benefits associated with the use of disc brakes, including greater resistance to fading.
14

Bendix stated that more powerful brakes, both disc and enhanced drum, are currently available and being used on the road with no significant operational problems.

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

Comments on the Proposal To Reduce Service Brake Stopping Distance Performance by 20-30 Percent in the Lightly Loaded Condition

Few comments were received on this topic. However, TMA stated that currently, standard three-axle unloaded tractors start to experience rear wheel slip during brake applications of approximately 30 psi or more.

Comments on the Proposal To Reduce Emergency Braking Stopping Distance by 20-30 Percent

Comments from the trucking industry opposed the proposed reduction in emergency braking stopping distance. Many commenters stated that NHTSA had not provided any crash data or any other rationale to justify why any such reduction is necessary. These commenters also stated that the occurrence of a crash-imminent situation at the same time as a primary or secondary brake system failure is likely to be extremely rare.

Comments on the Proposed Two-Year Lead Time

Trucking industry commenters and NADA argued that, for standard three-axle tractors, a two-year lead time is adequate to meet a 25 percent reduction in stopping distance. No specific recommendations were offered for two-axle or severe service tractors, although ATA suggested a two-stage implementation strategy for standard three-axle tractors and all other tractors. These commenters also stated that if the agency decides on a 30 percent reduction in stopping distance, longer lead times would be required for brake system development and evaluation.

Haldex and other commenters also recommended that the stopping distance reduction be timed as to not coincide with the 2010 effective date for new engine emission standards, set to become effective by the Environmental Protection Agency.

Vehicle Modifications Necessary To Meet Proposed Reductions in Stopping Distance

Commenters from the trucking and brake industry stated that the largest percentage of improvements in stopping distance would be achieved by using more powerful steer axle brakes; either enhanced drum brakes (larger in width and/or diameter than standard drum brakes) or disc brakes. Most commenters added that more powerful brakes on the drive axles would further contribute to braking performance. Freightliner indicated that 97 percent of its fleet would require brake improvements to meet a 25 percent stopping distance reduction.

Commenters from the trucking industry suggested, but provided little specific information on, other modifications to the vehicle that may be necessary to achieve the improved braking performance. These modifications include chassis structural analysis, redesign, and validation. TMA stated that packaging larger steer axle brakes could result in steering problems. On the other hand, brake suppliers suggested that these issues could be resolved.

For two-axle tractors, several commenters stated that instability could prove to be a problem. Accordingly, TMA stated that for two-axle tractors with a short wheelbase, the following modifications would be necessary to allow the tractor to comply with a 30 percent reduction in the FMVSS No. 121 test: (1) Steer axle brakes would need to be enhanced; and (2) drive axle brake torque would need to be reduced to prevent wheel lockup (a condition which would prove hazardous during normal road braking situations). TMA indicated that these problems could be mitigated by added electronic stability systems, but that such systems could increase stopping distance and dramatically increase cost.

Margin of Compliance Issues

Commenters on this issue stated that tractor manufacturers target a 10 percent margin of compliance to account for test conditions and vehicle variability. Haldex stated that with a 10 percent margin of compliance on a 25 percent reduction in stopping distance, manufacturers would strive to achieve a total reduction in stopping distance of 35 percent.

Cost and Weight of Improved Braking Systems

Few commenters provided information on the issues of cost and weight of improved braking systems in response to NHTSA's request. Freightliner provided cost information on improved foundation brakes, but without supporting data. According to Freightliner's figures, installing enhanced drum brakes on a three-axle tractor would add $222 to the cost,

while adding disc brakes would cost an additional $1,627; the cost of adding disc brakes to a two-axle tractor would be $963. TMA commented that for two-axle and severe service tractors, NHTSA did not provide a cost analysis, and it argued that increasing stopping performance would result in cessation of production of certain vehicles manufactured in low volumes because manufacturers would not be able to amortize the manufacturing/engineering costs, which would in turn limit market choice.

With regard to weight, Bendix stated that, currently, the heaviest drum brake weighs 32 lbs. more than the lightest disc brake, while the heaviest disc brake weighs 134 lbs. more than the lightest drum brake. WABCO stated that its disc brakes are equivalent in weight to high performance drum brakes.

Brake Balance Issues With Existing Trailers

Commenters provided relatively little information on the issue of brake balance with existing trailers. Truck manufacturers stated that brake balance information will need to be further evaluated. Some brake manufacturers provided comments as well. For example, Bendix stated that its tests of disc-braked tractors had shown no objectionable brake balance issues. ArvinMeritor, however, stated that if stopping distance were reduced by more than 25 percent, drive axle torque would need to be increased, which would cause disruptive issues with the existing trailer fleet.

Braking Performance of Single-Unit Trucks

Commenters provided relatively little information regarding single-unit trucks. Haldex and Bendix suggested that further testing needs to be done, and that the government should work with industry to develop test data on the subject. Bendix stated that currently, single-unit trucks have a higher center of gravity than tractors, and that their stopping distances are about 15 percent shorter than tractors.

Developments in Advanced ABS and ECBS Systems and Their Effects on Stopping Distance Performance

Several brake suppliers provided comments on the state of advanced ABS and ECBS on stopping distance performance. Specifically, WABCO stated that currently, ABS systems installed on tractors uses modified individual regulation (MIR), which reduces yaw movement
15

on split-coefficient road surfaces. According to the commenter, with larger foundation brakes, this system should not require significant modification, and it could help alleviate potential problems with larger brakes. Bendix also stated that electronic stability programs for rollover prevention and yaw stability are available on a variety of truck tractors.

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

Haldex stated that ECBS may improve stopping distance by reducing the interval it takes between the time when the vehicle operator depresses the brake pedal to the time when brake forces are actually generated. However, Haldex also stated that because FMVSS No. 121 requires redundant brake control systems, ECBS is not a viable option for heavy vehicles at this time. Haldex, like a number of other commenters, stated that advanced ABS does not reduce stopping distance.

Dynamometer Testing Requirements

Truck manufacturers and brake suppliers both recommended that there be no changes to the FMVSS No. 121 dynamometer requirements. Some brake manufacturers, such as Haldex and HDBMC, stated that current dynamometer testing procedures in FMVSS No. 121 impose no appreciable limitations on the useable brake torque, and expressed concern that changes in dynamometer requirements could have the effect of limiting their options.

Arvin Meritor and Bendix stated that they were planning on conducting further dynamometer testing, and would present the results to NHTSA. However, NHTSA has not received any additional information on this issue.

