13216 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

1Hereinafter referred to as ‘‘heavy vehicles.’’

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety

Administration

49 CFR Part 571

[Docket No. 92–29; Notice 5]

[Docket No. 93–69; Notice 2]

RIN 2127–AA00

RIN 2127–AE75

Federal Motor Vehicle Safety

Standards; Stability and Control of

Medium and Heavy Vehicles During

Braking

AGENCY: National Highway Traffic

Safety Administration (NHTSA), DOT.

ACTION: Final rule.

SUMMARY: In response to the Intermodal

Surface Transportation Efficiency Act

(ISTEA) of 1991, this final rule amends

Standard No. 105, Hydraulic Brake

Systems, and Standard No. 121, Air

Brake Systems, to require medium and

heavy vehicles to be equipped with an

antilock brake system (ABS) to improve

the directional stability and control of

these vehicles during braking. For truck

tractors, the ABS requirement is

supplemented by a 30-mph braking-ina-curve test on a low coefficient of

friction surface using a full brake

application. By improving directional

stability and control, these requirements

will significantly reduce deaths and

injuries caused by jackknifing and other

losses of directional stability and

control during braking.

In addition, this final rule requires all

powered heavy vehicles to be equipped

with an in-cab lamp to indicate ABS

malfunctions. Truck tractors and other

towing trucks are required to be

equipped with two separate in-cab

lamps: one indicating malfunctions in

the towing truck ABS and the other

indicating malfunctions in the towed

trailer or dolly ABS. Trailers produced

during an initial eight-year period must

also be equipped with an external

malfunction indicator that will be

visible to the driver through the

rearview mirror of the towing truck or

tractor. More specifically, the external

trailer indicator will indicate an ABS

malfunction to the driver, if the trailer

is being towed by an older vehicle that

is not equipped with an in-cab lamp for

trailer ABS malfunction indication. In

general, the indicators will provide

valuable information about ABS

malfunctioning to the driver and to

maintenance and Federal and State

inspection personnel.

DATES: Effective Dates: The amendments

to 49 CFR 571.105 become effective on

March 1, 1999. The amendments to 49

CFR 571.121 become effective on March

1, 1997. Compliance to § 571.121 with

respect to air-braked trailers and single

unit trucks and buses will be required

as of March 1, 1998.

Petitions for Reconsideration: Any

petitions for reconsideration of this rule

must be received by NHTSA no later

than April 10, 1995.

ADDRESSES: Petitions for reconsideration

of this rule should refer to Docket 92–

29; Notice 5 and should be submitted to:

Administrator, National Highway

Traffic Safety Administration, 400

Seventh Street, S.W., Washington, D.C.

20590.

FOR FURTHER INFORMATION CONTACT: Mr.

George Soodoo, Office of Crash

Avoidance, National Highway Traffic

Safety Administration, 400 Seventh

Street, SW., Washington, D.C. 20590

(202) 366–5892.

SUPPLEMENTARY INFORMATION:

I. Overview

II. Background

A. The Safety Problem: Loss of Control

Crashes

B. Braking Systems, Tires, Wheel Lockup,

and Loss of Control Crashes

III. US and Foreign Activities Related to

Stability and Control During Braking

Performance

A. Early US Regulatory History

B. PACCAR Case

C. US and Foreign Experience with ABS

since PACCAR

IV. Advance Notice of Proposed Rulemaking

(ANPRM)

V. Agency Proposal

VI. Comments on the Proposal

VII. Agency’s Supplemental Proposal

VIII. Comments on the Supplemental

Proposal

IX. Agency Decision

A. Requirement for and Definition of ABS

1. Legal Authority

2. Elements of the Requirement/Definition

for ABS

3. Dynamic Versus Equipment

Requirements

B. Independent Wheel Control

C. Braking-In-A-Curve Test

1. General Considerations

2. Test Surface

3. Test Speed

4. Type of Brake Application

5. Number of Test Stops for Certification

6. Test Weight

7. Loading Conditions

8. Initial Brake Temperature

9. Transmission Position

10. Summary of General Test Conditions

D. Reliability and Maintenance

E. Requirements for Durability, Reliability,

and Maintainability

F. Alleged Safety Problems

G. ABS Malfunction Indicator Lamps

1. Number and Location; Duration of

Trailer Requirement

2. Conditions for Activation

3. Activation Protocol for Malfunction

Indicators

4. Signal Storage

5. Disabling Switch

6. ABS Failed System Requirements

H. Power Source

I. Applicability of Amendments

1. Trailers with Hydraulic or Electric

Brakes

2. Hydraulically Braked Vehicles

J. Implementation

K. Intermediate and Final Stage

Manufacturers/Trailer Manufacturers

L. Benefits

M. Costs

IX. Rulemaking Analyses and Notices

A. Executive Order 12866 and DOT

Regulatory Policies and Procedures

B. Regulatory Flexibility Act

C. National Environmental Policy Act

D. Executive Order 12612 (Federalism)

E. Civil Justice Reform

I. Overview

As part of NHTSA’s plans to improve

the braking performance of medium and

heavy vehicles,1 this final rule amends

the agency’s two brake standards for

those vehicles by adopting requirements

to improve the directional stability and

control characteristics of these vehicles

while braking. The two Federal Motor

Vehicle Safety Standards (FMVSSs) are

Standard No. 105, Hydraulic Brake

Systems, and Standard No. 121, Air

Brake Systems. In formulating this final

rule, NHTSA has relied on extensive

fleet studies of tractor trailer

combinations equipped with antilock

systems, road testing of such vehicles at

the agency’s Vehicle Research Test

Center (VRTC), review of its Fatal

Accident Reporting Systems (FARS)

data and other crash data, the positive

experience with ABS-equipped heavy

vehicles in Europe and throughout the

world, comments to the public docket

about this rulemaking, and other

available information.

In order to fully understand the safety

problem being addressed by this

rulemaking, it is necessary to examine

in detail the reasons for wheel lockup

and the consequences of such lockup.

Moreover, in order to fully understand

the reasons for the agency’s decision to

require that heavy vehicles be equipped

with a closed-loop ABS, it is necessary

to understand the general characteristics

of brake systems, the force-generating

characteristics of tires, and the

interactions between brake systems and

tires.

To provide the reader with a means

for gaining this understanding, NHTSA

has included an Appendix in this

document, which provides a discussion

of basic service brake systems, loss-ofcontrol crashes, and ABS

characteristics. The Appendix discusses

the types of heavy brake systems that
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13217

2A closed-loop (control) system is one which

examines the output of the system and adjusts the

input to the system in response to that output. This

inclusion of the output (or some function of the

output) as part of the input to such a system is

referred to as feedback.

3 (Motor Vehicle Manufacturers’ Association v.

State Farm Insurance, 463 U.S. 29, (1983))

4See the Appendix for a discussion of this term

and directional stability.

5Chrysler Corp. v. DOT, 515 F.2d 1053, 1058–59

(1975).

6By powered vehicle, the agency means a vehicle

equipped with an engine that propels the vehicle.

In contrast, a non-powered vehicle, such as a trailer,

is towed by another vehicle.

7 Vehicles with a gross vehicle weight rating

(GVWR) of 26,001 or more pounds.

8PACCAR v. NHTSA, 573 F.2d 632 (9th Cir.

1978), cert. denied, 439 U.S. 862 (1978)

are currently in use, how brake systems

work, and why lockup occurs. It also

discusses the force-generating

characteristics of tires and how they are

affected by varying levels of wheel slip

and the need to take these

characteristics into account in

addressing the problem of loss-ofcontrol crashes. Finally, the Appendix

discusses the need for ABS and

describes their method of operation.

Several terms, such as ‘‘wheel slip’’ that

are used throughout this notice are

discussed in detail and defined in the

Appendix. When terms whose precise

meaning affects the understanding of

the agency’s rationale are introduced,

the reader could refer to the Appendix

for a discussion of the term.

Therefore, readers who lack a

technical background and who desire a

more complete understanding of this

rulemaking may wish at this point to

read the Appendix before moving on to

the rest of the preamble.

NHTSA has decided to require the

installation of ‘‘closed-loop’’ 2 antilock

systems on all heavy vehicles. The

agency, in accordance with Supreme

Court precedent that required the

agency to consider mandating the

installation of a particular type of

automatic restraint system (i.e., ‘‘airbags

only’’) for passenger cars,3 is adopting a

rule that defines antilock brake systems,

in performance terms, as systems that

‘‘automatically control the degree of

rotational wheel slip 4 during braking’’

through sensors and transmitters that

measure, transmit, and generate signals

concerning the rate of wheel angular

rotation to controlling devices which

adjust brake application pressure to

prevent wheel lockup. In addition, for

truck tractors, the rule prescribes a 30-

mph braking-in-a-curve dynamic test on

a low coefficient of friction surface.

Although some commenters

characterized NHTSA’s definition as an

impermissible design standard, NHTSA

has specifically sought to avoid

imposing unnecessary design

restrictions or impeding the future

development of ABS, by adopting a

definition that permits any antilock

brake system that ensures feedback

between what is actually happening at

the tire-road surface interface and what

the device is doing to respond to

excessive wheel slip. To the extent that

NHTSA’s definition restricts design

choices, e.g., by requiring a ‘‘feedback’’

system in which control devices must

respond to signals that monitor wheel

slip, the requirements are stated broadly

and in performance terms. Such an

approach is consistent with that

adopted in numerous other Federal

Motor Vehicle Safety Standards,

including Standard No. 108 which

requires vehicles to be equipped with

specified lamps and reflective devices,

Standard No. 111 which requires that

vehicles be equipped with rearview

mirrors, and Standard No. 208 which

requires vehicles be equipped with

safety belts.

Moreover, the United States Court of

Appeals for the Sixth Circuit has upheld

a dimensional restriction on rectangular

headlamps, reasoning that ‘‘uniformity

of headlamp size is an element of

headlamp performance.’’ 5 Accordingly,

NHTSA has decided to reject the

conceptual objections to ‘‘closed-loop’’

ABS systems expressed by commenters

whose economic self-interest militates

against the requirement, including

manufacturers of alternative, nonelectronic braking systems that are

incapable of sensing and adjusting

braking pressures to control that wheel

slip, and an association of fleet owners

that may wish to avoid incurring the

added expense of purchasing vehicles

that are equipped with electronic ABS

systems.

Currently, all powered 6 heavy

vehicles equipped with ABS are

required to be equipped with an in-cab

ABS malfunction indicator lamp

indicating malfunctions in the powered

vehicle’s ABS. Today’s final rule

requires trucks (including truck tractors)

equipped to tow another air-braked

vehicle to be equipped with another,

separate in-cab lamp indicating

malfunctions in the ABS(s) of the towed

vehicle(s). For an eight-year period, the

amendment requires trailers to be

equipped with an external ABS

malfunction indicator that will be

visible to the driver of the towing truck

or truck tractor through the rearview

mirror. In particular, the external trailer

indicator lamp will provide information

to the driver, if the trailer is being towed

by an older vehicle that is not equipped

with an in-cab lamp indicating trailer

ABS malfunctions. In general, the

indicators will provide valuable

information about ABS malfunctioning

to the driver and to maintenance and

Federal and State inspection personnel.

In separate, related documents

published elsewhere in today’s Federal

Register, NHTSA announces its

decision to reinstate stopping distance

requirements for air-braked heavy

vehicles and to establish such

requirements for hydraulically-braked

heavy vehicles. In addition, to carry out

the antilock requirement, the Federal

Highway Administration (FHWA) is

announcing its intent to require such

systems on heavy vehicles to be

operational.

NHTSA is issuing this final rule on

directional stability and control

pursuant to the Motor Carrier Act of

1991, a part of the Intermodal Surface

Transportation Efficiency Act (ISTEA)

of 1991. Section 4012 directs the

Secretary of Transportation to initiate

rulemaking concerning methods for

improving braking performance of new

commercial motor vehicles,7 including

truck tractors, trailers, and their dollies.

Congress specifically directed that such

a rulemaking examine antilock systems,

means of improving brake compatibility,

and methods of ensuring effectiveness

of brake timing. The Act requires that

the rulemaking be consistent with the

Motor Carrier Safety Act of 1984 (49

U.S.C. § 31147) and be carried out

pursuant to, and in accordance with, the

National Traffic and Motor Vehicle

Safety Act of 1966 (Safety Act) (49

U.S.C. 30101 et seq.).

NHTSA notes that, in the mid-1970’s,

Standard No. 121 was amended to

include stringent stopping distance

requirements, coupled with a ‘‘no

lockup’’ requirement, which had the

effect of requiring heavy vehicles to be

equipped with antilock brake systems.

In response to a legal challenge, the U.S.

Court of Appeals for the 9th Circuit

invalidated the stopping distance and

‘‘no lockup’’ requirements in Standard

No. 121, along with certain other

provisions, holding that the standard

was ‘‘neither reasonable nor practicable

at the time it was put into effect.’’ 8

As explained throughout this

document, the underlying conditions

related to equipping heavy vehicles

with antilock brake systems differ

markedly from 20 years ago when the

petitioners challenged the agency in

PACCAR. First, antilock brake

technology has advanced dramatically

since the mid-1970’s, and antilock brake

systems are now in widespread,

everyday use, both in this country and
13218 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

9See the Appendix which defines and discusses

this term.

10A skid number describes the friction properties

of pavement. A skid number of 75 is representative

of a dry surface with a relatively high coefficient of

friction. See the Appendix for a discussion of this

term.

throughout the world. Second, NHTSA’s

extensive fleet study about heavy

vehicle antilock systems demonstrates

that these systems are reliable when

placed in use. Third, the agency’s

testing of truck tractors equipped with

antilock systems indicates that they

provide significantly improved

directional stability and control

compared to vehicles without antilock

systems. Fourth, while the antilock

systems used in the mid-1970s also

incorporated significantly larger, more

aggressive foundation brakes, which

were sometimes incompatible with less

aggressive systems on existing vehicles

when the antilock system

malfunctioned, the requirements being

adopted today do not necessitate such

aggressive brakes. Therefore, they do not

have the potential for creating a more

dangerous highway environment. Fifth,

the performance requirements adopted

in today’s final rule do not raise

practicability concerns. Based on these

and other considerations discussed

throughout this document, NHTSA

believes that today’s final rule satisfies

the concerns raised by the PACCAR

court.

II. Background

A. The Safety Problem: Loss of Control

Crashes

Crashes involving heavy vehicles

result in a significant number of

fatalities and injuries, and a significant

amount of property damage each year.

Based on available statistics, NHTSA

has estimated the number of crashes in

1992 for several different groups of

heavy vehicles. For heavy combination

vehicles, the agency estimates that there

were about 168,000 crashes. These

crashes resulted in about 13,600 injuries

and 387 fatalities to the occupants of

heavy combination vehicles and about

51,500 injuries and 2,452 fatalities to

the occupants of the other vehicles

involved. For truck tractors operating

without a trailer, also known as

‘‘bobtail’’ truck tractors, the agency

estimates that there were about 8,400

crashes, resulting in about 1,200 injuries

and 39 fatalities to truck tractor

occupants and about 2,600 injuries and

178 fatalities to occupants of other

involved vehicles. For heavy single-unit

trucks and school buses, the agency

estimates that there were about 192,600

crashes, resulting in about 15,700

injuries and 165 fatalities to truck and

school bus occupants and about 48,300

injuries and 891 fatalities to occupants

of other involved vehicles. For transit

and intercity buses, the agency

estimates that there were about 49,500

crashes, resulting in about 19,500

injuries and 28 fatalities to bus

occupants and about 9,100 injuries and

230 fatalities to occupants of other

involved vehicles.

Based on analyses of both national

and state accident data, NHTSA

estimates that between 10 percent and

15 percent of the crashes involving

heavy combination vehicles (including

bobtail truck tractors) involved in a

jackknife or other braking-induced

instability or loss of control. For a more

detailed discussion of the injury

statistics, the reader should refer to the

Final Economic Assessment (FEA) for

this rulemaking.

This rulemaking focuses on crashes

involving loss-of-control. Such

incidents result from braking-induced

wheel lockup with subsequent loss of

the ability of the vehicle’s tires to

generate ‘‘stabilizing forces.’’ 9 This loss

of tire stabilizing forces can result in

either vehicle directional instability if it

occurs at the vehicle’s rear wheels or

loss of steering control if it occurs at the

vehicle’s steering (front) wheels.

B. Braking Systems, Tires, Wheel

Lockup, and Loss of Control Crashes

When a vehicle driver makes a brake

application that is too ‘‘hard’’ for

conditions, the driver is likely to lock

some or all of the vehicle’s wheels (i.e.,

the wheels will be ‘‘sliding’’ rather than

‘‘rolling’’). Locking up wheels is more

likely to occur under conditions where

the maximum forces that can be

generated by the vehicle’s tires are

reduced, i.e., when the vehicle is lightly

loaded or empty and/or when the road

is slippery. When wheel lockup occurs,

vehicle loss-of-control can result.

Incorporation of an ABS decreases the

likelihood of wheel lockup, and

increases the driver’s ability to maintain

control during severe braking

maneuvers, that would otherwise lead

to wheel lockup and resultant loss of

directional stability and control, if the

vehicle is not equipped with an ABS.

III. US and Foreign Activities Related

to Stability and Control During Braking

Performance

A. Early US Regulatory History

NHTSA has been concerned about the

safety of heavy vehicle braking systems

since the agency’s inception. On

October 11, 1967, the predecessor of

NHTSA, the FHWA’s National Highway

Safety Bureau, published a notice of its

intention to promulgate brake standards

for hydraulic and air-braked trucks and

buses, and air-braked trailers. (32 FR

14279.) The initial notice of proposed

rulemaking (NPRM) for air-braked

systems proposed various requirements,

including requiring vehicles equipped

with such systems to stop within certain

distances, from certain speeds, without

leaving a 12-foot wide lane and without

lockup of any wheel ‘‘more than

momentarily.’’ (35 FR 10368, June 25,

1970.) A companion NPRM for

hydraulic brake systems proposed

essentially identical performance

requirements for heavy vehicles

equipped with those systems. (35 FR

17345, November 11, 1970.) These

notices proposed that heavy vehicles

would have to stop from 60-mph within

216 feet on a surface with a skid number

of 75.10 The ‘‘no lockup’’ provision was

intended to minimize skidding,

spinning, and jackknifing due to wheel

lockup and loss of directional stability.

In the final rule establishing Standard

No. 121, the agency decided to increase

the 60-mph stopping distance from 216

feet to 245 feet. (36 FR 3817, February

27, 1971.) The final rule amending

Standard No. 105 to extend its

applicability to heavy vehicles, also

increased the 60-mph stopping distance

for those vehicles to 245 feet. (37 FR

17970, September 2, 1972.) The

requirements for air-braked vehicles

were to become effective on September

1, 1973, and those for hydraulic-braked

vehicles, on September 1, 1974.

Although neither standard

specifically required antilock, NHTSA

anticipated that manufacturers would

equip heavy vehicles with antilock

brake systems to comply with these

requirements. The agency explained

that the less stringent stopping distance

was being required to reflect more

accurately the vehicle performance

given the test track road surface’s

friction characteristics.

Since the required stopping distances

were shorter than the stopping

performance achieved by certain heavy

vehicles, new, more aggressive

foundation braking systems were

necessary for those vehicles. In

particular, vehicles with short

wheelbases needed to have considerably

more aggressive front axle brakes to

meet the shorter stopping distance

requirements. If not kept properly

adjusted, these more aggressive front

brakes might produce a brake ‘‘pull’’ to

one side, which was disconcerting to

drivers, particularly on vehicles without

power steering. In addition, drivers

were concerned about loss of steering

control caused by wheel lockup on the
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13219

steering axle. At the time, most

manufacturers equipped their vehicles

with antilock devices because the

standards required stops to be made

without more than momentary lockup of

the wheels. These devices served to

prevent steering axle lockup problems

as well, but there was concern that

safety problems could result on shortwheelbase, high-center-of-gravity

vehicles, in the event that the antilock

system should malfunction.

NHTSA extended the effective dates

for the stopping distance requirements

in Standard No. 105 and Standard No.

121. (37 FR 3905, February 24, 1972; 38

FR 3047, February 1, 1973; 39 FR 17550,

17563, May 17, 1974.) Prior to the final

effective date for Standard No. 105, the

amendments pertaining to heavy

vehicles were withdrawn, so the

requirements for heavy hydraulicbraked trucks and buses never went into

effect. (40 FR 18411, April 28, 1975.)

Standard No. 121 became effective on

January 1, 1975, for trailers, and on

March 1, 1975, for trucks and buses. At

that time, the 60-mph stopping distance

requirement remained at 245 feet.

However, after several revisions to the

stopping distance requirements, NHTSA

amended the standard by extending the

60-mph stopping distance requirement

to 293 feet, as requested by Freightliner

in a petition for reconsideration. (41 FR

8783, March 1, 1976.)

B. PACCAR Case

In January 1975, PACCAR (a truck

manufacturer), the American Trucking

Associations (ATA), and the Truck

Equipment and Body Distributors

Association (TEBDA) sued the agency,

challenging the stopping distance

requirements in Standard No. 121,

which they believed required the use of

antilock brake systems.

Specifically, the petitioners

challenged the 245-foot stopping

distance. The subsequent increase to

293 feet, a distance that did not

necessitate such aggressive front brakes,

occurred after the suit was filed. The

petitioners argued that the agency failed

to demonstrate a safety need for the

standard and that the testing procedures

were not objective, impracticable, and

unreasonable. TEBDA objected to the

standard’s certification requirements.

In response to the suit, the stopping

distance and ‘‘no lockup’’ requirements

in Standard No. 121, along with certain

other provisions, were invalidated by

the United States Court of Appeals for

the 9th Circuit in PACCAR. The court

held that NHTSA was justified in

promulgating a standard requiring

improved air brake systems and stability

mechanisms. However, after reviewing

the record about reliability problems

with antilock brake systems then in use,

the court further held that the standard

was ‘‘neither reasonable nor practicable

at the time it was put into effect.’’ Id. at

640. Among the court’s other findings

were that the agency had a

responsibility (1) to examine the results

of its rulemakings by investigating more

fully the safety of vehicles in use, (2) to

assure that the new systems it requires

are reliable when placed in use, and (3)

to determine that its regulations do not

produce a more dangerous highway

environment than that which existed

prior to government intervention. Based

on these findings, the court stated that

* * * those parts of the Standard requiring

heavier axles and the antilock device should

be suspended. The evidence indicates that

this can be accomplished if we hold, as we

do, that the stopping distance requirements

from 60 mph are invalid * * * We hold only

that more probative and convincing data

evidencing the reliability and safety of

vehicles that are equipped with antilock and

in use must be available before the agency

can enforce a standard requiring its

installation.

Id. at 643.

The court also ruled on the objectivity

and practicability of the testing

procedures in Standard No. 121. First,

the court stated that road surface skid

numbers used for testing certified

vehicles were ‘‘ill-chosen’’ where they

assumed the use of a particular tire no

longer in production. Id. at 644. Second,

the skid number method of testing was

not objective. Id. at 644. Third, the

testing procedure was not practicable

because fluctuations in skid numbers on

a given road surface made it

impracticable for manufacturers to

conduct tests that assure that their

vehicles will exactly meet the objective

standard when tested by NHTSA. Id. at

644. Fourth, manufacturers are entitled

to testing criteria that they can rely on

with certainty. Id. at 644. Fifth, the

standard failed to specify formal and

reasonably specific testing criteria about

the time intervals between tests, the

duration of permissible wheel lockup

during tests, and the amount of curving

in testing track roadways. Id. at 645.

Sixth, the agency’s suggestions of

alternative methods of satisfying the

Safety Act’s ‘‘due care’’ provision were

inadequate since such alternatives were

not set forth in the regulations. Id. at

645.

The court remanded the matter to

NHTSA to clarify certain provisions in

Standard No. 121. In response to

PACCAR, the agency issued several

notices amending the standard to be

consistent with the decision. (43 FR

39390, September 5, 1978; 43 FR 48646,

October 19, 1978; 43 FR 58820,

December 18, 1978; 44 FR 46849,

August 9, 1979.) In the September 1978

notice, the agency amended the

standard to specify test procedures and

conditions for frictional characteristics

of the test track surface, duration of time

intervals between road tests, duration of

permissible wheel lockup during road

tests, the amount of curving in the test

track, and the means for establishing the

frictional resistance of the road test

surface. In the October 1978 notice, the

agency set forth its interpretation of

PACCAR to guide continuing

compliance with the standard.

Specifically, the notice explained that

the court had invalidated the ‘‘no

lockup’’ provisions in S5.3.1 and S5.3.2

as they apply to trucks and trailers,

along with the related stopping

distances established for 60-mph

stopping tests for heavy vehicles. That

notice also amended the requirements to

provide for ‘‘due care certification.’’ In

the December 1978 notice, NHTSA

responded to petitions for

reconsideration of certain aspects of the

September 1978 notice, including

vehicle exclusions and road test

procedures. The agency withdrew the

changes to specification of initial brake

temperatures, skid number ranges, and

duration of wheel lockup that were

made in the September notice. In the

August 1979 notice, the agency further

clarified its interpretation of certain

findings of PACCAR.

C. US and Foreign Experience With ABS

Since PACCAR

As a result of the 1978 PACCAR

decision, U.S. manufacturers chose to

halt development and production of

ABS for heavy vehicles. For instance,

before the 1978 ruling, A-C Sparkplug,

a domestic manufacturer of ABS,

produced about 180,000 ABS units per

year. By 1984, it was producing only

about 500 units annually.

NHTSA continued to study the

effectiveness of heavy truck antilock

brake systems. Among other things, the

agency studied the in-use experience

with ABS in other countries, conducted

performance testing of ABS equipped

heavy vehicles, and conducted an

extensive domestic fleet in-use test of

ABS equipped heavy vehicles.

In response to section 9107 of the

Truck and Bus Regulatory Reform Act of

1988, NHTSA submitted a report to

Congress titled ‘‘Improved Brake

Systems for Commercial Vehicles’’

(Report No. DOT HS 807 706). (April

1991) After discussing crash data

concerning heavy vehicle brake systems,

the report examined factors related to

braking effectiveness, stability and
13220 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

11 ‘‘European/Australian Experience with

Antilock Braking Systems in Fleet Service,’’ U.S.

Department of Transportation, NHTSA, DOT HS

807 269, March 1988.

12The Economic Commission for Europe (ECE) is

a United Nations organization comprised of

European countries plus the United States and

Canada, which establishes requirements applicable

to the type approval of motor vehicles and other

products for sale in those nations that choose to

apply the requirements.

13Annex 13 is titled ‘‘Requirements Applicable to

Tests for Braking Systems Equipped with Anti-Lock

Devices (Wheel-Lock Preventers).’’ It is Annex 13 of

ECE Regulation No. 13, which is titled ‘‘Uniform

Provisions Concerning the Approval of Vehicles

with Regard to Braking.’’ Regulation No. 13 is

Addendum 12 of the ‘‘United Nations Agreement

Concerning the Adoption of Uniform Conditions of

Approval and Reciprocal Recognition of Approval

for Motor Vehicle Equipment and Parts,’’ done at

Geneva on March 20, 1958, which is commonly

known as the ‘‘1958 Agreement.’’

14 ‘‘NHTSA Heavy Duty Vehicle Brake Research

Program Report No. 9, Stopping Distances of 1988

Heavy Vehicles,’’ (DOT HS 807 531, February 1990)

15 DOT HS 807 531, Table 4, page 19; Table 5,

page 23; Table 6, page 25)

16 ‘‘An In-Service Evaluation of the Reliability,

Maintainability, and Durability of Antilock Braking

Systems (ABS) for Heavy Truck Tractors,’’ (DOT HS

807 846, Final Report, March 1992.)

17 ‘‘An In-Service Evaluation of the Performance,

Reliability, Maintainability, and Durability of

Antilock Braking Systems (ABSs) for Semitrailers’’

(DOT HS 808 059, Final Report, October 1993.)

control during braking, and braking

system compatibility of heavy

combination vehicles. Among other

things, the report indicated that the

stopping distances and directional

stability of heavy vehicles could be

improved by equipping those vehicles

with ABS.

With respect to the in-use experience

with ABS in other countries, NHTSA

conducted a study of the performance,

reliability, and maintainability of inservice commercial air-braked vehicles

equipped with ABS in Europe and

Australia.11 At the time of the study in

1987, there were approximately 1.5

million ABS-equipped trucks and

tractors, and 0.9 million ABS-equipped

trailers in use in Western Europe, and

92,000 trucks and tractors and 80,000

trailers in Australia. ABS market

penetration, at that time, in Western

Europe was estimated to be 4.5 percent

for trucks and tractors and 5.6 percent

for trailers, while in Australia the

comparable figures were 1.3 percent for

trucks and tractors, and less than 1

percent for trailers. Based on data

derived from interviews with fleets

which were using ABS and surveys

conducted by ABS and vehicle

manufacturers, the reliability of ABS

when equipped on European vehicles

was estimated to be 1 to 2 ABS

component failures per 1000 vehicles

per month. Based on those data, it was

predicted that between 4 and 20

malfunctions would occur with the 200

ABS-equipped truck tractors involved in

the NHTSA-sponsored two-year inservice fleet study, which was

subsequently performed between 1989–

91. In fact, nineteen ABS components

failed, which is within the range

predicted by the European study.

Among the study’s other findings

were that maintenance was done only

when a malfunction indicator activated;

malfunction indications did not cause

drivers to disrupt their operations and

stop en route; no special maintenance

was performed on the ABS beyond

routine periodic inspections; no

problems with electronic and radio

frequency interference (RFI) were

reported; with proper maintenance, ABS

life was expected to equal that of the

vehicle; and carriers reported that

drivers liked driving ABS-equipped

vehicles. Although some problems were

encountered with wiring and connector

failures, ABS manufacturers believed

that their systems were generally

reliable and expected future

improvements.

Since the completion of NHTSA’s

study, several European countries have

issued regulations requiring heavy

vehicles to be equipped with antilock

brake systems. Specifically, the

Economic Commission for Europe 12

(ECE) Regulation No. 13 includes

technical requirements for antilock

systems in Annex 13 of its regulation.13

Annex 13 sets forth definitions of

antilock brake systems and component

parts, various ‘‘types’’ of antilock

systems, and test procedures. ECE’s

Annex 13 specifies a design requirement

and dynamic performance requirements.

The European Economic Community

(EEC Common Market) directive has

identical requirements. As a result,

since October 1, 1991, all heavy trucks

(with GVWR greater than 16 metric

tons), interurban buses (with GVWR

greater than 12 metric tons), and heavy

trailers (with GVWR greater than 10

metric tons) submitted for new type

approvals in European countries

adopting the standard have been

required to be equipped with ABS.

Accordingly, ABS have been installed

on tens of thousands of European heavy

vehicles that have traveled millions of

miles over the last few years. All

vehicles for which ABS is mandatory

under Annex 13 are required to have a

Category 1 system. Such systems are

essentially the same as those required

by today’s final rule.

With respect to performance testing,

NHTSA has issued two reports on the

stopping distance capability of several

different types of heavy air-braked

vehicles at various loading conditions.14

The agency also tested some vehicles

equipped with ABS, thus allowing

comparisons about stopping distances

with and without these devices. At the

beginning of each test series, these

vehicles were equipped with new tires

and with new original equipment brake

system components to provide

consistency in test results. At the

beginning of each testing series, the tests

were conducted on various vehicles

(school buses, transit buses, single unit

trucks, tractor trailers) at the loaded and

empty conditions and with various

equipment (with ABS activated and

deactivated). All the tests were straight

line stops from 60 mph on a dry

concrete surface. The test results

indicated that: (1) All stops made with

ABS were stable, regardless of whether

the vehicle was operating fully loaded

or empty, and (2) stopping distance

improvements with ABS (compared to

no ABS) were greatest in the bobtail

configuration (+47 percent in one case),

were significant with an empty trailer

(+29 percent in one case) and were

smallest (+4 percent) in the fully loaded

condition.15

NHTSA’s fleet testing program of

ABS-equipped truck tractors evaluated

the reliability, maintainability, and

durability of 200 truck tractors equipped

with ABS. The fleet study found that

current generation ABSs are reliable and

can be successfully installed on

commercial motor vehicles.16 The

agency added trailers to the fleet study

program in 1990–1991 and found

similar results. A copy of that study has

been submitted to the public docket.17

The findings of the fleet testing program

are discussed later in this preamble.

IV. Advance Notice of Proposed

Rulemaking (ANPRM)

On June 8, 1992, NHTSA responded

to Congress’ 1991 mandate in ISTEA by

publishing an advance notice of

proposed rulemaking (ANPRM)

announcing the agency’s interest in

measures to improve the directional

stability and control of heavy vehicles

during braking. (57 FR 24212.) The

advance notice stated the agency’s

tentative conclusion that ABS

represents the best available and most

reliable technology to reduce

jackknifing and other loss-of-control

crashes during braking. The notice

posed questions about such matters as

the occurrence of loss-of-control

crashes; the availability and

performance of systems to improve

directional stability and control under

all conditions of braking and vehicle
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13221

18AAMA submitted joint comments on behalf of

eight major domestic manufacturers of heavy

vehicles: Chrysler, Ford, Freightliner, General

Motors (GM), Mack Trucks, Navistar, PACCAR, and

Volvo-GM).

load; potential regulatory approaches to

improve the directional stability and

control of heavy vehicles during

braking, including anticipated

performance requirements, test

procedures, and equipment

requirements; a schedule for

implementing requirements; diagnostic

equipment to ensure in-use functioning

of the systems; and anticipated costs of

such requirements.

V. Agency Proposal

On September 28, 1993, NHTSA

proposed to amend Standard No. 105

and Standard No. 121, to add

requirements that would improve the

directional stability and control of

heavy vehicles during braking. (58 FR

50738.) NHTSA decided to propose that

each heavy vehicle must be equipped

with an antilock braking system that

satisfies the agency’s proposed

definition of ABS. In addition, as a

verification of the performance of the

ABS, the agency proposed that a heavy

vehicle comply with a braking-in-acurve test.

NHTSA stated that, in proposing

these amendments, its overriding goal

was to ensure the directional stability

and control of heavy vehicles during

braking. The agency stated that, to

ensure adequate ABS performance by

means of dynamic test requirements, it

would need to establish a broad array of

performance requirements that would

test the directional stability and control

of vehicles under a number of loading

conditions, travel speeds, and

deceleration rates, and on a wide variety

of road surfaces, including roads that

are dry, wet, icy, and ‘‘split mu.’’ In

addition, to ensure that directional

stability and control are not provided at

the expense of stopping distance, each

of these tests would need to require the

vehicle to stop within a specified

distance.