Brake Burnish Issues

A comment by HDBMC stated that in order to achieve a reduction in stopping distance, higher torque front brakes would be required on truck tractors. According to the commenter, the higher torque front brakes would do more of the work during burnish, thus lowering the rear brake temperatures and reducing the conditioning of the rear brakes. HDBMC stated that coupled with the trend toward wider rear brake configurations, this will result in lower temperatures for rear brakes, and the critical temperature needed to properly condition the rear brakes would not be achieved. In order to address this issue, HDBMC recommended the agency reinstate the FMVSS No. 121 burnish procedure that existed prior to 1993. HDBMC also stated that because the specification for rear-axle burnishing was reduced when the standard was amended in 1993,
16

parking brake performance has been negatively affected, and this problem would be expected to worsen under the agency's reduced stopping distance proposal.

16
Docket # 2005-21462-20.

Arvin Meritor also commented on the burnish issue, requesting that an optional burnish procedure be added to the FMVSS No. 121 dynamometer test. The commenter's recommended procedure calls for six optional stops, using 100 PSI pressure from a starting speed of 60 mph, at the conclusion of the 350 °F brake burnish.

Comments on Tractor Stopping Distance Data

Comments from manufacturers raised two objections to the stopping distance data provided by NHTSA. To begin with, several commenters stated that the agency's proposal was non-specific, because it specified a range of potential stopping distance reductions, rather than a pinpoint proposal. Further, commenters stated that NHTSA performed testing only on typical three-axle tractors. For example, TMA stated that the absence of data on two-axle and severe service tractors should preclude the agency from issuing a rulemaking on those types of tractors at this time. TMA and Bendix provided their own testing data from tractors with enhanced foundation brakes, which in general showed significant improvements in performance.

With regards to the Radlinski testing data referred to in the NPRM, few commenters provided specific comments. Instead, most commenters simply noted that the data were limited to standard three-axle tractors. Bendix added that it believes the Radlinski test data is representative of improvements that can be achieved.

A cooperative testing system for tractor stopping distance was recommended by a variety of commenters, including International, Freightliner, HDBMC, and Arvin Meritor. In addition, the TMA recommended the agency initiate a test program for two-axle and severe service tractors.

In-Use Truck Brake System Maintenance

Several commenters (truck manufacturers and brake suppliers) commented on the need for better servicing and maintenance of truck brakes, noting that in-service brakes frequently fall short of the standards set for brakes sold with new vehicles. Brake

Pro stated that the vast majority (85 percent) of trucks, tractor-trailers, and trailers in North America have had some form of brake system component maintenance work or replacement work done on them, and would no longer necessarily meet the new vehicle stopping distance standards. TMA stated that 45 percent of trucks involved in crashes where brakes were the primary avoidance system had non-compliant brakes.

Reduced Test Speed Stopping Distance Requirements

HDBMC and Bendix argued that brake system reaction time is not taken into account in the NPRM's proposed tables in the reduced speed test requirements. They argued that this resulted in unrealistic stopping distances. Both commenters provided recommendations for adjusting the lower test speed stopping distances to account for brake system reaction time.

Cargo Securement

OOIDA commented that if tractors with improved brake systems are able to achieve higher deceleration rates, this could affect the safety of cargo securement systems, and they provided information on the Federal Motor Carrier Safety Administration's (FMCSA's) recent regulatory changes in this area.
17

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

III. The Final Rule and Response to Public Comments

a. The Final Rule

i. Summary of Requirements

In light of the estimated benefits, in terms of lives saved and property damage avoided, we are upgrading the brake performance requirements of FMVSS No. 121 for air-braked tractors. The requirements of this regulation have been drafted so as to advance the safety and braking performance of truck tractors without imposing overly high costs on the trucking industry or requiring technical advances beyond what are available in the commercial market today. In overview, the final rule specifies 30 percent decreases in required stopping distance for the vast majority of air-braked tractors. The rule also sets somewhat less stringent requirements for a small percentage of truck tractors in light of practicability concerns.

Specifically, the upgrade to FMVSS No. 121 set forth in this final rule specifies a 30 percent reduction in stopping distance that is expected to apply to approximately 99 percent of air-braked tractors. The reduction lowers the maximum stopping distance from the current distance of 355 feet to 250 feet when tractors are tested in the loaded-to-GVWR condition from 60 mph. For three-axle tractors with a GVWR of over 70,000 pounds, and four (or more) axle tractors with a GVWR of over 85,000 pounds, the stopping distance requirement in the loaded-to-GVWR condition is being set at 310 feet.

The decision to adopt a 250-foot stopping distance is based on the agency's analysis of the potential safety benefits that may be achieved by using enhanced braking technology and the costs and feasibility of upgrading the requirements to the new level. NHTSA research demonstrated that for most tractors—including standard three-axle tractors which comprise over 80 percent of the commercial fleet—the upgrade could be achieved at relatively low cost and with minimal impact to tractor design specifications. Specifically, research demonstrated that relatively low-cost enhanced drum brakes would be adequate to achieve stopping distances within 250 feet, with a margin of compliance of 10 percent.
18

For most of the remaining tractors, including two-axle and most severe service tractors, NHTSA concluded that the upgraded requirements were also attainable, although more powerful disc brakes and other design changes may need to be implemented in order to stop within the required limits without detrimental effects on stability or brake balance.

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

For a small number of severe service tractors with three axles and a GVWR of 70,000 pounds or more, or equipped with four or more axles and a GVWR of 85,000 pounds or more, the agency is setting a 310-foot requirement (similar to the current loaded-to-GVWR requirement for air-braked single-unit trucks). This is due to the fact that even when fitted with current disc brakes at all wheel positions, it has been demonstrated that these vehicles cannot achieve 30 percent reductions in stopping distance.

For all tractors, the stopping distance requirement in the lightly-loaded test condition is set at 235 feet, as it was determined that with improved foundation brakes, this requirement is well within the capabilities of all heavy truck manufacturers to achieve.

The required improvement in stopping distance performance is limited to service brakes, and does not include emergency braking. Several commenters argued persuasively that improvements to emergency braking performance could have deleterious effects on lateral stability and control, due to modifications to the ABS algorithms that would be required to meet the emergency braking requirements. Further, there are no data to show that tractors operating in the bobtail condition (
i.e.,
with no trailer attached) and experiencing an emergency braking situation are contributing to the heavy truck crash problem.

ii. Compliance Dates

There are two compliance dates on which the new stopping distance requirements become mandatory. For standard three-axle tractors, the new stopping distance requirements become mandatory on August 1, 2011. “Standard three-axle tractor” refers to typical three-axle tractors that have a steer axle GAWR less than or equal to 14,600 pounds and a combined drive axle GAWR less than or equal to 45,000 pounds, for a total GVWR equal to or less than 59,600 pounds. The agency's test data show that, for these tractors, compliance with the new stopping distance requirements can be readily achieved.

The compliance date for all two-axle tractors, as well as severe service tractors with a GVWR greater than 59,600 pounds, is August 1, 2013. NHTSA's test data indicate that two-axle tractors can meet a 250-foot loaded-to-GVWR stopping distance requirement with improved brake systems. However, additional lead time is needed for manufacturers to more fully evaluate new brake systems to ensure compatibility with existing trailers and converter dollies when used in multi-trailer combinations. Further, more time is needed to minimize the risk of vehicle stability and control issues. With regard to severe service tractors, the available test data and analysis indicate that the respective 250-foot and 310-foot stopping distance requirements can be met by improved brake systems. However, as only limited development work has been performed, these vehicles require additional lead time to ensure complete testing and validation of new brake systems.

iii. Margin of Compliance

Manufacturers need to ensure that all of their vehicles meet a test requirement established by a Federal safety standard. To account for variability, including vehicle-to-vehicle variability, they typically design vehicles with a margin of compliance.

With regard to stopping distance, the comments stated that the traditional industry compliance margin is 10 percent.
19

We note that this does not necessarily mean that manufacturers do not sometimes certify vehicles with a smaller margin of compliance. However, they do need to take whatever steps are necessary to ensure that each vehicle they certify complies with applicable requirements.

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

We believe that calculations of 10 percent compliance margins are useful for analytical and discussion purposes in considering what stopping distance requirements are appropriate and practicable.

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

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

i. Testing Conducted on Three-Axle Truck Tractors

Available test data demonstrate that typical three-axle tractors can meet a requirement with a 30 percent reduction in stopping distance using only enhanced drum brakes, the least expensive type of improved foundation brake available. NHTSA used the same definition for a “typical three-axle tractor” as TMA and HDBMC, which is a 6x4 configuration (three axles with six wheel positions; a non-driven steer axle and two rear drive axles) with a GVWR below 59,600 pounds, a steer axle with a GAWR equal or less than 14,600 pounds, and tandem drive axles rated equal or less than 45,000 pounds total capacity. According to the test data from the Radlinski
20

reports (7 tests), typical three-axle tractors with enhanced S-cam drum brakes at all wheel positions achieved the target 30 percent reduction in stopping distance, with margins of compliance (based on a 250-foot stopping distance requirement) ranging from 12 to 18 percent. This is superior to the ten percent threshold used by most manufacturers.

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

NHTSA also conducted testing at its Vehicle Research Test Center (VRTC), using a variety of foundation brake systems.
21

The VRTC tests of two tractors showed that with disc brakes at all wheel positions, both tractors could meet the 30 percent target with compliance margins between six and 13 percent, while one of these tractors could meet the 30 percent target using a hybrid (disc/drum) configuration with disc brakes on the steer axle and standard drive axle drum brakes (16.5″ diameter drum x 7″ wide brake linings) with a six percent margin of compliance.

21

See Class 8 Truck Tractor Braking Performance Improvement Study,
available at:
http://www.nhtsa.dot.gov/staticfiles/DOT/NHTSA/NRD/Multimedia/PDFs/VRTC/ca/capubs/DOTHS809700.pdf

The above tests show that disc brakes provide an alternative means to achieve compliance with a 30 percent reduction in the stopping distance requirement. All of the all-disc braked examples could meet or exceed the ten percent margin of compliance with one exception (one VRTC test). Moreover, the agency is confident that the performance of that one example could readily be improved by increasing the torque output of that disc brake (or switching to newer, readily-available, and more powerful disc brakes).

Results for the hybrid combination of disc brakes on the steer axle and standard drum brakes on the drive axle were mixed, with one tractor meeting the 30 percent reduction in stopping distance with a six percent margin, even though the performance would be expected to match or exceed the performance of a tractor with enhanced drum brakes at all wheel positions (which, as the Radlinski testing showed, was able to meet the 30 percent reduction with margins over ten percent). Also, the agency did not test any hybrid configurations using enhanced drum brakes (standard 16.5″ x 7″ drive axle brakes were used in the agency's hybrid tests). Based on these results, one conclusion that can be drawn regarding cost is enhanced drive axle S-cam drum brakes will be necessary, at a minimum, whether used on the steer or drive axles of a standard three-axle tractor, because the available data show that standard drum brakes (15″ x 4″ steer, 16.5″ x 7″ drive) have not been able to achieve the necessary performance to meet the requirements in this final rule.

ii. Testing Conducted on Two-Axle Truck Tractors

NHTSA's testing after publication of the NPRM indicated that a Sterling 4x2 tractor is capable of complying with a 250-foot stopping distance with enhanced foundation brakes.
22

In the VRTC testing, the test tractor was purchased new and was originally equipped with larger steer axle S-cam drum brakes of 16.5″ diameter by 5″ lining width, and standard S-cam drum brakes (16.5″ x 7″) on the drive axle. In the as-received state (approximately 1,000 miles of normal road use, half of the time in the bobtail condition and half of the time towing a 48-foot flatbed trailer), the average stopping distance (based on six stops) was 241 feet from 60 mph at GVWR plus 4,500 pounds of weight on the single axle, unbraked control trailer as specified in FMVSS No. 121. However, when the foundation brakes were replaced with all new components and subjected to a complete FMVSS No. 121 burnish, the average stopping distance increased to 332 feet. Further investigation of this problem indicated that the replacement brake linings generated less torque than the original linings. This is discussed in further detail in the brake burnish section below.