NHTSA explained, however, that an

approach that relied exclusively on

dynamic test requirements would raise

serious practicability concerns, given

the inherent variability of stopping

distance performance on low coefficient

of friction surfaces and the costs

associated with requiring such an

extensive array of dynamic performance

test requirements. NHTSA, therefore,

focused its efforts on expressly requiring

that heavy vehicles be equipped with

ABS, and on supplementing that

requirement with feasible and

practicable dynamic tests that check the

directional stability and control, and

stopping distance of vehicles under a

limited set of circumstances that may be

experienced in the real world.

The proposal that heavy vehicles be

equipped with antilock systems would

have required that the front axle and at

least one rear axle of each heavy vehicle

be equipped with an ABS that would

automatically control rotational wheel

slip during braking by (1) sensing the

rate of angular rotation of the wheels, (2)

transmitting signals regarding the rate of

wheel angular rotation to one or more

devices which interpret those signals

and generate controlling output signals,

and (3) transmitting those controlling

signals to one or more devices which

adjust brake actuating forces in response

to those signals. The agency stated its

belief that these characteristics,

specified in the definition of ABS,

would permit the installation of any

antilock braking system, provided that it

is a ‘‘closed-loop’’ system that ensures

feedback between what is actually

happening at the tire-road surface

interface and what the device is doing

to respond to excessive wheel slip.

NHTSA tentatively concluded that these

criteria were necessary to ensure the

introduction of systems that control

wheel slip and sustained wheel lockup

under a wide variety of real world

conditions and thus would significantly

improve safety.

In addition, the NPRM contained a

detailed discussion of the braking-in-acurve test, including the test track’s

configuration, lane width, and test

surface, the vehicle’s test speed, the

type and number of brake applications,

loading conditions, control trailer

requirements, and the initial brake

temperature.

NHTSA also proposed requirements

for the ABS malfunction lamps and the

power source for trailer antilock

systems. The agency also addressed

such considerations as requirements for

diagnostic systems, the types of vehicles

to be covered by the rulemaking, the

implementation schedule for the

proposed requirements, the

rulemaking’s potential effects on

intermediate and final stage

manufacturers and trailer

manufacturers, and its costs and

benefits.

VI. Comments on the Proposal

NHTSA received over 60 comments in

response to the NPRM. Commenters

included heavy vehicle manufacturers,

brake manufacturers, safety advocacy

groups, heavy vehicle users, trade

associations, State entities, and other

individuals.

Most commenters agreed that the

agency should issue requirements to

improve the stability and control of

heavy vehicles during braking, thereby

reducing the number of loss-of-control

crashes. Advocates for Highway and

Auto Safety (Advocates), the Heavy

Duty Brake Manufacturers Council

(HDBMC), the Insurance Institute for

Highway Safety (IIHS), and Rockwell

WABCO generally supported the

agency’s proposal to require heavy

vehicles to be equipped with an ABS.

These commenters stated that ABS will

improve vehicle safety by providing

improved braking performance and

vehicle stability and control during

braking.

The American Automobile

Manufacturers Association (AAMA) 18,

the American Trucking Associations

(ATA), and fleet operators expressed

mixed support for the rulemaking.

AAMA stated that it ‘‘reluctantly

accepts the design specific proposal,’’

given its concerns about the proposed

braking-in-a-curve test procedure. ATA

stated that it supports the use of ABS,

but is concerned that the proposed

effective dates would require universal

use of ABS too soon to assure safety and

reliability. AAMA and ATA stated that

they would fully support the

rulemaking, if the agency revised

various aspects of the proposals. AAMA

was primarily concerned about the

practicability of the braking-in-a-curve

test. ATA was primarily concerned

about the ABS equipment requirement

and alleged problems with the

reliability of separate tractor-to-trailer

electrical cables/connecters. The agency

notes that some of ATA’s requested

revisions would be major departures

from the original proposal.

The National Private Truck Council

(NPTC), the National Truck Equipment

Association (NTEA), the National

Association of Fleet Administrators

(NAFA), and the National Association of

Trailer Manufacturers (NATM) opposed

requiring heavy vehicles to be equipped

with ABSs. These commenters were

primarily concerned about the costs that

an ABS requirement would impose on

fleets, final stage manufacturers of

vehicles produced in multiple stages,

and small trailer manufacturers. NTEA

stated that it would be impracticable for

final stage manufacturers to certify

compliance with the braking-in-a-curve

test.

Commenters also addressed specific

issues raised in the NPRM, including

the proposal to require vehicles to be

equipped with ABS, the type of and

definition for ABS, the braking-in-acurve test procedure, the

implementation schedule for the
13222 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

19Comments on the SNPRM will be specifically

labeled as such. Other comments will be assumed

to be in response to the NPRM.

20The reader may wish to review the Appendix

which provides a technical explanation of how

antilock brakes work, including various methods of

wheel control.

21See the Appendix for a discussion of this term.

22 ‘‘MVMA/NHTSA/SAE Round Robin Brake

Test,’’ Transportation Research Center of Ohio,

Report No. 091194, August 26, 1991.

23AAMA’s specific concerns about the brakingin-a-curve test are discussed in a later section of

this document.

requirements, the malfunction indicator

requirements, the power requirement,

and the rulemaking’s cost. A more

specific discussion of the comments,

and the agency’s responses, are set forth

below.

VII. Agency’s Supplemental Proposal

Based on its analysis of comments on

the NPRM and other available

information, NHTSA issued a

supplemental notice of proposed

rulemaking (SNPRM) proposing a

modified implementation schedule for

the requirements in the agency’s

September 1993 NPRM and a

requirement for independent wheel

control on at least one axle. (59 FR

17326, April 12, 1994.)

With respect to leadtime, the agency

proposed concurrent effective dates for

the heavy vehicle stability and control

requirements and for the heavy vehicle

stopping distance requirements.

Specifically, the agency proposed the

following implementation schedule for

both sets of requirements:

Truck tractors—2 years after final rule

(1996)

Trailers—3 years after final rule (1997)

Air-braked single unit Trucks and

buses—3 years after final rule (1997)

Hydraulic-braked single unit trucks

and buses—4 years after final rule

(1998)

With respect to independent wheel

control, NHTSA proposed to require

heavy vehicles to be equipped with an

ABS that controls the wheels on at least

one front and one rear axle, and

independently controls the wheels on at

least one of these two axles. The agency

tentatively concluded that this would

provide a necessary level of stopping

distance performance on low mu and

split mu surfaces. The agency posed a

number of questions about the need for

independent wheel control.

VIII. Comments on the Supplemental

Proposal

NHTSA received comments from

AAMA, other vehicle manufacturers,

brake manufacturers, safety advocacy

groups, ATA, and others.19 Aside from

ATA, almost all the commenters favored

the proposed implementation schedule.

Several commenters, including AAMA,

Ford, Bendix, and Midland-Grau were

concerned that the proposed

requirements addressing independent

wheel control were unreasonably design

restrictive.

Among the other issues raised by

commenters were whether the proposal

is a performance requirement, alleged

reliability and maintenance problems

with ABS, alleged safety problems

caused by ABS, the regulation’s benefits

and costs, its applicability to hydraulic

systems, and the possible need for a

phased-in implementation schedule and

a separate power circuit for operating

the ABS.

IX. Agency Decision

A. Requirement for and Definition of

ABS 20

In developing the proposal for this

rulemaking, NHTSA considered what

requirements are necessary to ensure

improved stability and control for heavy

vehicles. Among other things, the

agency considered whether adequate

performance relating to stability and

control could be ensured solely by

means of dynamic vehicle performance

test requirements.

The agency stated in the NPRM its

belief that, in order for an approach

relying solely on dynamic tests to be

successful, it would be necessary to

establish a broad array of dynamic

performance requirements that would

test the directional stability and control

of vehicles under a variety of loading

conditions, travel speeds, and

deceleration rates, and on a variety of

road surfaces, including ones that have

coefficients of friction that are low,

high, and split mu. In addition, in order

to ensure that stopping distance

performance is not compromised in the

attempt to improve directional stability

and control during braking, it would be

necessary for these performance

requirements to specify maximum

stopping distances.

NHTSA explained, however, that the

poor correlation between stopping

distance performance and the peak

friction coefficient 21 (PFC) of low

coefficient of friction surfaces,

combined with the costs associated with

such an extensive array of dynamic

performance requirements, would, at

this time, raise serious practicability

concerns about any approach that

included such an array of dynamic test

requirements.22 NHTSA therefore

focused its efforts on a single provision

expressly requiring that heavy vehicles

be equipped with antilock systems, and

on identifying feasible and practicable

dynamic tests that could supplement

that provision by directly assessing the

directional stability, control and

stopping distance of vehicles under

some of the wide variety of

circumstances that may be experienced

in the real world.

This section discusses the proposed

provision expressly requiring that heavy

vehicles be equipped with antilock

systems. More specifically, NHTSA

proposed to require that each heavy

vehicle be equipped with an ABS that

satisfies the following definition:

‘‘Antilock braking system’’ means a portion

of a service brake system that automatically

controls the degree of rotational wheel slip

during braking by:

(1) sensing the rate of angular rotation of

the wheels;

(2) transmitting signals regarding the rate

of wheel angular rotation to one or more

devices which interpret those signals and

generate responsive controlling output

signals; and

(3) transmitting those controlling signals to

one or more devices which adjust brake

actuating forces in response to those signals.

In developing this definition, the

agency specifically sought to avoid

unnecessary design restrictions or

impede the future development of ABS.

NHTSA stated in the NPRM that it

believed that the proposed requirement

would permit any ABS, provided that it

was a closed-loop system that ensures

feedback between what is actually

happening at the tire-road surface

interface and what the device is doing

to respond to changes in wheel slip.

For a number of reasons discussed in

the NPRM (and below), NHTSA

tentatively concluded that a device that

satisfies these criteria is necessary in

order to prevent wheel lockup under a

wide variety of real world conditions,

thereby significantly improving safety.

A number of commenters, including

vehicle manufacturers and brake

manufacturers, recognized the

practicability problems currently

associated with some dynamic

performance requirements and

accordingly supported the agency’s

proposal to require heavy vehicles to be

equipped with ABSs. AAMA stated that

despite its strong preference for what it

termed ‘‘performance requirements,’’ it

would accept an explicit ABS

requirement, provided that the brakingin-a-curve test is not adopted and the

effective date for the proposed stopping

distance requirement is made

concurrent with the other effective dates

for this rulemaking.23 That organization

stated that, in general, manufacturers

‘‘much prefer performance over design

specifications because performance
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13223

24This discussion has been presented in past

NHTSA letters, including a May 2, 1979 letter to the

Insurance Institute for Highway Safety.

requirements allow new, improved and

more cost-efficient technological means

to achieve desired safety ends.’’

Nevertheless, AAMA indicated that it

was willing to accept an ABS equipment

requirement because it believes there

are significant practicability problems

associated with various dynamic tests

that the agency has considered,

including the braking-in-a-curve test.

Similarly, Rockwell WABCO stated

that it ‘‘reluctantly accepts the proposal

for an ABS equipment standard rather

than a performance standard.’’ That

commenter stated that it normally

opposes equipment standards since they

have the potential of restricting the

implementation of new technology.

However, it stated that, in this case, ‘‘the

current difficulty in formulating valid,

repeatable performance criteria prohibit

a true performance standard at this

time.’’ Rockwell WABCO concluded

that ‘‘the proposed combination of an

equipment specification and a

performance test is both understandable

and acceptable’’ for now.

Advocates stated that it is convinced

that:

The agency’s resolve to mandate a basic

level of ABS as required equipment on all

tractors, trucks, trailers, and buses with

verification of desirable safety performance

gained through a single major operating test,

is the most appropriate way to ensure that

the substantial safety benefits of heavy

vehicle ABS are realized quickly.

Midland-Grau stated that the

characteristics specified in the proposed

definition will permit any antilock

brake system, provided that it is a

‘‘closed-loop’’ system that ensures

feedback between what is actually

happening at the tire-road surface

interface and what the device is doing

to respond to changes in wheel slip.

Mr. John Kourik, a brake engineer,

stated that the proposed definition:

1. Selects the proper technology to assure

optimum stability and control, [and]

2. Supplements the intent of the original

definition with a high degree of

sophistication. This should eliminate the

inferior mechanisms and devices that have

been offered by ‘toying’ with the brevity of

the original definition while making

representations and distorted claims to

suggest equivalency to ABS. Thus, the new

definition should end the ‘‘smoke and

mirrors’’ promotions of alleged substitutes

for ABS.

According to Mr. Kourik, the

proposed definition would preclude the

use of unsophisticated equipment that

does not sense changes in the wheel

rotation rate, e.g., equipment such as

mechanical devices, pneumatic

dampeners, hydraulic dampeners,

hydro/mechanical units, and electro/

mechanical units.

Other commenters strongly opposed

the proposed ABS requirement. ATA

argued that NHTSA had proposed a

‘‘design standard for ABS’’ that is

‘‘unlawful because it is contrary to the

agency’s statutory mandate to issue only

performance standards.’’ Citing the

statutory definition of ‘‘motor vehicle

safety standard,’’ that organization

stated that, under the Safety Act, the

requirements in Federal motor vehicle

safety standards must prescribe

performance, not design obligations.

ATA claimed that, despite the

statutory mandate, much of the agency’s

proposal represents design

requirements. Specifically, ATA stated

that there were additional

impermissible design aspects to the

proposal, including the definition of

ABS, and the requirements for trailer

electrical power to be transmitted by a

separate circuit specifically provided for

that purpose and for warning systems to

be electrical.

ATA also argued that the proposed

definition for ABSs is unnecessarily

design-restrictive, and would stifle

innovation and require continual

updating of the standard. ATA stated

that the requirements would preclude

anything but electronic systems, thereby

prohibiting mechanical systems. That

organization also argued that the

requirements would impair efforts to

develop new electronic technologies.

Several small companies which

manufacture or sell brake products also

argued that the proposed requirements

are inappropriately design-restrictive.

They argued that NHTSA should change

the proposed definition of ABS so that

devices other than computerized ABS

can be used to meet the requirements.

Trade International Corporation (TIC)

argued that the proposed definition for

ABS is fundamentally flawed because it

does not specify what the system is

supposed to accomplish but rather

specifies how the system is supposed to

work. It argued that a system could

satisfy the definition but not accomplish

the desired function.

After carefully considering the

comments, NHTSA has decided to

adopt the proposed requirement for and

definition of ABS. The agency’s

response to the comments, including a

more detailed discussion of some of the

comments summarized above, is

presented in the sections which follow.

1. Legal Authority

NHTSA disagrees with ATA’s

allegation that the agency does not have

the statutory authority to issue a ‘‘design

standard.’’ NHTSA’s longstanding

position 24 on this subject, which is

presented in the form of a hypothetical

discussion concerning the agency’s

authority to regulate the width of motor

vehicles, is set forth below:

We believe that the National Traffic and

Motor Vehicle Safety Act * * * would

permit issuance of a safety standard that

regulated or limited vehicle width, if it were

found that such a regulation ‘‘meets the need

for motor vehicle safety’’ (§ 103(a), 15 U.S.C.

1392(a)). As is true with every motor vehicle

safety standard, however, it would be

necessary to establish a reasonable, objective

basis for the conclusion that this regulation

can be justified by safety benefits obtainable,

to avoid a judicial conclusion that the action

is ‘‘arbitrary, capricious, [or] an abuse of

discretion.’’ (5 U.S.C. 706). The issue, in

other words, would not be one of basic

authority, but of justification.

Although it may be argued that such a

safety standard would be a regulation of

‘‘design, and not performance’’, for reasons

set forth below we feel that this argument is

insubstantial and reflects an inadequate

understanding of the Act and the safety

standards * * *.

Section 102(2) of the Act (15 U.S.C. 1391)

defines a motor vehicle safety standard as ‘‘a

minimum standard for motor vehicle

performance, or motor vehicle equipment

performance, which is practicable, which

meets the need for motor vehicle safety and

which provides objective criteria.’’ Section

103(f) of the Act also requires the standards

to be ‘‘reasonable, practicable and

appropriate for the particular type of motor

vehicle * * * for which it is prescribed.’’

It has sometimes been suggested that the

inclusion of the word ‘‘performance’’ in this

definition suggests the existence of a

dichotomy between vehicle design and

performance. We do not, however, consider

that there is a dividing line between

standards that regulate performance and

standards that affect design. Senator

Magnuson recognized the absence of any

dichotomy when he said that some safety

standards would necessarily determine the

configuration of some vehicle components.

(112 C.R. 20600 (Aug. 31, 1966.)). In fact, all

safety standards have a strong effect on

vehicle or equipment design, in spite of their

being phrased in ‘‘performance’’ terms. This

is necessarily so since the design of vehicles

and equipment determines the quality of

their performance. (Some confusion over

‘‘design’’ may arise from the common use of

the word to mean appearance or shape. In

our work, however, the word means the sum

of all of the characteristics that a product is

intended to have, e.g., size, weight,

interrelationship of components, materials,

and markings.)

Each of our safety standards meets the

need for motor vehicle safety by specifying

requirements for the performance of a

particular vehicle or item of equipment. Any

design that will satisfy the requirements may

be used for the system or item of equipment.

The extent to which the choice of a design
13224 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

25The Society of Automotive Engineers is a

voluntary professional organization that establishes

recommended practices related to various aspects of

motor vehicles.

is restricted by a particular standard is purely

a matter of degree, depending on the

specificity of the requirement. We try, in

carrying out the congressional mandate, to

make the requirements as broad as the safety

need allows. We will probably never have to

reach the level of a true ‘‘design

specification’’ as an engineer would use the

term, i.e., a detailed description of every

significant aspect of a product including the

materials and manufacturing processes used.

This is true because the standards deal only

with the safety-related characteristics of the

regulated items, e.g., the height, width, and

strength of a head restraint and the light

output of a headlamp.

In some cases, the configuration of a

vehicle component or item of equipment is

the characteristic that relates to safety. A

good example of this is our standard on

transmission shift levers (No. 102), which

standardizes the position of Park, Reverse,

etc., on all our passenger cars today. There,

standardization of at least some external

aspects of the component is needed for

safety’s sake. A second example is our

standard on control identification (No. 101),

where again an enforced similarity in the

words and symbols used to identify vehicle

controls is the heart of the safety requirement

* * *.

Thus, if the width of a vehicle is, in fact,

the characteristic that is found to require

regulation for safety purposes (analogously to

the spacing of headlamps in Standard 108 or

the width of a head restraint in Standard

202), there should be no doubt of NHTSA’s

authority to regulate it.

NHTSA’s requirements for specified

safety equipment are at the heart of

many of the Federal motor vehicle

safety standards. Indeed, thousands of

the lives saved and the injuries reduced

or prevented by Federally-mandated

safety features are the direct result of

requirements for specific types of

equipment. Most prominent among

these requirements is the 25-year-old

requirement in Standard No. 208,

Occupant Crash Protection, for the

installation of specific types of safety

belts. This is the most heavily judicially

and Congressionally scrutinized safety

standard, and no question has ever been

raised about the agency’s authority to

issue such a standard.

Equipment requirements are critical

for helping to ensure that vehicles have

many of the items necessary to

guarantee safety. For example, it is

critical for drivers to be able to see

where they are going, and for their

vehicle to be seen by other drivers. The

safety standards therefore require items

that are critical for driver visibility and

vehicle conspicuity in the rain and at

night. Standard No. 104 requires

vehicles to have a windshield wiping

system, Standard No. 108 requires

vehicles to be equipped with specified

lamps and reflective devices, Standard

No. 111 requires that vehicles be

equipped with rearview mirrors, and

Standard No. 205 specifies the types of

glazing which may be used in various

locations.

Many other safety standards,

including the existing brake standards,

specify equipment requirements that

meet equally important safety needs.

Thus, the extremely narrow reading of

the word ‘‘performance’’ advocated by

ATA is inconsistent with the entire

history of the Federal program for motor

vehicle safety standards, and indeed

with a majority of the existing

standards.

The case law addressing this issue has

clearly upheld NHTSA’s authority to

issue safety standards that directly affect

design. In Chrysler v. DOT, 515 F.2d

1053 (6th Cir. 1975), for example, the

court upheld a dimensional restriction

on rectangular headlamps. That court

reasoned that:

Uniformity of headlamp size is an element

of headlamp performance. Design freedom

would inhibit safety, and certainly the

congressional purpose of encouraging safetyrelated competition among manufacturers is

meaningless in this context.

We conclude that the dimension restriction

at issue here essentially serves to ensure

proper headlamp performance and lies

within the regulatory authority granted by

Congress to the NHTSA.

515 F.2d at 1058, 1059.

Moreover, in Motor Vehicle

Manufacturers Association v. State

Farm, 463 U.S. 29 (1983), the United

States Supreme Court held that, before

rescinding a general requirement for

automatic restraints because one type of

automatic restraint (e.g., the detachable

automatic safety belt) might be

ineffective, NHTSA must consider

establishing an airbag-only requirement.

The Court further stated that the agency

could prohibit detachable automatic

safety belts if the agency determined

that they would not provide effective

passenger protection. Therefore, the

Supreme Court clearly recognized

NHTSA’s authority both to require

specific safety equipment deemed to

provide superior safety protection and

to prohibit specific equipment that the

agency deemed to provide inferior

safety protection.

NHTSA therefore rejects ATA’s

argument concerning the agency’s

authority to require specified safety

equipment. However, as indicated

above, the agency does, in carrying out

its statutory mandate, attempt to make

its safety requirements as broad as the

safety need allows. The relevant issue

for this rulemaking is thus not whether

the agency proposed an unlawful

‘‘design standard,’’ but instead whether

the proposed requirement/definition for

ABS is unnecessarily design-restrictive.

For the reasons discussed below,

NHTSA has concluded that each

element of the proposed requirement/

definition for ABS is necessary to meet

the safety need for improved stability

and control.

2. Elements of the Requirement/

Definition for ABS

Far from proposing a detailed ‘‘design

requirement,’’ NHTSA simply proposed

to require vehicles to be equipped with

an ABS consistent with the generally

understood meaning of that term among

brake engineers. The agency used this

approach precisely to avoid imposing

unnecessary design restrictions or

impeding the future development of

ABS. As discussed in the NPRM, the

definition is sufficiently broad to permit

the installation of any antilock braking

system, provided that it is a ‘‘closedloop’’ system that ensures feedback

between what is actually happening at

the tire-road surface interface and what

the device is doing to respond to

changes in wheel slip.

In developing the proposed

definition, the agency relied on the

Society of Automotive Engineers 25

(SAE) J656 (Apr88) ‘‘Automotive Brake

Definitions and Nomenclature’’ and the

Economic Commission for Europe’s

Regulation 13, Annex 13 (1988). SAE

J656 refers to ABSs as ‘‘wheel slip brake

control systems’’ that automatically

control rotational wheel slip during

braking. Among the terms related to

ABS that are defined in SAE J656 are

‘‘modulator’’ and ‘‘wheel slip sensor.’’

These terms are used in SAE’s test

procedure for antilock systems, as

specified in SAE J46 (JUN80) ‘‘Wheel

Slip Brake Control System Road Test

Code.’’ Similarly, Annex 13 of ECE

Regulation 13 refers to ‘‘anti-lock

devices’’ as systems which

automatically control the degree of slip,

in the direction of rotation of the

wheel(s). The Annex 13 definition of

ABS also states that such devices

include ‘‘a sensor or sensors, a

controller or controllers and actuating

valves.’’ The agency’s proposed

definition of ABS incorporated the

terms set forth in SAE J656 and ECE

Regulation 13 to reflect the attributes of

antilock systems as commonly

understood by the automotive

engineering industry.

The proposed equipment requirement

specifies simply that vehicles must be

equipped with an ABS which is defined
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13225

26 ‘‘Improved Brake Systems for Commercial

Motor Vehicles,’’ DOT 807 706 Section 3.2.2; pages

3–5.

27As discussed in the Appendix, wheel slip refers

to the proportional amount of wheel/tire skidding

relative to vehicle forward motion, and lockup is

simply the condition of 100 percent wheel slip.

as a system that automatically controls

the degree of rotational wheel slip

during braking, by (1) sensing the rate

of wheel rotation, (2) transmitting

signals regarding the rate of wheel

rotation to a device which interprets

those signals and generates responsive

controlling signals, and (3) transmitting

those controlling signals to a device

which adjusts brake actuating forces in

response to those signals. For reasons

discussed below, each of these elements

is necessary to meet the need for safety.

In addition, the definition only states

the performance required of the ABS

components, not how the components

must detect wheel rotation, etc.

As discussed earlier in this preamble,

the safety problem being addressed by

this rulemaking is that whenever the

driver applies the brakes with too much

force relative to extant tire and road

conditions, sustained wheel lockup

occurs. This usually results in loss of

vehicle directional stability and/or

steering control; i.e., a jackknife, spinout or skid, and often a crash. Such

sustained lockup most often occurs

when the road is slippery or when the

vehicle is lightly loaded or has no cargo.

This is because drivers are likely to

make a hard brake application in a

panic situation, and the resulting

braking forces easily cause lockup when

the road is slippery or when the vehicle

is lightly loaded or empty. Moreover,

drivers are unable to sense lockup

quickly enough to control it.26

In order to address this safety

problem, NHTSA has determined that it

is necessary to prevent the brake system

from generating forces that result in

uncontrolled lockup. This need is

addressed in part by the first element of

the requirement/definition: each ABS

must automatically control the degree of

rotational wheel slip during braking.27

Automatic control is necessary since

drivers cannot control lockup in an

emergency situation. By the time a

driver can sense that lockup has

occurred, it is often too late to prevent

the sustained lockup that results in loss

of directional stability or control.

The second element of the

requirement/definition (sensing rate of

wheel rotation and transmitting signals

about the rate to a device that generates

responsive control signals) is necessary

to ensure that lockup will be prevented

or controlled for all road surfaces and

under all load conditions, and also to

ensure that stability is not provided at

the expense of stopping distance. The

prevention of sustained lockup, and

resulting loss of directional stability and

control, should not be accomplished

simply by putting weak brakes on the

vehicle or lowering braking forces under

all conditions. Thus, in addressing this

safety problem, the agency must

consider the twin goals of preventing/

controlling lockup and ensuring good

stopping distance under all road surface

and load conditions.

In a braking situation, the more the

driver depresses the brake pedal, and

thereby increases braking forces, the

more quickly the vehicle will stop, so

long as the braking force is not so high

that it causes wheel lockup. Thus, if

stopping distances are to be minimized

during braking, it is necessary to permit

the hydraulic or air pressure to rise to

a point just below the point where

lockup would occur.

Moreover, the amount of pressure that

causes lockup will vary dramatically

depending on the road surface and

vehicle loading. In order to ensure that

braking force rises to a point just below

the point where lockup would occur, it

is necessary for an ABS to sense either

each of the factors on which lockup is

dependent, i.e., road surface friction,

vehicle loading, dynamic weight

transfer during braking, condition of

brake linings, etc., or the product of all

of those factors, i.e., the rate of wheel

rotation from which wheel slip can be

determined. Since it may not be

technologically feasible for an ABS to

sense all of the factors which may lead

to lockup, the definition specifies that

an ABS must sense the product of those

factors, i.e., the rate of wheel rotation.

The rest of the second element of the

definition is necessary to ensure that an

ABS uses the relevant information, i.e.,

rate of wheel rotation, to control wheel

slip and prevent lockup. The relevant

information must be transmitted to a

device which interprets the information

and generates responsive controlling

signals. Those controlling signals must

then be transmitted to a device which

adjusts brake actuating forces in

response to those signals.

NHTSA has determined, based on all

available information, that a device that

lacks any one of the elements specified

in the definition could not meet the

need for safety addressed by this

rulemaking, since, for the reasons

discussed above, its operation would

not be dependent on factors that are

relevant to the desired safety

performance.

The agency notes that while several

commenters asserted that the proposed

definition is unnecessarily design

restrictive, none attempted to explain

how a device not meeting one or more

of the elements could ensure stability

and control for heavy vehicles for a

wide range of test surfaces and loading

conditions.

Most of the commenters arguing that

the proposed definition is unnecessarily

design restrictive were small companies

which manufacture or sell brake

products. In essence, they wished the

agency to change the proposed

definition of ABS so that their devices

can be used to meet the requirements.

These companies are, of course, free to

develop and sell products that meet the

definition. Also, to the extent that these

companies produce products that do not

meet the definition, they are free to sell

them as supplemental equipment, so

long as the products do not create

compliance problems or contain safety

defects. However, for the reasons

discussed above, and expanded on

below in the context of these comments,

products which do not meet the

definition would not prevent sustained

wheel lockup.

Strait-Stop, a company which

manufactures what it calls a

‘‘noncomputerized ABS,’’ argued that

the proposed ABS definition is

discriminatory and excessively designrestrictive because it necessitates the

use of electronic computerized systems

with wheel speed sensors. It argued that

the agency’s tests ‘‘(do) not prove,

conclusively, that the computerized

ABS is the only alternative to

accomplish stability and control.’’

Strait-Stop also stated that NHTSA’s

fleet study indicated that computerized

ABS activated very rarely, only 1.4

times per 10,000 brake applications or

1.1 times per 10,000 miles driven, and

that it is a tool with which drivers will

not gain familiarity. In contrast, StraitStop stated that its device activates

approximately 98 percent of the time

that the driver applies the brakes,

thereby enabling drivers to become

familiar with the system. While StraitStop did not describe how its ‘‘noncomputerized ABS’’ works or precisely

what it does, that company stated that

its device uses ‘‘modulation but not

reduction of braking pressure.’’

Moreover, literature about its system

indicates that the air flow from the foot

(treadle) valve to the relay valve is

interrupted through the Strait-Stop

system and pulsates the brake chambers.

The ‘‘system intermittently repeats the

on and off cycle at a pre-set rate.’’

Jenflo Brake-Aid (Jenflo) also argued

that the proposed ABS definition is

discriminatory, and that the definition

should be revised to permit braking

devices other than the ones tested by the
13226 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

agency. Jenflo manufactures a device for

air brake systems which causes a

‘‘pulsing (or air pressure to) the brake

actuators hundreds of times per minute,

(that will) cause the tires to approach

lock-up, then the brakes are off for a

‘small’ fraction of a second and are just

as rapidly reapplied.’’ As a result, the

air pressure is continually released and

reapplied on all the controlled wheels

during all but ‘‘normal’’ braking.

Trade International Corporation (TIC)

stated that the proposed ABS definition

is unnecessarily narrow and could

preclude the use of available, beneficial

products and technologies, and also

impede the development of other useful

products and technologies. TIC argued

that a system which continuously

modulates the braking force applied to

every wheel whenever braking force is

applied would not satisfy the definition

because it lacks the specified sensing

and transmitting functions, regardless of

its ability to prevent wheel lockup and/

or enhance braking effectiveness.

The devices referred to by Strait-Stop,

Jenflo Brake-Aid, and TIC all ‘‘pulse’’

the air pressure for essentially all but

normal brake applications. These

commenters did not explain in detail

how these products work. However,

based on the available information, they

provide the same ‘‘pulsing’’ of air

pressure at a fixed pulsation rate for all

brake applications above some braking

or turning threshold. Regardless of how

they work, however, the devices cannot

ensure the twin goals of preventing/

controlling lockup and ensuring good

stopping distance under all road surface

and load conditions, if they do not meet

the proposed definition. This is because,

for the reasons explained above, their

operation would not be dependent on

the factors that are relevant to the

desired safety performance. Only by

continuously sensing and responding to

what is actually happening at the tire/

road surface interface can an ABS

system optimize the braking pressure so

as to both prevent lockup and minimize

stopping distances. As discussed in the

ABS Wheel Slip Control Strategies

section of the Appendix, one effect of

varying road surface and vehicle load

conditions on the operation of ABSs is

the varying controlling frequencies that

are needed to adapt to these varying

conditions. The fact that these other

devices incorporate a fixed pulsation

rate demonstrates their lack of

adaptability to varying road surface and

vehicle load conditions. As shown in

Figures 17 and 18 in the Appendix, the

ABS controlling frequency needs to be

relatively slow, between 1 and 2 cycles

per second, in order to prevent

sustained excessive wheel slip on very

low friction surfaces and needs to be

much faster, approaching 10 cycles per

second, in order to achieve very short

stopping distances on high friction

surfaces. The increase in stopping

distance on high friction road surfaces

that would result from a system which

exhibited a slower than optimum ABS

controlling frequency may not be great.

However, the impact of a much faster

than optimum ABS controlling

frequency on a very low friction surface

would be sustained and excessive wheel

lockup. As shown in Figure 17 in the

Appendix, wheel lockup can occur very

rapidly. Figure 17 also shows that from

the time that the ABS solenoid is

activated to reduce brake pressure it

takes about 0.25 seconds before the

wheel even begins to spin up, about

0.35 seconds for the wheel to reach onehalf of the vehicle’s speed and more

than 0.6 seconds for the wheel to reach

the vehicle’s speed. If the devices

referred to by Strait-Stop and Jenflo

Brake-Aid pulse the brakes several times

a second, the ‘‘off’’ portion of pulsation

cycle would not be sufficiently long to

allow the locked wheel to spin up prior

to the next ‘‘on’’ portion of the cycle

which would result in sustained wheel

lockup.

The basic problem with devices that

do not incorporate feedback on what is

happening at the tire/road surface

interface (as required by the definition

of ABS mandated by this amendment)

such as those described by Strait-Stop,

Jenflo and TIC, is that they are ‘‘blind’’

to the road and surface conditions on

which the vehicle is operating and thus

make the same response each time,

regardless of whether that response is

appropriate for the existing

circumstances. In other words, the

systems cannot appropriately adjust

their cycle rate or the degree of pressure

variation to compensate for the effects

that load condition and road surface

friction can have on the lockup and

spinup times of a vehicle’s wheels. This

lack of ‘‘adaptability’’ to changes in load

and road surface conditions results

either in sustained wheel lockup (and

resultant loss of stability and control) or

in stopping distances that are much

longer than the vehicle would otherwise

be able to achieve under those

conditions for which the system was not

optimized. As a result, even if these

systems enhanced vehicle stability on

one type of surface, they would provide

inferior braking on a different surface.

For instance, the relatively high brake

pressure required for short stopping

distance on a high coefficient of friction

surface would lock the wheels on a

slippery surface because wheel lockup

occurs when the braking force at the

tire/road surface interface, needed to

resist the torque generated by the brake,

is greater than that which can be

generated from the available surface

friction. Because wet surfaces have

lower friction levels, vehicles on these

roads will lock up at lower levels of

brake pressure. Conversely, if the

pulsating mechanical system were

designed so that brake pressure was

reduced in a manner that ensured that

lockup would not occur during hard

braking on a slippery surface, stopping

distances would be very long when

braking on high coefficient of friction

surfaces.