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

The same VRTC test tractor was also tested with disc brakes. The first configuration of the VRTC testing was a hybrid brake system test. In this test, the tractor was equipped with disc brakes on the steer axle and the standard S-cam drum brakes on the drive axle (hybrid brake configuration), and again subjected to an FMVSS No. 121 burnish. The average loaded-to-GVWR stopping distance was 223 feet, meeting the proposed 250-foot stopping distance requirement with a margin of compliance of 11 percent. In the final configuration, the tractor was equipped with disc brakes on both the steer axle and drive axle. Here, the average loaded-to-GVWR stopping distance was 200 feet, a 20 percent margin of compliance.

iii. Testing Conducted on Severe Service Tractors

After publication of the NPRM, the agency conducted additional testing on a severe service truck judged to have similar service braking characteristics as a tractor of similar size and weight dimensions.
23

The test truck was a three-axle Peterbilt Model 357 with a steer axle GAWR of 18,000 pounds and tandem drive axle GAWR of 44,000 pounds. The total GVWR was 62,000

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

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

The substantive difference in braking performance for this vehicle in the truck versus tractor configuration would be apparent in emergency braking performance, for which the truck configuration would likely need to utilize spring brake modulation to meet the stopping distance requirement at GVWR (this is because there is no equivalent test requirement for tractors, since emergency braking requirements only apply in the unloaded condition), and there are also differences in parking brake performance requirements for single-unit trucks and tractors. However, neither of these brake system differences were factors during the normal service brake tests for the Peterbilt truck.

The truck used in the VRTC testing was tested with a variety of brake configurations in order to determine its stopping distance performance. The truck was originally manufactured with enhanced 16.5″ x 6″ S-cam drum brakes on the steer axle, and standard 16.5″ x 7″ S-cam drum brakes on the drive axles. It was also equipped with a 6S/6M ABS system that should provide the highest braking efficiency because the braking forces are modulated individually at each wheel position. With the OEM S-cam drum brakes, the average loaded-to-GVWR, 60 mph stopping distance was 280 feet, which would not meet the enhanced 250 feet stopping distance requirement. In a hybrid configuration with disc brakes on the steer axle and standard S-cam drum brakes on the drive axles, the average stopping distance was 251 feet. With disc brakes at all wheel positions, the average stopping distance was 224 feet, meeting the target reduced stopping distance with a better than 10 percent margin of compliance.

Another test condition that was evaluated for the severe service Peterbilt truck was to up-load the vehicle to a GVWR of 76,000 pounds and conduct 60 mph stops using all disc brakes. The average stopping distance for six stops was 254 feet and the minimum stopping distance out of the six stops was 251 feet. The standard deviation of all six stops was 3.2 feet, indicating that there was very little stop-to-stop variability, and thus this vehicle achieved very repeatable performance with disc brakes.
24

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

In July 2006, the VRTC also ran simulation testing based on the results of the Peterbilt truck testing to determine braking performance at 80,000 pounds GVWR.
25

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

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

c. Response to Public Comments

i. Straight-Line Braking Performance of Tractors With Improved Brake Systems

In this section, we discuss data and arguments relating to the performance of tractors with improved braking systems. The purpose of this section is to address whether various tractor configurations are capable of meeting the proposed performance requirements of FMVSS No. 121 with improved braking systems. In addition, we provide additional insight on what kind of improved brakes will be necessary for various tractor configurations to meet the requirements of the standard, and provide further refinement of our cost estimates. This portion of the final rule deals only with straight-line braking performance. Issues of stability, control, brake balance, burnish, and other issues are dealt with later in the rule.

1. Braking Performance of Typical Three-Axle Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

In the NPRM, the agency proposed to amend the standard's fully-loaded service brake stopping distance, at 60 mph, from the currently-required 355 feet to a new, reduced distance in the range of 284 feet (20 percent reduction) to 249 feet (30 percent reduction). The agency requested comments on the proposed reductions in the required stopping distance.

A number of commenters supported the agency's decision to reduce the stopping distance for typical three-axle tractors by 30 percent. Advocates and IIHS supported the 30 percent reduction proposal over the 20 percent reduction proposal, citing the significantly higher estimated benefits in terms of the number of injuries, fatalities, and property damage prevented. Advocates also suggested that the agency should mandate the use of disc brakes in addition to the reduced stopping distances, arguing that under actual service conditions, disc brakes will out-perform hybrid systems and drum brakes because disc brakes are relatively immune to fade from either water or heat. IIHS also stated that an additional benefit of the reduced stopping distance would be encouraging the use of disc brake systems, citing similar fade-resistant attributes of disc brakes.

One brake manufacturer, Bendix, commented that it supported a 30 percent reduction in stopping distance for three-axle tractors, and submitted test data to support the feasibility of this requirement. Eight tests with disc brakes at all wheel positions showed that all of the tractors tested could meet the 30 percent target with compliance margins between 21 percent and 18 percent. Data on one hybrid three-axle tractor showed that the 30 percent target was met with an eight percent margin of compliance. Finally, one all drum brake equipped tractor (drum brake sizes were not specified) met the 30 percent target with a 14 percent margin of compliance.

The TMA recommended that the stopping distance for three-axle tractors be reduced by a maximum of 25 percent, a position shared by International, Haldex, and NADA. TMA supplied test results for three-axle

tractors as well. For three-axle tractors equipped with all disc brakes (8 tests), the 30 percent target in stopping distance reduction was met with margins of compliance ranging from 10-20 percent. In hybrid configurations with disc brakes on the steer axle and enhanced drum brakes on the drive axles (eight tests) and in all enhanced S-cam drum configurations (eight tests), the margins of compliance ranged from two to 20 percent.

In its comments, ArvinMeritor stated that for typical three-axle tractors to achieve tractor stopping distance reductions greater than 25 percent, an increase in drive axle torque would be needed. Based on the vehicle testing conducted by NHTSA (
see
above, section III, B), the agency agrees with this comment, and recognizes that improved drive axle foundation brakes will be part of meeting a requirement that reduces stopping distance by 30 percent.

For the final rule, the agency has decided to reduce the stopping distance for typical three-axle tractors in the loaded-to-GVWR condition, at 60 mph, from the currently-required 355 feet to 250 feet.
26

In arriving at this requirement, the agency reviewed the available test data of typical three-axle tractors with improved brake systems. That data showed that a 30 percent reduction is possible using a variety of enhanced brake systems. In addition, to ensure that the amended standard is practicable, the agency considered the margin of compliance that truck manufacturers typically would use during compliance to ensure that all similar production tractors would comply with the requirement, which specifies a target stopping distance of 225 feet.