NHTSA also notes that in order to

optimize stopping distance and

maintain vehicle stability, an antilock

system must be capable of reducing,

holding, and reapplying braking

pressure to each controlled wheel. The

wheel speed sensor monitors the

rotational speed of the wheel. When a

monitored wheel approaches a lockup

condition, there is a sharp rise in

peripheral wheel deceleration and in

wheel slip. If this rise exceeds the

designed threshold levels, the ECU

sends signals to the modulator device to

hold or reduce the build-up of wheel

brake pressure until the danger of wheel

lockup has passed. The brake pressure

must then be increased again to ensure

that the wheel is not underbraked for

the road surface conditions. During

automatic brake control, it is important

for the wheel speed to be constantly

monitored so that the maximum braking

force for the conditions could be

achieved by a succession of pressurereduction, pressure-holding, and

pressure-reapplication phases. The

agency notes that the systems described

by Strait-Stop, Jenflo and TIC reduce

and reapply pressure, without reference

to road conditions, brake forces, or

impending wheel lockup.

With respect to Strait-Stop’s argument

that drivers will not gain familiarity

with the kinds of ABS systems tested by

NHTSA because the systems activate

only rarely, the agency notes that no

special familiarity is necessary to

operate the system properly. ABS is a

safety device which operates

automatically in emergency situations.

Strait-Stop also alleged that the

system defined and tested by NHTSA

does not prevent lockup. While that

company did not explain this comment,

the agency assumes that Strait-Stop is

distinguishing between momentary

lockup and sustained lockup. All of the

systems tested by NHTSA prevent

sustained lockup.

Strait-Stop argued that the inference

that the screened-out systems would not
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13227

meet the braking-in-a-curve test

requirement is unsupported since the

agency has not tested and, in some cases

has refused to provide testing for them.

As discussed above, it is possible that a

system not meeting the proposed

definition could be optimized to

provide enhanced stability for a

particular test on a particular test

surface. However, such a system would

provide inferior braking performance on

other surfaces and/or under different

test conditions.

There is no requirement or reason for

the agency to test every invention

identified by commenters in a

rulemaking proceeding. The agency can

use its technical and engineering

analysis to determine what performance

attributes are necessary to meet the need

for safety, and it can also often make

determinations about whether particular

devices would provide safety benefits

by the same means.

NHTSA has also analyzed another

type of device, from Emergency Brake

Technologies, described by Dr. Barry

Wells. This is an emergency braking

device that is manually activated by the

driver through a dash-mounted switch

that activates arms that drop

polyurethane wedges and rubber flaps

under the vehicle’s wheels. After the

device is activated, the vehicle must be

stopped and reversed so that the wedges

can be removed from beneath the

wheels. Emergency Brake Technologies

claims that this device ‘‘could stop a

fully loaded vehicle in the same

distance as an automobile and

completely eliminate jackknifing.’’

While NHTSA does not have any

opinion concerning whether this device

might provide benefits in some

emergency stopping situations, the

device would not meet the need for

safety being addressed by this

rulemaking, i.e., ensuring stability and

control during braking. In fact, the

dropping of polyurethane wedges and

rubber flaps under the wheels would

create essentially the same condition as

fully-locked wheels, and therefore could

result in a loss of control. Once the

driver activated this system, the driver

would be committed to a quick, sliding

stop. The driver would have no

capability to release the device once

applied, and could also have difficulty

steering around a problem. While such

a device could provide short stopping

distances under dry-road conditions, it

would do so by sacrificing vehicle

stability and control.

ATA and Strait-Stop commented that

the proposed definition would preclude

anything but electronic systems, thereby

prohibiting mechanical systems.

NHTSA notes that this is incorrect,

since the definition does not require

electronics for the sensing of the wheel

rotation, or transmission of wheel

rotation or controlling signals. Such

functions could be performed using

pneumatic, hydraulic, optic, or other

mechanical means. The agency notes

that it is likely that electronic systems

will be used, given currently available

technologies. All ABSs currently

marketed in the United States are

electronic in nature.

In the case of an ABS that does not

require electrical power for operation,

the only mandatory electrical

requirement in this rulemaking

(addressed later in this document) is for

malfunction indicator lamps used to

signal a problem in the ABS.

ATA also argued that the

requirements would impair efforts to

develop new electronic technologies.

ATA stated that the restrictions would

limit engineers’ abilities to develop

electronic braking (brake-by-wire)

systems (EBS) by forcing the logic for

such systems to be based on existing

ABS designs. According to ATA, EBS is

designed to handle all braking

functions: compatibility, load sensing/

brake proportioning, balance, timing,

ABS, traction control, and failure

control. ATA stated that successful

development of these systems may

require that designers not be tied to a

rotational slip view of wheel lockup.

NHTSA disagrees that the proposed

ABS requirements will impair efforts to

develop EBS. The agency notes that

Robert Bosch GmbH currently markets

the Bosch-ELB Electronically Controlled

Commercial Vehicle Brake, in Europe.

This system includes ABS, traction

control, and electronic service braking

(with pneumatic backup) functions, and

uses the same wheel speed sensor

arrangement as does Bosch’s ABS sold

without EBS. This indicates that EBS is

fully compatible with current ABS

technology, including wheel speed

sensors. Furthermore, a combinationunit vehicle with good brake balance,

compatibility, and timing may still be

capable of being over-braked by the

driver, especially when operated lightlyloaded or on slippery road surfaces, and

such a vehicle would still require ABS

to prevent wheel lockup when operated

under these conditions. The

development of the Bosch electronic

braking system proves that the

rotational slip view of wheel lockup

does not hinder the development of

successful EBS.

ATA also stated that the requirements

could ‘‘hold back’’ disc brake

technology since disc brakes are

‘‘virtually incompatible’’ when used

together with drum brakes on a

combination vehicle. ATA appears to

believe that because EBS can make the

‘‘decisions’’ to compensate for those

major differences, it is needed for disc

brake technology to come into general

use. The agency notes that, according to

product literature, the Bosch-ELB

system measures wheel speeds and

brake actuator pressures at each wheel

position, and microcomputers in the

electronic control unit store and process

these data and transmit the correcting

commands accordingly. This system

could, therefore, compensate for

incompatibilities in brake force balance

on a vehicle, and would permit safe

introduction of disc brakes on vehicles.

This system incorporates ABS

technology that complies with the

agency’s proposed ABS requirements, as

well as ECE Regulation 13. Therefore,

NHTSA disagrees with ATA’s argument

that ABS requirements will hold back

disc brake technology.

In a somewhat different vein, TIC

argued that a system could satisfy the

proposed definition but not accomplish

the desired function of preventing

lockup. As part of this argument, TIC

stated that the proposed definition for

ABS is fundamentally flawed because it

does not specify what the system is

supposed to accomplish but rather

specifies how the system is supposed to

work. TIC’s comment in essence raises

the issue of whether the definition is

sufficient, by itself or with other

requirements, to meet the need for

safety.

As indicated at the beginning of this

section, the agency developed a broad

definition precisely to avoid imposing

unnecessary design restrictions or

impeding the future development of

ABS. The ABS definition is based on the

premise that wheel lockup is the source

of a vehicle’s loss of directional stability

and steering control during braking, and

that any device designed to improve

such stability during braking must

control the source of that instability.

Hence, the definition establishes a

linkage between the input, signals that

sense wheel lockup, and the output,

modulated brake pressure to prevent

wheel lockup. This is essentially the

extent of the design constraints

established by the agency, and it gives

the industry considerable latitude to

design and develop individual

components, ranging from sensor design

and placement, to the ECU control

algorithm and to brake pressure

modulation frequency.

NHTSA rejects TIC’s argument that

the definition does not specify what the

system is supposed to accomplish but

rather how the system is supposed to

work. Modulating brake pressure in
13228 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

response to information about rate of

angular rotation is part of what is

supposed to be accomplished. As

discussed above, the rate of angular

rotation reflects what is happening at

the tire/surface interface.

NHTSA further concludes that the

requirement/definition for ABS is

sufficient at this time to meet the need

for safety. In arguing that a system can

satisfy the definition but not accomplish

the desired function, TIC provided the

following ‘‘extreme example’’:

Consider the following system: (1) a set of

angular rate of rotation sensors, one on every

wheel; which (2) transmit signals whose level

is proportional to the rate of angular wheel

rotation to a device which compares the

signals and generates control signals; and (3)

transmits those control signals to devices

which increase the braking force applied to

any wheel which has an angular rotation rate

higher than the wheel which has the lowest

angular rotation rate. Such a system satisfies

every element of the proposed definition,

however, the result of implementing such a

system would be that if any wheel locked up

during braking all wheels would lock up!

While TIC itself acknowledged that its

example was ‘‘extreme,’’ NHTSA notes

that its basic premise also is silly, since

it assumes that a manufacturer would

deliberately build a brake system that

could not work. In considering the

impacts of its standards, NHTSA must

assess how manufacturers are likely to

respond, not unrealistic hypothetical

situations. The basic premise

underlying this rulemaking is that

manufacturers will respond to the

definition/requirement for ABS by

providing systems that will prevent

wheel lockup. This view is confirmed

by the comments of the vehicle and

brake manufacturers. There is no

evidence that manufacturers would

respond by deliberately building

systems that do not prevent lockup but

instead cause lockup.

Moreover, the definition for ABS does

not stand in a theoretical vacuum.

Manufacturers must design their brake

systems to meet other safety

requirements (including stopping

distance requirements and, for some

vehicles, the braking-in-a-curve test). It

might not be possible to meet those

requirements with systems that did not

prevent lockup but instead caused

lockup. Manufacturers are also subject

to Federal requirements concerning

safety-related defects. And, of course,

manufacturers must ensure customer

satisfaction.

The agency also notes that there is

absolutely no incentive for

manufacturers to provide ABS systems

that do not function as they intended.

TIC’s comment essentially raises the

possibility that a manufacturer might

spend all the money necessary to meet

the definition of ABS and then include

a faulty ECU control algorithm.

However, there is no basis to believe

that this would happen. The agency

only addresses unreasonable safety risks

in developing safety standards and need

not address unrealistic hypothetical

possibilities.

3. Dynamic Versus Equipment

Requirements

As discussed in the NPRM and above,

NHTSA considered whether adequate

performance relating to directional

stability and control could be ensured

solely by means of dynamic test

requirements, but concluded that, at this

time, there would be practicability

problems associated with the broad

array of dynamic test requirements that

would be associated with such an

approach. The agency therefore decided

to propose a single provision expressly

requiring that heavy vehicles be

equipped with antilock systems, and on

identifying feasible and practicable

dynamic tests that could supplement

that provision by directly assessing the

directional stability, control and

stopping distance of vehicles under

some of the wide variety of

circumstances that may be experienced

in the real world.

ATA commented that the desired

result from mandating the installation of

ABS is ensuring that a vehicle can be

controlled during a stop, and asserted

that the proposed braking-in-a-curve

performance requirement, with certain

changes, would accomplish this

conceptually. However, ATA did not

substantiate its assertion about the

efficacy of such a requirement, standing

by itself. ATA did not address the

practicability problems of adopting a set

of dynamic performance requirements,

or even the practicability problems

associated with applying the braking-ina-curve requirement to all affected

vehicles. ATA did, however, suggest

that the agency initiate additional

research and development for what it

called ‘‘true performance tests.’’

While NHTSA plans to continue

research on dynamic performance tests

for trucks, buses and trailers, it has

concluded that the desired safety

benefits of ABSs could be achieved now

by means of a specific equipment

requirement for ABS and (as discussed

below) a dynamic performance test

requirement applicable to truck tractors

only. NHTSA is charged by the Safety

Act with promulgating safety standards

that meet the need for safety. Moreover,

Congress was sufficiently concerned

about the directional stability and

control problems associated with heavy

vehicles that it specifically required

NHTSA to conduct a rulemaking that

examines and could result in requiring

the installation of ABSs in these

vehicles. The agency has concluded that

large safety benefits can be obtained by

requiring ABSs on heavy vehicles, and

has developed requirements that will

ensure installation of this safety

equipment.

NHTSA disagrees with the suggestion

that it delay implementation of this lifesaving rule while it conducts further

research in search of the type of rule

ATA desires. The overall history of

agency rulemaking is one of gradual

progression, when and where

practicable and beneficial to safety,

toward increasingly sophisticated and

increasingly more dynamic performance

standards. However, relying exclusively

on dynamic performance requirements

has never been a statutorily mandated

requirement. Were it so, there would be

many fewer Federal motor vehicle safety

standards today—and many thousands

more deaths and injuries, occurring

annually.

B. Independent Wheel Control

In the NPRM, NHTSA proposed to

require that the antilock brake system

monitor and control the wheels of the

front axle (i.e., steering axle) and the

wheels of at least one rear axle. NHTSA

believed that this would ensure that the

wheels on the steering axle and the

wheels on the selected rear axle were

directly controlled by the ABS. By

‘‘directly controlled,’’ the agency meant

that the signal provided at the wheel or

on the axle of the wheel would directly

modulate the braking forces of that

wheel or axle. The agency tentatively

concluded that it is necessary to specify

that the ABS directly control the

steering axle because some ABSs control

only a vehicle’s drive-axle, which could

result in the loss of steering control if

the front wheels locked during braking.

Several commenters addressed the

need for front wheel control. ATA

strongly opposed mandating ABS for the

steering axle of single-unit trucks and

suggested that the agency reconsider the

requirement for tractors. In contrast,

Rockwell, WABCO, Freightliner,

AAMA, Advocates, and IIHS favored

requiring that an ABS be installed on

front axles. AAMA favored equipping

each vehicle with an ABS that has at

least one independent channel of

control for the wheels on a front axle

and at least one independent channel of

control for the wheels on a rear axle.

However, AAMA objected to mandating

more than two independent channels of

control.
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13229

28See the Appendix for a discussion of this term.

29As explained in the appendix, tandem control

refers to having two adjacent axles being controlled

by the same modulator valve. Specifically, while

each axle has its own wheel speed sensor, the

brakes on two axles are controlled by one

modulator valve.

30The agency proposed to define ‘‘Independently

Controlled Wheel’’ as a ‘‘wheel at which the degree

of rotational wheel slip is sensed and corresponding

signals are transmitted to one controlling device

that adjusts the brake actuating forces only at that

wheel in response to those signals.’’

31See the Appendix for a discussion of this term.

NHTSA did not specifically address

the concept of independent control in

the NPRM, but addressed it in the

SNPRM by proposing that the wheels on

at least one axle be independently

controlled. The agency in today’s final

rule defines an ‘‘independently

controlled wheel’’ to mean a directly

controlled wheel for which the

modulator device does not modulate the

brake forces at any other wheel on the

same axle. This means that a side-byside control strategy on a tandem axle

could have the wheels on the sensed

axle of the tandem being independently

controlled by a modulator, and the

wheels of the other axle of the tandem

being indirectly controlled by the

modulator for the wheel on the sensed

axle on the same side of the vehicle.

Rockwell, Freightliner, Advocates,

and IIHS commented that the regulatory

language in the NPRM requiring each

axle to be directly controlled by an ABS

would allow select low 28 antilock

systems on any axle. These commenters

believed that an antilock system must

provide independent control at each

wheel of a heavy vehicle to ensure good,

overall ABS performance in the areas of

stability and stopping distance.

Accordingly, they recommended that

the equipment requirement include

language that would require

‘‘independent control of each wheel’’ of

the axles that are required to be ABScontrolled. They believed that the

inclusion of such a requirement would

prevent significant degradation in

stopping performance, particularly on a

split mu surface. Bosch recommended a

minimum requirement of a four-sensor,

three- modulator-valve (which is

referred to as a 4S/3M system) ABS.

Freightliner favored requiring at least

four independent channels of control,

i.e., two for each axle, to allow

independent control of each wheel on

the front and a rear axle. Similarly, IIHS

favored requiring the brakes for each

wheel on the front axle and the brakes

for each wheel on one rear axle to be

independently controlled. Advocates

recommended that the ABS be

functional on all axles, not just one axle

in each multiple axle set on a heavy

vehicle.

Based on its analysis of these

comments and other available

information, NHTSA issued an SNPRM

proposing modifications to the NPRM to

require heavy vehicles to be equipped

with systems that independently control

each wheel on at least one axle of a

truck, a truck tractor, or a bus (i.e., 4S/

3M systems). As explained in the

SNPRM, the agency tentatively

concluded that a minimum requirement

that ABS provide independent wheel

control on at least one axle would

provide an acceptable level of stopping

distance performance on low mu and

split mu surfaces. The agency believed

that a vehicle with independent ABS

wheel control would stop in a shorter

distance than either a vehicle equipped

with an axle-by-axle ‘‘select low’’

control ABS, or a non-ABS equipped

vehicle operated by a driver making his

or her best efforts to minimize stopping

distance through manually modulating

the brake pedal. The agency also

proposed to prohibit tandem control 29

by an ABS, by requiring that no more

than two wheels be controlled by one

modulator valve. NHTSA requested

comments about its proposal for

independent control of each wheel on at

least one axle and about prohibiting

tandem control by an antilock system.

In response to the SNPRM, NHTSA

received comments from Ford, AAMA,

Strait-Stop, GM, Navistar, White GMC,

Bosch, PACCAR, Eaton, Midland-Grau,

Truck Trailer Manufacturers

Association (TTMA), Advocates, and

ATA about the proposal to require

independent control on at least one

axle. Aside from Freightliner, WABCO,

Bosch, Advocates, and IIHS, most other

commenters opposed the proposal

claiming that requiring independent

control would be unreasonably designrestrictive. Bosch stated that the

proposal is appropriate since at least

one of the axles that contributes most to

vehicle deceleration in the loaded

condition should have the ability to

have its wheels individually controlled.

Ford, AAMA, GM, Navistar, PACCAR,

Eaton, and Midland-Grau stated that the

agency should specify direct control as

a minimum requirement but not require

independent control. AAMA stated that

the standard should permit any control

system that provides stability without

substantial degradation in stopping

distance. Ford claimed that any

requirement that ABS must employ

more than two channels of control

would not result in any safety advantage

over its two-channel system, but would

result in substantial and unnecessary

incremental costs to Ford and might

jeopardize its ability to meet early

implementation dates. Midland-Grau

strongly opposed the SNPRM’s

approach, claiming that it presented a

major change in scope from

performance requirements and minimal

design requirements. Specifically, it

complained that the SNPRM changed

the rulemaking’s focus from directional

stability and control to stopping

distance on split mu surfaces.

Consistent with their comments on

control philosophies, AAMA, GM,

White GMC, PACCAR, and MidlandGrau also opposed the proposed

definition of ‘‘independently controlled

wheels.’’ 30 AAMA and PACCAR

claimed that the proposed definition

does not accommodate widely used

ABS algorithms and control

technologies. It requested that the word

‘‘only’’ be omitted since its inclusion in

the definition would inappropriately

preclude antilock systems that ‘‘rely on

wheel speed information from both

wheels on an axle to modulate brake

pressure at each of the wheels.’’

Ford, AAMA, GM, Navistar, White

GMC, PACCAR, Eaton, and MidlandGrau opposed prohibiting tandem

control. TTMA requested that trailers

equipped with more than three axles be

excluded from the requirements,

claiming that it would be very

expensive to equip these vehicles,

which account for only four percent of

trailer production, with ABS.

ATA and Strait-Stop opposed

specifying the type of wheel control,

claiming that doing so creates an

impermissible design requirement.

Strait-Stop stated that the proposed

approach prohibits creativity in the

development of other technology that

may accomplish the performance

standards more effectively with greater

economic efficiency.

Several commenters submitted test

data about various ABS configurations.

WABCO and Freightliner submitted

simulated test data showing that 4S/2M

systems on truck tractors provide very

poor stopping distance performance on

split mu surfaces, compared with 4S/4M

systems. These commenters reported

that the 4S/2M systems they tested took

between 316 percent and 353 percent of

the norm to stop on a split mu surface,

with driver best effort being defined as

the norm, or 100 percent. Ford and

Bendix submitted simulated data

showing that 4S/2M systems

incorporating the modified select high

regulation (MSHR31) wheel slip control

strategy on truck tractors perform

acceptably. Bendix also submitted

vehicle test data showing that the

stopping distance performance with
13230 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

32SLR, MSHR, MIR and other wheel slip control

strategies are discussed in the Appendix.

33 ‘‘Improved Brake Systems for Commercial

Motor Vehicles,’’ DOT HS 807 706, April 1991,

tandem control ABS incorporating the

MSHR wheel slip control strategy (2S/

1M) on trailers is comparable to the

performance of a 2S/2M system.

As explained above, in establishing

the requirements applicable to the

stability and control of heavy vehicles,

NHTSA has decided that, at a

minimum, wheels on the steering axle

and at least one rear axle of a powered

vehicle must be controlled by a closedloop antilock system. Similarly, the

wheels on at least one axle of a

semitrailer and dolly, and the wheels of

at least one front axle and one rear axle

of a full trailer must be controlled by a

closed-loop antilock system. The agency

has decided that requiring a closed-loop

antilock system is necessary to ensure

the directional stability and control of

heavy vehicles during braking.

NHTSA emphasizes that requiring a

closed-loop antilock system is a

minimum requirement that the agency

believes will ensure the safety of heavy

vehicles. The agency has also decided to

establish supplementary requirements

beyond these minimum requirements

that address the type of wheel control

for various types of vehicles. In

establishing these supplementary

requirements, the agency has sought an

approach that is responsive to the many

and oftentimes disparate views of the

commenters and that ensures safety

performance objectives, while

considering practicability, costs and, to

the extent possible, stated industry

practice.

The supplementary equipment

requirements, which specify the type of

wheel control, are based on the

philosophy that, for the reasons set forth

below, an incrementally higher level of

stability performance during braking is

warranted for truck tractors compared to

that which is appropriate and needed

for trailers, single-unit trucks, and

buses. First, truck tractors, when used in

a combination vehicle, are articulated

and therefore are more likely to lose

control than single-unit vehicles.

Second, truck tractors typically have

shorter wheelbases than single-unit

trucks, trailers and buses and therefore

are more susceptible to locked wheelinduced, unrecoverable loss of control

than are any of these other vehicle

types. This loss of control typically

manifests itself as a jackknife when

tractors are coupled to semitrailers.

Third, truck tractors typically travel

approximately five times more annual

miles than single-unit trucks, three

times more miles than trailers (since

there are proportionally three times as

many trailers in use than there are

tractors which tow them), and

approximately seven times as many

miles as buses. This substantially larger

use proportionally increases a truck

tractor’s exposure to risk. Fourth, truck

tractors typically operate on roads (i.e.,

interstate highways and rural State and

U.S. routes) that have comparatively

higher posted speed limits and vehicle

operating speeds than the roads on

which single-unit trucks and many

buses generally operate. A higher

operating speed exacerbates the

consequences of braking-induced wheel

lockup and loss-of-control. This is a

significant contributing factor to the

high proportion of heavy vehicle

braking instability-related crashes,

fatalities and injuries that involve

combination-unit trucks.

Based on the above considerations,

NHTSA has decided that the

requirements for truck tractors must be

more stringent than those for the other

vehicle types. Specifically, on at least

one of the truck tractors’s axles, each

wheel must be independently controlled

by an ABS modulator. With respect to

a given wheel, ‘‘independently

controlled’’ means a wheel at which the

degree of rotational wheel slip is sensed

and corresponding signals are

transmitted to a modulator that adjusts

the brake actuating forces at that wheel

on the axle or at other wheels on other

axles. The agency has decided to revise

the definition in response to AAMA’s

comment on the definition of

independently controlled, since its

inclusion might inadvertently prohibit

acceptable systems. Requiring

independent control ensures that a

wheel provides optimal braking forces

on all surfaces, enabling the vehicle to

achieve near optimal braking on all

surfaces, especially split mu ones.

In most cases, the axle with

independent wheel control will likely

be the tractor’s drive axle(s).

Commenters, including AAMA,

Midland-Grau, and Bendix, submitted to

the agency road testing data about how

certain antilock systems improved the

braking efficiency and directional

control and stability of various vehicle

configurations. Based on these data, the

agency believes that independently

controlling the drive axle(s) will result

in incrementally better braking

performance on split mu road surfaces

than the other ABS equipment

configurations that are permitted on the

other vehicle types covered by this rule.

Rockwell WABCO correctly stated

that allowing select low ABS on all

axles will result in substantially longer

stopping distances on split mu surfaces,

particularly when the differences

between the coefficients of friction on

the two surfaces is large.

Notwithstanding this shortcoming, the

agency believes that a select low system

is appropriate for the front axle for the

following reasons. First, since the front

axle brakes typically provide about 25

percent of the braking on a truck tractor,

the stopping distance degradation with

select low on the front axle will be

small. Second, having equal braking

forces at each wheel alleviate steering

wheel ‘‘pull’’ that would occur on a

split mu surface with ABS

independently controlled front brakes.

Third, current antilock systems installed

on the front axle of heavy vehicles tend

to use SLR, MSHR, or MIR wheel slip

control strategies.32 No vehicle

manufacturer uses a system in which

front axle control is purely independent

wheel control. Accordingly, the agency

has determined that it would be

inappropriate and impracticable to

prohibit the use of select low control on

front axles.

NHTSA has also decided that it is

necessary to prohibit tandem control on

tractors to further ensure the safe

braking performance for tractor trailers.

This decision is based on test data 33

which indicate that tandem control does

not provide an acceptable level of

stopping distance performance for truck

tractors, even though it may ensure a

heavy vehicle’s stability and control.

Notwithstanding its decision to

prohibit tandem control on truck

tractors, NHTSA has decided that

tandem control is appropriate for

vehicles other than truck tractors, such

as trailers and single unit vehicles.

Vehicle test data submitted by Ford,

Bendix, and Midland showed

comparable vehicle stopping distance

performance, and in some cases

superior performance, of tandem control

(2S/1M) systems compared with sideby-side control (2S/2M) systems,

without any difference in vehicle

stability performance. Vehicle test data

also showed comparable ABS

performance with MSHR tandem

control on trailer axles. Accordingly,

today’s requirements permit direct

control 2S/1M systems for converter

dollies, semitrailers, and the front axles

of full trailers. The agency further notes

that single unit vehicles equipped with

4S/2M systems have been approved for

use in Europe as ‘‘Category 1’’ systems.

C. Braking-In-A-Curve Test

1. General Considerations

As explained in the previous section

on equipment requirements, NHTSA

proposed requiring heavy vehicles to be
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13231

34TRC of Ohio, Report No. 091194, page 4,

August 26, 1991.

equipped with antilock systems, and

supplementing that requirement with

dynamic performance requirements to

check the directional stability, control

and stopping distance of such vehicles.

The agency proposed only those

dynamic performance requirements that

it believed would be feasible and

practicable for checking the directional

stability of a vehicle when it is

maximally braked. Specifically, in its

September 1993 NPRM, the agency

proposed a ‘‘braking-in-a-curve

requirement’’ on a low coefficient of

friction surface without a stopping

distance requirement. Under this

proposed requirement, heavy vehicles

would have to be capable of stopping

without loss of directional stability or

control, while turning on a slippery

surface during an aggressive or ‘‘hard’’

stop. Separately, in its February 1993

NPRM, the agency proposed braking

effectiveness requirements through the

use of high speed (60 mph) stopping

distance requirements on a high

coefficient of friction road surface.

NHTSA explained, in the September

1993 NPRM, its tentative conclusion

that the braking-in-a-curve test on a low

mu surface is an objective, repeatable,

and practicable procedure for evaluating

a heavy vehicle’s directional stability

and directional control. The agency

further explained that the proposed

braking-in-a-curve test is consistent

with industry’s views, since the

Antilock Test Procedure Task Force of

the Motor Vehicle Safety Research

Advisory Committee (MVSRAC)

recommended this procedure and the

SAE has proposed it in Recommended

Practice J1626, Braking, Stability, and

Control Performance Test Procedures

for Air-Brake-Equipped Truck Tractors.

In response to the NPRM, Advocates

stated that the agency’s proposal to

specify both an equipment and dynamic

performance requirement was the most

appropriate way to ensure that the

substantial safety benefits of heavy

vehicle ABS are realized quickly.

Rockwell WABCO reluctantly supported

the proposed combination of an

equipment specification and a dynamic

performance test, given the current

difficulty in formulating valid

additional, repeatable performance

criteria. Midland-Grau favored this

approach for truck tractors since it

believed that merely issuing an ABS

requirement, without an accompanying

performance requirement, would allow

ineffective systems in the marketplace.

Allied Signal supported the brakingin-a-curve test for truck tractors, but

opposed the test for other vehicles,

stating that vehicles other than truck

tractors have not been tested using this

maneuver. Midland-Grau was also

concerned that very little test data have

been collected on vehicle types other

than truck tractors. Volvo-GM stated

that the test is unsafe for many vehicles,

and that a dynamic performance

requirement is not necessary, given the

provision requiring ABSs. AAMA stated

that although it generally favors

performance-based dynamic

requirements for Federal Motor Vehicle

Safety Standards, it opposes the

braking-in-a-curve test given what it

perceives as its ‘‘overwhelming

practicability and objectivity problems.’’

Among AAMA’s concerns were that (1)

there has been no test program by

NHTSA to decide whether the test is

suitable for single-unit trucks, buses,

and trailers, (2) the braking-in-a-curve

test alone cannot evaluate the

effectiveness of an ABS, (3) there is a

lack of repeatability of the braking-in-acurve test procedure, and (4) no suitable

test facilities exist for vehicle

manufacturers to conduct compliance

testing. Given these concerns, AAMA

favored adopting, on an interim basis,

an equipment requirement only.

ATA, Strait-Stop, and several other

commenters supported a dynamic

performance-based requirement instead

of an equipment requirement. They

believed that this approach would

encourage further development of

antilock technology and would enable

users to find the system that best suits

their operation. ATA was concerned

that an equipment requirement would

preclude the development of more

effective systems for different

applications.

TTMA believed that the braking-in-acurve test is inappropriate for trailers. It

stated that trailer manufacturers, many

of which are small entities, do not have

the financial resources or the facilities

to conduct road testing.

After reviewing the comments and

other available information, NHTSA has

decided to amend the Standard to

include the braking-in-a-curve test for

certain vehicles. The agency considered

requiring surface transition tests (i.e., a

test maneuver in which vehicle braking

begins on a high coefficient of friction

surface and then completes the stop on

a low mu surface, and vice versa), a lane

change test, and split mu or side-to-side

differential coefficient of road surface

friction tests, to achieve that objective.

The tests would ideally be conducted at

various speeds with different loading

conditions and test surfaces. However,

the agency has decided that it would be

unnecessarily burdensome and costly to

impose such an array of tests on heavy

vehicle manufacturers. NHTSA has

determined that the performance testing

and equipment requirements imposed

in today’s final rules are the most

appropriate method of ensuring

directional control and stability.

NHTSA has decided at this time to

apply the braking-in-a-curve test to

truck tractors, but not to other heavy

vehicles. The agency believes that

opposition by AAMA, Volvo-GM, and

Midland Grau to the braking-in-a-curve

test requirement is based primarily on

uncertainty about whether the test

would also be required for single-unit

vehicles, since the MVSRAC ABS Task

Force developed the braking-in-a-curve

test procedure for testing only truck

tractors. Since neither the agency nor

the Task Force included single-unit

vehicles in the test program, NHTSA

believes that AAMA and the others are

concerned about whether the brakingin-a-curve test would appropriately

evaluate directional stability and control

of single-unit vehicles. Accordingly,

NHTSA’s decision to apply the brakingin-a-curve test at this time only to truck

tractors should reduce the concerns of

AAMA and other commenters that

opposed this dynamic performance test.

With respect to truck tractors, NHTSA

has concluded that the road tests

performed by the agency and the ABS

Task Force provide sufficient

justification to apply the braking-in-acurve test to these vehicles. The agency

notes that the industry, through the

MVSRAC, previously endorsed and

recommended to the agency, essentially

the same dynamic performance test that

is contained in this final rule. The Task

Force test data and final report indicate

that the braking-in-a-curve procedure is

safe, practicable, and repeatable for

truck tractors. Accordingly, the agency

believes that this recommendation

remains valid for tractor trailers.34

NHTSA has decided not to require

single unit trucks, buses, and trailers to

comply with the braking-in-a-curve test

requirement at this time. The agency’s

limited testing of single unit trucks to

the braking-in-a-curve maneuver

revealed no specific safety problems.

However, additional testing on a wider

variety of trailers, dollies, and singleunit vehicles, including buses and

trucks, would be appropriate to ensure

that these vehicles could be safely tested

to the braking-in-a-curve maneuver.

Specifically, the agency is concerned

that certain vehicles, especially ones

with a high center of gravity, might be

prone to roll over or otherwise lose

control during such tests. NHTSA

intends to develop performance test

requirements equivalent to the braking-
13232 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

35Maximum-drive-through-speed is defined as

‘‘the highest possible constant speed that the

vehicle can be driven through 200 feet of a 500-foot

radius curve arc without leaving the 12-foot lane.’’

in-a-curve test for the other vehicle

types covered by this rule, assuming

that future research indicates it possible

to conduct the test in a safe fashion and

to obtain meaningful, repeatable results.

The agency anticipates conducting

additional research and road tests to

decide whether heavy vehicles other

than truck tractors should be subject to

this road test.

Today’s notice, including the agency’s

decision not to apply the braking-in-acurve test to vehicles other than truck

tractors, completes the comprehensive

rulemaking to establish directional

stability and control requirements that

was initiated by the June 1992 ANPRM.

If NHTSA decides that it is in the

interest of motor vehicle safety to apply

the braking-in-a-curve test to single-unit

vehicles or trailers, then it will issue a

new proposal to initiate a subsequent

rulemaking on this matter.

2. Test Surface

In the NPRM, NHTSA proposed that

the braking-in-a-curve test be conducted

on a test surface with a peak friction

coefficient (PFC) of 0.5 to represent a

low coefficient of friction surface. In

formulating the proposal, NHTSA

considered whether the proposed test

surface specification raised

practicability or objectivity concerns in

light of PACCAR. The agency

specifically requested comments on the

proposed test surface specification.

Three commenters addressed the test

surface specification. Midland-Grau

stated that since maintaining a precise

PFC value is not feasible, reasonable

fluctuations of ±10 percent are to be

expected. Notwithstanding these

inherent fluctuations, Midland-Grau

commented that its testing shows that

variability in the test surface PFC value

of less than 10 percent does not affect

the braking-in-a-curve test since no

stopping distance is prescribed. AAMA

stated that it is not possible to maintain

a surface at a precise PFC. It further

stated that it is not apparent whether it

would be more conservative to conduct

testing at a higher PFC than the

proposed PFC. AAMA stated that the

variability in the peak to slide ratio is

significantly greater on wet surfaces

than on dry surfaces, and that this ratio

directly affects performance. Mr. Robert

Crail, a brake engineer, stated without

elaboration that using PFC rather than

skid numbers will ensure that the test

surfaces and test conditions will be

reasonable and repeatable during actual

vehicle testing.

Before addressing the specific

comments about the test surface, the

following discussion summarizes the

PACCAR decision’s findings with

respect to variability and how today’s

rulemaking responds to that ruling. As

a result of that case, NHTSA has

considered ways to better specify test

surface adhesion. Prior to the Standard

No. 135, Passenger Car Brake Systems,

rulemaking, NHTSA defined road test

surfaces by specifying skid numbers. A

skid number is the frictional resistance

of a pavement measured in accordance

with a test procedure defined by the

American Society for Testing and

Materials (ASTM). However, given the

fluctuations of skid numbers on a given

surface, the PACCAR ruling invalidated

certain aspects of Standard No. 121’s

reliance on this measure based on its

potential impracticability. In the

rulemaking proposing Standard No. 135,

several commenters advocated

specifying the peak friction coefficient

as an alternative measure of a test

surface’s adhesion. The agency has

concluded that PFC is more relevant for

the stopping distance tests required by

the standard because, unlike a skid

number, the maximum attainable

deceleration in a non-locked wheel stop

is more directly related to PFC. As

discussed in the Appendix, the skid

number characterizes the slide (locked

wheel) value of the coefficient of

friction of a given road surface, and the

PFC characterizes the peak (rolling

wheel) value of the coefficient of

friction of a given road surface. Since

the agency’s brake test procedures

generally prohibit or limit wheel lockup

during brake testing, specifying the peak

friction coefficient is more relevant than

specifying the skid number of the

surface.

NHTSA has also conducted ‘‘Round

Robin’’ testing to understand further

how fluctuations of PFC affect the

stopping performance of heavy vehicles.

Based on the above, NHTSA has

decided that the braking-in-a-curve test

should be performed on a test surface

with a PFC of 0.5, which appropriately

represents a typical low coefficient of

friction road surface. Moreover, in

today’s companion rule adopting

stopping distance requirements, the

agency has decided it is appropriate to

perform the primary 60 mph stopping

distance tests on a test surface with a

PFC of 0.9. Agency and industry testing

indicate that a PFC of 0.9 represents a

typical dry road surface.

The requirement to specify test

surfaces in terms of PFC rather than skid

numbers also responds to PACCAR’s

concern about practicability problems

caused by skid number fluctuations.

Because the PFC values of surfaces

measured may also indicate some

fluctuation, the agency has considered

whether the fluctuation significantly

affects the requirement’s objectivity. In

an earlier rulemaking about Standard

No. 208, the agency explained that since

some variability in any test procedure is

inherent, the agency need only be

concerned about preventing

‘‘unreasonable’’ or ‘‘excessive’’

variability to avoid causing

manufacturers to ‘‘overdesign’’ vehicles

to exceed the minimum levels of

protection specified by the Federal

safety standards. (49 FR 20465, May 14,

1984; 49 FR 28962, July 17, 1984.) With

respect to the braking-in-a-curve test,

variability of the PFC value of the test

surface will have a negligible impact on

a vehicle’s ability to comply with the

requirements, which is to stay within

the 12-foot lane. Since the test speed is

set at the lesser of 30 mph or 75 percent

of the maximum drive-through speed 35

of the vehicle in the curve, any

variability in the test surface will be

compensated for by an increase or

decrease of the maximum drive-through

speed of the vehicle. If the maximum

drive-through speed is less than 40

mph, this will result in a corresponding

increase or decrease of the test speed,

which cannot be higher than 30 mph.

As a result, the variability of the test

surface is not as critical an issue for the

braking-in-a-curve test as it is for a

stopping distance test on a high

coefficient of friction surface, which

includes a stopping distance

measurement that is more affected by

test surface variation. Based on these

considerations, the agency has

determined that the results of the

braking-in-a-curve test will not be

affected by minor variations in the test

surface.

The road surface requirements

comply with PACCAR’s holding that

manufacturers are entitled to testing

criteria that they can rely on with

certainty, since they include objective

terms and requirements, i.e., the test

surface is at a PFC of 0.5. For the same

reason, the requirements also comply

with PACCAR’s requirement that all

methods to demonstrate compliance

with the requirement be set forth in the

regulation.

In evaluating the requirement’s

practicability, NHTSA has considered

possible difficulties with respect to

building and maintaining test surfaces

with a PFC of 0.5 for the braking-in-acurve test and 0.9 for the high

coefficient stopping test. (Those

interested in building and maintaining a

test surface should refer to NHTSA’s
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13233

36TRC Report, August 21, 1991, page 6. 37TRC Report, August 26, 1991. 38TRC Report, page 10.

‘‘Manual for the Construction and

Maintenance of Skid Surfaces,’’ (DOT

HS 800 814.) Variations in PFC for high

coefficient of friction surfaces do not

affect stopping distance test results

appreciably. Moreover, while variations

in PFC for low coefficient friction

surfaces may affect the distance in

which a vehicle stops, such variations

are not relevant for the braking-in-acurve test, which requires a vehicle to

remain stable while it is stopped, not

that it stop within a specified distance.

After reviewing the comments and

available information, NHTSA has

concluded that specified test surfaces

can be achieved and maintained. As

explained above, recent ‘‘Round Robin’’

testing related to research about heavy

vehicle braking by the agency and

others on several test tracks indicates

that the test surface specification does

not raise practicability or objectivity

concerns.36

One of the PACCAR court’s concerns

was that the road surface skid numbers

were based on an out-of-production tire.

That concern is not relevant to today’s

final rule since it specifies a currentlyproduced tire. The requirements comply

with PACCAR’s concern about the

testing method’s objectivity because the

peak coefficient of friction is an

objective measure.

NHTSA disagrees with AAMA’s

comment that it is not apparent whether

it would be more conservative to

conduct testing at a higher PFC than the

proposed PFC. Data from the roundrobin testing and other sources show

that the stringency of a braking-in-acurve test increases as the PFC of the

test surface decreases, if the tests are

conducted at the same vehicle speed.

Since the requirement specifies a test

speed based on the vehicle’s maximum

drive-through speed, which decreases as

the test sequence PFC decreases, the

resulting test speed will also be lower as

the PFC decreases. Hence, the

stringency of the braking-in-a-curve test

should not change with minor changes

in the PFC of the test surface.

NHTSA has decided that AAMA’s

other comments about the test surface

requirement are without merit. That

organization did not provide any data to

substantiate its statements. Nor did it

explain why it believes that ‘‘variability

in the peak to slide ratio’’ is relevant.

Similarly, AAMA’s comment about

‘‘simultaneously maintaining a given

surface at a precise PFC and sliding

coefficient (i.e., skid number) [being]

completely infeasible’’ is irrelevant to

this rulemaking. The agency has never

proposed a test surface requirement that

specifies both the PFC and skid number

values.

3. Test Speed

In the NPRM, NHTSA proposed that

the braking-in-a-curve test be conducted

at 30 mph, unless the vehicle could not

stay within the 12-foot lane when

driven through the curve at 30 mph. If

the vehicle could not do so, the brakingin-a-curve test would be conducted at

75 percent of the maximum drivethrough speed. NHTSA believed that the

proposed vehicle test speed was

sufficiently high to test ABS

performance, but low enough so as not

to pose an unsafe condition during the

maneuver to the test driver of most

vehicles, based on testing conducted by

the agency 37 and SAE J1626 Proposed

Recommended Practice. The agency

requested comments about the proposed

test speed.

Advocates opposed any reduction in

the test speed below 30 mph.

Specifically, it opposed permitting

vehicles that cannot negotiate the curve

at 30 mph to be tested at the 75 percent

drive-through speed because it believed

that this would be a ‘‘free-floating

criterion’’ that could lead to ineffective

antilock systems.

Rockwell WABCO, Allied Signal,

Midland-Grau, and AAMA requested

that the test speed be clarified. Rockwell

WABCO recommended that the vehicle

test speed requirement be revised to

read ‘‘stopped from 30 mph or 75% of

the maximum drive through speed,

whichever is less.’’ Similarly, Allied

Signal suggested that the vehicle test

speed be clarified to say that testing

cannot exceed 30 mph. Midland-Grau

recommended that the agency revise the

requirement so that the test be

conducted at only 75 percent of the

maximum drive-through speed

capability. It further stated that

conducting the braking-in-a-curve test at

speeds greater than 30 mph on a low mu

surface could cause safety problems.

AAMA stated that the NPRM incorrectly

applied SAE J1626, which requires

testing at 75 percent of drive-through

speed to a maximum of 30 mph braking

speed. It stated that under the proposal,

a vehicle with a drive-through speed of

30 mph would be tested at 30 mph,

while a vehicle with a drive-through

speed of 29 mph would be tested at less

than 22 mph. In opposing the proposed

requirement, AAMA further stated that

the determination of the drive-through

speed is highly sensitive to driver skill,

subtle vehicle maneuvers, and

environmental conditions, and is

therefore not repeatable.

ATA recommended that NHTSA

establish stopping or snubbing distance

requirements for vehicles in a curve,

using a braking speed which is between

95 and 100 percent of their maximum

drive through speed.

After reviewing the comments and

available information, NHTSA has

decided to specify that a vehicle’s test

speed for the braking-in-a-curve test is

‘‘30 mph or 75% of the maximum drivethrough speed, whichever is less.’’ This

modification responds to the comments

by Rockwell WABCO, Allied Signal,

and Midland-Grau that the proposal was

not consistent with SAE J1626. The

agency believes that making the speed

consistent with SAE 1626 will eliminate

the possibility of discontinuities in the

test’s stringency for different vehicles.

As AAMA correctly stated, the proposed

test speed created an anomaly that

benefitted vehicles with a maximum

drive-through speed slightly below 30

mph. For example, a vehicle with a

maximum drive-through speed of 29

mph would have been tested at 22 mph,

while a vehicle with a maximum drivethrough speed of 30 mph would have

been tested at 30 mph. This would have

meant that a 1 mph difference in

maximum drive-through speed would

have resulted in a 8 mph difference in

test speed. This could have caused

significant variations in test results for

vehicles with slight differences in

maximum drive-through speed. By

establishing a test speed that is adjusted

for differences in maximum drivethrough speed and that would be more

specific and distinct for each vehicle

and test surface, the agency has

minimized potential compliance testing

problems that might occur due to

variability in the test speeds for

different vehicle and road test surface

conditions.

NHTSA notes that ATA’s requested

test speed and test conditions have not

been tested by the agency or industry

and therefore their adoption would not

be appropriate at this time. The agency

may evaluate ATA’s proposal in future

test programs.

NHTSA believes that Advocates’

opposition to permitting test speeds

below 30 mph is unfounded. Similarly,

the agency believes that AAMA’s

concern about the drive-through speed

being unrepeatable is irrelevant. By

allowing vehicles to be tested at 30 mph

or 75 percent of maximum drivethrough speed, whichever is less, the

effects of test surface variation are

eliminated.38
13234 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

39The final rule also adopts the 1,000 pound

allowance for a roll bar.

4. Type of Brake Application

In the NPRM, NHTSA proposed that

the stops be achieved through full brake

applications in which the pressure at

the treadle valve must reach 100 psi

within 0.2 seconds after the application

is initiated. The agency believed that

these values properly represent full

brake applications, in terms of both the

application’s degree of force and its

duration. The agency stated that the

stability and control requirements

should evaluate worst case braking

applications in an aggressive or ‘‘hard’’

stop and that full brake applications are

more readily repeatable than the ‘‘driver

best effort’’ applications.

Midland-Grau agreed with the

proposal to specify a full treadle

application of 100 psi in 0.2 seconds for

air braked vehicles. According to

Midland-Grau’s test data, full treadle

applications at 100 psi were achieved in

0.12 to 0.18 seconds, with the

measurement taken at the treadle valve’s

primary output circuit located at the

rear axle brakes. However, more time is

needed to reach 100 psi at the secondary

circuit located at the front axle brakes

because its output supplies air to the

quick release valves and then to the

front axle brake chambers. Allied Signal

stated that it is not possible to reach 100

psi within 0.2 seconds at the front axle

output circuit of the treadle valve.

After reviewing these comments,

NHTSA has decided to revise the brake

application requirement for air braked

vehicles to require 100 psi in at least

one of the treadle valve’s output circuits

within 0.2 seconds, thereby allaying

Allied Signal’s concern. This

modification to the test condition

should eliminate potential ambiguity

concerning where the application

pressure is to be measured.

5. Number of Test Stops for Certification

In the NPRM, NHTSA proposed that

a vehicle comply with the proposed

braking-in-a-curve test in each of three

consecutive stops for each combination

of weight and road conditions. In

contrast, the vehicle stopping

performance tests in Standard No. 105

and Standard No. 121 specify that the

vehicle must meet the requirements at

least once in six attempts through a best

effort brake application. The agency

tentatively concluded that six stops

should not be needed to achieve the

required performance in the braking-ina-curve test, given the presence of an

antilock brake system. The agency

requested comments about the number

of brake applications that should be

required.

Advocates, Midland-Grau, and Mr.

Crail stated that three stops are

sufficient for a vehicle with an antilock

brake system to display compliance

with the braking-in-a-curve test. They

stated that without stopping distance

requirements, this test procedure entails

a simple performance test for the

vehicle to maintain control in the 12-

foot lane. Midland-Grau added that it

uses three stops when conducting ABS

performance tests, and that this number

of brake applications is consistent with

the SAE J1626 Recommended Practice

and with the MVSRAC Antilock Brake

System Task Force’s final

recommendations.

AAMA argued that specifying three

passes in three consecutive stops places

an unrealistic burden on the driver to

control the vehicle immediately with no

opportunity to become familiar with the

vehicle or test surface. AAMA

recommended that manufacturers be

given the option of conducting ten or

more stops and certifying that the

vehicle stayed within the 12-foot lane

for any three consecutive stops.

After reviewing the comments and the

available information, NHTSA has

decided that requiring compliance with

the braking-in-a-curve requirements

during three consecutive stops is

appropriate. The agency notes that

specifying three consecutive full treadle

test stops is consistent with both the

agency’s own testing at VRTC and its

testing in conjunction with the motor

vehicle industry through the MVSRAC

ABS Task Force. The use of full treadle

brake applications to test an ABSequipped vehicle to the braking-in-acurve maneuver requires less driver

skill than the use of a driver’s-best-effort

modulated brake application (i.e., the

type of application used in stopping

distance performance tests) because the

ABS automatically modulates the

brakes. Further, more than three stops

are unnecessary since the braking-in-acurve test requirement is not coupled

with a stopping distance requirement.

Therefore, NHTSA has decided not to

adopt AAMA’s suggestion that

manufacturers be given the option of

complying with only three of ten stops.

Adopting that suggestion would make

the braking-in-a-curve requirement

unreasonably lenient.

6. Test Weight

In the NPRM, NHTSA proposed that

single unit trucks, buses and bobtail

truck tractors be tested at their curb

weight (including full fuel tanks) plus

500 pounds to account for the driver

and instrumentation. The agency also

proposed to allow a manufacturer to

conduct the braking-in-a-curve test with

a roll bar structure weighing up to an

additional 1,000 pounds to protect the

driver, based on a recommendation by

the MVSRAC ABS Task Force. The

agency requested comments about the

appropriate unloaded test weight.

Rockwell WABCO recommended that

unloaded heavy vehicles be allowed to

have less than 500 pounds added in the

unloaded condition.

After reviewing Rockwell WABCO’s

comment, NHTSA has decided to

amend the test condition in the brakingin-a-curve test to specify the weight in

the unloaded condition to be ‘‘up to 500

pounds’’ for driver and

instrumentation.39 The agency notes

that instrumentation hardware has been

getting more compact and lightweight.

Using the regulatory language ‘‘up to

500 pounds’’ will simplify the test

condition since manufacturers will not

have to add ballast to ensure that the

weight is 500 pounds. This change

provides manufacturers with greater

incentive to use the newer, lighter

hardware. The agency believes that this

modification will have no measurable

effect on a vehicle’s performance during

the braking-in-a-curve test since a

weight range of a few hundred pounds

is of little significance in relation to a

tractor’s typical empty weight of more

than 26,000 pounds.

7. Loading Conditions

In the NPRM, NHTSA proposed that

braking-in-a-curve tests be performed in

both the empty and loaded conditions,

since a vehicle’s braking performance

varies depending on the amount of load

that it is carrying. With respect to

testing truck tractors in the loaded

condition, the agency proposed two

alternatives regarding the use of control

trailers: (1) use a braked control trailer

and (2) use an unbraked control trailer.

Most commenters, including AAMA,

Rockwell WABCO, and Midland-Grau,

supported the unbraked control trailer

alternative. These commenters believed

that using an unbraked control trailer

instead of a braked control trailer would

eliminate many sources of variability

and would provide more consistent and

repeatable test data. AAMA stated that

if the braked control trailer alternative

were adopted, every aspect of the

control trailer brake system would have

to be precisely specified because the

tractor’s performance is directly affected

by the performance of the control trailer.

Midland-Grau stated that using an

unbraked control trailer is consistent

with SAE J1626 and the testing
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13235

40TRC Report #091194, page 4.

41 ‘‘Heavy Duty Vehicle Brake Research

Program—Report No. 1,’’ April 1985.

performed by the MVSRAC ABS Task

Force.

Similarly, commenters on the

February 1993 stopping distance NPRM

strongly supported the unbraked control

trailer alternative. Those commenters

believed that the agency would have

great difficulty defining the required

performance of a braked control trailer

and its ABS if the braked control trailer

alternative were adopted.

Mr. Crail and Strait-Stop stated that a

truck tractor should be tested with an

ABS-equipped control trailer because it

is not normal for a combination vehicle

to be operated with an unbraked control

trailer. They believed that a braked

control trailer would more closely

reflect real world braking. Mr. Crail also

stated that an unbraked control trailer

could result in instability during testing.

After reviewing the comments and

other available information, NHTSA has

decided to specify that truck tractors be

tested with an unbraked control trailer

for the braking-in-a-curve test. As the

agency explained in the NPRM, the

unbraked control trailer eliminates

certain types of variability and provides

more repeatable test data. Moreover, this

approach eliminates the need for the

agency to specify and vehicle

manufacturers to comply with detailed

foundation brake design requirements

for the control trailer. Accordingly, the

unbraked control trailer will provide

more readily comparable test data

among vehicles and more repeatable test

parameters for manufacturers.

NHTSA acknowledges that an

unbraked control trailer does not

represent a typical operating condition

for a combination vehicle. As a result,

real world combination vehicles will

stop more effectively than a test

combination vehicle that has brakes on

its tractor but not on its trailer.

Nevertheless, as most commenters

stated, the unbraked control trailer

provides significant benefits for testing

a loaded truck tractor. Further, using the

unbraked control trailer is consistent

with SAE J1626 and the testing

performed by the MVSRAC Task Force.

As for Mr. Crail’s concern about

stability problems during testing,

NHTSA does not agree that the use of

an unbraked control trailer will result in

such problems. It is true that using an

unbraked control trailer will result in

the kingpin receiving additional forces,

since the trailer will still be pushing on

the kingpin while the tractor is braking.

However, the agency and industry

conducted several braking-in-a-curve

tests with unbraked control trailers that

indicated that these additional kingpin

forces will not increase a vehicle’s

instability during testing.40

8. Initial Brake Temperature

In invalidating parts of Standard No.

121, the court in PACCAR stated that

the standard failed to specify formal and

reasonably specific testing criteria about

the time intervals between tests. The

time interval between tests is important

because it may affect brake temperature

and thus brake lining performance. In

response to PACCAR, the agency

amended the standard to specify that

the average brake lining temperature of

the hottest axle be between 150° and

200 °F before performance tests could be

conducted.

In the February 1993 NPRM on

stopping distance and the September

1993 NPRM on stability during braking,

NHTSA proposed that the average brake

lining temperature of the hottest axle be

between 250° and 300° F before

performance tests could be initiated.

This range was based on testing

conducted by VRTC41. The agency

believed that compared to current

requirements, this provision would

allow tests on heavy vehicles to be

conducted within a shorter time

between measurements at temperatures

representative of in-service conditions,

without affecting brake performance.

Only Advocates commented on the

proposal in the stability and control

NPRM to increase the initial brake

temperature from 150–200 °F to 250–

300 °F. Advocates supported the higher

temperature range, stating that it is

reasonable and representative of inservice temperature conditions.

However, NHTSA received numerous

comments about this issue in response

to the stopping distance NPRMs. All

commenters addressing the issue of

initial brake temperature in those

rulemakings strongly opposed the

proposed change in temperature from

150–200 °F to 250–300 °F. Lucas argued

that the higher initial brake temperature

would be detrimental to drum brake

performance. Lucas, HDBMC, and

Rockwell WABCO stated that the

proposed initial brake temperature

would invalidate the vehicle

manufacturer’s data bank from Standard

No. 121 testing at 150–200 °F, which

has been accumulating since the 1970s.

Midland-Grau commented that, among

other things, the higher initial brake

temperature would lead to more

aggressive lining materials and vehicle

compatibility problems.

Abex, AAMA, and HDBMC stated that

the proposed higher initial brake

temperature would shorten testing time

between 5 and 10 hours. However, they

believed that problems associated with

brake fade resulting from the higher

initial brake temperature would far

outweigh the nominal cost savings

obtained by having a shorter test time.

Test data provided by AAMA showed

that while the higher initial brake

temperature has a slight adverse effect (a

7–28 foot increase) on full service brake

stopping distance, it has a significant

adverse effect (a 25–98 foot increase) on

emergency brake stopping distance.

Rockwell WABCO stated that the

perceived benefits of the higher initial

brake temperature do not justify the

increased vehicle testing and redesign

that would be required to meet the

proposed initial brake temperature.

After reviewing the comments, the

test data, and other available

information, NHTSA has decided that

an initial brake temperature in the 150

°F to 200 °F range is more appropriate

than the proposed temperature range.

As the commenters stated, testing using

the 150 °F to 200 °F temperature range

is more repeatable and results in less

variation between runs, compared to

testing conducted using an initial brake

temperature of 250 °F to 300 °F,

particularly for the emergency brake

stops. The agency further notes that an

initial brake temperature of 150 °F to

200 °F is within the 150 °F to 300 °F

range recommended by the VRTC test

report. The agency is aware that the

lower temperature range increases the

total test time by 5 to 10 hours.

Nevertheless, because the other

advantages to the lower temperature

range outweigh this concern, NHTSA

has decided not to change the

specification that the initial brake

temperature be between 150 to 200 °F.

9. Transmission Position

In the NPRM, NHTSA proposed that

the transmission be in neutral or the

clutch pedal be depressed (clutch

disengaged).

ATA commented that, in real world

panic stops, drivers will neither put the

transmission in neutral nor depress the

clutch pedal before making a brake

application. Nevertheless, ATA

acknowledged that retardation by the

drivetrain could cause vehicle

instabilities that would necessitate

testing at speeds lower than the drive

through speed.

NHTSA has concluded that testing

with the transmission in neutral or the

clutch disengaged is appropriate to

ensure that engine retardation does not

affect a test which is intended to
13236 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

42The agency notes that it is requiring powering

through a separate circuit, not a separate connector.

evaluate the influence of brake systems

on vehicle dynamic stability. Engine

and drivetrain retardation forces vary

from vehicle to vehicle and can affect

vehicle stability on low coefficient of

friction surfaces. Nevertheless, this is

not the purpose of this test. By requiring

that the transmission be placed in

neutral for brake testing, the standard

attempts to reduce these drive-train

related braking influences on the service

brake performance. Therefore, testing

with the transmission in neutral or the

clutch disengaged will eliminate

influences that engine or drivetrain

retardation would have on braking

performance. This test condition

therefore helps to ensure test

repeatability and reproducibility.

10. Summary of General Test Conditions

For the convenience of the reader, this

section summarizes the general test

conditions being adopted in this notice,

as follows:

• Vehicle Position—Centered in the

test lane at the initiation of braking.

• Steering—Driver to steer as

necessary during braking to maintain

vehicle control.

• Initial Brake Temperature—The

average brake lining temperature of the

hottest axle between 150 to 200 °F.

• Transmission—Neutral (or clutch

pedal depressed).

• Loading for Truck Tractors

Empty (Bobtail): Curb Weight

(including full fuel tanks) plus up to 500

pounds for driver and instrumentation,

and, at the manufacturer’s option, a roll

bar weighing up to 1,000 pounds.

Loaded: Tractor is loaded with an

unbraked control trailer, loaded above

the kingpin only, so that the tractor is

at GVWR and the trailer axle is at 4500

pounds. Tractor weight is distributed in

accordance with the Gross Axle Weight

Ratings (GAWRs). If the tractor’s fifth

wheel is fixed, preventing such loading,

then the trailer is loaded until any one

tractor axle reaches its GAWR.

• Brake Burnish—Follow procedures

in S6.1.8(b) of Standard No. 121.

Low Mu Braking-In-A-Curve Test

• Run vehicle, empty and loaded.

• Test Surface—PFC of 0.5, as

determined with the ASTM E1136 SRTT

tire on ASTM traction trailer using

ASTM E1337–90 procedure.

• Track Configuration—500 foot

radius at lane center line.

• Test Speed—30 mph or 75 percent

of the maximum drive-through speed,

whichever is less. Maximum drivethrough speed is the highest constant

speed at which the vehicle can be

driven through 200 feet of curve arc

without any part of the vehicle leaving

the 12-foot lane.

• Brake Application—Three fulltreadle applications (i.e., air pressure of

100 psi at any treadle valve output

circuit within 0.2 second) for each

loading condition.

• Test Failure Condition—Vehicle

must stay within the 12- foot lane

during all three stops in order to comply

with requirement.

D. Reliability and Maintenance

In response to the SNPRM, ATA,

United Parcel Service (UPS), and

Tramec expressed concern about the

durability, reliability, and maintenance

of ABSs. ATA stated that the rule, if

adopted, would result in significant

maintenance problems, especially with

respect to failures of electrical circuits

and of the power source. It claimed that

ABS components fail too often and that

real world failure rates are higher than

those in NHTSA’s demonstration

program. ATA further stated that it is

inappropriate to compare the failure

rates of ABS components that are not

subject to wear with the rates for

components, like brake linings and tires,

that are subject to wear. ATA stated that

existing connectors fail in large numbers

and that what it mistakenly termed a

‘‘separate connector requirement’’

would double the failure rate, resulting

in unreasonable costs.42 It also stated

that there have been many problems

resulting from inadequate installation of

ABSs, since malfunctions are frequently

due to design problems, faulty

installation, and lack of knowledge

about ABS maintenance. ATA also

stated that NHTSA did not take

seriously enough malfunctions noted

during the agency-sponsored in-service

fleet study, which were rectified with

only the expenditure of labor, namely

corrections that involved inspections or

minor adjustments.

ATA and UPS stated that new ABS

equipped heavy vehicles have a high

percentage of ‘‘direct from factory’’ ABS

failures. UPS stated that ‘‘these systems

are still plagued by incidents of failure

that far exceed the normal level of

problems encountered with other

components of heavy duty trucks.’’ ATA

also stated that NHTSA did not take

labor only failures (i.e., malfunctions

that can be fully corrected through the

use of labor without the need for new

parts) seriously enough. ATA believes

that they are a costly and serious

problem that takes vehicles out of

service.

To evaluate the reliability of currentgeneration ABSs, NHTSA has

conducted extensive field studies of

ABS-equipped heavy truck tractors and

semitrailers in developing this final

rule. In response to the PACCAR

decision, these studies were structured

to assess whether current-generation

heavy vehicle antilock brake systems

were reliable and fail-safe, whether they

inordinately increased vehicle

maintenance costs, and whether they

could be successfully maintained and

would remain functioning in typical

U.S. heavy truck operating

environments.

Between 1988 and 1993, NHTSA

tracked the maintenance performance

histories of 200 truck tractors and 50

semitrailers equipped with ABS, as well

as the histories of a comparison group

of 88 truck tractors and 35 semitrailers

not equipped with ABS, to determine

the incremental maintenance costs and

patterns associated with installing ABS

on these heavy vehicles. Additionally,

special on-board vehicle recorders were

used to monitor the functioning and

performance of the ABSs. Finally,

drivers and mechanics at the

participating test fleets were

periodically interviewed to ascertain

their views about the ABS test vehicles’

performance and ease of maintenance.

This multimillion dollar program was

the largest of its kind that has ever been

conducted by the agency or throughout

the world. The study’s authors

concluded that, based on the data

collected during the fleet study,

currently available antilock braking

systems are reliable, durable and

maintainable.

While ABS is not a zero-cost

maintenance item, its presence on a

vehicle did not substantially increase

maintenance costs (less than 1 percent

for tractors, less than 2 percent for

trailers) or decrease vehicle operational

availability. Specifically, ABS use does

not involve appreciably more intensive

maintenance than present brake

systems. The agency finds that the

average annualized increase in lifetime

maintenance costs ($3.47–$27.49 per

vehicle) occasioned by the use of ABS,

as indicated in the Final Economic

Assessment (FEA) for this rulemaking,

is a reasonable amount of additional

maintenance. Further, the agency notes

that a significant portion of the costs

noted during the fleet study (i.e., those

attributed to intermittent malfunction

warning indications for which no

problem was found and the system was

simply reset or a simple adjustment was

made) are likely to be reduced or

eliminated as the algorithms inside the

ECU that trigger ABS malfunction

warnings are further refined to make

them more discriminating, and as
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13237

quality control and installation skill

improve.

NHTSA further emphasizes that

system malfunctions do not render the

vehicle’s braking system unsafe, since

the brake system merely reverts to one

without an ABS; in other words,

foundation brakes are unchanged when

ABS is added. The few incidents noted

during the test program in which an

ABS malfunction did compromise the

vehicle’s underlying brake system

performance involved defective

components.

In both the tractor and the trailer

studies, some test vehicles either arrived

in the test fleets with faulty ABS or had

ABS malfunction indications shortly

thereafter, as a result of what was

termed installation or pre-production

design related problems. In general,

these problems were easily remedied.

Many were corrected by adjustments or

minor repairs. Most were at least

partially attributable to the prototype

nature of many of the installations

accomplished for this test program.

The following examples illustrate the

relatively minor nature of correcting

most of the problems. (The agency notes

that none of the problems listed affected

vehicle braking.)

• The electrical power source for the

ABS ECU on a group of four trucks was

incorrectly wired, at the time of

installation, through the starter

solenoid. These four trucks had to be

rewired to make the ABS function

properly.

• Intermittent failure warnings were

noted on three trucks from the

beginning of their operation. Upon

inspection, the trucks were found to

have an incompletely assembled

connector in the wiring harness. When

this problem was corrected, the failure

warnings ceased.

• A group of 23 tractors had to be

rewired to provide a separate electrical

power source for the dash-mounted

failure warning lamp so that it could

function properly. The miswiring

occurred during installation.

• The ABS modulator valves on a

group of 12 tractors had to be relocated

on the vehicles’ frame rails to eliminate

an inadvertent physical interference

problem with the vehicles’ driveshafts.

This problem occurred as a result of an

oversight during installation.

• On one truck, a sensor cable needed

to be rerouted and resecured because of

an interference/pinching problem with

the wire and the steering gear.

NHTSA emphasizes that these

problems and others like them do not

reflect inherent design flaws with ABS’s

principal components (i.e., the ECU,

modulators, and wheel speed sensing

hardware). Instead, they involve wiring

and installation problems. This

highlights the importance of using high

quality wiring components and paying

close attention to installation details.

The agency anticipates that the

frequency of these problems will be

lower than that experienced during the

agency’s test program once ABS

production/installations increase to a

level high enough to enable the quality

control programs typically utilized by

suppliers and truck manufacturers to

take effect.

An average of 1.35 labor hours and

$106.46 in replacement component

parts costs per test truck tractor were

necessary to rectify these installation/

pre-production design related problems.

Comparable figures for semitrailers were

1.9 labor hours and $65.36 in parts

costs. All these costs are usually

recovered by fleets under the terms of

typical warranties offered by ABS

suppliers and/or truck manufacturers.

NHTSA notes that the start-up or

installation/pre-production design

related problems that the test fleets

experienced are similar to the

experiences that fleets were reported to

have had with other devices such as

electronically-controlled engines when

they were first introduced on heavy

trucks in the mid-1980’s.

During the two-year period in which

the reliability of these systems was

evaluated, 200 ABS-equipped test

tractors accumulated 39,818,659 miles

of travel. During that time period, 126

trucks (63 percent) needed ABS-related

maintenance that could best be

attributed to normal service wear factors

rather than installation or preproduction design related problems. A

total of 421 incidents of this type

occurred with the 125 trucks, the

majority (321 or 76 percent) of which

involved inspections/adjustments. The

remainder (100 or 24 percent) involved

repairs/replacements. All brands of the

ABSs involved in the test program

experienced incidents of this type at one

time or another during their in-service

operation.

Forty vehicles experienced more than

one failure warning, interspersed over

time, with two vehicles experiencing 35

and 31 separate indications (23 percent

of the total resets), respectively, without

the source of the problem being

uncovered. Two other trucks

experienced 12 and 10 separate

indications respectively. These four

vehicles (4.5 percent of the trucks

experiencing this problem) accounted

for 30 percent of the total intermittent

failure warning indications and resets.

All five ABS suppliers’ systems

experienced intermittent failure

indications with at least one of their

forty test trucks involved in the test

program. In each case, the ABS was

either manually reset or the warning

light did not reactivate when the truck’s

ignition was turned off and

subsequently turned on again at some

later time. However, 61 percent of the

total failure warning indications of this

type, and 34 percent of the vehicles

experiencing intermittent failure

indications, were attributable to one

supplier’s ABS. Another supplier’s

system accounted for another 18 percent

of total failure warning indications and

an additional 28 percent of the total

vehicles involved. Since the time of the

agency’s test, both suppliers’ systems

have been modified to reduce the

number of these false-positive

malfunction indications.

The table shown below indicates the

maintenance related to in-service wear

that was required during the tractor

portion of the program on each of the

ABS components. Data are displayed by

maintenance category (adjustments/

inspections and repairs/replacements).

Inspections and ECU resets associated

with intermittent failure warning

indications were the principal

occurrence. In general, most of the work

did not involve parts replacements.