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

Given the totality of the data provided by TMA and Bendix, NHTSA believes the test data demonstrate that for typical three-axle tractors a 30 percent reduction in stopping distance is readily achievable. In most cases a 10 percent margin of compliance was met or exceeded. Both NHTSA and commenters'data are consistent with the agency's position that a 30 percent reduction is feasible. For example, some tests demonstrate that typical three-axle tractors with enhanced drum brakes at all wheel positions are readily capable of attaining 30 percent reductions with more than a 10 percent margin of compliance, although the upper range (lowest performing) of the data from TMA on at least one tractor with enhanced drum brakes showed that the margin of compliance was approximately five percent.

NHTSA does not agree with the recommendation from Advocates that it mandate disc brakes for use in all heavy truck tractors. NHTSA has not mandated the use of disc brakes because these presumed safety benefits have not been quantified, and no data to this extent was provided by Advocates. Further, we have no information as to what the net benefit of any safety benefit unique to disc brakes would be, and how it would compare to the increased costs of disc brakes.

The agency believes that the available data demonstrate that 30 percent reductions in stopping distance are readily achievable on typical three-axle tractors. A ten percent margin of compliance has been demonstrated for the majority of tractors using disc brakes and enhanced drum brakes (the exact percentage for margin of compliance cannot be determined for some of the data for which only ranges in performance for several tests were indicated). Therefore, the agency concludes that it is practicable to achieve 30 percent reductions in stopping distance when currently-available improved foundation brakes are applied to typical three-axle tractors. We also note that many tests demonstrate that enhanced drum brakes on the steer and drive axles were sufficient for many standard three-axle tractors to meet the 30 percent reduction, allowing the lowest-cost option to be used for the vast majority of heavy truck tractors.

2. Braking Performance of Two-Axle Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

NHTSA proposed in the NPRM to reduce the stopping distance for all truck tractors, which includes two-axle tractors. As discussed below, based on agency testing and comments received, the agency concludes that all two-axle tractors can meet the 30 percent reduction in stopping distance requirements with improved braking systems. Although the agency did not include test data on two-axle tractors when the NPRM was published, since that time, the agency has completed a foundation brake study at the VRTC on a typical two-axle tractor. In addition, testing data from the TMA and Bendix also indicate that two-axle tractors are capable of meeting a 30 percent reduction in stopping distance with a ten percent margin of compliance if equipped with disc brakes.

While industry commenters generally did not support reducing stopping distance for two-axle tractors, TMA data submitted in response to the NPRM indicated that for regular service two-axle tractors (
i.e.,
with a drive axle GAWR below 23,000 pounds), the 250-foot stopping distance requirement could be met using disc brakes.
27

TMA tested two-axle tractors in hybrid brake configurations and an all-disc configuration. The first hybrid configuration (one test; disc brakes on the steer axle and standard 16.5″ x 7″ S-cam drum brakes on the drive axle) was able to meet the 250-foot requirement with a margin of compliance of approximately 12 percent. A second hybrid configuration (two tests; with disc brakes on the steer axle and enhanced 16.5″ x 8.625″ S-cam drum brakes on the drive axle) indicated that both test vehicles met the 250 foot requirement, one with a margin of approximately 15 percent, and the other with a margin of only two percent. Finally, an all-disc configuration (one test) met the proposed 30 reduction with a 22 percent margin of compliance.

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

TMA also provided supplemental comments in October 2006,
28

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

28
Docket # NHTSA-2005-21462-35.

Bendix also provided data indicating that two-axle tractors could meet the 30 percent stopping distance reduction.
29

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

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

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

Finally, in its original comments, TMA stated that drive axle brake torque would need to be reduced to prevent wheel lockup (a condition which would prove hazardous during normal road braking situations). However, we believe ABS, which has been required on all new truck tractors manufactured on or after March 1, 1997, prevents wheel lockup. Hence, this comment is not persuasive.

Based on the testing data accumulated by NHTSA and provided by the commenters, the agency has concluded that meeting a 30 percent reduction in stopping distance is achievable for currently-produced two-axle tractors with at least a 10 percent margin of compliance with all-disc configurations. To a lesser extent, the hybrid disc/drum configurations (some of which had good margins of compliance, and some of which had poor margins) may also be able to achieve the 30 percent reduction in stopping distance.

3. Braking Performance of Severe Service Tractors With Improved Brake Systems in the Loaded-to-GVWR Condition

a. Definition of Severe Service Tractor and Specific Safety Benefits

With the exception of certain vehicles with extremely high GVWRs or GAWRs that are excluded from the requirements of Standard No. 121, the reduced stopping distance requirements proposed in the NPRM were to apply to all severe service tractors. For purposes of this document, NHTSA is using TMA's definition of a three-axle severe service tractor, as a three-axle tractor having a steer axle GAWR greater than 14,600 pounds and tandem drive axles with a total GAWR greater than 45,000 pounds. In addition, severe service tractors include those tractors with twin steer axles, auxiliary axles (
e.g.,
lift axles), and/or tridem drive axles. Chassis configurations include 6x4, 8x4, 8x6, 10x6, and 14x4 layouts. Based on comments from TMA and Freightliner, the GVWR of severe service tractors is greater than 59,600 pounds and can exceed 100,000 pounds. The commenters explained that severe service tractors are used in special purpose applications such as oil field service, extreme heavy hauling, transporting earth moving equipment, and logging. The commenters further stated that operation is both on-road and off-road, and in some cases, on-road use is at relatively low speeds with the tractor-trailer combinations being accompanied by escort vehicles.

Freightliner
30

stated that severe service tractors comprise approximately seven percent of tractor production and are involved in 5.6 percent of fatal tractor crashes, according to the UMTRI report on Class 8 tractors involved in fatal crashes (included with TMA's comments).
31

To the extent possible, the agency compares fatal crash involvement rates of vehicle types based upon fatalities per 100 million vehicle miles traveled (VMT) (
see
Section II of the NPRM). As described in the NPRM, tractors have a lower overall crash rate per 100 million VMT compared to light vehicles (passenger cars, light trucks, and SUVs), but are over-represented in fatal crashes. The UMTRI report submitted by TMA
32

did not analyze tractor crash data for the three types of tractors studied (typical three-axle, two-axle, and severe service tractors) based upon VMT exposure, and the agency is not aware such VMT exposure data being available from the known crash data sources. Based upon the comments received, it appears that the on-road mileage exposure for severe service tractors is lower than for typical three-axle or two-axle tractors.
33

Nonetheless, the 5.6 percent fatality involvement rate does not indicate that severe service tractors are underrepresented in fatal crashes to an extent that the agency should consider excluding them from this final rule. Given the potential safety benefits, we believe the deciding factor in determining the loaded-to-GVWR stopping distance requirements for severe service tractors under this final rule should be dependent on the best performance that can be achieved using the available improved brake systems.