Parts replacement incidents totaled 40,

with 55 percent of these (22) involving

failure warning lamp bulbs or fuses. The

total average number of in-service wear

related maintenance incidents,

including all inspections, adjustments,

repairs and replacements was 2.11

incidents per truck over the two-year

period of the test.
13238 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

ABS IN-SERVICE WEAR RELATED MAINTENANCE INCIDENTS OVER THE TWO-YEAR PERIOD OF THE TEST, BY SYSTEM

COMPONENT NEEDING WORK

ABS component

Number of

trucks requiring inspections, adjustments, or repairs on this

component

Number of

trucks requiring replacement of this

component

Wiring Cables ........................................................................................................................................................... 26 4

Wiring Connectors ................................................................................................................................................... 19 2

Sensors and Related Parts ...................................................................................................................................... 22 3

Modulator Valves and Related Parts ....................................................................................................................... 3 2

ECUs ........................................................................................................................................................................ 19 7

Fuses and Lamps .................................................................................................................................................... 7 18

System Resets ......................................................................................................................................................... 84 0

Total No. of Trucks per Column ................................................................................................................... 118 32

Overall No. of Trucks Involved in the In-Service Related Incidents ....................................................................... 125

Note: Columns are not additive.

Replacing the 19 faulty major ABS

components, and performing all the

other inspections, adjustments and

repairs that were in-service wear

related, resulted in approximately 403

hours of labor expenditure and $4,068

for parts replacements. At a standard

hourly rate of $35 per hour, the total

cost of $18,173 for labor and parts

amounts to 0.046 cent-per-mile (based

on 39,818,659 total miles of travel) for

the cost of maintaining the ABSs over

the two-year period.

Inspections/ECU resets, which only

involved labor expenditure, accounted

for 45 percent of these total costs. Even

though they occurred infrequently, ECU

replacements tend to be costly,

accounting as they did for 21 percent of

the in-service wear related maintenance

costs.

Similar findings were noted for the 50

ABS-equipped semitrailers that also

were evaluated. The test vehicles

accumulated 4,001,369 miles of inservice use during almost two years of

operation during the program. During

that time period, 23 semitrailers (46

percent) needed ABS-related

maintenance that could best be

attributed to normal service factors,

rather than installation or preproduction design related problems.

This compares favorably to the 63

percent of tractors requiring ABS service

during the tractor program. A total of 44

incidents of this type occurred with the

semitrailers, with the majority (29, or 66

percent) involving inspections or

adjustments. The remainder (15, or 34

percent) involved repairs or

replacements. These percentages are

similar to the 76 percent for adjustments

and inspections and 24 percent for

repairs and replacements seen during

the tractor program.

The following table shows in-service

trailer maintenance that was required

during the program for each category of

ABS components. Inspections and ECU

resets associated with failure warning

indications were the principal

occurrence. Parts replacement incidents

totaled six, with three of these being

status light bulbs and three speed

sensors. In general most of the work did

not involve parts replacement.

The average number of in-service

maintenance incidents, including all

inspections, adjustments, repairs, and

replacements was 0.88 incidents per

semitrailer over the two-year test period.

This compares well with the 2.11

incidents per tractor seen during the

tractor portion of this program.

Replacing six faulty ABS components,

plus performing all other inspections,

adjustments, and repairs that were inservice related, resulted in about 44

man-hours of labor expenditure and

$234 for parts replacements. At a

standardized hourly rate of $35 per

hour, the total cost of maintaining the

ABSs, for labor and parts, over two

years ($1774) amounts to 0.044 centsper-mile (based on 4,001,369 total miles

of travel). The inspections and ECU

resets (which only involved labor

expenditure) accounted for 35 percent

of the total costs. Comparable tractor

figures are 0.046 cents-per-mile for total

costs and 45 percent of the total costs

for inspection and ECU reset, indicating

that semitrailers performed very much

like tractors.

ABS IN-SERVICE WEAR RELATED MAINTENANCE INCIDENTS OVER THE TWO-YEAR TEST PERIOD BY SYSTEM COMPONENT

NEEDING WORK

ABS component

Number of

semitrailers requiring inspections, adjustments or repairs on this

component

Number of

semitrailers requiring replacements of

this component

Wiring Cables ........................................................................................................................................................... 4 0

Wiring Connectors ................................................................................................................................................... 2 0

Sensors and Related Parts ...................................................................................................................................... 10 3

Inspection, with No Problem Found (NPF) .............................................................................................................. 12 0

ECUs ........................................................................................................................................................................ 4 0

Fuses and Lamps .................................................................................................................................................... 3 3
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13239

43 DOT HS 8070846, pages 3–24; DOT HS 808–

059, pages 3–19, 3–20.

ABS IN-SERVICE WEAR RELATED MAINTENANCE INCIDENTS OVER THE TWO-YEAR TEST PERIOD BY SYSTEM COMPONENT

NEEDING WORK—Continued

ABS component

Number of

semitrailers requiring inspections, adjustments or repairs on this

component

Number of

semitrailers requiring replacements of

this component

Total No. of Semitrailers per Column ........................................................................................................... 23 6

Overall No. Semitrailers Involved in the In-Service Related Incidents ................................................................... 23

Note: Columns are not additive.

At the completion of the overall 5-

year test program, NHTSA conducted a

final follow-up survey among the

participating fleets. Among the 13 fleets

that were continuing to maintain the

ABS on the original test tractors, 97

percent of those tractors had functioning

ABS. On the other hand, ABSs were not

functioning on two-thirds of the original

test tractors in the three fleets surveyed

that chose not to continue maintaining

the systems. This demonstrates that

fleets must be willing to maintain the

ABS if it is to be kept operational. An

analogy can be drawn between the need

to periodically inflate tires and the need

to periodically perform minor, routine

maintenance of ABS systems. Even

though neither is time-consuming or

costly, this type of maintenance is

necessary if anticipated performance is

to be achieved.

ATA commented on the SNPRM that

the ABS repair/replacement rate (14–33

incidents per 100 vehicles per year)

indicated in the agency’s fleet study

significantly understated the actual rate,

citing the experience of one of its

member carriers which recorded six to

thirteen times as many ‘‘repair

incidents.’’

Although NHTSA has not had the

opportunity of reviewing the records

ATA cited, the agency is inclined to

believe that the difference in rates may

be attributable to a difference in the

definition of a ‘‘repair incident.’’ The

agency fleet study data cited by the ATA

(i.e., 14–33 incidents per 100 vehicles

per year) were for ‘‘repairs/

replacements’’ of ABS components.

They did not include instances in which

‘‘inspections’’ or ‘‘adjustments’’ were

made. For instance, adjustments of

wheel speed sensors are not included in

this total. This exclusion was necessary

because comparable inspection/

adjustment data were not available for

the other vehicle components whose

maintenance histories were being

compared in the fleet study to that for

the ABSs.

The above discussion accounts for all

the in-service maintenance activity that

was performed on the test ABSs. The

‘‘monitoring’’ to which ATA refers did

not in any way contribute to or detract

from the reliability data for the ABSs

under evaluation. That monitoring was

intended to ensure that all the

maintenance work that was performed

was recorded, so that a complete picture

could be portrayed of the extent and

nature of maintenance work that could

be expected if U.S. heavy trucks were

equipped with ABSs. Based on those

data, the agency concludes that, overall

neither unreasonable amounts or

excessively costly additional

maintenance will be imposed on U.S.

heavy truck operators in order to

maintain ABS. Thus, the agency

disagrees with ATA’s assessment that

significant maintenance problems will

arise ‘‘* * * when the equipment is

used outside the close monitoring it

received in the NHTSA demonstration

program.’’

ATA further stated that ABSs are

‘‘* * * not yet as durable as they must

be for successful operation * * * in the

U.S.’’ That organization cited the fact

that, as described above, three of the

original participating fleets which

ceased participating in the test program

had appreciable proportions of nonfunctioning ABSs on their original test

vehicles because they no longer

maintained the systems.

NHTSA notes that this outcome could

be anticipated with many other

components besides ABS, that are

installed on motor vehicles, for

example, tires, engines, etc. All such

components require periodic, and

occasionally non-periodic, nonscheduled maintenance, in order to

remain functional. Notwithstanding, the

agency believes that the data contained

in the two fleet study reports indicate

that equipping vehicles with ABS is

appropriate. Taken in total, those data

indicate that, while ABS is not a zeromaintenance component, it is neither

difficult nor unduly expensive to

maintain. The fleet test results indicate

that the level of maintenance attention

needed to keep ABS functional is

reasonable relative to the safety benefits

that are estimated to result from use of

these systems.

ATA also disagreed with the

comparisons that were made in the

agency’s fleet study of repair and

malfunction rates of ABS compared to

other components on the vehicle that

were susceptible to wear-related

replacement. In the fleet study,

comparisons were made between the

maintenance histories of ABS and

comparable histories for wheels/hubs,

foundation brake components,

pneumatic brake components, electrical

system components, and tires.43 These

items were chosen because the agency

believed that the maintenance patterns

and costs of only these components

could have been affected by the

presence of ABS on the vehicle. The

agency decided that it would be

inappropriate to compare ABS

maintenance results to items, such as

engines and other drivetrain

components, whose maintenance

histories and costs would be unaffected

by the presence of ABS.

ATA also questioned whether

maintenance problems could have been

underreported by a factor of 2.5 because

the on-board recorders used during the

trailer fleet study recorded less miles of

travel (1.6 million vehicle miles of

travel) than were accumulated by all the

test trailers (4 million miles) during the

test program. NHTSA notes that the

maintenance history and cost data

reported in the two studies were not

affected by this discrepancy. The

recorders were primarily used to obtain

statistical information on the relative

frequency of ABS activations per mile of

travel. While their secondary purpose

was to monitor ABS functioning, this

was done only as a backup to the

standard maintenance reporting and
13240 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

44Memos about these meetings have been placed

in the public docket.

record-keeping activities of the

participating fleets. The ABS

maintenance histories that are reported

in the fleet studies were derived from

those maintenance records and are

known to be thorough and complete.

ATA further believed that NHTSA’s

fleet studies underreported ABS

maintenance problems. That

organization cited incidents in which

drivers failed to couple the second

tractor-to-trailer electrical connector

that was installed to power the ABS and

instances in which drivers drove for an

extended time period without reporting

an ABS malfunction.

NHTSA believes that ATA’s

additional concerns about maintenance

problems with ABSs are without merit.

With regard to the first point, even

though a limited number of drivers did

not, in some instances, couple the

separate tractor-to-trailer electrical

connector, this fact does not affect

whether those trailers’ antilock systems

received electrical power. The trailer

ABSs in question were all wired

redundantly to accept backup power

from the stop lamp circuit on the other

tractor-to- trailer electrical connector

that the drivers did connect. Therefore,

the ABSs on these trailers were

functioning throughout the test using

backup power from the standard tractorto-trailer electrical connector, and were

exposed to the possibility of

malfunctioning just as much as the

other test trailers in the study were.

As to ATA’s claim that some drivers

did not report a malfunction for an

extended period of time, there were

only a few instances of drivers driving

for a time with non-functioning ABSs.

The functional status of ABSs on test

vehicles was checked, no less than

monthly, by test study personnel, and

often more frequently by fleet

maintenance personnel. Therefore, in

each case, the existence of a

nonfunctioning ABS was detected after

only a limited number of trips were

made under that condition.

ATA attached to its comments letters

from some of its members, including

Consolidated Freightways, Inc.

(Consolidated), UPS, and Ruan

Transportation Management Systems

(Ruan). ATA characterized these letters

as indicating that ABS ‘‘* * * failures

are still happening and that other things

are going wrong also’’. Consolidated’s

submittal contained a sample listing of

maintenance shop orders describing

various repairs performed on ABS

installed on its vehicles.

NHTSA could not ascertain the

statistical prevalence of these incidents

in Consolidated’s fleet, given the way

Consolidated presented its data. Thus,

these incidents have only anecdotal

value. Nevertheless, the nature and

description of these incidents parallels

those experienced and recorded during

the agency’s fleet study. For instance,

several incidents cited by Consolidated

involved faulty wheel bearings that

knocked wheel speed sensors out of

adjustment. NHTSA believes that these

incidents should not be viewed as ABS

failures. Further, other carriers have

suggested that the ABS’ ability to detect

faulty wheel bearing conditions, which

fail regardless of whether a vehicle is

equipped with ABS, is a safety and

maintenance benefit, not a detriment.

The majority of other incidents cited by

Consolidated involved minor wiring/

connector problems that can be readily

solved by tractor manufacturers’ use of

higher quality wiring/connector

components or better attention to

installation quality control. Carriers may

address such situations through

traditional warranty and customer

complaint channels and, if necessary,

through buying vehicles from

manufacturers with higher overall

product quality ratings.

UPS cited data indicating that the

ABS malfunction warning light on 40

percent of a sample of ABS-equipped

vehicles received from the factory since

1990 was activated when the vehicles

were delivered. UPS did not provide

detailed information listing the causes

of these malfunction indications.

Further, UPS did not explain whether

the problems were remedied by simple

adjustments of the same sort that are

typically done during ‘‘dealer

preparation,’’ prior to a dealer’s

delivering a vehicle to the customer.

The agency notes that many large fleets

such as UPS assume the dealership role

when they receive large orders of

vehicles directly from the factory. As a

result, they assume responsibility for

making this type of minor ‘‘make-ready’’

adjustments.

UPS also cited high proportions of

ABS ‘‘hard repairs or replacements,’’ but

did not define what constituted a ‘‘hard

repair.’’ Thus, it is not possible for

NHTSA to determine whether some of

these might have been considered

‘‘inspections/adjustments’’ under the

reporting scheme used in the agency

fleet study or to put any of these figures

in context or interpret them relative to

the study’s findings.

Ruan indicated that it was having

difficulty getting an ABS supplier to

respond to its requests for problemsolving help. Ruan listed a series of

problems, similar to those noted in the

agency’s fleet study and cited by other

carriers. Ruan’s comments were

anecdotal in nature and did not include

any statistical information that would

help portray the extent to which this

affected their overall maintenance

activities or costs. Nevertheless, all of

the ABS suppliers and the major truck

manufacturers have indicated, in the

discussions they held with the agency

on May 3, 4, and 19, 1994 44, that they

are committed to providing field service

support staff, training, maintenance

information, and other help to remedy

the problems cited by Ruan and others.

NHTSA has repeatedly stated that

manufacturers must make service

support available to fleets to ensure the

success of this rulemaking effort. The

agency anticipates that the ABS

suppliers and major truck

manufacturers will provide this support,

given their statements in response to the

NPRM that they are prepared to and are

now doing so.

In response to ATA’s comment about

the occurrence of ABS malfunctions due

to out of adjustment wheel speed

sensors, NHTSA believes that there are

several reasons other than faulty ABS

design for this phenomenon. Among the

most common reasons observed during

the agency’s fleet study were sensor

misadjustment during initial

installation; faulty sensor retaining

clips; sensor wires being installed with

too little slack, resulting in the sensor’s

being partially pulled out from its

mounting block when the vehicle’s

steering gear or suspension moved;

faulty or improperly installed wheel

bearings; or failure to readjust the sensor

after performing maintenance work in

the wheel end area that results in the

sensor being knocked out of adjustment.

NHTSA emphasizes that the relative

frequency of these types of incidents

was not high. Five of the two hundred

test trucks experienced problems of this

type before being, or shortly after being

placed in service. In addition, twentytwo of the trucks experienced problems

of this type over the two year, 40

million mile test program. With the

exception of the faulty clip problem,

which has been permanently rectified,

all the remaining reasons for the

occurrence of this condition are the

result of installation quality control

lapses, faults with other components, or

misinformed maintenance practices.

The failures were not caused by faulty

sensor design. The agency anticipates

that the rate of incidence of even these

few events will decrease as quality

control efforts and mechanics’

awareness and skill in maintaining ABS

improves.
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13241

45 DOT HS 807–846, page 3–17.

46 DOT HS 808 059, page 3–14.

47 Modern Bulk Transport Magazine, June 1994,

page 84.

48NHTSA responds to the issue of the alleged

safety risk in the next section.

In response to ATA’s comment that

mechanics will have difficulty installing

and maintaining ABS, NHTSA

recognizes that mechanic training will

be necessary to ensure the long term

viability of ABS systems. However,

based on the agency’s fleet test results,

the agency finds that, once trained,

mechanics can successfully maintain

the systems. The study’s results indicate

that those fleets committed to providing

mechanics the support needed to deal

with ABSs can keep the systems

operational with relative ease and

efficiency and at reasonable cost. ABS

suppliers and truck manufacturers have

indicated a commitment to providing

field service support for the systems. If

fleets begin utilizing these services now,

mechanics will be capable of

maintaining the systems as more ABSequipped vehicles are introduced into

fleet service.

Based on its anecdotal experience

with electronic engines, ATA stated that

truck manufacturers will not correct the

wiring and installation related problems

evidenced in the test. Specifically, ATA

stated that ‘‘* * * none of the OEM’s

yet follow the engine manufacturer’s

guidelines on how wiring/sensors are to

be placed and no two of them do it the

same way’’.

NHTSA believes that ATA’s

comparison between electronic engines

and ABS is not relevant. That

organization’s comparison fails to

portray the extent of problems that were

reported to have occurred with

electronic engines when they were first

introduced in the mid to late 1980’s.

The lower malfunction rates now being

experienced with electronic engines are

the result of having worked through

initial design and installation problems,

a pattern the agency notes is now

repeating with ABS, as it becomes more

widely installed and used. In addition,

ATA’s comments about wiring/sensor

placement on electronic engines appear

to imply that the lack of uniformity in

this regard adds complexity to the task

of maintaining these engines, rather

than implying that truck manufacturers

are improperly or inadequately

installing engines in vehicles they

produce. Unless there is some

compelling reason or requirement for

manufacturers to install a given

component in a single way, the fact that

they do it differently is to be expected,

given the need and desire for design

flexibility. The same flexibility is likely

to be true with ABS installations.

Electronic engines are in widespread

use within the trucking industry today.

It is therefore reasonable to infer that

truck manufacturers are installing them

properly. Based on the data collected in

its two fleet studies, the agency believes

that the carriers can and will be able to

successfully maintain ABS as well.

ATA further stated that the agency’s

thinking was ‘‘* * * seriously flawed

* * *’’ because the agency-supported

fleet study contained listings of ABS

malfunctions that were remedied with

only the expenditure of labor and did

not require repair or replacement of a

component part, with added partsassociated costs. ATA claimed that the

report’s inclusion of these type

malfunctions implied ‘‘* * * some

lesser class of failure’’. ATA’s reference

in this regard was to instances in which

a false- positive ABS malfunction

indication occurred which necessitated

an inspection and system reset, with no

other problem being found or remedy

needed.

NHTSA disagrees. Rather than

minimizing the consequences of these

occurrences, the inclusion of them in

the two reports highlighted the agency’s

concern about such events. During the

tractor portion of the study, they

occurred comparatively frequently with

88 of the 200 test tractors experiencing

a total of 290 intermittent malfunction

warning indications.45 The situation

improved markedly, however, in the

later trailer portion of the study. Here,

12 of the 50 test trailers experienced a

total of 15 of these false-positive

malfunction warnings.46 The cost

impact of these occurrences is noted in

the fleet study reports. The reports

further noted that such malfunctions

accounted for 45 percent of the total inservice maintenance costs for tractors

and 35 percent for trailers.

Notwithstanding these findings, the fact

that a significant reduction in the

frequency of these occurrences was

noted between the time of the tractor

and trailer portions of the study,

indicates that the reliability of the

components greatly improved.

ATA further implied that these types

of failures resulted in lost vehicle

productivity, because an affected

vehicle would have to be taken out of

service to remedy the situation.

Contrary to ATA’s assertion, none of the

test vehicles were pulled out of

operational service by the fleets as a

result of these malfunction indications.

Instead, corrections were made when

the vehicle returned to its dispatch

point and before it was next dispatched.

Further, no dispatch opportunities were

missed because of these incidents.

NHTSA notes that the agency’s fleet

study summarized the cost impact of

‘‘false-positive’’ ABS malfunctions.

Specifically, these incidents accounted

for 45 percent of the total in-service

maintenance costs for tractors and 35

percent for trailers. The agency’s fleet

study report summarized the cost

impacts as follows: In the case of

tractors, those costs were $0.00021 per

mile, while for trailers the figure was

$0.00015 per mile. These figures are

reasonable, given that it costs $1.38–

$1.54 per mile to operate a truck with

a driver.47 Moreover, based on the trailer

fleet study, NHTSA expects these costs

to decrease significantly over time, since

many of them were associated with ECU

malfunction warning algorithms that

ABS suppliers have since modified to

make them less prone to inappropriate

activation.

Based on the above considerations,

NHTSA concludes that there is no basis

for accepting ATA’s position that more

leadtime beyond that specified in this

final rule is needed to successfully

implement ABS use in heavy vehicles.

NHTSA further concludes that

maintenance costs associated with ABS

are neither excessive nor unreasonable

compared to other maintenance costs

and that these costs will not be

significantly reduced if the

implementation dates of this rule are

further delayed.

E. Requirements for Durability,

Reliability, and Maintainability

ATA requested that the Standard

include requirements to address the

durability, reliability, and

maintainability of ABSs. ATA was

concerned that premature degradation

of ABS performance would create a

safety risk associated with loss of ABS.

Specifically, that organization requested

requirements addressing corrosion

resistance and electromagnetic

susceptibility. It stated that such

requirements are ‘‘necessary to assure

that the equipment provided to meet the

stability and control requirements

proposed in this standard can do so

repeatedly.48’’

NHTSA concludes that separate

requirements addressing the durability,

reliability, and maintainability of ABS

are not needed at this time. As detailed

above, the ABS fleet evaluation

conducted by the agency on 200 tractors

and 50 trailers demonstrated that

current generation ABSs are durable,

reliable, and maintainable. Based on the

fleet study and comments by

manufacturers, NHTSA concludes that
13242 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

49 DOT HS 808 059, page 3–18; DOT 807 846,

page 3–23.

50Annual Report on Program Quality and

Effectiveness, Fiscal Year 1992, U.S. Federal

Highway Administration, Office of Motor Carriers,

June 1993

51Heavy Vehicle Air Brake Performance, National

Transportation Safety Board Report No. SS–92/01,

April, 1992.

separate component tests are not

necessary.

F. Alleged Safety Problems

ATA contends that current-generation

ABSs can fail ‘‘unsafe,’’ i.e., ABS

malfunction can result in the foundation

brakes becoming inoperative. That

organization states that this is a

‘‘significant * * * safety problem’’ and

cites five incidents, two of which

occurred during the agency’s fleet

studies, as corroboration for this

suggestion. No other commenter alleged

that current-generation ABSs fail in an

unsafe manner.

The issue raised by ATA concerns the

likelihood of ABS malfunctions that

would either reduce brake system

performance or render a vehicle’s

underlying brake system completely

inoperative. Based on the data collected

during the NHTSA’s in-service fleet

evaluation of ABS, the agency finds that

the likelihood of such occurrences is

negligible. Therefore, NHTSA concludes

that ATA’s concern is unwarranted and

unsubstantiated.

During the two-year evaluation of 200

ABS-equipped truck tractors, a total of

421 incidents were recorded involving

in-service wear related ABS

malfunctions. The vast majority (99.8

percent) of these malfunctions were

benign. When the ABS became

inoperative, the vehicle reverted to a

normally-braked vehicle without ABS

protection and remained fully

operational until the malfunction was

remedied. Similarly, during the twoyear evaluation of 50 ABS-equipped

semitrailers, 44 such incidents were

noted. All (100 percent) were benign.

Only one ABS malfunction incident

occurred during the tractor fleet study

that resulted in the vehicle having

reduced, braking performance. Even this

incident, which involved a

manufacturing defect in the surface

coating of a piston slide valve in the

modulator section of a drive-axle-only

ABS on one tractor, did not totally

compromise the brake performance.

When the ABS supplier involved found

the cause of this failure, a design change

was made to rectify the problem and all

the other test units in the fleet study

were retrofitted with the improved

design. Despite making this change, the

ABS supplier involved subsequently

chose not to produce this system. The

agency emphasizes that this failure did

not result in the complete loss of

braking power on the vehicle. When the

failure occurred, the vehicle

experienced reduced braking capability

on two of its five axles. The driver was

able to maintain control of the vehicle

and stop it. Despite the fact that it took

longer than usual for the vehicle to stop,

there were no adverse consequences as

a result of this incident.

As ATA acknowledged in its

comments, failures such as this are rare.

In this case, the failure was the result of

a manufacturing defect, an atypical

situation. This incident is not indicative

of a general flaw in presently designed

ABS systems of the type that would

support the contention that ABSs

typically fail unsafely.

By comparison, during the same time

period, the fleet studies reported 580

incidents involving the tractors, and 170

incidents involving the trailers, in

which repairs or replacements were

made to brake system components that

were not related to the ABS.49 These

malfunctions could have compromised

the brake system performance of the

affected vehicles. Included among these

were repairs or replacements of leaking

or faulty relay or quick release valves,

leaking or worn brake chambers or air

hoses, and other miscellaneous repairs

of leaking fittings. The agency notes

that, despite their potential gravity,

these failures went unheralded, and

were simply repaired when detected.

Fleet maintenance personnel expressed

no special concern about this type of

malfunction, treating them as routine

occurrences.

NHTSA’s fleet study experience

parallels the experience found during

roadside inspections of heavy vehicles.

FHWA’s Office of Motor Carriers 50,

reports that in 1992, 1,655,668 heavy

vehicles were inspected by state and

federal officials under the Motor Carrier

Safety Assistance Program (MCSAP),

and 461,715 (28 percent) of these were

placed out-of-service for mechanical

defects that were deemed significantly

hazardous enough to warrant repairs at

that location before the vehicle was

operated again. A total of 908,184 outof-service defects were noted, 54

percent (487,238) of which were brake

system related. The majority of these (68

percent) involved out-of-adjustment

brakes, but the remainder (157,717)

involved defects in either the

foundation or pneumatic portions of the

system (e.g., cracked brake drums,

chafed or worn air hoses, leaking brake

chamber diaphragms, etc.), all of which

could significantly compromise brake

system performance in a severe braking

maneuver. These data indicate that, on

average, nearly one of every ten in-use

heavy vehicles is operating with at least

one significant non-adjustment related

brake system defect, that, for whatever

reason, goes unnoticed and/or is not

repaired by fleet personnel, until the

condition is discovered in an

inspection. The National Transportation

Safety Board 51, among others, has

concluded that this situation is already

serious enough to warrant more ‘‘* * *

consistent attention to brake system

maintenance.’’

Problems associated with the

foundation brakes appear to far exceed

those caused by a potential malfunction

to the ABS. Moreover, neither the

frequency of ABS malfunctions nor their

consequences, as noted in the fleet

study, indicate that adding ABS will

worsen this situation. In fact, the agency

concludes that adding ABS will

significantly contribute to improving it

by partially compensating for brake

system force imbalances that result from

poorly performing or inoperative

individual brakes on a vehicle.

Ordinarily, under lightly loaded or

empty operating conditions, the

operative/properly performing brakes

attempt to compensate for the reduced

braking power absent from the

inoperative/poorly performing brake(s).

As a result, they over-brake and tend to

lock up as increasing levels of brake

pressure are applied in an effort to stop

the vehicle. Although ABS is not a

substitute for proper maintenance,

under these conditions, its addition to a

vehicle’s braking system will be

beneficial, since it will prevent lockup.

NHTSA emphasizes that the one

isolated incident identified in its fleet

study that involved an ABS malfunction

that compromised the vehicle’s braking

performance is markedly different from

those described in PACCAR. In that

case, it was argued that when an ABS

failed, the vehicle’s underlying brake

system was unsafe. The circumstances

that gave rise to such concerns are very

different from those of today. ABS

technology for motor vehicles was very

new in the 1970s. In response to

aggressive stopping distance

requirements and a prohibition against

wheel lockup, manufacturers equipped

their vehicles with ABSs and

extensively redesigned the pneumatic

and foundation brake portions of their

braking systems. The new foundation

brakes in many cases incorporated

highly aggressive brake linings. When

malfunctions occurred with a vehicle’s

ABS, the vehicle was left with a much

more aggressive and powerful

foundation brake system than the brake
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13243

systems that had been in general use.

Additionally, since the pneumatic

portion of the system was different from

what had been in use, brake application

and release timing on vehicles with

malfunctioning ABSs were also

different. Thus, for example, if the ABS

on an ABS equipped tractor became

inoperative, and the tractor was coupled

to a non-ABS-equipped trailer, the

tractor’s brakes still functioned but were

extremely incompatible with those of

the trailer. The tractor’s brakes applied

and released differently and were much

more aggressive. These differences led

to braking force imbalance problems

that were very disconcerting to drivers.

While situations such as this did not

constitute brake failures per se, drivers

nevertheless perceived the performance

of their vehicles to be very unacceptable

and termed these situations brake

system failures.

In the 1970s, there were several

highly publicized incidents in which

radio frequency interference (RFI)

problems caused the ABS to cycle

continuously during a brake

application, thereby greatly diminishing

braking power by venting brake system

air pressure. The agency notes that

manufacturers have completely

eliminated the potential for RFI

problems since current generation ABSs

have been designed with shielded

wiring systems and more sophisticated

electronics that are better able to

recognize spurious signals. No RFI

problems have been reported with

current-generation ABSs.

The numerous complaints of brake

system malfunctions reported by drivers

prompted the PACCAR court to find that

the agency had a responsibility to

determine that its regulations do not

produce a more dangerous highway

environment than that which existed

prior to government intervention.

NHTSA has determined that today’s

final rule requiring heavy vehicles to be

equipped with ABSs will result in a

significantly safer highway environment

than if no regulation were issued.

Unlike 20 years ago, the manufacturers

will not need to significantly redesign

their braking system or use aggressive

brake linings to meet stopping distance

requirements. Further, ABS is no longer

an immature technology. It has

undergone 20 more years of

development, been installed on tens of

thousands of European vehicles

pursuant to the 1991 ECE requirement,

and been fleet tested extensively in this

country by NHTSA and the industry.

NHTSA is aware of no consistent

pattern of incidents in this country in

which current generation antilock

systems have experienced malfunctions

like those that concerned the PACCAR

court. As for the incidents cited by ATA

alleging that an ABS malfunction

resulted in an unsafe condition, the first

one involving a manufacturing defect is

discussed above. The second incident

involved leaking air in the relay valve

portion of a combined relay valve/ABS

modulator valve on the steer axle of one

truck involved in the agency’s fleet

study. Strictly speaking, this is not an

ABS malfunction, since the air leak that

occurred involved the service brake

portion of this combined ABS/relay

valve. The leakage was caused by oily

sludge in the air system, which clogged

the relay valve, thereby allowing service

brake air pressure to vent, rather than

being directed to the brake chamber

controlled by that relay valve. The

vehicle was equipped with an

aftercooler type air cleaner/dryer. Such

a leak would result in reduced braking

performance, not total loss of the

vehicle’s brakes. This type of failure is

similar to the non ABS related

malfunctions that are described above

and which were noted in both the fleet

study and during roadside MCSAP

inspections.

ATA’s comments implied that the

ABS suppliers’ recommended solution

for this problem (i.e., that tractors be

equipped with desiccant style air

cleaners, in order to provide cleaner

air), was unacceptable and that to use

such cleaner/dryers demonstrates that

ABS require a higher level of

maintenance. NHTSA believes that it is

reasonable to expect that fleets will use

desiccant air dryers, or another type of

comparably performing air cleaning

system, since such systems will enhance

the durability and safety of tractor and

trailer braking systems by keeping the

pneumatic portion of the brake system

cleaner. The marketplace appears to

have recognized this fact and is

responding accordingly. Air cleaning/

drying systems are now being installed

on more than 80 percent of all new air

brake-equipped powered heavy

vehicles, with more than 90 percent of

these being the desiccant type. Based on

current usage, the agency anticipates

that air cleaning/drying systems will be

in almost universal use within the next

few years.

ATA provided few details about the

third incident cited in its comments.

That incident involved an ABS

equipped tractor trailer combination

participating in an ATA test program.

That organization stated that the vehicle

was ‘‘* * * generating consistent

stopping distance results when, in the

middle of one run, there was a loss of

braking which significantly increased

the stopping distance.’’ ATA offered no

explanation or reason for this outcome,

except to indicate that ‘‘* * * no

indication of an ABS failure by either

the tractor or trailer ABS warning lamps

* * *’’ was noted. Since ABS

malfunction was not indicated as the

reason for the unexplained increase in

stopping distance that occurred during

the test of one of its fleet member’s

trucks, there is no reason to believe that

this incident is indicative of an ABS

problem.

The fourth incident ATA cited

involved a vehicle that was retrofitted

with an ABS by the carrier and

experienced reduced braking

effectiveness during a test stop. Agency

discussions with ATA staff and with the

ABS supplier indicate that the vehicle

was a truck tractor that was tested after

the tractor had been equipped with an

upgraded ABS. The ABS supplier

subsequently concluded that a soldered

connection had broken in the ECU and

that this may have caused intermittent

activation of one of the four modulators

controlled by the ECU. Based on its

investigation of the ECU in question,

and its knowledge of how the ABS was

configured, the ABS supplier believed

that the truck had experienced a

reduction in braking, but not a total loss

of braking power. NHTSA emphasizes

that this incident is atypical and not

indicative of normal ABS performance,

since the fleet study identified no

similar incident.

The fifth and final incident described

by ATA is reminiscent of the ‘‘phantom

failures’’ that were reported to have

occurred with early 1970’s vintage

ABSs. The causes of most of those

‘‘failures’’ were neither fully explained

nor linked to ABS flaws. In this

incident, the accident report simply

claimed that ‘‘* * * the vehicle would

not stop.’’ ATA’s account of this

incident indicates that no problems

were found in either the tractor’s or the

trailer’s braking system after this

incident.

NHTSA notes that other factors such

as slippery road conditions or

improperly adjusted brakes are just as

likely as ABS malfunction to have

caused the driver to believe that the

vehicle would not stop or that it was

stopping too slowly. Without additional

information, it is not possible for the

agency to assess the cause of this

incident, or respond to the implication

that the incident is somehow indicative

of an inherent ABS flaw.