30
Docket # NHTSA-2005-21462-25.

31
Docket # NHTSA-2005-21462-26.

32
Docket No. NHTSA-2005-21462-26;
see
attachment, p. 16.

33
Docket # NHTSA-2005-21462-26, p. 11.

In its comments, TMA delineated several broad categories of severe service tractors that the agency believes comprise highly relevant categories. The first is three-axle severe service tractors with GVWRs ranging from approximately 60,000-70,000 pounds. These tractors have a steer axle GAWR in the 13,000-14,500-pound range and tandem drive axles rated in the approximate range of 46,000-55,000 pounds (as depicted in Figure 5 in TMA's April 2006 comments, which shows a three-axle tractor towing double trailers.) The second category of severe service tractors described by TMA are three-axle severe service tractors with GVWRs above 70,000 pounds. Finally, there are severe service tractors in 8x4, 8x6, 10x6, 14x4, and other configurations. This group of vehicles is used in special purpose or extreme heavy haul applications (as depicted in Figure 6 of TMA's comments, which shows a 10x6, twin-steer tractor with tridem drive axles.) Based upon the information provided to the agency in several
ex parte
meetings that have been held since the publication of the NPRM,
34

the typical weight ratings for the 10x6 tractor photographed would be 14,500 pounds GAWR for each steer axle and 20,000 pounds for each drive axle, yielding a GVWR of 89,000 pounds. This tractor would not be excluded from FMVSS No. 121 based on its axle ratings. Other unusual tractor configurations would also tend to have high GVWRs over 70,000 pounds and still be subject to FMVSS No. 121.

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

b. Three-Axle Severe Service Tractors With a GVWR Under 70,000 Pounds

Based on the agency's testing, as well as test data provided by the commenters, NHTSA believes that severe service three-axle tractors with a GVWR under 70,000 pounds can meet a 250-foot stopping distance requirement using enhanced foundation brake systems. VRTC test results and commenter data lead the agency to believe that three-axle severe service tractors with a GVWR between 60,000 and 70,000 pounds are capable of meeting the 30 percent reduction in stopping distance using available enhanced braking systems.

NHTSA's testing indicated that lower-GVWR three-axle severe service tractors will be able to meet a 250-foot stopping distance requirement. Here, NHTSA refers to the Peterbilt truck, tested by the VRTC, which is very similar to three-axle severe service tractors of the 60,000-70,000 pounds GVWR category. As stated above, the VRTC testing used a single-unit truck with comparable braking performance to a severe-service three-axle truck tractor. This tractor, when equipped with disc brakes and tested at a GVWR of 62,000 pounds, was able to meet the 250-foot stopping distance requirement with a 10 percent margin of compliance.
35

Therefore, the

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

35
Docket # NHTSA-2005-21462-40.

TMA's supplemental comments include data that enhance NHTSA's confidence in the practicability of this requirement. The data indicate that for lower GVWR three-axle severe service tractors, a 250-foot stopping distance and a ten percent margin of compliance can be achieved for three-axle, all-disc braked tractors of 62,000 and 66,000 pounds GVWR.
36

Both VRTC and TMA test data show that three-axle severe service tractors under 70,000 pounds GVWR are capable of meeting the reduced stopping distance with improved foundation brakes and can also achieve a 10 percent margin of compliance.

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

In its original comments,
37

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

37
Docket # NHTSA-2005-21462-26.

In October 2006, TMA submitted supplemental comments that included additional information on severe service tractor stopping distance performance. The TMA testing included six drum and six disc brake configurations, performed on vehicles with three different drive axle GAWRs. TMA stated that the disc brakes used in these tests were prototype models that had not been fully tested for production (as dynamometer and other test data were not yet available). The agency assumes that these would be the largest practical disc brakes that would work within the available wheel and suspension envelope.

TMA's test results are discussed below, but the result we believe to be most noteworthy is that the TMA testing indicated that the proposed 30 percent reduction in stopping distance could be achieved using disc brakes. To summarize the TMA test results, when tested at a steer axle weight of 20,000 pounds and a tandem drive axle weight of 46,000 pounds, yielding a GVWR of 66,000 pounds, the baseline all-drum brake configuration (it was not specified whether the drum brakes were standard or larger sized) had a stopping distance of 262 feet. Testing of a hybrid configuration using the prototype disc brakes on the steer axle yielded a stopping distance of 229 feet, thus meeting the target with an eight percent margin of compliance. Finally, when tested with disc brakes at all wheel positions; the stopping distance was 223 feet, yielding an 11 percent margin of compliance. We note that the data for the all-disc brake test are consistent with the performance obtained by VRTC in its tests of the Peterbilt truck with a 62,000 pounds GVWR.

c. Three-Axle Severe Service Tractors With GVWR Over 70,000 Pounds

In contrast to three-axle tractors with a GVWR between 59,600-70,000 pounds, agency testing and commenters' data indicate that it is not practicable at this time for higher-GVWR three-axle severe service tractors to meet a 250-foot stopping distance requirement. In making this determination, the agency carefully considered its own data, as well as the data on high-GVWR three-axle truck tractors provided by the TMA in its comments. Nonetheless, NHTSA believes that improvements in stopping distance for these vehicles should be pursued, albeit at a level less than a 30 percent reduction. TMA's supplemental comments indicate that tractors with very high GVWRs (with regard to three-axle tractors, these have single axle weight ratings of 26,000 pounds or more, or tandem axle weight ratings of 52,000 pounds or more) make up less than one percent of annual tractor production.

The agency believes that severe service tractors over 70,000-pound GVWR can meet the stopping distance requirements for similar vehicles that are configured as single-unit trucks rather than tractors, because similarly-configured single unit trucks are currently being manufactured in compliance with FMVSS No. 121. As the service brake stopping distance requirement for single-unit trucks is 310 feet in the loaded-to-GVWR condition, the agency believes that specifying this standard on severe service tractors of similar weight is a practicable alternative to a 30 percent reduction in stopping distance.