Contrary to ATA’s allegations that

existing ABSs have significant safety

problems, most commenters, including

vehicle and brake manufacturers, appear

to agree with NHTSA’s assessment that

current generation ABSs are safe and
13244 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

52The eight-year time period for this interim

proposal was intended to represent the average

lifespan of a truck tractor.

reliable. Unlike the 1970’s when several

vehicle and brake manufacturers

objected to the rulemaking, and ATA,

TEBDA, and PACCAR challenged the

antilock standard in court, comments to

the September 1993 NPRM indicate that

vehicle and brake manufacturers now

generally believe that the proposal was

appropriate and today’s antilock

systems provide significant safety

benefits. Along with the safety advocacy

groups, HDBMC, AAMA, GM, Rockwell

WABCO, Midland-Grau, and Bendix

generally supported the agency’s

September 1993 proposal to require

heavy vehicles to be equipped with an

antilock brake system. No vehicle or

brake manufacturer opposed the

rulemaking, aside from objecting to

details in the proposal. These

commenters stated that ABS will

improve vehicle safety by providing

improved braking and vehicle stability

and control. Specifically, such systems

will prevent wheel lockup, thereby

preventing jackknifing and other loss of

control accidents. Neither the vehicle

nor brake manufacturers expressed

concern that today’s ABSs would fail in

such a way as to compromise basic

braking performance, as ATA alleges.

Strait-Stop stated that computerized

ABSs will not prevent brake fade since

these systems do not avoid or minimize

heat build up. As a result, it alleged that

computerized ABSs will not avert

accidents related to runaway trucks. In

contrast, it stated that its system results

in cooler and therefore better brakes.

The agency is not in a position to

respond to Strait-Stop’s claim that its

product minimizes brake heat build up.

Strait-Stop did not submit any data to

substantiate its claim and the agency

has no data of its own on this issue.

NHTSA emphasizes that Strait-Stop

has not suggested that an ABS will

contribute to brake heat build-up, but

merely stated that it will not reduce

brake heating. Reducing brake heating,

and thus the potential for brake fade, is

not one of the design goals of an ABS,

nor is it the focus of this rulemaking.

ABS is intended to prevent wheel

lockup. Brake fade is most typically

caused by one or more of the brakes on

a vehicle being out of adjustment,

thereby causing the other properly

adjusted brakes to have to absorb a

disproportionate share of the kinetic

energy that needs to be dissipated when

a fully loaded heavy truck attempts to

descend a grade. In this situation, the

properly adjusted brakes are

overworked, causing them to overheat

and fade. This in turn results in a loss

of braking power. Equipping a vehicle

with either ABS or the Strait-Stop

product will not rectify brake

maladjustment(s). Likewise, equipping a

vehicle with ABS will not decrease the

motor carriers’ existing need to properly

adjust their vehicles’ brakes in order to

avoid brake overheating and fade on

downgrades.

G. ABS Malfunction Indicator Lamps

Since the discussion on ABS

malfunction indicator lamps is lengthy,

NHTSA first summarizes its decisions

regarding this subject and then

addresses the details of each decision.

In today’s final rule, NHTSA is

amending Standard No. 105 and

Standard No. 121 to require all powered

heavy vehicles to be equipped with an

in-cab lamp for indicating a malfunction

of the ABS on that vehicle. In addition,

the final rule requires truck tractors and

other trucks that are equipped to tow

trailer(s) to be equipped with a second

in-cab lamp. The purpose of the second

lamp is to indicate malfunctions in the

trailer ABS. Finally, trailers

manufactured during an interim eightyear period are required to be equipped

with an external malfunction indicator

lamp.

Each of these ABS malfunction

indicator lamps is required to activate

whenever there is a malfunction

affecting the generation or transmission

of response or control signals in the

ABS that it is monitoring. In addition,

the lamp is required to store information

about a malfunction in that ABS until

the next start up. Vehicle manufacturers

are prohibited from equipping their

vehicles with a device to disable any

malfunction indicator lamp.

NHTSA also has amended the failed

ABS system requirements to prohibit

any change in brake timing in the event

of an ABS malfunction that affects the

generation or transmission of response

or control signals.

1. Number and Location; Duration of

Trailer Requirement

Standard No. 121 now requires that

each tractor, truck, and bus be equipped

with an in-cab lamp that indicates

malfunctioning in the ABS of that

vehicle. In the NPRM, the agency

proposed that truck tractors be equipped

with a second in-cab lamp that would

indicate malfunctions in the trailer ABS.

The agency proposed further that the incab lamps be required to be ‘‘mounted

in front of and in clear view of the

driver.’’ The agency noted that this

requirement is essentially the same as

the current requirements in Standard

No. 105 and Standard No. 121. These

existing provisions require a continuous

message to a driver when the ignition is

in the ‘‘on’’ or ‘‘run’’ position.

NHTSA has decided to adopt its

proposal that each truck tractor and

single unit vehicle be equipped with an

in-cab lamp to indicate malfunctions in

the ABS of that vehicle. The agency

believes that it is essential that a driver

be notified about an ABS malfunction,

so that the problem can be corrected.

The commenters, including vehicle

manufacturers and brake manufacturers,

generally supported the proposal for an

in-cab malfunction indicator. Only

Strait-Stop opposed this proposal,

stating that it would necessitate the use

of an electrical ABS.

NHTSA proposed to require that each

trailer equipped with ABS be capable of

sending a signal about a malfunction in

the trailer ABS to a towing vehicle, and

that all powered towing vehicles

equipped with ABS have an in-cab lamp

that would be activated when the

towing vehicle receives signals

indicating malfunctions in a trailer ABS.

In addition, the agency proposed to

require the installation of an external

ABS malfunction lamp on trailers and

dollies manufactured during the eightyear period after trailers are first

required to be equipped with ABS.52

The agency believed that the external

lamp would not be necessary on new

trailers manufactured after the end of

that period because, by that time, a

significant majority of tractors in the

heavy vehicle fleet, which would be

responsible for the vast majority of

miles driven by tractors, would be

manufactured in compliance with the

requirement for an in-cab lamp capable

of receiving a malfunction signal from a

trailer.

Commenters offered mixed views

about requiring each towing vehicle to

have a separate in-cab lamp to indicate

a malfunction in a trailer ABS. Bosch,

Midland-Grau and several other

commenters supported the agency’s

proposal for requiring tractors to have

two separate in-cab ABS malfunction

indicator lamps: one indicating

malfunctions in the tractor ABS, and the

other, malfunctions in the trailer ABS.

They stated that a driver would be able

to respond to and possibly alter braking

actions in the event of an ABS

malfunction during emergency

situations if the driver knew whether

the malfunction was in the tractor ABS

or in the trailer ABS. Midland-Grau

strongly opposed having a single

indicator, claiming that the tractor lamp

sequence would camouflage the

situation in which the trailer ABS

lacked power. Midland-Grau further
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13245

53 ‘‘An In-Service Evaluation of the Performance,

Reliability, Maintainability, and Durability of

Antilock Braking Systems for Semitrailers,’’

(October 1993),

stated that a single lamp would make it

difficult to identify which vehicle had a

malfunction without using separate

diagnostic equipment.

ATA, Allied Signal and fleet operators

opposed the proposal that tractors have

a separate in-cab malfunction lamp for

the trailer ABS, claiming that these

indicators were ‘‘neither needed nor

practicable at this time.’’ AAMA

supported a single in-cab malfunction

lamp for each tractor to indicate an ABS

malfunction on either the tractor or the

trailer. It believed that there is no safety

need for the driver to know immediately

whether the ABS malfunction is in the

tractor or the trailer. While AAMA

stated that separate indicators would

cause needless complexity to the

instrument panel, it did not state that

such a requirement would be

impracticable.

After reviewing the comments and

other available information, NHTSA has

decided to require each powered towing

vehicle to have one in-cab malfunction

lamp for the towing vehicle’s ABS and

another in-cab lamp for the trailer ABS.

The agency believes that the ABS trailer

fleet study final report 53 indicated that

drivers are more likely to observe an incab malfunction indicator for a trailer

than a malfunction indicator lamp on

the front of the trailer, particularly if the

trailer ABS is powered through the

stoplamp circuit. This is so because the

stoplamp circuit only activates when

the brake is applied, a time when the

driver will be paying more attention to

the traffic conditions ahead. The report

also indicated that ABS malfunctions

were present on some vehicles for a long

time, but were not reported, primarily

because the drivers ‘‘spent very little

time looking in their mirrors while

stopping’’ and did not notice that the

trailer ABS malfunction lamp was

lighted.

NHTSA does not agree with AAMA’s

recommendation for a single in-cab

malfunction lamp for both the tractor

and trailer antilock systems. As

Midland-Grau stated, a driver would not

be able to identify which vehicle in a

combination was experiencing an ABS

malfunction if only a single in-cab

malfunction indicator lamp were

required, since a single in-cab lamp

would result in some trailer ABS

malfunctions being camouflaged.

Further, notwithstanding comments by

AAMA and ATA that separate in-cab

lamps add unnecessary complexity,

combination vehicles in Europe have

been equipped with such indicators for

several years.

NHTSA believes that it is appropriate

also to require an external malfunction

lamp on trailers and dollies for the

eight-year period during which some

non-ABS-equipped tractors are likely to

be towing ABS-equipped trailers. The

external lamp will indicate trailer ABS

malfunctions to the driver of a non-ABS

tractor, and will also assist Federal or

State inspectors in determining the

operational status of a trailer’s antilock

system. Nevertheless, notwithstanding

Midland-Grau’s recommendation to

require the external trailer lamp

permanently, the agency has decided

not to do so, since after the transition

period, the vast majority of trailer

malfunctions would be expected to be

indicated in-cab.

In response to the SNPRM, TTMA

stated that instead of locating the trailer

lamp on the ‘‘roadside nose of trailer, it

should be located near the electronic

control unit where the driver can check

it during his walk-around inspection of

the tractor trailer combination.’’ It stated

that some ABS may require that the

trailer be moved at a low speed (less

than 5 mph) to activate the check

function (i.e., some antilock systems

check the status of wheel speed sensors

by looking for proper signals as the

vehicle goes from 0 to 8 mph). TTMA

also commented that it is not practical

to mount an ABS malfunction lamp on

converter dollies in a location in which

the lamp will be visible in a driver’s

rearview mirror, yet not be susceptible

to damage.

While NHTSA recognizes the

possibility of some susceptibility to

damage, placing the external

malfunction lamp in a different location

on dollies would largely negate its

benefits, because it would not be visible

to the driver. For that reason, the agency

has decided that the requirement will

apply to dollies as well as other trailers.

NHTSA is revising Standard No. 101,

Controls and Displays, to clarify that the

malfunction indicator lamp must be

labeled with the words ‘‘ABS’’ or

‘‘Antilock’’ for trucks and truck tractors

with air brakes. The agency notes that

Table 2 in Standard No. 101 currently

refers to Standard No. 105, but makes no

reference to Standard No. 121. For the

in-cab trailer ABS malfunction

indicator, NHTSA is adopting the

identification of controls in Standard

No. 101 (i.e., ‘‘Trailer ABS’’ or ‘‘Trailer

Antilock’’) as proposed in the NPRM.

2. Conditions for Activation

Before this amendment, S5.1.6 of

Standard No. 121 required the ABS

warning signal to activate ‘‘in the event

of total electrical failure.’’ In the NPRM,

NHTSA proposed that the malfunction

indicator lamp activate ‘‘in the event of

any malfunction in the system.’’ The

agency tentatively concluded that a

driver needs to be informed about any

malfunction because every ABS

malfunction could affect the way in

which drivers respond to a safety

problem. The agency invited comments

about when and in what situations the

malfunction lamp should be required to

activate.

Fleet operators, AAMA, Rockwell

WABCO, HDBMC, and Midland-Grau

stated that the proposal to require the

ABS malfunction lamp to activate upon

‘‘any’’ malfunction in the antilock

system is impracticable, unreasonably

costly, and overly broad. These

commenters believed that it is only

practicable and realistic for current

technology to detect certain types of

electrical malfunctions, namely those

involving electrical discontinuities or

electronic malfunctions, not mechanical

failures of ABS components. AAMA and

HDBMC stated that it would be

unreasonably costly to provide

continuous monitoring of all ABS

malfunctions because many possible

malfunctions are temporary in nature or

may not directly affect ABS

performance.

Commenters suggested various ways

to narrow the requirement. Rockwell

WABCO recommended that the ABS

malfunction indicator activate whenever

a ‘‘malfunction occurs affecting the

generation and/or transmission of

response and control signals.’’ It stated

that this should be a minimum

requirement applicable to electrical

faults in sensors, control valves and

associated wiring. ATA, Allied Signal

and fleet operators stated that a more

practicable requirement for the ABS

malfunction indicator would be to

require activation in the event of (1)

failure to sense angular rotation, (2)

failure of the controlling device to

generate controlling output signals, and

(3) failure to transmit controlling signals

to devices that modulate brake actuating

forces.

Based on the comments and other

available information, NHTSA has

decided to require ABS malfunction

indicator lamps to activate for any

malfunction that affects the generation

or transmission of response or control

signals in the vehicle’s antilock brake

system. The requirement does not apply

to malfunctions such as sticking

solenoid valves, small air leaks in the

solenoid valve, or mechanical binding

of a valve. The agency agrees with the

commenters’ arguments that the

malfunction indicator requirement
13246 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

54By pattern, the agency meant a common way

that an indicator would react in response to a

malfunction. Specifically, upon a failure, the

indicator would activate and provide a continuous

yellow signal.

should be modified because requiring

activation in the case of ‘‘any’’

malfunction might have been

impracticable. Under the modified

requirement, only those malfunctions

that are directly related to the antilock

brake system must be indicated.

Applying the indicator requirement to

the ‘‘generation’’ of response and

control signals serves to cover the

components in the ABS that produce

these signals. These components

include wheel speed sensors which

produce response signals for the control

unit, and the control unit which

produces control signals for input into

the valves that modulate brake pressure.

Applying the indicator requirement to

the ‘‘transmission’’ of response and

control signals serves to cover the

components in the ABS through which

the generated signals are transmitted.

These components include wiring,

connectors, belts used in mechanical

systems, and all components through

which a generated signal can be

transmitted.

NHTSA notes that the generation and

transmission of signals in ABSs are

typically electrical in nature.

Nevertheless, the agency has decided

not to include the term ‘‘electrical’’ in

the requirement so that the malfunction

indicator requirements are applicable to

non-electrical, i.e., mechanical, ABSs as

well. Accordingly, mechanical ABSs

will have to comply with the

malfunction indicator requirements.

3. Activation Protocol for Malfunction

Indicators

In the NPRM, NHTSA proposed

standardizing the ABS malfunction

indicator lamp system so that trucks and

trailers would have the same activation

pattern 54 and same colored lamps to

indicate an ABS malfunction. The

agency believed that such a common

indicator pattern would reduce

ambiguity and confusion and expedite

Federal and state inspections. The

agency proposed that each ABS

malfunction indicator lamp be yellow

and activate when a problem exists but

not activate when the system is

functioning properly. In addition, the

proposal would have required that

whenever the ABS receives electrical

power, the indicator lamp would

provide a continuous visible indication

until a function check of the ABS was

completed. Under the proposal, the

check function would have to be

completed and the lamp extinguished

(assuming that there was no underlying

condition that warranted activating the

lamp) before the vehicle was driven.

Rockwell WABCO stated that both the

existing format in which a continuous

signal is activated upon the ABS’s total

electrical failure and the proposed

format for the ABS malfunction lamp

are acceptable approaches. That

company strongly recommended that

the agency adopt a single approach for

all heavy vehicles. Midland-Grau

accepted the agency’s proposal to

require the lamp to extinguish before

the vehicle is driven, even though it was

concerned about an incomplete sensor

check function.

AAMA stated that the agency ‘‘should

allow the ABS malfunction indicator to

be either illuminated or extinguished

during low speed drive away after keyon.’’ That organization requested that

the agency affirm its view that the

proposed language did not require the

ABS indicator to be either illuminated

or extinguished during low-speed

driveaway after key-on. That

organization was concerned that the

proposal might prohibit certain existing

systems that have an illuminated

indicator until the vehicle reaches a

speed of five to seven mph after key-on.

Bosch recommended that an ‘‘on-offon’’ blink sequence be used to indicate

an ABS malfunction when the ignition

is turned to the ‘‘on’’ or ‘‘run’’ position.

It believed that this pattern would

inform a relief driver of the presence of

a malfunction and would assist Federal

and State inspectors in determining the

operational status of the vehicle’s ABS.

After reviewing the comments and

other available information, NHTSA has

decided to require the malfunction

indicator lamp to activate when a

problem exists and not activate when

the system is functioning properly.

Under this requirement, the indicator

lamp is required to provide a

continuous indication until a function

check of the ABS is completed. The

agency believes that this ABS

malfunction lamp format, together with

the requirement that the system stores

malfunctions until the next key-on, is

necessary to enable Federal and State

inspectors to determine the operational

status of an ABS without moving the

vehicle. Elsewhere in today’s Federal

Register, the FHWA’s Office of Motor

Carrier Standards is issuing a notice

explaining its intent to issue a

companion regulation requiring that the

ABSs on heavy vehicles be operational.

NHTSA further notes that all vehicles

will be required to have a continuously

burning lamp in response to a

malfunction. Accordingly, this

requirement will standardize the

activation format for all vehicles. Under

that format, the ABS malfunction lamp

extinguishes after a function check, and

before the vehicle is driven. Since light

vehicle ABSs currently use this format,

the agency believes that heavy vehicle

drivers will find it easier to understand

the heavy vehicle ABS malfunction

indicator if the same format is used.

Furthermore, the adopted format is also

consistent with the ECE requirement

and therefore is consistent with the goal

of international harmonization.

NHTSA has concluded that the ‘‘onoff-on’’ blink sequence recommended by

Bosch to indicate a malfunction during

vehicle start-up would place an

unwarranted burden on the driver, who

would have to pay close attention to the

malfunction lamp to observe the blink

sequence during vehicle start-up and

drive-away. Therefore, the agency

rejects this recommendation.

4. Signal Storage

In the NPRM, NHTSA proposed that

the ABS indicator lamp system be

capable of storing information regarding

any malfunction that existed when the

ignition was last turned to the ‘‘off’’

position. For instance, if the wheel

speed sensors were malfunctioning

before the vehicle was turned ‘‘off,’’ the

system would be required to store a

signal for that malfunction. As a result,

the malfunction would be displayed

when the vehicle was turned ‘‘on’’

again, as part of the function check.

AAMA, Midland-Grau, Rockwell

WABCO and several other commenters

opposed the proposal to require the

storage of ABS malfunctions that exist

when the ignition is turned to the ‘‘off’’

position. AAMA stated that it is not

appropriate to mandate this capability,

claiming that many error messages are

spurious or represent transient

conditions, and therefore do not warrant

automatic reactivation the next time the

key is turned to the ‘‘on’’ position. It

further stated that if a malfunction is

non-transient, then the warning will

reappear and that therefore it need not

be stored. Midland-Grau believed that

the proposal was design restrictive and

would eliminate systems that do not

have non-volatile memory (i.e., a system

that remembers malfunctions when the

system is shut down). Rockwell

WABCO stated that this area does not

need to be regulated, even though it

acknowledged that all current electronic

ABS have non-volatile memories to

store and communicate current and past

malfunctions. After reviewing the

comments and other available

information, NHTSA has decided that

the malfunction storage requirement is

necessary to ensure that relief drivers
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13247

55 Section S5.5.2 of Standard No. 105 requires

that in the event of any failure in the antilock

system, the vehicle must be capable of meeting the

stopping distance requirement of 613 feet, as

specified for a service brake system partial failure.

and Federal and State inspectors are

advised about any malfunctions in a

vehicle’s ABS without having to move

the vehicle. This capability is important

since inspectors would need to

determine the operational status of the

vehicle’s ABS without moving the

vehicle. Moreover, this capability is

necessary since the agency has decided

to require that the ABS malfunction

indicator lamp extinguish before the

vehicle is driven, provided that there is

no existing ABS malfunction that

warrants activation of the indicator.

NHTSA disagrees with AAMA’s claim

that nontransient malfunctions will

always reappear at the next key-on and

therefore do not need to be ‘‘stored.’’ A

nontransient malfunction of the wheel

sensor, which involves the generation of

a wheel speed signal, is typically

detected only when the vehicle is

moving at a speed exceeding 8 to 10

mph, since a signal is only produced

when the wheel rotates at some

threshold wheel speed. Therefore, no

signal is generated and hence no sensor

malfunction is indicated if the vehicle is

stationary. As explained in the NPRM

and in the previous paragraph, one

reason for requiring malfunctions to be

stored is to ensure that preexisting

malfunctions involving sensors are

indicated before the vehicle is driven.

5. Disabling Switch

NHTSA, in response to a rulemaking

petition from ATA, proposed in a

separate NPRM to allow a switch that a

driver could use to turn ‘‘off’’ and ‘‘on’’

the in-cab malfunction lamp for a

vehicle’s ABS. (58 FR 50732, September

28, 1993.)

Advocates and vehicle and brake

manufacturers strongly opposed the

proposal. AAMA, Bosch, and MidlandGrau believed that such a switch would

encourage drivers to disable the

malfunction indicator of an important

safety system, and thus set an

undesirable precedent for allowing

mechanisms that would disable other

vehicle safety systems. These

commenters stated that a constant

reminder of a malfunction is the best

way to inform drivers of a malfunction

condition and encourage them to seek a

repair of an ABS malfunction. In

addition, they claimed that if the switch

were used to turn off the malfunction

lamp and the ignition remained ‘‘on,’’ a

relief driver would not necessarily be

informed of an ABS malfunction unless

the relief driver used the switch to

reactivate the malfunction indicator.

ATA, Allied Signal, and fleet

operators supported the proposal to

allow an optional switch for turning the

ABS malfunction indicator off, claiming

it would enable the driver to prevent the

malfunction indicator from being a

distraction, especially at night when the

amber light can appear to be excessively

bright.

NHTSA recognizes that some drivers

view the malfunction indicator as an

annoyance and thus might favor having

a switch to turn it off. The agency is also

aware of isolated cases in the truck

tractor ABS fleet study in which

malfunction indicators were disabled or

taped over. Nevertheless, NHTSA agrees

with AAMA and the brake

manufacturers that permitting a

disabling switch is inconsistent with

motor vehicle safety. The information

about a malfunction of an important

safety system such as an antilock brake

system should be communicated to the

driver and should not be disregarded.

Allowing drivers to turn off the ABS

malfunction indicator would reduce the

likelihood that a malfunction would be

reported and corrected in a timely

fashion. Use of such a switch might

mask a potential safety problem, since

an ABS malfunction could go

undetected by the driver, if the

disabling switch were activated.

Allowing such a switch would also

implicitly condone actions by some

drivers that disable the malfunction

indicator, since the agency would be

allowing a disabling switch based on the

argument that without a disabling

switch drivers would defeat the switch.

Moreover, allowing a malfunction

indicator to be turned off would be

inconsistent with Standard No. 101.

Based on the above considerations,

NHTSA has decided not to permit an

optional disabling switch.

NHTSA notes that ATA’s concern

about driver distraction may be reduced

if the antilock malfunction indicator is

dimmed at night. In specifying

requirements for the illumination of

various controls and displays including

the ABS malfunction indicator, Section

S5.3.4(b) of Standard No. 101 states that

The means for providing the required

visibility may be adjustable manually or

automatically, except that the telltales and

identification for brakes, highbeams, turn

signals, and safety belts may not be

adjustable under any driving condition to a

level that is invisible.

Under this provision, an ABS

malfunction lamp may be manually or

automatically dimmed, provided that it

is still visible to the driver.

Nevertheless, the agency emphasizes

that a malfunction indicator that is not

visible to the driver would be

prohibited.

6. ABS Failed System Requirements

Section S5.5.1 of Standard No. 121

currently requires that the application

and release times of the service brakes

not increase when there is an electrical

failure in the ABS. In the NPRM,

NHTSA proposed removing the word

‘‘electrical.’’ That change would

prohibit any malfunction in an ABS,

whether or not electrical, from

increasing the application and release

times of the service brakes. The change

would also make the requirement

applicable to nonelectronic ABSs.

ATA stated that the proposed

requirement in Standard No. 121 for

failed ABSs would be difficult to meet.

It further stated that the failed ABS

requirement for heavy vehicles in

Standard No. 105 is more reasonable

than the proposed requirements in

Standard No. 121,55 since some types of

ABS malfunctions in a vehicle with air

brakes, such as a leaky valve, could

result in an increase in service brake

actuation and release times.

NHTSA acknowledges that the

proposed failed ABS requirement for

heavy vehicles in Standard No. 121 is

more stringent than the requirement in

Standard No. 105. The agency could

resolve this difference by making

Standard No. 105 more stringent by

deleting the word ‘‘electrical’’ or by

amending Standard No. 121 to prohibit

any change in brake timing in the event

of certain, but not all, ABS

malfunctions.

After reviewing the alternatives,

NHTSA has decided to revise Standard

No. 121 to prohibit any change in brake

timing in the event of those ABS

malfunctions that affect the generation

or transmission of response or control

signals. The agency believes that this

modification will ensure that the brake

system reverts to normal braking

without antilock control, in the event of

such a malfunction in the antilock

system. NHTSA notes that this

modification parallels the change the

agency made to the requirements

governing the types of malfunctions that

must be indicated by the malfunction

lamp. This requirement will not apply

to mechanical ABS malfunctions such

as sticky valves. While mechanical

malfunctions do happen, electrical

malfunctions are far more prevalent.

The agency believes that simply

deleting the word ‘‘electrical’’ would

have made the requirement too broad

and potentially impracticable, while
13248 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

56Multiplexing is the process of combining

several measurements for transmission over the

same signal path.

57Reference Table 3.4, DOT Report No. HS 808

059.

58 DOT HS 808 059, Table 3.4, page 3–27.

leaving the word in without additional

changes would make the requirement

too narrow.

NHTSA notes that Standard No. 105’s

stringency cannot be increased in this

final rule because the agency did not

propose amending that Standard’s failed

ABS requirements. Nevertheless, the

agency may conduct future rulemaking

to make Standard No. 105’s ABS failed

systems requirements more consistent

with the requirements in Standard No.

121 and proposed Standard No. 135.

H. Power Source

Section S5.5.2 currently permits the

power source for trailers equipped with

ABSs to be either the stop lamp circuit

or a separate electrical circuit

specifically provided to power the

trailer ABS. In the NPRM, NHTSA

proposed that ABSs be required to

receive full-time power through a

separate circuit, and to have backup

powering through the stop lamp circuit.

The agency tentatively decided that a

full-time power source would be

necessary to ensure that adequate power

for the trailer’s ABS is available,

particularly for doubles and triples, and

that a driver is aware of any ABS

malfunction related to the trailer, since

the stop lamp circuit is powered only

when brakes are applied.

The commenters had mixed views

about whether full-time power for trailer

ABSs should be provided through a

separate circuit. AAMA, ABS suppliers,

TTMA, and Advocates believed that the

agency’s proposed approach is

appropriate and that the industry will

be able to develop appropriate voluntary

standards through the SAE for electrical

circuits or connectors. Upon

standardizing with one approach,

uniformity would be ensured. MidlandGrau stated that it ‘‘strongly supports’’

the agency’s proposal for full-time

powering for the following reasons:

1. The antilock systems being

produced today are very reliable, but

only as reliable as the power supply

circuit which is supplying power to the

antilock system.

2. Having continuous power to the

trailer ABS will allow for full-time

diagnostics continually updating the

driver of the status of the trailer antilock

system, and not just during braking.

3. A separate electrical circuit is

needed to have adequate and reliable

power available should all the solenoids

in the control valves be activated in

double and triple combinations.

4. To provide incentive to the

industry (SAE, TTMA, TMC, etc.) to

develop a ‘‘common’’ circuit for ABS on

trailers, which may or may not

ultimately involve a separate connector.

5. To facilitate the use of higher

capability trailer antilock systems, along

with other electronic systems such as

low air pressure, height sensing, and

electronic braking.

Midland-Grau further stated that

‘‘Because of cost, most fleets would

prefer to power through the stop lamp

switch not realizing that they are asking

for the ABS reliability problems of the

late 1970s to reappear again.’’

ATA and fleet operators opposed

requiring full-time power for trailer

ABSs. ATA stated that this requirement

is an untested, unnecessary, and costly

burden that NHTSA did not justify on

a safety basis. ATA is concerned that a

full-time power requirement would

result in significant maintenance and

reliability problems, basing its claims on

the agency’s fleet study. ATA also stated

that requiring full-time power is

premature since the industry is working

on multiplexing systems,56 which,

when fully developed and proven,

would provide many opportunities for

powering accessories on trailers.

In response to the SNPRM, ATA

elaborated on its initial comments

opposing a requirement that trailer

ABSs be electrically powered using a

separate electrical circuit. ATA alleged

that the requirement could not be

justified and that no practicable method

had been demonstrated for providing

this separate source of power.

Specifically, it stated that NHTSA’s fleet

study did not identify a single electrical

powering system that performed in a

reliable manner in the test. ATA further

stated that it is impermissible for the

agency to require a separate dedicated

circuit after it had permitted stop signal

powering as an option. (57 FR 30911,

July 13, 1992.) It claimed that the

agency has not justified what it terms a

‘‘proposed rescission of the prior

rulemaking decision to allow power

through the stop lamp circuit.’’

NHTSA has decided to adopt the

proposed full-time power requirement

for trailer ABSs. The wording of the

standard has also been amended to

clarify that towing vehicles must have a

corresponding separate circuit. By

requiring a separate circuit, the agency

will ensure the strongest possible source

of electrical power from the tractor to

ensure the functioning of all the ECUs

and modulators that are employed in

the antilock brake system, or systems,

on single trailers, or multiple trailers

and converter dollies in multitrailer

combinations. Another important safety

justification is that a separate circuit

will ensure a continuous malfunction

indication whenever a malfunction

exists. As noted above, an ABS

malfunction indicator powered by a

stop lamp circuit would function only

when the driver is applying the brakes.

During braking, a driver would most

likely be concentrating on traffic

conditions ahead, and would therefore

be less likely to see an ABS malfunction

indication on the trailer. However, a

driver is more likely to be aware of a

trailer ABS malfunction, if the tractor

has an in-cab malfunction indicator for

the trailer ABS, since a continuous

malfunction indication could be more

noticeable.

Typically, shared circuits that power

other electrical devices besides the

trailer ABS, such as stoplamps, cannot

provide as much electrical power to the

ABS as can a separate circuit dedicated

to powering only the trailer ABS. This

was demonstrated during the agency’s

trailer fleet study 57 in which all the

alternative approaches that utilized a

separate dedicated electrical circuit to

power the ABS, (except one approach

involving the trailer battery approach,

which has been abandoned by the ABS

supplier that suggested it), provided

higher voltage levels than did the shared

stoplamp circuit system approach. The

data shown in the table cited in

Footnote 33 58 were for single

semitrailer combinations. Voltage levels

would have been even lower had

doubles or triples combinations been

part of the fleet study.

If electrical voltage levels drop below

7–10 volts, an ECU cannot function

properly and will automatically shut

down. The system will automatically

reset itself if sufficient power is once

again provided. However, during

periods of low power, the ABS will not

operate. The likelihood of power

dropping below the point at which the

trailer ABS shuts down increases as the

number of additional stoplamps, or

other power draining devices, such as

ABS ECUs and modulators, increases.

Trailer ABS systems on a single

semitrailer typically consist of one ECU

and one or two modulators. A twotrailer combination (i.e., a double)

would utilize 3 ECUs and 3 to 6

modulators, while a three-trailer

combination (i.e., a triple) would utilize

5 ECUs and 5 to 10 modulators. While

the electrical current draw of ECUs is

minimal, modulators typically draw 2–

2.5 amps each. Depending on a system’s

configuration, the ABS on a single

semitrailer could draw 2–5 amps, that
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13249

59Herein after referred to as the 15-pin plug.

on a doubles combination could draw

6–15 amps, and that on a triple

combination 10–25 amps. If a stoplamp

circuit of the existing 7-pin cable

connector/plug system were used to

power the trailer ABS, the current draw

of the stop lamp bulbs, added to that of

the ABS, would create an overall

current draw that could exceed 45 amps

on a triples combination. Under such

levels of current draw, there is a greatly

increased likelihood that the ABS will

no longer function on the second and

third trailers in a triples combination.

At present, standard industry practice

throughout the trucking industry is to

provide electrical power for a trailer

from the tractor through a cable and

connector/plug assembly, the SAE J560

connector. This connector uses a 7-pin

configuration, with six power circuits

and one common ground. All six power

pins are now utilized for one electrical

function or another.

Although never directly stated, ATA’s

comments appear to be based on the

premise that NHTSA’s proposed

requirement for a separate circuit is a

directive that a second separate tractorto-trailer cable and connector/plug

system be used. Such a requirement

would preclude the continued exclusive

use of a single SAE J560 connector.

However, the agency wishes to clarify

that a second separate connector is not

required. Accordingly, the agency has

not specified a set method for providing

the separate circuit. The agency

intentionally left this choice to the

industry in an effort to provide design

latitude.

NHTSA notes that there are many

alternative ways of providing a separate

circuit to power ABS. During the trailer

fleet study, the agency evaluated several

alternative methods of providing

electrical power. To provide a baseline

for comparisons with other approaches,

the stoplamp circuit of the standard

tractor-to-trailer electrical cable/

connector supplied power to the trailer

ABSs for two of the five participating

fleets. For these systems, the ABS

received power every time the

stoplamps were activated, but received

no power when the brakes were not

being applied.

In addition, NHTSA evaluated three

distinct methods of supplying a

constant source of electrical power to

trailer ABSs. First, one fleet used a 15-

pin ‘‘halo’’ cable/connector/plug system

(supplied by the Cole Hersee

Company,59 which completely replaced

the SAE J560 cable/connector/plug. Two

of the additional 8 pins (one for power,

the other for a separate ground as well)

were used to power the trailer ABSs.

Second, another fleet used a second 6-

pin connector/plug/cable, with backup

power provided by the stoplamp circuit

of the SAE J560 connector. Third,

another fleet used an auxiliary battery

which was mounted on the semitrailer

and was charged by electrical power

from the semitrailer’s refrigeration unit.

NHTSA is studying the SAE J560

stoplamp-circuit-powered approach

further, using ABS-equipped LCV

combinations (known as Rocky

Mountain doubles and triples). This

study is part of the joint NHTSA/FHWA

operational test program being

conducted in response to Section

4007(d) of ISTEA. The basis for wiring

these combinations in this manner was

not, as ATA suggested in its comments,

a decision by the agency that ‘‘* * *

there is no safety need for separate new

requirements related to the ABSs

electrical system.’’ Instead, the agency’s

decision was based on the need to

determine the ability of the redundant

stoplamp-circuit to provide sufficient

electrical power to operate the ABSs on

all the trailers and dollies of a triples

combination. In this test, the stoplamp

circuit was wired in parallel with

additional heavy duty wiring to the

ABS, in an effort to maximize the

possibility of success.

NHTSA evaluated two aspects of the

separate connector powering for trailer

ABS in its in-service fleet studies: (1)

the ability of each approach to provide

a robust source of electrical power,

through a separate dedicated circuit, to

the trailer ABS, and; (2) the durability,

reliability, and maintainability of these

secondary powering approaches as well

as the incremental costs associated with

using any of those approaches. With

respect to the first point, the data

contained in Table 3.4, DOT Report No.

HS 808 059, page 3–27 indicate that all

but one of the separate connector/

separate circuit approaches provided

higher voltage levels than did the shared

stoplamp-circuit-system approach. The

exception was the battery approach

which, as previously stated, has been

abandoned. NHTSA has concluded that

these data justify the requirement for

separate circuit powering of ABS.

NHTSA has also concluded that

providing a separate source of power to

trailers can be done practicably and

economically. Regardless of whether a

separate circuit or a shared circuit is

used to power trailer ABS, ATA and

other truck users have stated their

preference for only one electrical cable/

connector/plug system between tractors

and trailers. The principal reason for

wanting only one cable/connector is

cost. All else being equal, utilizing two

connectors would double the truckuser’s replacement maintenance costs

for these items, regardless of (and

separate from) any costs associated with

maintaining trailer ABSs by themselves.

UPS commented that, on average, it

already replaces two entire SAE J560

cable/connectors for each of their 15,791

vehicles each year. TNT Red Star

Express fared somewhat better in this

regard, reporting that it replaces 1.2 of

these connectors per vehicle per year.

In comparison, in NHTSA’s fleet

study of electrical system maintenance,

the agency found that 0.4 SAE J560

cable/connector repairs/replacements

were made per vehicle per year. This is

a level substantially better than either

UPS or TNT reported but, nevertheless

twice the repair/replacement rate noted

for ABS components (0.2 per vehicle per

year). Since the cost of these cables/

connectors is less than ABS component

part costs, repair/replacement costs

were less for these SAE J560 cable/

connectors ($0.0002 per mile) than the

overall repair replacement costs for all

the ABS components ($0.00044 per

mile).

ATA commented that the overall cost

of ABS-related maintenance would be

on the order of 50 percent higher than

indicated in the fleet study (i.e., $0.0002

+ $0.00044 = $0.00064 per mile), if

trailer ABS use necessitated a second

tractor-to- trailer cable/connector/plug.

As NHTSA has stated repeatedly,

although today’s final rule requires a

separate circuit, it in no way mandates

that a second cable/connector be used.

The agency has left the decision to the

industry about what approach to use.

Moreover, even if the industry decides to

use two connectors temporarily or

permanently, the agency believes the

associated incremental maintenance

costs associated with doing so are

reasonable.

NHTSA expects that one of four

approaches will be chosen with respect

to trailer ABS powering. First, the

industry, through the SAE committees

that are now considering this issue,

could voluntarily settle on a new pin/

circuit assignment scheme for the

existing SAE J560 connector, thereby

‘‘freeing up’’ a dedicated power circuit

for the ABS. This approach could

involve multiplexing of some signals.

Second, the industry could develop and

standardize a variant of the SAE J560

connector that is compatible with the

existing connector but which provides

additional pins/circuits. Third, the

industry could develop a totally new

connector that will handle present and

future tractor-to-trailer powering and

signalling/communication needs, and a

transition could be made away from the
13250 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

SAE J560 connector to this new

connector. Fourth, the industry could

decide to use a separate connector in

addition to the existing SAE J560

connector.

NHTSA is aware that the industry,

through the SAE and the ATA’s

Maintenance Council, is actively

considering the first three of these

alternatives and that prototypes and, in

some cases, production versions

representing each alternative are

currently available and being evaluated.

A connector for the fourth approach has

been standardized by the International

Organization for Standardization (ISO).

This connector (ISO 7638) is mandated

for ABS connections in Europe, and

thus is commercially available and in

widespread use. The agency does not

wish to hinder industry options in this

regard or limit the design development

process. Therefore, the agency has not

specified the exact method for providing

a separate circuit to trailer ABSs.

NHTSA notes that hardware for one of

these approaches is currently

commercially available, and hardware

for the other three may evolve within

the time period between now and the

effective date for implementing trailer

ABS. Thus, practicable methods for

achieving the separate circuit

requirement are currently available, and

either market forces or industry

consensus is all that is needed to

determine which will be the

standardized method.

Advocates were concerned that

allowing the industry to develop a

connector without government

regulation could result in several

connectors being available, which in

turn would lead to incompatibility

between tractors and trailers. AAMA

stated that it was developing

appropriate standards for trailer ABS

power supply in cooperation with

trailer manufacturers. In addition, SAE

is interested in standardizing the ABS

power supply.

Based on the available information,

NHTSA believes that the industry will

decide on an appropriate electrical

circuit and standardized connector to

meet the proposed full-time power and

in-cab malfunction lamp requirements,

without the need for a detailed

requirement. The agency emphasizes

that it is important that the industry

standardize on only one approach, to

ensure compatibility between towing

vehicles and their trailers. If the

industry cannot voluntarily agree on a

single approach, additional rulemaking

may be necessary.

NHTSA is aware that the industry is

also working on multiplexing for tractor

trailer electrical circuits, which could

reduce the number of electrical wires

needed for the various systems on the

trailer. Nevertheless, multiplexing for

combination vehicles is still in the

developmental stage for most tractor

trailer applications. The agency further

notes that requiring that trailer ABSs

receive full-time power will not prohibit

multiplexing. Therefore, the agency

believes that ATA’s comments about

multiplexing are not relevant.

NHTSA further notes that ATA has

misinterpreted the agency’s previous

1992 rule to permit powering through

either the stop lamp circuit or through

a separate circuit. That rulemaking

responded to a petition for rulemaking

from WABCO, a brake manufacturer, to

amend Standard No. 121 to eliminate a

design restriction. Specifically, while

trailer ABS was required to be powered

by the stop lamp signal circuit prior to

the amendment, the amendment

permitted trailer ABS powering through

either the stop lamp signal circuit or a

separate circuit. The agency was

concerned that the pre-amendment

requirement might inhibit the use of

some state-of-the-art trailer ABS that

have more performance features, but

also have higher power requirements.

Therefore, contrary to ATA’s statements

that the agency was acting prematurely

thereby preventing the development of

multiplexing, the 1992 amendment

broadened the flexibility afforded to

manufacturers rather than limited it. In

the notice adopting that amendment,

NHTSA stated that the approach it

adopted to remove the design restriction

will provide truck and trailer manufacturers

and operators the flexibility needed to

develop and use new trailer ABS systems. By

providing such flexibility, the agency

anticipates that more vehicle operators will

decide to purchase ABS-equipped trailers.

This is consistent with the agency’s attempt

[at that time] to foster voluntary adoption of

trailer ABS by avoiding the specification of

costly regulations that would act as

disincentives for voluntarily equipping

trailers and converter dollies with ABS. 57

FR at 30914.

Moreover, in the September 1993 NPRM

proposing a full-time power

requirement, NHTSA emphasized that

the 1992 amendment was issued to

‘‘provide regulatory relief to

manufacturers in developing new trailer

ABS designs, at a time when trailer ABS

was optional’’ and that ‘‘the agency

would revisit the issue of trailer ABS

powering in the context of rulemaking

in which trailer ABS would be

required.’’

Today’s final rule culminates

precisely the type of rulemaking

envisioned in the 1992 notice. In today’s

final rule mandating that heavy vehicles

be equipped with ABSs, the agency is

addressing an entirely different

situation from the one it was

considering in 1992. NHTSA is

analyzing how best to ensure safety

through a mandatory requirement, not

how to encourage the use of an optional

safety device.

I. Applicability of Amendments

In the NPRM, NHTSA proposed

applying the ABS requirements to all

vehicles with GVWRs exceeding 10,000

pounds. The agency explained that this

proposal went beyond ISTEA’s statutory

directive for the agency to initiate

rulemaking concerning methods for

improving braking performance of ‘‘new

commercial motor vehicles,’’ which are

defined as vehicles with a GVWR of

26,001 or more pounds, including truck

tractors, trailers, and their dollies.

1. Trailers With Hydraulic or Electric

Brakes

Manufacturers of trailers with electric

or hydraulic brakes commented that

they could not comply with the

requirement because ABSs are not

available for these types of vehicles.

NHTSA wishes to clarify that the

equipment requirement in today’s final

rule applies to powered heavy vehicles

and to air-braked trailers and dollies,

but not to trailers equipped with

hydraulic or electric brakes. NHTSA

notes that no FMVSS addresses vehicles

equipped with electric brakes and that

Standard No. 105 applies ‘‘to passenger

cars, multipurpose passenger vehicles,

trucks and buses with hydraulic service

brake systems.’’ (see S3 ‘‘Application.’’)

Since electric brakes are not covered by

any FMVSS and Standard No. 105 does

not cover trailers equipped with

hydraulic brakes, today’s amendment is

not applicable to trailers with these

types of brakes. The agency notes,

however, that a trailer equipped with an

air-over-hydraulic brake system will

have to comply with the ABS

requirement, since an air-over-hydraulic

system is a subsystem of an air-braked

system, and is therefore subject to

Standard No. 121.

2. Hydraulically Braked Vehicles

NAFA stated that it is premature to

mandate ABSs on medium vehicles

with a GVWR between 10,000 and

26,000 pounds, claiming that there are

no accident or safety data supporting an

ABS requirement for these vehicles. In

response to both the NPRM and the

SNPRM, ATA commented that the

agency should not require ABSs on

hydraulically braked commercial

vehicles until proven ABSs are

available. It stated that it is not aware of
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13251

60On February 23, 1993, NHTSA proposed that

the stopping distance requirements take effect two

years after the final rule for all applicable vehicles.

(58 FR 11009)

any proven ABS for hydraulic systems

nor of any effort by the government to

obtain such systems for fleet tests,

which it believed is necessary before

mandating such equipment. In response

to the SNPRM, UPS stated that this

requirement should not be adopted

because NHTSA has performed no tests

or demonstrations on hydraulically

braked vehicles. Moreover, it stated that

it is aware of no proven technology that

could be applied to satisfy the new

NHTSA rule.

Allied Signal and Midland-Grau, two

antilock brake system manufacturers,

commented on the proposed

requirements for ABSs on hydraulically

braked heavy vehicles. Allied Signal

stated that the technology for ABSs on

heavy vehicles is the same as that used

on passenger cars and light trucks and

should not present significant

technological problems. It indicated that

some components such as the

modulator and ECU are identical or

nearly identical to those used in light

vehicle applications. In addition, wheel

speed sensors for hydraulically braked

heavy vehicles incorporate the same

technology used in wheel speed sensors

for light vehicles and air braked heavy

vehicles. Allied Signal commented that

the agency’s time frame can be achieved

with proven technology. (i.e., ABS are

increasing in use in this country on

vehicles under 10,000 pounds GVWR).

Midland-Grau commented that the

industry is only about three years away

from having ABSs for hydraulic braked

single-unit trucks. In response to the

SNPRM, AAMA stated that it is

optimistic that validated ABSs will be

available for all hydraulic vehicles

within the proposed time frames.

Nevertheless, because the availability of

such systems is uncertain, it stated that

there may be delays for certain types of

hydraulic vehicles if development

problems arise.

Based on the available information,

NHTSA believes that a March 1999

effective date for requiring antilock

brake systems on hydraulic braked

single-unit trucks and buses provides

sufficient time for vehicle

manufacturers and ABS manufacturers

to complete the development and

testing of these systems. In addition,

some Japanese and European

manufacturers are currently marketing

ABS for medium and large hydraulically

braked vehicles. In their comments,

brake manufacturers expressed

confidence that such antilock systems

will be available in this country.

NHTSA notes that ATA and UPS are

incorrect in their belief that the agency

can only issue a requirement after

conducting tests or demonstrations on

that specific subcategory of vehicles.

Nothing in the Safety Act mandates

such specific vehicle testing. Based on

comments by vehicle and ABS

manufacturers and the positive

experience in other countries with ABSequipped hydraulic vehicles, NHTSA

has determined that requiring hydraulic

vehicles with ABS is practicable and

appropriate. Moreover, the agency notes

that manufacturers, which have fully

developed antilock systems for

hydraulic brakes on passenger cars and

light vehicles, will be able to apply the

underlying technology (i.e., wheel speed

sensors, ECU, and modulators) to heavy

vehicles. The agency has provided a

lead time of four years to ensure that

manufacturers will have sufficient time

to develop and test antilock systems for

hydraulic braked heavy vehicles.

The agency is aware that Isuzu and

Mitsubishi Fuso have marketed

hydraulic braked heavy trucks with

GVWRs of up to 16,000 pounds, with

optional ABS since 1991. The ECU of

the hydraulic ABS available on the

Isuzu trucks is manufactured by

Akebono and the remainder of the

system is manufactured by Transtron.

The hydraulic ABS on the Mitsubishi

Fuso Trucks is manufactured by Japan

ABS Co. Mercedes-Benz, offers

hydraulic-braked heavy trucks with

GVWRs of up to 26,000 pounds, with

Bosch’s ABS.

Based on this information on the

current availability of hydraulic ABS in

Europe and Japan and comments by

vehicle and ABS manufacturers,

NHTSA is confident that there will be

sufficient time for the development and

testing of reliable antilock brake systems

for hydraulically braked vehicles.

Accordingly, NHTSA believes that it is

appropriate and necessary for motor

vehicle safety to require hydraulicallybraked vehicles to be equipped with

antilock brake systems. Nevertheless,

the agency plans to monitor this

development closely and could modify

the implementation schedule if

development of antilock systems for

hydraulically braked vehicles faced

unexpected development problems.

J. Implementation

In the NPRM, NHTSA stated that its

goal is to achieve significant

improvements in braking performance

at a reasonable cost to manufacturers

and consumers. The agency proposed

the following implementation schedule:

Truck Tractors ......... 2 years after final

rule (1996).

Trailers, including

converter dollies.

3 years after final

rule (1997).

Single-unit trucks .... 4 years after final

rule (1998).

Buses ........................ 5 years after final

rule (1999).

NHTSA stated that this implementation

schedule was appropriate, given the

current state of ABS technology. The

agency believed that the schedule

would provide the industry, ABS

manufacturers, and maintenance

personnel sufficient leadtime to prepare

for the changes that would be required

to accommodate the new technology.

AAMA recommended that the

effective dates for the proposed heavy

vehicle stability and control

requirements and the previously

proposed stopping distance

requirements be ‘‘synchronized for the

various vehicle types.’’ 60 AAMA

recommended that the agency adopt the

following effective dates for both the

stability and control requirements and

the stopping distance requirements,

assuming that the two rules are issued

before September 1994:

Truck tractors ........... 2 years after final

rule (1996).

Trailers, including

converter dollies.

3 years after final

rule (1997).

Air-braked singleunit trucks and

buses.

3 years after final

rule (1997).

Hydraulic-braked

single-unit trucks

and buses.

4 years after final

rule (1998).

Similarly, HDBMC requested that the

implementation schedule for the

directional stability and control

requirements be accelerated and that the

effective dates of this rulemaking and

the stopping distance rulemaking be

‘‘made coincident to allow the industry

to maximize its efforts by effectively

utilizing its limited resources.’’

ATA recommended effective dates of

December 31, 1999 for tractors and

December 31, 2001 for trailers, claiming

that this schedule would permit each

fleet, through its own tests, to determine

which ABS is best suited to its

operations and to phase in ABS

accordingly. In contrast, Advocates

favored the proposed implementation

schedule and opposed any schedule that

moved the compliance calendar to the

next century.

Based on its analysis of these

comments, NHTSA issued a SNPRM

that proposed the following

implementation schedule for both sets

of requirements:
13252 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

Truck tractors ........... 2 years after final

rule (1996).

Trailers ..................... 3 years after final

rule (1997).

Air-braked singleunit trucks and

buses.

3 years after final

rule (1997).

Hydraulic-braked

single unit trucks

and buses.

4 years after final

rule (1998).

The agency stated that making the

effective dates for the two rulemakings

concurrent would facilitate a more

orderly implementation process, avoid

the need for manufacturers to redesign

the brakes on individual vehicles twice,

and reduce the development and

compliance costs that manufacturers

would face as a result of these

regulations. NHTSA requested

comments about the implementation

schedule proposed in the supplemental

notice.

AAMA, HDBMC, Ford, GM, White

GMC, Bosch, Eaton, Midland-Grau,

Allied Signal, Advocates, and Gillig

favored the implementation schedule

proposed in the SNPRM. AAMA stated

that the supplemental proposal would

provide a more orderly and cost

effective implementation of new

requirements, thereby helping to avoid

unnecessary redesign and redundant

testing. Ford requested that the agency

specify that the requirements have

September 1 effective dates. Strait-Stop

favored keeping the stopping distance

requirements separate from the stability

and control ones.

ATA favored a phased in

implementation schedule under which

manufacturers would be required to sell

(or consumers would be required to

purchase) air braked powered vehicles

with at least 25 percent ABS in 1996, 50

percent in 1997, 75 percent in 1998, and

100 percent in 1999. Trailers would

have a similar phase-in beginning in

1998. ATA stated that a phase-in is

necessary to allow manufacturers the

opportunity to offer a wider selection of

ABS and to provide time to improve

existing systems. Moreover, ATA

claimed that a phase-in was essential to

users because it would allow

experimentation with different systems,

thereby increasing public acceptance of

the ABS mandate. Similarly, Tramec

favored introducing the requirements

over a period of time instead of all at

once. Eaton cautioned that unforeseen

manufacturing problems may impact

product quality and availability.

Therefore, it stated that a gradual

increase in ABS usage would reduce

concerns about manufacturer capacity

and end-user support abilities.

After reviewing the available

information, NHTSA has decided to

adopt an implementation schedule

similar to the one proposed in the

SNPRM. Specifically, truck tractors

manufactured on or after March 1, 1997

will have to be equipped with ABS and

comply with the braking-in-a-curve test

and high coefficient of friction stopping

distance requirements; trailers and

single-unit air braked trucks and buses

manufactured on or after March 1, 1998

will have to be equipped with ABS, and

single-unit air braked trucks and buses

will also have to comply with the high

coefficient of friction stopping distance

requirements; and hydraulic braked

trucks and buses manufactured on or

after March 1, 1999 will have to be

equipped with ABS and comply with

the high coefficient of friction stopping

distance requirements. The agency has

decided that these effective dates, which

were widely supported by vehicle

manufacturers, brake manufacturers,

and safety advocacy groups, will

provide for an efficient implementation

of Congress’s desire that NHTSA require

heavy vehicles to be equipped with

ABSs. This implementation schedule

phases in ABS for heavy vehicles over

a three-year period. Truck tractors, the

vehicle type with the largest potential

safety benefit from ABS, are required to

comply with the rule first.

This phase-in should facilitate

consumer acceptance, since truck

tractors, the most standardized type of

heavy vehicle, will be subject to the

regulation first. Only after this relatively

uniform type of vehicle is equipped

with ABS, will single unit vehicles

which include more niche vehicles (e.g.,

dump trucks) be required to comply

with the regulation?

In deciding on the most appropriate

implementation schedule, NHTSA gave

serious consideration to ATA’s

suggestion that the requirements of this

rule be phased in on a percentage basis

over a four-year period. However, for

the reasons set forth below, NHTSA has

determined that the implementation

schedule being adopted in today’s final

rule will provide the most benefits in

the most cost effective manner. The

agency emphasizes that adopting ATA’s

recommended phase-in would have

resulted in needless and protracted

delay, thereby resulting in a

significantly less safe highway

environment.

Such a delay is unnecessary given the

current state of development for ABS.

At the time of publication of this final

rule, six of the seven major U.S.

manufacturers of heavy trucks,

Freightliner Corporation, Peterbilt

Motors Corporation, Kenworth Truck

Company, Ford Motor Company, Mack

Corporation, and Navistar International

Corporation, have publicly announced

that some or all of their product line of

truck tractors, and in some cases singleunit trucks, will be equipped with ABS,

as standard equipment, beginning with

the 1995 model year. For heavy vehicle

manufacturers, that model year began

the summer of 1994. Thus, it appears

that the marketplace has already

addressed ATA’s concern that

manufacturers cannot meet increasing

market demand for ABS. Also,

manufacturers are typically warranting

ABS for 300,000 miles or three years, a

fact that should allay ATA’s concerns

that manufacturers will not support

their product offerings.

NHTSA further notes that the final

rule includes a phase-in requirement in

which the vehicles for which braking

stability is the greatest concern (truck

tractors and trailers) are required to be

equipped with ABS first. Single-unit

trucks and buses follow at a later date.

This will facilitate vehicle

manufacturers’ efforts to engineer these

systems into their entire line of product

offerings over a period of time spanning

four years, instead of having to do it all

in one year. This should substantially

reduce burdens on manufacturers and

give them sufficient time to engineer

and accomplish high quality

installations of ABS, which is a major

concern of ATA.

K. Intermediate and Final Stage

Manufacturers/Trailer Manufacturers

In the NPRM, NHTSA provided an

extensive discussion about the potential

effect of the proposed requirements on

intermediate, final stage, and trailer

manufacturers. The agency explained

that it is aware of the concerns of final

stage and intermediate stage

manufacturers about road testing their

vehicles. In particular, the agency

explained how an incomplete vehicle

manufacturer could pass through

certification to the final stage

manufacturer and how a final stage

manufacturer could certify compliance

with the proposed requirements.

NTEA commented that many of its

members, most of whom are final stage

manufacturers of vehicles produced in

two or more stages, would not be able

to use the pass-through certification

because it believed that the guidelines

provided by the incomplete vehicle

manufacturer would be very restrictive.

NTEA stated that these final stage

manufacturers would, therefore, have no

practicable and objective means of

demonstrating compliance with the

braking-in-a-curve requirement because

they have neither the financial nor

engineering resources to conduct their

own compliance testing. NTEA
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13253

therefore requested that the agency

exclude from this requirement all

‘‘multi-staged produced vehicles that

are equipped with a cargo-carrying body

or work-related equipment.’’ Likewise,

Midland-Grau stated that final stage

manufacturers do not have the resources

to certify their vehicles, and believed

that it would be difficult for chassis

manufacturers to establish

comprehensive guidelines for final stage

manufacturers to follow. AM General

commented that small vehicle

manufacturers will face undue burdens,

and suggested that the rulemaking be

limited to only Class 7 and 8 vehicles

(which are the largest heavy vehicles,

typically truck tractors over 26,000

pounds).

As explained above, NHTSA has

decided to apply the braking-in-a-curve

test only to truck tractors at this time.

These vehicles are manufactured almost

exclusively by large, single stage

manufacturers. This final rule does not

require manufacturers of single-unit

vehicles and trailers, such as NTEA’s

members, to establish compliance with

today’s amendments through road

testing. While incomplete single unit

vehicles and trailers will have to be

equipped with ABSs, the final stage and

trailer manufacturers can ensure the

presence of the equipment on their

vehicles and can reasonably rely on a

brake manufacturer’s assurances that its

ABS complies with the standard.

Specifically, certification of compliance

with the equipment requirement for

ABS does not necessitate road testing.

Nothing in the preceding discussion

should be understood as indicating that

the agency agrees with NTEA’s

comment that it would be impracticable

for a final stage manufacturer to certify

compliance with the braking-in-a-curve

test. As explained in the NPRM, while

a manufacturer must certify that its

vehicles meet all applicable safety

standards, a manufacturer need not

necessarily conduct the specific tests set

forth in an applicable standard.

Certifications may be based on, among

other things, engineering analyses,

actual testing, and computer

simulations. Moreover, a manufacturer

need not conduct these operations itself.

A manufacturer can utilize the services

of independent engineers and testing

laboratories. It can also join together

with other manufacturers through trade

associations to sponsor testing or

analysis. Finally, it can rely on testing

and analysis performed by other parties,

including the brake manufacturers.

L. Benefits

As detailed in the FRE, NHTSA

estimates that the use of ABS on all

heavy vehicles will help prevent

between 320 and 506 fatalities, between

15,900 and 27,413 injuries, and between

$458 million and $553 million of

property damage each year. Based on its

evaluation, NHTSA believes that the

rulemaking is cost beneficial since a

significant number of crashes resulting

in fatalities and property damage will be

prevented by this rulemaking.

In its comments, ATA questioned

NHTSA’s benefit analysis, arguing that

recent accident data analyses have

indicated that ABS on passenger cars

does not result in significant reductions

in crashes. The agency believes that it

is neither appropriate nor possible to

project effectiveness estimates for ABS,

or for that matter, other safety

equipment/features from one type of

vehicle to another. As ATA is aware,

vehicle loading characteristics for heavy

vehicles differ significantly from those

of passenger cars. Although the study

upon which NHTSA based its benefit

estimates did not specifically analyze

whether heavy vehicles equipped with

ABS have statistically lower accident

rates, the results of that study carefully

analyzed and reconstructed heavy

vehicle crashes to estimate the likely

benefit of ABS. The agency believes that

its benefit analysis accurately estimates

the benefits of heavy vehicle ABS.

ATA also argues that ‘‘the presence of

ABS did not lead to a reduction in the

accident rate, since in NHTSA’s tractor

fleet study, the proportion of crashes

involving ABS-equipped tractors is the

same as their proportion of the total

fleet. NHTSA disagrees with this

contention. The agency’s fleet studies of

ABS were never intended to result in

estimates of the safety benefit of ABS.

The total number of crashes that

occurred during the tractor fleet study,

fourteen, is too small to draw any

statistically significant conclusions

about the relative safety of ABSequipped versus non-ABS-equipped

vehicles.

M. Costs

In the ANPRM, NHTSA estimated that

the unit cost to a manufacturer for a

complete six-channel ABS installed on

a 6 x 4 tractor would be approximately

$1400 or approximately $1100 for a full

Select Low ABS. It estimated that the

unit cost to a manufacturer to install

ABS on a trailer would be $900.

In response to comments to the

ANPRM, NHTSA reevaluated its initial

cost estimates to include several

additional components including the

wiring harnesses, mounting hardware,

and in-cab warnings. As the Preliminary

Regulatory Impact Analysis (PRIA)

explained in detail, the agency

estimated that the unit cost for a vehicle

purchaser to comply with the proposed

requirements (including the connectors

and cables that provide full-time power)

would be approximately $2900 for the

average truck tractor, $2350 for the

average single-unit truck and bus, $1850

for a non-towing trailer, $1700 for a

towing trailer, and $1475 for a trailer

converter dolly. Based on these

estimates of consumer costs and

estimated annual production of 137,000

truck tractors, 160,000 single unit trucks

and school buses, and 7000 transit and

intercity buses, the agency estimated

that the annual costs for these vehicles

would be $790 million. For trailers,

these consumer cost estimates together

with an annual production of 115,000

non-towing trailers, 32,000 towing

trailers, and 3,000 trailer converter

dollies yields an estimated annual cost

of $272 million.

Since the preparation of the PRIA,

NHTSA has completed a detailed

engineering process-cost analysis study

in which antilock braking systems from

three ABS manufacturers were

evaluated. The cost evaluation entailed

a physical tear-down of the system, in

which the cost of each part was

determined based on the actual

manufacturing process used in its

production. The study estimated the

weight and various costs related to the

production and installation of three 4S/

4M tractor ABS, each from a different

ABS manufacturer, and three different

trailer ABS configurations, a 6S/3M, a

4S/2M and a 2S/1M, each from a

different manufacturer. Based on that

cost information, the agency estimates

that the cost for the minimum ABS

needed to comply with the requirements

in this amendment would be: $749.33

for a truck tractor, $682.51 for a singleunit truck, and $439.64 for a trailer.

Separate analyses estimated the cost and

weight of tractor-to-trailer connectors/

cables and related wiring ($93.97 for a

truck tractor, $39.52 for a non-towing

trailer, and $133.49 for a towing trailer

or trailer converter dolly), and of in-cab

ABS malfunction indicator lamps (MIL)

for tractors and trailer-mounted ABS

MILs for trailers ($13.66 for a truck

tractor, $9.47 for a single-unit truck, and

$9.43 for a trailer). The total estimated

cost to the vehicle purchaser is

estimated to be: $856.96 for a truck

tractor, $691.98 for a single-unit truck or

bus, $488.59 for a non-towing trailer,

and $582.56 for a towing trailer or

trailer converter dolly. Based on these

estimates of increased cost to the

vehicle purchaser and estimated annual

production of 147,600 truck tractors,

248,300 single unit trucks and school
13254 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

buses, and 7000 transit and intercity

buses, the agency estimates that the

annual costs for these vehicles would be

$303 million. For trailers and trailer

converter dollies, these estimates of

increased cost to the vehicle purchaser

together with an annual production of

139,400 non-towing trailers, 46,700

towing trailers, and 2,900 trailer

converter dollies yields an estimated

annual cost of $97 million. Therefore,

the agency estimates that the total

annual increased cost for equipping

heavy vehicles with ABS will be $400

million.

Along with estimating the cost

increases to the new vehicle purchaser,

NHTSA also estimated the increases in

the cost of operating heavy vehicles

equipped with ABS. Three categories of

operating costs were examined: lifetime

maintenance costs, lifetime fuel costs

due to the additional weight of the ABS,

and lifetime revenue loss due to payload

displacement. The range of the increase

in total lifetime operating costs related

to equipping heavy vehicles with ABS

is from $201.47 to $786.65. Since the

estimates for these various operating

costs are dependent upon the type of

fuel used for powered vehicles and on

the estimated lifetime vehicle miles

travelled (VMT) for the various vehicle

types, the heavy vehicles were divided

into 18 different fuel type/VMT

categories. The total estimated increase

in vehicle operating costs associated

with ABS for all heavy vehicles is $232

million. The reader is referred to the

FEA for a detailed discussion of the

costs for these different categories.

In its comments, ATA questioned

NHTSA’s portrayal of the increases in

vehicle maintenance costs as not being

significant compared to overall cost of

maintaining the air brake system on

heavy vehicles. ATA did not, however,

question the actual increased

maintenance cost per mile estimates

derived from the agency’s fleet studies.

It is these estimates of the increased

maintenance cost per mile that were

used in estimating the total cost impact

of this rulemaking and determining that

the amendment is cost effective. As

such, the agency believes that the

relative increase in vehicle maintenance

that would result in different fleets is

not the important factor in evaluating

the impact of this Final Rule.

IX. Rulemaking Analyses and Notices

A. Executive Order 12866 and DOT

Regulatory Policies and Procedures

NHTSA has considered the impacts of

this rulemaking action and determined

that it is ‘‘significant’’ within the

meaning of the Department of

Transportation’s regulatory policies and

procedures. In addition, the Office of

Management and Budget has

determined that it is ‘‘significant’’

within the meaning of Executive Order

12866. The agency has prepared a Final

Economic Assessment describing the

economic and other effects of this

rulemaking action. Summary

discussions of those effects are provided

above. For persons wishing to examine

the full analysis, a copy is being placed

in the docket.

B. Regulatory Flexibility Act

NHTSA has also considered the

effects of this rulemaking action under

the Regulatory Flexibility Act. I hereby

certify that it will not have a significant

economic impact on a substantial

number of small entities. Accordingly,

the agency has not prepared a final

regulatory flexibility analysis.

The primary cost effect of the

requirements will be on manufacturers

of heavy vehicles which are generally

large businesses. However, final stage

manufacturers are generally small

businesses. A detailed discussion about

the anticipated economic impact on

these businesses is provided in the

FRIA.

C. National Environmental Policy Act

NHTSA has analyzed this rulemaking

action for the purposes of the National

Environmental Policy Act. The agency

has determined that implementation of

this action will not have any significant

impact on the quality of the human

environment.

D. Executive Order 12612 (Federalism)

NHTSA has analyzed this action

under the principles and criteria in

Executive Order 12612. The agency has

determined that this notice does not

have sufficient Federalism implications

to warrant the preparation of a

Federalism Assessment. No State laws

will be affected.

E. Civil Justice Reform

This final rule does not have any

retroactive effect. Under 49 U.S.C.

30103, whenever a Federal motor

vehicle safety standard is in effect, a

State may not adopt or maintain a safety

standard applicable to the same aspect

of performance which is not identical to

the Federal standard, except to the

extent that the State requirement

imposes a higher level of performance

and applies only to vehicles procured

for the State’s use. 49 U.S.C. 30161 sets

forth a procedure for judicial review of

final rules establishing, amending or

revoking Federal motor vehicle safety

standards. That section does not require

submission of a petition for

reconsideration or other administrative

proceedings before parties may file suit

in court.

List of Subjects in 49 CFR Part 571

Imports, Incorporation by reference,

Motor vehicle safety, Motor vehicles,

Rubber and rubber products, Tires.

In consideration of the foregoing, the

agency is amending Section 571.3,

Standard No. 101, Controls and

Displays, Standard No. 105, Hydraulic

Brake Systems and Standard No. 121,

Air Brake Systems, in Title 49 of the

Code of Federal Regulations at Part 571

as follows:

PART 571—[AMENDED]

1. The authority citation for Part 571

continues to read as follows:

Authority: 49 U.S.C. 322, 30111, 30115,

30117, and 30166, delegation of authority at

49 CFR 1.50.

2. Part 571.3 is amended in paragraph

(b) to add a definition of ‘‘Full Trailer’’

as follows:

§ 571.3 Definitions.

* * * * *

Full trailer means a trailer, except a

pole trailer, that is equipped with two

or more axles that support the entire

weight of the trailer.

* * * * *

3. In § 571.101, Table 2 is revised to

appear as follows:

§ 571.101 Standard No. 101; Controls and

Displays.

* * * * *

BILLING CODE 4910–59–P
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13255

BILLING CODE 4910–59–C
13256 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

* * * * *

4. Section 571.105 is amended in S4

by removing the definition of ‘‘Antilock

system’’ and by adding the definitions

of ‘‘Antilock brake system,’’ ‘‘Directly

controlled wheel,’’ ‘‘Indirectly

controlled wheel,’’ and ‘‘Peak friction

coefficient;’’ by revising S5.1, S5.3,

S5.3.1(c), S5.3.3; and S5.5; and adding

S5.3.3(a), S5.3.3(b), S5.5.1 and S5.5.2 to

read as follows:

§ 571.105 Standard No. 105, hydraulic

brake systems.

* * * * *

Antilock brake system or ABS means

a portion of a service brake system that

automatically controls the degree of

rotational wheel slip during braking by:

(1) Sensing the rate of angular rotation

of the wheels;

(2) Transmitting signals regarding the

rate of wheel angular rotation to one or

more controlling devices which

interpret those signals and generate

responsive controlling output signals;

and

(3) Transmitting those controlling

signals to one or more modulators

which adjust brake actuating forces in

response to those signals.

* * * * *

Directly Controlled Wheel means a

wheel at which the degree of rotational

wheel slip is sensed and corresponding

signals are transmitted to one or more

modulators that adjust the brake

actuating forces at that wheel. Each

modulator may also adjust the brake

actuating forces at other wheels in

response to the same signal[s].