TMA provided simulation test data for hybrid and all-disc foundation brake configurations of three-axle severe service tractors with a GVWR over 70,000 pounds.
38

The data that TMA used in its comments were based upon unspecified simulations, presumably similar to the Truck Sim work performed by VRTC. A footnote in the supplemental TMA submission indicates that one all-drum brake configuration at 72,000 pounds GVWR was verified by actual vehicle testing. The simulation results for a 72,000-pound GVWR tractor (20,000-pound steer axle load and 52,000-pound tandem drive axle load) estimated that the hybrid configuration would achieve a 248-foot stopping distance (within the 30 percent reduction target, but with little margin of compliance). When equipped with disc brakes at all wheel positions, the stopping distance was estimated at 242 feet, which would meet a 30 percent reduction in stopping distance with a three percent margin of compliance. The configuration with drum brakes
39

at all wheel positions was road tested at 72,000 pounds GVWR and had a stopping distance of 285 feet, above the 250-foot limit. TMA also stated that it is unclear what technologies would be needed to achieve high levels of braking performance improvements for tractors in this weight category.

38
Docket # NHTSA-2005-21462-34.

39
TMA did not provide dimensions for these brakes, but described them as the highest available performance brakes.

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

requirements for severe service tractors as part of this final rule.

In its October 2006 comments, TMA presented testing that indicated trucks with a GVWR over 70,000 pounds are incapable of meeting a 250-foot stopping distance requirement. In one example, a 72,000-pound GVWR tractor equipped with all disc brakes only achieved a three percent margin of compliance, which the agency does not consider to be enough for manufacturers to reliably build tractors with assured compliance to FMVSS No. 121. Similarly, a 78,000-pound GVWR three-axle tractor equipped with all disc brakes stopped in 261 feet, thus it did not meet a 250-foot stopping distance requirement. Because all-disc brake configurations generally produce the best available braking performance, it is not clear what advancements could be used to bring trucks of this weight within a 250-foot stopping distance. The agency therefore concludes that three-axle tractors with a GVWR greater than 70,000 pounds should be provided with a longer stopping distance requirement.

The agency has considered all of the available data and comments regarding severe service tractors to determine appropriate loaded-to-GVWR stopping distance requirements for these vehicles. The agency agrees with TMA that, based on all available information, foundation brakes that could provide loaded-to-GVWR stopping distance performance in the 250-foot range at 60 mph are not available for three-axle severe service tractors with a GVWR over 70,000 pounds. There are little or no test data available for tractors with a GVWR over 70,000 fitted with the largest available disc brakes to demonstrate that they would be able to meet a 30 percent reduction in stopping distance. In making this statement, the agency notes the TMA supplemental comments, which discuss the lack of extensive testing of prototype disc brakes.
40

Therefore, the agency does not believe it is practicable at this time to require three-axle severe service tractors over 70,000 pounds GVWR to meet the 30 percent reduction in stopping distance.

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

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

As previously discussed, the tests at VRTC of a severe service truck (used as a surrogate severe service tractor), loaded to a GVWR of 76,000 pounds and equipped with all disc brakes, had an average stopping distance of 254 feet. This represents an 18 percent margin of compliance to the 310-foot stopping distance requirement implemented under this final rule.

d. Severe Service Tractors With Four or More Axles

For severe service tractors with more than three axles, there is a similar distinction to be made between lower-GVWR tractors and higher-GVWR tractors. While the NPRM proposed reducing the stopping distance for all tractors uniformly, commenters and agency testing have indicated that a distinction should be made, similar to the distinction within severe service three-axle tractors. With regard to severe service tractors with four or more axles, we believe there are some tractor configurations that, even though they are in the severe service category, can comply with a 250-foot stopping distance requirement when most or all of the brakes are upgraded to disc brakes. A small percentage of these tractors, however, will not be able to currently comply with this requirement, and thus necessitate a different approach.

Some extra-axle tractors are based on, and perform very similarly to, severe service three-axle truck tractors. One example of this is a severe service three-axle tractor that has an auxiliary axle installed by either the truck manufacturer or by a vehicle alterer. The agency believes that its testing of a single-unit truck at VRTC provides a basis for determining the scope of this final rule with regard to similarly configured tractors. Using the VRTC three-axle Peterbilt truck as a guideline, which had GAWRs of 18,000 pounds for the steer axle, 44,000 pounds for the tandem drive axles, and a total GVWR of 62,000 pounds, we considered the installation of a lift axle placed in front of the drive axles with a GAWR of 20,000 pounds. We note that this is on the upper end of axle weight ratings for lift axles; many lower GAWR ratings for lift axles are also available. The GVWR would now be increased to 82,000 pounds, and although the agency has no full vehicle test data, the loaded-to-GVWR service braking performance of the tractor would not be expected to decrease substantially from the performance in the original three-axle configuration (this vehicle was tested with three axles at 62,000 pounds GVWR and was able to stop in 224 feet when equipped with disc brakes at all wheel positions). We make this assumption because of the auxiliary brake requirements FMVSS No. 121, which mandate high levels of fade resistance and stopping power requirements.

Although the agency does not have data on the dynamic load increases on lift axles under hard braking, we expect load transfer increases (if any) to be minimal. This assumption is based on prior analyses that show the greatest load transfer to be on the steer axle, while drive axles (and trailer axles in the case of combination vehicle tests) typically have small decreases in vertical load under hard braking.
41

Thus, it would not be expected that lift axle foundation brakes would need to be substantially increased in size to provide the needed retardation force to meet the new stopping distance requirements.

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

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

are typically installed on auxiliary axles should be available for a 20,000-pound auxiliary axle; in other words, it is not expected that disc brakes would be needed on the auxiliary axles in order to achieve satisfactory performance.

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

e. Two-Axle Severe Service Tractors

We also respond to TMA's April 2006 comments regarding what it identified as a distinct class of severe service two-axle tractors, which TMA defined as a two-axle truck tractor having a drive axle GAWR of 23,000 pounds or more. Based on our review of the commenters' data, the agency does not believe that the commenters have provided sufficient information to justify allowing these tractors to be subject to a less rigorous stopping distance requirement than other two-axle tractors, and that the proposed specifications for improved stopping distances are practicable.

Commenters' test data show that two-axle truck tractors with a higher GVWR have similar braking performance to other two-axle tractors. TMA provided test data for one severe service two-axle tractor with standard 16.5″ x 5″ S-cam drum brakes on the steer axle and standard 16.5″ x 7″ S-cam drum brakes on the drive axle.
42

The stopping distance for this tractor was approximately 315 feet, so this brake configuration would not meet a 250-foot stopping distance requirement. However, this test result does not make it necessary to exclude severe service tractors from the improved stopping distance requirement entirely.

42
Docket # NHTSA-2005-21462-26.

First, we note that the two-axle tractor cited by TMA is not a typical severe service tractor because it does not have a GVWR in excess of 59,600 pounds, thereby putting it outside the standard definition of a severe service tractor.

Second, of particular significance is the fact that this test result does not show how this vehicle would perform with upgraded brakes, specifically disc brakes. Disc brakes are the type of brakes that have been demonstrated to typically provide the shortest stopping distance. Therefore, the agency declines to use the TMA data on this “severe service two-axle tractor” in formulating the requirements of this final rule.

We do not have test data for this specific configuration of vehicle equipped with disc brakes. However, considering that the achieved stopping distance of the severe service two-axle tractor is roughly equivalent to what many other two-axle tractors can achieve when equipped with standard S-cam drum brakes at all wheel positions,
43

NHTSA believes that “severe service two-axle” tractors will be able to achieve similar enhancements using enhanced S-cam drum brakes or disc brakes in lieu of standard S-cam drum brakes. Therefore, the agency is not specifying a longer stopping distance for these vehicles. However, for reasons discussed below, the agency is providing a longer lead time for all two-axle tractors.

43
Docket # NHTSA-2005-21462-26.

f. Summary of Severe Service Tractors

Based upon the above analysis, the agency is setting the loaded-to-GVWR stopping distance requirements for severe service tractors as follows:

• A tractor with three axles and a GVWR of 70,000 pounds or less must stop within 250 feet.

• A tractor with three axles and a GVWR greater than 70,000 pounds must stop within 310 feet.

• A tractor with four or more axles and a GVWR of 85,000 pounds or less must stop within 250 feet.

• A tractor with four or more axles and a GVWR greater than 85,000 pounds must stop within 310 feet.

Further, the agency does not recognize a class of two-axle severe service tractors, and notes that all two-axle tractors are required to meet a 250-foot stopping distance requirement.

The agency believes that these requirements will enhance vehicle safety by ensuring that the vast majority of tractors (estimated to be approximately 99 percent of annual tractor production) will meet a requirement with a 30 percent reduction in stopping distance. The remaining one percent of tractors, which are high-GVWR severe service tractors, will be required to meet a requirement with a 13 percent reduction in stopping distance, which is equal to the current required stopping distance performance for single-unit trucks. Finally, those tractors with any axle with GAWR of 29,000 pounds or greater will continue to be excluded from the FMVSS No. 121 requirements.

4. Braking Performance of Tractors With Improved Brake Systems in the Unloaded Weight Condition

In the NPRM, the agency proposed to reduce the existing FMVSS No. 121 unloaded weight stopping distance for heavy truck tractors from 335 feet by 20 percent (
i.e.,
to 268 feet) to 30 percent (
i.e.,
to 235 feet). Testing in the unloaded weight condition (also known as lightly-loaded vehicle weight or LLVW) is performed without any trailer attached to the tractor (
i.e.,
bobtail condition), plus up to an additional 500 pounds allowed for the test driver and vehicle instrumentation. In addition, up to 1,000 pounds is allowed for a roll bar structure. The tractor is required to meet the unloaded stopping distance requirement for at least one out of six test stops.

One potential issue that arises when reducing stopping distance in the lightly-loaded condition is the issue of wheel lockup, as there is far less available tire-road friction than in the loaded-to-GVWR condition. Requirements in FMVSS No. 121, S5.3.1, paragraphs (a) through (d), specify allowances for wheel lockup during either a service brake stopping distance test in the loaded or unloaded

condition, and applies to trucks, tractors, and buses. At speeds above 20 mph, wheel lockup on certain axles is only permitted to be momentary (less than one second), while unlimited wheel lockup on auxiliary axles is permitted. At speeds below 20 mph, unlimited wheel lockup is permitted on any wheel. These wheel lockup provisions were necessary before ABS was mandated, to ensure that the test driver could bring the vehicle to a stop without loss of control due to unlimited wheel lockup. In the case of a tractor in the unloaded condition, the drive axle wheels are very easy to lock up, as there is little vertical load on them. Prior to the advent of ABS, some tractors were equipped with bobtail proportioning valves to reduce the brake pressure to the drive axles in the unloaded condition and make it easier to stop the vehicle within the required distance (using more steer axle brake power, where a substantial vertical load exists), and also to improve the on-road drivability of bobtail tractors.

However, since March 1, 1997, all tractors have been required to be equipped with ABS on at least one steer axle and one drive axle, which has virtually eliminated wheel lockup in tractors. While the relevant FMVSS No. 121 requirement states that only one rear axle of a tractor needs to be equipped with ABS, most tractors also indirectly control the wheels on the other rear axle in the case of tandem drive axles, or they employ direct ABS control of both tandem drive axles. In the case of a severe service truck or tractor with non-liftable auxiliary axles mounted rearward of the tandem drive axles, an auxiliary ABS system may be necessary on those auxiliary axles to meet the wheel lockup provisions in S5.3.1, but trucks and tractors with liftable auxiliary axles typically do not need to have ABS on those axles. In addition, the braking-in-a-curve test in S5.3.6 was included in FMVSS No. 121 to ensure that the ABS provides adequate vehicle control and stability when in a curve on slippery pavement and subjected to a full-treadle brake application. The braking-in-a-curve test ensures that the ABS is regulating the braking forces at the wheels to keep the tires rolling, so they can generate the lateral forces required for maintaining the curve, and the vehicle does not plow out of the curve during braking.

In addition, ABS systems can help greatly decrease the stopping distances for lightly-loaded tractors. Since the addition of these ABS requirements, conducting braking tests on trucks and buses in the unloaded condition has been greatly simplified. Rather than requiring the driver to modulate the brake treadle to try to achieve the required stopping distance while staying within the wheel lockup provisions in S5.3.1, the test driver can make a full treadle brake application at the initiation of the stop and the ABS ensures that the wheel lockup provisions are met. The result is much greater braking efficiency and shorter stopping distances compared to driver-modulated stops. This is evident by reviewing the VRTC test data for tractors tested in the unloaded condition. Compared to the FMVSS No. 121 requirement of stopping within 335 feet (unloaded condition), typical bobtail tractor stopping distances for tractors with improved foundation brake systems are approximately 180 feet, or 46 percent lower than the current 335-foot requirement. As an example, VRTC tests of the tractors equipped with hybrid disc/drum brakes and all-disc brakes resulted in unloaded stoppin

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3AE9-17533. Public record. Not legal advice.