* * * * *

Indirectly Controlled Wheel means a

wheel at which the degree of rotational

wheel slip is not sensed, but at which

the modulator of an antilock braking

system adjusts its brake actuating forces

in response to signals from one or more

sensed wheels.

* * * * *

Peak friction coefficient or PFC means

the ratio of the maximum value of

braking test wheel longitudinal force to

the simultaneous vertical force

occurring prior to wheel lockup, as the

braking torque is progressively

increased.

* * * * *

S5.1 Service brake systems. Each

vehicle shall be equipped with a service

brake system acting on all wheels. Wear

of the service brake shall be

compensated for by means of a system

of automatic adjustment. Each passenger

car and each multipurpose passenger

vehicle, truck, and bus with a GVWR of

10,000 pounds or less shall be capable

of meeting the requirements of S5.1.1

through S5.1.6 under the conditions

prescribed in S6, when tested according

to the procedures and in the sequence

set forth in S7. Each school bus with a

GVWR greater than 10,000 pounds shall

be capable of meeting the requirements

of S5.1.1 through S5.1.5 under the

conditions prescribed in S6, when

tested according to the procedures and

in the sequence set forth in S7. Each

multipurpose passenger vehicle, truck,

and bus (other than a school bus) with

a GVWR greater than 10,000 pounds

shall be capable of meeting the

requirements of S5.1.1, S5.1.2, and

S5.1.3 under the conditions prescribed

in S6, when tested according to the

procedures and in the sequence set forth

in S7. Except as noted in S5.1.1.2 and

S5.1.1.4, if a vehicle is incapable of

attaining a speed specified in S5.1.1,

S5.1.2, S5.1.3, or S5.1.6, its service

brakes shall be capable of stopping the

vehicle from the multiple of 5 mph that

is 4 to 8 mph less than the speed

attainable in 2 miles, within distances

that do not exceed the corresponding

distances specified in Table II. If a

vehicle is incapable of attaining a speed

specified in S5.1.4 in the time or

distance interval set forth, it shall be

tested at the highest speed attainable in

the time or distance interval specified.

* * * * *

S5.3 Brake system indicator lamp.

Each vehicle shall have a brake system

indicator lamp or lamps, mounted in

front of and in clear view of the driver,

which meet the requirements of S5.3.1

through S5.3.5. A vehicle with a GVWR

of 10,000 pounds or less may have a

single common indicator lamp. A

vehicle with a GVWR of greater than

10,000 pounds may have an indicator

lamp which is common for gross loss of

pressure, drop in the level of brake

fluid, or application of the parking

brake, but shall have a separate

indicator lamp for antilock brake system

malfunction. However, the options

provided in S5.3.1(a) shall not apply to

a vehicle manufactured without a split

service brake system; such a vehicle

shall, to meet the requirements of

S5.3.1(a), be equipped with a

malfunction indicator that activates

under the conditions specified in

S5.3.1(a)(4). This warning indicator

shall, instead of meeting the

requirements of S5.3.2 through S5.3.5,

activate (while the vehicle remains

capable of meeting the requirements of

S5.1.2.2 and the ignition switch is in the

‘‘on’’ position) a continuous or

intermittent audible signal and a

flashing warning light, displaying the

words ‘‘STOP-BRAKE FAILURE’’ in

block capital letters not less than onequarter of an inch in height.

* * * * *

S5.3.1 * * *

(c) A malfunction that affects the

generation or transmission of response

or control signals in an antilock brake

system, or a total functional electrical

failure in a variable proportioning brake

system.

* * * * *

S5.3.3 (a)Each indicator lamp

activated due to a condition specified in

S5.3.1 shall remain activated as long as

the malfunction exists, whenever the

ignition (start) switch is in the ‘‘on’’

(run) position, whether or not the

engine is running.

(b) For vehicles with a GVWR greater

than 10,000 pounds, each message about

the existence of a malfunction in an

antilock brake system shall be stored

after the ignition switch is turned to the

‘‘off’’ position and automatically

reactivated when the ignition switch is

turned to the ‘‘on’’ position. The

indicator lamp shall also be activated as

a check of lamp function whenever the

ignition is turned to the ‘‘on’’ (run)

position. The indicator lamp shall be

deactivated at the end of the check of

the lamp function unless there is a

malfunction or a message about a preexisting malfunction.

* * * * *

S5.5. Antilock and Variable

Proportioning Brake Systems.

S5.5.1 Each vehicle with a GVWR

greater than 10,000 pounds, except for

any vehicle that has a speed attainable

in 2 miles of not more than 33 mph,

shall be equipped with an antilock

brake system that directly controls the

wheels of at least one front axle and the

wheels of at least one rear axle of the

vehicle. Wheels on other axles of the

vehicle may be indirectly controlled by

the antilock brake system.

S5.5.2 In the event of any failure

(structural or functional) in an antilock

or variable proportioning brake system,

the vehicle shall be capable of meeting

the stopping distance requirements

specified in S5.1.2 for service brake

system partial failure.

* * * * *

§ 571.121 Standard No. 121, air brake

systems.

5. Section 571.121 is amended in S4

by removing the definitions of

‘‘Antilock system’’ and ‘‘skid number’’

and by adding the definitions of

‘‘Antilock brake system,’’ ‘‘Directly

Controlled Wheel,’’ ‘‘Full-treadle brake

application,’’ ‘‘Independently

Controlled Wheel,’’ ‘‘Indirectly

Controlled Wheel,’’ ‘‘Maximum drive-
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13257

through speed,’’ ‘‘Peak friction

coefficient;’’ by revising S5.1.6 and

adding S5.1.6.1, S5.1.6.2, and S5.1.6.3;

by adding S5.2.3, S5.2.3.1, S5.2.3.2, and

S5.2.3.3; by revising S5.3; by adding

S5.3.6, S5.3.6.1, and S5.3.6.2; by

revising S5.5.1, S5.5.2, S6.1.7, S6.1.10,

S6.1.10.2, S6.1.10.3, and S6.1.10.4; by

removing and reserving S6.1.10.1; by

removing S6.1.10.5, S6.1.10.6, and

S6.1.10.7, and by adding S6.1.15 to read

as follows:

§ 571.121 Standard No. 121; air brake

systems.

* * * * *

Antilock Brake System or ABS means

a portion of a service brake system that

automatically controls the degree of

rotational wheel slip during braking by:

(1) Sensing the rate of angular rotation

of the wheels;

(2) Transmitting signals regarding the

rate of wheel angular rotation to one or

more controlling devices which

interpret those signals and generate

responsive controlling output signals;

and

(3) Transmitting those controlling

signals to one or more modulators

which adjust brake actuating forces in

response to those signals.

* * * * *

Directly Controlled Wheel means a

wheel at which the degree of rotational

wheel slip is sensed and corresponding

signals are transmitted to one or more

modulators that adjust the brake

actuating forces at that wheel. Each

modulator may also adjust the brake

actuating forces at other wheels in

response to the same signal[s].

* * * * *

‘‘Full-treadle brake application’’

means a brake application in which the

treadle valve pressure in any of the

valve’s output circuits reaches 100 psi

within 0.2 seconds after the application

is initiated.

* * * * *

Independently Controlled Wheel

means a directly controlled wheel for

which the modulator does not adjust the

brake actuating forces at any other

wheel on the same axle.

* * * * *

Indirectly Controlled Wheel means a

wheel at which the degree of rotational

wheel slip is not sensed, but at which

the modulator of an antilock braking

system adjusts its brake actuating forces

in response to signals from one or more

sensed wheel(s).

* * * * *

‘‘Maximum drive-through speed’’

means the highest possible constant

speed at which the vehicle can be

driven through 200 feet of a 500-foot

radius curve arc without leaving the 12-

foot lane.

* * * * *

Peak friction coefficient or PFC means

the ratio of the maximum value of

braking test wheel longitudinal force to

the simultaneous vertical force

occurring prior to wheel lockup, as the

braking torque is progressively

increased.

* * * * *

S5.1.6 Antilock Brake System.

S5.1.6.1(a) Each single-unit vehicle

manufactured on or after March 1, 1998

shall be equipped with an antilock

brake system that directly controls the

wheels of at least one front axle and the

wheels of at least one rear axle of the

vehicle. Wheels on other axles of the

vehicle may be indirectly controlled by

the antilock brake system.

S5.1.6.1(b) Each truck tractor

manufactured on or after March 1, 1997

shall be equipped with an antilock

brake system that directly controls the

wheels of at least one front axle and the

wheels of at least one rear axle of the

vehicle, with the wheels of at least one

axle being independently controlled.

Wheels on other axles of the vehicle

may be indirectly controlled by the

antilock brake system. A truck tractor

shall have no more than three wheels

controlled by one modulator.

S5.1.6.2 Antilock Malfunction

Circuit and Signal.

(a) Each truck tractor manufactured

on or after March 1, 1997 and each

single unit vehicle manufactured on or

after March 1, 1998 shall be equipped

with an electrical circuit that is capable

of signalling a malfunction that affects

the generation or transmission of

response or control signals in the

vehicle’s antilock brake system.

(b) Each truck tractor manufactured

on or after March 1, 1997 and each

single unit vehicle manufactured on or

after March 1, 1998 shall have an

indicator lamp, mounted in front of and

in clear view of the driver, which is

activated whenever there is a

malfunction that affects the generation

or transmission of the response or

control signals in an antilock brake

system. The indicator lamp shall remain

activated as long as the malfunction

exists, whenever the ignition (start)

switch is in the ‘‘on’’ (run) position,

whether or not the engine is running.

Each message about the existence of a

malfunction in an antilock brake system

shall be stored after the ignition switch

is turned to the ‘‘off’’ position and

automatically reactivated when the

ignition switch is turned to the ‘‘on’’

position. The indicator lamp shall also

be activated as a check of lamp function

whenever the ignition is turned to the

‘‘on’’ or ‘‘run’’ position. The indicator

lamp shall be deactivated at the end of

the check of lamp function unless there

is a malfunction or a message about a

pre-existing malfunction.

(c) Each truck tractor manufactured

on or after March 1, 1997 and each

single unit vehicle manufactured on or

after March 1, 1998 that is equipped to

tow another air-braked vehicle, shall be

equipped with an electrical circuit that

is capable of transmitting information

about a malfunction in the antilock

brake system on one or more towed

vehicle(s) (e.g., trailer(s) and dolly(ies)).

Each such vehicle shall also be

equipped with an indicator lamp,

mounted in front of and in clear view

of the driver, capable of receiving, from

one or more antilock equipped towed

vehicle(s), information transmitted

about a malfunction of a towed vehicle’s

antilock system and then activating the

indicator lamp when there is a

malfunction in the towed vehicle’s

antilock brake system. The indicator

lamp shall remain activated as long as

the malfunction exists, whenever the

ignition (start) switch is in the ‘‘on’’

(run) position, whether or not the

engine is running. The indicator lamp

shall also be activated as a check of

lamp function whenever the ignition is

turned to the ‘‘on’’ or ‘‘run’’ position.

The indicator lamp shall be deactivated

at the end of the check of lamp function

unless there is a malfunction or a

message about a pre-existing

malfunction.

S5.1.6.3 Antilock Power Circuit for

Towed Vehicles. Each truck tractor

manufactured on or after March 1, 1997

and each single unit vehicle

manufactured on or after March 1, 1998

that is equipped to tow another airbraked vehicle shall be equipped with

one or more separate electrical circuits,

specifically provided to power the

antilock system on the towed vehicle(s).

Such a circuit shall be adequate to

enable the antilock system on each

towed vehicle to be fully operable.

* * * * *

S5.2.3 Antilock Brake System.

S5.2.3.1(a) Each semitrailer

(including a trailer converter dolly)

manufactured on or after March 1, 1998

shall be equipped with an antilock

brake system that directly controls the

wheels of at least one axle of the

vehicle. Wheels on other axles of the

vehicle may be indirectly controlled by

the antilock brake system.

(b) Each full trailer manufactured on

or after March 1, 1998 shall be equipped

with an antilock brake system that

directly controls the wheels of at least
13258 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

one front axle of the vehicle and at least

one rear axle of the vehicle. Wheels on

other axles of the vehicle may be

indirectly controlled by the antilock

brake system.

S5.2.3.2 Antilock Malfunction

Circuit and Signal. Each trailer

(including a trailer converter dolly)

manufactured on or after March 1, 1998

that is equipped with an antilock brake

system shall be equipped with an

electrical circuit that is capable of

signalling a malfunction in the trailer

antilock brake system, and shall comply

with the requirements of S5.2.3.3. A

trailer manufactured on or after March

1, 1998 that is not designed to tow

another air brake equipped trailer shall

have the means for connection of the

antilock malfunction signal circuit and

ground, at the front of the trailer. A

trailer manufactured on or after March

1, 1998 that is designed to tow another

air brake equipped trailer shall be

capable of transmitting a malfunction

signal from the antilock systems of

additional trailers in a combination and

shall have means for the connection of

the antilock malfunction signal circuit

and ground, at both the front and rear

of the trailer. Each message about the

existence of a malfunction in an

antilock brake system shall be stored

whenever power is no longer supplied

to the system. The indicator lamp shall

also be activated as a check of lamp

function whenever power is supplied to

the antilock brake system. The indicator

lamp shall be deactivated at the end of

the check of lamp function unless there

is a malfunction or a message about a

pre-existing malfunction.

S5.2.3.3 Antilock Malfunction

Indicator. Each trailer (including a

trailer converter dolly) manufactured on

or after March 1, 1998 and before March

1, 2006 shall be equipped with a lamp

indicating a malfunction of a trailer’s

antilock brake system. Such a lamp

shall remain activated as long as the

malfunction exists whenever the power

is supplied to the antilock brake system.

The display shall be visible within the

driver’s forward field of view through

the rearview mirror(s), and shall be

visible once the malfunction is present

and power is provided to the system.

* * * * *

S5.3 Service Brakes—road tests. The

service brake system on each truck

tractor manufactured before March 1,

1997 shall, under the conditions of S6,

meet the requirements of S5.3.3 and

S5.3.4, when tested without adjustments

other than those specified in this

standard. The service brake system on

each truck tractor manufactured on or

after March 1, 1997 shall, under the

conditions of S6, meet the requirements

of S5.3.1, S5.3.3, S5.3.4, and S5.3.6,

when tested without adjustments other

than those specified in this standard.

The service brake system on each bus

and truck (other than a truck tractor)

manufactured before March 1, 1998

shall, under the conditions of S6, meet

the requirements of S5.3.3, and S5.3.4,

when tested without adjustments other

than those specified in this standard.

The service brake system on each bus

and truck (other than a truck tractor)

manufactured on or after March 1, 1998

shall, under the conditions of S6, meet

the requirements of S5.3.1, S5.3.3, and

S5.3.4 when tested without adjustments

other than those specified in this

standard. The service brake system on

each trailer shall, under the conditions

of S6, meet the requirements of S5.3.3,

S5.3.4, and S5.3.5 when tested without

adjustments other than those specified

in this standard. However, a heavy

hauler trailer and the truck and trailer

portions of an auto transporter need not

meet the requirements of S5.3.

* * * * *

S5.3.6 Stability and Control During

Braking—Truck Tractors. When stopped

three consecutive times for each

combination of weight, speed, and road

condition specified in S5.3.6.1 and

S5.3.6.2, each truck tractor

manufactured on or after March 1, 1997

shall stop each time within the 12-foot

lane, without any part of the vehicle

leaving the roadway.

S5.3.6.1 Using a full-treadle brake

application, stop the vehicle from 30

mph or 75% of the maximum drivethrough speed, whichever is less, on a

500-foot radius curved roadway with a

wet level surface having a peak friction

coefficient of 0.5 when measured using

an American Society for Testing and

Materials (ASTM) E1136 standard

reference test tire, in accordance with

ASTM Method E1337–90, at a speed of

40 mph, with water delivery.

S5.3.6.2 Stop the vehicle with the

vehicle

(a) loaded to its GVWR, and

(b) at its unloaded weight plus up to

500 pounds (including driver and

instrumentation), or at the

manufacturer’s option, at its unloaded

weight plus up to 500 pounds

(including driver and instrumentation)

and plus not more than an additional

1000 pounds for a roll bar structure on

the vehicle.

* * * * *

S5.5.1 Antilock System Malfunction.

On a truck tractor manufactured on or

after March 1, 1997 and a single unit

vehicle manufactured on or after March

1, 1998 that is equipped with an

antilock brake system, a malfunction

that affects the generation or

transmission of response or control

signals of any part of the antilock

system shall not increase the actuation

and release times of the service brakes.

* * * * *

S5.5.2 Antilock System Power—

Trailers. On a trailer (including a trailer

converter dolly) manufactured on or

after March 1, 1998 that is equipped

with an antilock system that requires

electrical power for operation, the

power shall be obtained from one or

more separate electrical circuits

specifically provided to power the

trailer antilock system. The antilock

system shall automatically receive

power from the stop lamp circuit, if the

separate power circuit or circuits are not

in use. Each trailer (including a trailer

converter dolly) manufactured on or

after March 1, 1998 that is equipped to

tow another air-braked vehicle shall be

equipped with one or more separate

electrical circuits specifically provided

to power the antilock system on the

towed vehicle(s). Such circuits shall be

adequate to enable the antilock system

on each towed vehicle to be fully

operable.

* * * * *

S6.1.7 Unless otherwise specified,

stopping tests are conducted on a 12-

foot wide level, straight roadway having

a peak friction coefficient of 0.9. For

road tests in S5.3, the vehicle is aligned

in the center of the roadway at the

beginning of a stop. Peak friction

coefficient is measured using an ASTM

E1136 standard reference test tire in

accordance with ASTM method E1337–

90, at a speed of 40 mph, without water

delivery for the surface with PFC of 0.9,

and with water delivery for the surface

with PFC of 0.5.

* * * * *

S6.1.10 In a test other than a static

parking test, a truck tractor is tested at

its GVWR by coupling it to an unbraked

flatbed semi-trailer (hereafter, control

trailer) as specified in S6.1.10.2 to

S6.1.10.4.

* * * * *

S6.1.10.1 [RESERVED]

S6.1.10.2 The center of gravity

height of the ballast on the loaded

control trailer shall be less than 24

inches above the top of the tractor’s fifth

wheel.

* * * * *

S6.1.10.3 The control trailer has a

single axle with a gross axle weight

rating of 18,000 pounds and a length,

measured from the transverse centerline

of the axle to the centerline of the

kingpin, of 258 ± 6 inches.
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13259

1Much of the discussion which follows is

adapted from U.S. v. General Motors Corp., 656

F.Supp 1555, 1562–1566 (D.D.C. 1987,), ‘‘The

Anatomy of a Tractor Trailer Jackknife’’ by Richard

Radlinski, Vehicle Research and Test Center,

National Highway Traffic Safety Administration,

and ‘‘Antilock Systems for Air-Braked Vehicles’’ by

William A. Leasure, Jr. and Sidney F. Williams, Jr.,

National Highway Traffic Safety Administration,

SP–789, Society of Automotive Engineers, Inc.,

February 1989.

3A vehicle’s brake system includes both the

service brake system which the driver uses to slow

or stop the vehicle, and the parking brake system

which the driver uses to hold the vehicle stationary

while unattended. The notice only addresses the

service brake system and does not discuss parking

brake system performance.

4Hysteresis is:

1. the time lag exhibited by a body in reacting to

changes in the forces affecting it, and

2. the phenomenon exhibited by a system in

which the reaction of the system to changes is

dependent upon its past reactions to change.

S6.1.10.4 The control trailer is

loaded so that its axle is loaded at 4,500

pounds and the tractor is loaded to its

GVWR, loaded above the kingpin only,

with the tractor’s fifth wheel adjusted so

that the load on each axle measured at

the tire-ground interface is most nearly

proportional to the axles’ respective

GAWRs, without exceeding the GAWR

of the tractor’s axle or axles or control

trailer’s axle.

* * * * *

S6.1.15 Initial Brake Temperature.

Unless otherwise specified, the initial

brake temperature is not less than 150

°F and not more than 200 °F.

* * * * *

Issued on: March 1, 1995.

Ricardo Martinez,

Administrator.

Note.—The following appendix will not

appear in the Code of Federal Regulations:

Appendix—Braking Systems, Tires, Wheel

Lockup, and Loss-of-Control Crashes

1. Introduction

NHTSA is providing a brief discussion 1 of

braking systems, tires, wheel lockup, and

loss-of-control crashes in this Appendix;

interested persons are referred to several

agency reports 2 for a more complete

discussion.

An ABS is a closed-loop feedback control

system that, above a preset minimum speed,

automatically modulates brake pressure in

response to measured wheel speed

performance to control the degree of wheel

slip during braking and provide improved

utilization of the friction available between

the tires and the road. These systems,

therefore, could justifiably be called antilock

brake/tire systems since their function is to

balance brake torque with tire/road friction to

obtain that wheel slip which optimizes

braking performance. Antilock system

designers must take into consideration the

characteristics of brake systems and tires—

both must be understood in order to optimize

the performance of antilock systems.

2. Heavy Vehicle Brake Systems

The function of a motor vehicle’s brake

system is to slow or stop the vehicle or to

hold it stationary. Service brake systems 3

consist of foundation brake assemblies (the

portion of the system that actually creates

brake torque and the resulting retarding

forces at the tire/road interface) and a service

brake control system.

There are two principal types of

foundation brakes in use: drum and disc

brakes. Drum brakes create retarding friction

by pressing contoured brake linings against

the inside walls of brake drums that are

attached the vehicle’s wheels. Disc brakes

perform the same function by squeezing or

clamping both sides of a brake rotor between

two or more brake pads.

There are two principal types of service

brake control systems, hydraulic and

pneumatic. These service brake control

systems consist of the components necessary

to distribute and control the fluid pressure to

the foundation brake assemblies. In the case

of an air brake system, this is pneumatic

pressure; i.e., compressed air, and in the case

of an hydraulic brake system, this is

hydrostatic pressure; i.e., pressurized brake

fluid.

In the case of an air brake system, the

service brake control system modulates the

air pressure in the service brake system.

Pressurized (compressed) air stored in

reservoirs is supplied through a foot-actuated

service brake control valve (treadle valve).

This air pressure, which varies in proportion

to how far the treadle valve is depressed, is

then applied through a series of pneumatic

valves (relay valves, and in the case of

vehicles equipped with antilock brake

systems, modulator valves) to the service

brake chambers located near each wheel on

the vehicle. This air pressure in the service

brake chambers in turn applies forces to the

brake linings or pads within the foundation

brakes to create brake torque. Pneumatic

systems are open, in that air, once utilized at

a brake chamber, is exhausted to atmosphere.

Air pressure levels in reservoirs are

maintained by an engine-driven compressor.

Hydraulic brake systems utilize an

incompressible fluid (a petroleum-based

brake fluid), metered through a combined

valve and reservoir (brake master cylinder),

to create variable amounts of hydrostatic

pressure within a closed system of brake

lines. The brake lines transmit this pressure

to wheel cylinders or brake caliper pistons

which, in turn, apply force to the brake

linings or pads in proportion to the amount

of manual force being applied to the brake

pedal.

It should be noted that hydraulic

foundation brake assemblies (either drum or

disc brakes) are sometimes used in air brake

systems (commonly called air-over-hydraulic

brake systems) with the hydraulic pressure

produced by a hydraulic master cylinder

which is powered by an air brake chamber.

One important characteristic of brake

systems that effects the control modes used

by ABSs to control wheel slip is the

hysteresis 4 of both the service brake control

systems and foundation brakes. In the case of

service brake control systems, the hysteresis

of concern is the time lag between the ECU

signalling the modulator valve to release

(reduce) or apply (increase) brake application

pressure and the time at which that increased

or decreased pressure is actually applied at

the foundation brakes. This pneumatic

hysteresis time lag can be up to several tenths

of a second for an air braked system, but for

a hydraulic brake system, this time lag is very

short, usually less than one-tenth of a second.

The foundation brakes’ hysteresis

significantly affects ABS design. This

hysteresis is characterized by the foundation

brake’s torque output not immediately falling

in response to and in proportion to a

reduction in brake application pressure. This

is shown in Figure 1 for an air-actuated

foundation brake. As is the case for service

brake control systems, the hysteresis in

hydraulic foundation brakes is much less

than that of air-actuated foundation brakes.

The amount of deceleration that a braking

vehicle can attain is dependent on three

factors: the amount of brake torque that can

be generated; tire-friction properties; and

road surface friction characteristics.

The ability to generate braking torque is

primarily dependent upon the size of the

foundation brake components used (i.e.,

brake drums, linings, and actuating chambers

or pistons) and the amount of hydraulic or

pneumatic pressure delivered to these

components. Brake system designers size

systems to provide sufficient brake torque

generating capability to lock (or come

relatively close to locking) the brakes

(wheels) on the vehicle (except those on the

steering axle) when it is loaded with the

maximum weight it is designed to carry and

when operating on all types of road surfaces.

It is necessary to provide such brake torque

generating capability if a vehicle is to have

adequate stopping distance performance

when it is fully loaded.

Most heavy trucks built today can thus

generate sufficient brake torque to lock (or

come relatively close to locking) all their

wheels (except those on the steering axle) on

all road surfaces at all loading conditions. If

a brake is ‘‘big’’ enough to lock a wheel, the

issue of stopping capability of that wheel

then focuses on tire properties and not the

brake since, in effect, any further increase in

braking torque cannot be utilized. The limit

of tire traction in such a case determines the

maximum capability of each wheel (brake) to

contribute to the vehicle’s stopping ability.

For passenger cars, maximum loaded

weight includes the empty weight of the

vehicle, up to as many as six adult

passengers, assorted luggage or cargo, and a

full tank of fuel. For a heavy truck, maximum

loaded weight includes the empty weight of

the vehicle, typically one or two passengers,

a full load of fuel, and the maximum weight

of cargo that can be carried in the truck. The

ratio of loaded to empty weight for passenger

cars is generally in the range of 1.5 to 1 or

less. For heavy vehicles, especially

combination-unit trucks, this ratio can

exceed 3 to 1.

Standard design practice in the U.S. is to

use fixed brake force distributions on heavy

vehicles (i.e., a brake force distribution that

does not change with axle load changes). The
13260 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

5A moment, or the moment of a force, is a torque,

and is a measure of the tendency of that force acting

on an object to produce torsion and rotation of that

object about an axis.

6 Inertial forces are those forces occurring within

an object that resist the tendency of external forces

on the object to accelerate the object. They are

defined by Newton’s Second Law, which basically

states that an object at rest tends to remain at rest

and an object in motion tends to remain in motion,

and are equal to the mass of the object times its rate

of acceleration.

7 Inertial moments are those moments occurring

within an object that resist the tendency of external

moments on the object to accelerate the rotation of

the object. They are also defined by Newton’s

Second Law and are equal to the moment of inertia

of the object times its rate of rotational acceleration.

8The following definitions are based on those

which appear in ‘‘SAE J670e—Vehicle Dynamics

Terminology, Society of Automotive Engineers, Inc.

July 1976. The reader is referred to that document

for a more complete description of these terms.

9Similarly for the vehicle, the vehicle’s

longitudinal axis, direction, is the direction in

which the vehicle is pointed.

10Similarly for the vehicle, the vehicle’s lateral

axis, direction, is perpendicular to the direction in

which the vehicle is pointed.

11Throughout the remainder of this discussion,

the effects of camber angle are not addressed, and

force distribution is established by selecting

particular ‘‘size’’ or torque capacity brakes for

each axle. Because load distribution is so

variable on heavy vehicles, a fixed brake

balance is a compromise and cannot be

expected to provide high braking efficiency

(i.e., high braking rates without locking

wheels) under all conditions. Generally

speaking, heavy vehicle brakes are balanced

for the fully loaded, low deceleration stop.

This results in too much braking at the rear

axle(s) when the vehicles are empty.

Heavy vehicles have a comparatively much

greater propensity for brake-induced wheel

lockup than passenger cars for two reasons.

The first is the much less than optimum

brake force distribution in the lightly loaded

and empty load conditions, which leads to

rear wheel lockup under such conditions.

The second is the difference in loaded to

empty weight ratio and the resulting

difference in brake sizing. Since a heavy

vehicle’s brakes must be sized for the fully

loaded condition, such a vehicle tends to be

very overbraked when it operates lightly

loaded or empty or when it operates on a

slippery, low friction road surface. Under

either of these operating conditions, and

especially when both conditions exist, it is

very easy for the driver to inadvertently lock

some or all of the vehicle’s wheels, even

when making only a moderate or light brake

application.

3. Tire/Road Friction

Ultimately, the retarding (braking) forces at

the tire/road interface, that result from the

braking torque that is applied to the vehicle’s

wheels, are transmitted to the road surface at

that interface. Tire and road surface friction

properties that affect these forces are

significant factors in determining the amount

of deceleration that the vehicle can achieve.

In fact, the forces and moments 5 that the

vehicle’s tires are capable of generating at the

tire/road interface are not only the only

means by which a driver is able to control

the velocity of the vehicle (not only slowing

and stopping the vehicle by applying the

brakes, but also accelerating the vehicle by

actuating the accelerator), but they are also

the only means by which the driver is able

to control the direction and path of a vehicle

by turning the steering wheel.

These forces and moments result when the

driver turns the steering wheel, applies the

brakes and/or actuates the accelerator and are

reactions to the inertial forces 6 and

moments 7 that act on the vehicle. Therefore,

in order to understand those factors that

influence the control and stability (and the

loss thereof) of a vehicle, it is necessary to

understand how tires generate those forces

and moments.

Tire-road friction is an interaction between

the tire and the road resulting in reaction

forces and moments acting in the plane of the

road at the tire-road interface. Reaction forces

and moments result from control inputs (e.g.,

braking, accelerating, steering) and/or

external disturbances (e.g., wind, road

geometry and condition, etc.). The direction

and magnitude of the resultant reaction

forces and moments are determined by these

inputs.

Before discussing these tire-road friction

properties, several terms need to be defined.

In order to understand the conditions under

which a tire generates forces at the tire-road

interface, the axis system used to define a

tire’s operating condition needs to be

defined.8 First, the position of the tire is

defined by the wheel plane, the road plane,

and the center of tire contact. The wheel

plane is the central plane of the tire, normal

(perpendicular) to the spin axis, which is the

axis of rotation of the wheel (tire). The road

plane is the plane of the road surface. The

center of tire contact is the intersection of the

wheel plane and the vertical projection of the

spin axis of the wheel onto the road plane.

The axis system is then defined as follows:

1. The origin of the tire axis system is the

center of the tire contact.

2. The X′ axis is the intersection of the

wheel plane and the road plane with a

positive direction forward. The X′ axis

defines the longitudinal 9 axis of the tire and

is positive in the direction in which the tire

is pointed.

3. The Z′ axis is perpendicular to the road

plane with a positive direction downward. If

the road surface is flat and level, the Z′ axis

is vertical.

4. The Y′ axis is in the road plane, its

direction being chosen to make the axis

system orthogonal and right-handed. The Y′

axis defines the lateral 10 axis of the tire and

is perpendicular to the direction in which the

tire is pointed and positive to the right when

looking in the direction in which the tire is

pointed.

With this axis system as a basis, the tire

angles which affect the forces and moments

generated by a tire are defined as follows:

1. Slip angle is the angle between the X′

axis and the direction of travel of the center

of tire contact. In simple terms, the slip angle

is the angle between the direction in which

the tire is pointed and the direction in which

the tire is moving.

2. Inclination (camber) angle is the angle

between the Z′ axis and the wheel plane. In

simple terms, the inclination angle is a

measure of how far the top of the tire is tilted

to one side or the other when looking in the

direction in which the tire is pointed.

The other important operating condition of

a tire is that which produces braking and

driving forces. This condition, which is

referred to as longitudinal slip in the SAE

terminology, is also called percent slip,

wheel slip, or simply, slip. Throughout this

notice, the term wheel slip is used and is

defined as: the ratio of the longitudinal slip

velocity to the spin velocity of the straight

free-rolling tire, expressed as a percentage,

where:

1. the longitudinal slip velocity is the

difference between the spin velocity of the

driven or braked tire and the spin velocity of

the straight free-rolling tire, with both spin

velocities measured at the same linear

velocity at the wheel center in the X′

direction,

2. the spin velocity is the angular velocity

of the wheel on which the tire is mounted,

about its spin axis, and

3. the straight free-rolling tire is a loaded

rolling tire operated without application of

driving or braking torque moving in a straight

line at zero inclination angle and zero slip

angle.

It should be noted that wheel slip is

sometimes expressed as the ratio of the

difference between the velocity of the wheel

center and the velocity of a point on the tread

of the tire that is not in contact with the road

to the velocity of the wheel center. Using this

definition, a free-rolling tire operates at a

small amount of wheel slip, usually less than

1 or 2 percent, due to the rolling resistance

of the tire. Throughout the preamble, the

definition of longitudinal slip given above is

used.

The final terms that need to be defined are

those that describe the forces and moments

generated by the tire. Tire force is the

external force acting on the tire by the road.

Longitudinal force is the component of tire

force in the X′ direction, i.e., in the direction

which the tire is pointed. Braking force is the

negative longitudinal force resulting from

braking force application. Lateral force is the

component of tire force in the Y′ direction,

i.e., perpendicular to the direction the tire is

pointed. Normal force is the component of

tire force in the Z′ direction. Vertical force is

the normal reaction of the tire on the road

which is equal to the negative of the normal

force. Braking force coefficient, muX, is the

ratio of the braking force to the vertical load.

Lateral force coefficient, muY, is the ratio of

the lateral force to the vertical load.

With these definitions as a basis, the

following discusses the forces and moments

generated by a tire, how those forces are

affected by wheel slip, and how those forces

influence a vehicle’s control and stability.

Tire-road traction properties determine the

maximum limits of forces and moments

which can be developed at the tire-road

interface at given operating and

environmental conditions. They also affect

tire force and moment slip characteristics,

i.e., relationships between lateral tire force

and slip angle (and camber angle); 11 and
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13261

when discussing the operating condition of a tire,

the camber angle is assumed to be zero.

12To eliminate confusion regarding the meaning

of lateral, several technical terms are defined that

will be used throughout the remainder of this

notice.

braking or driving torque and wheel slip.

These properties have a substantial effect on

a vehicle’s dynamics and its control and

stability characteristics.

a. Braking (Longitudinal) Friction

Application of braking torque inputs to a

wheel, rolling at zero slip and camber angles,

results in a longitudinal force acting parallel

to the wheel plane in a direction opposite to

the direction of wheel motion. Longitudinal

reaction force is modified by the rolling

resistance of the tire which increases braking

force.

As the braking force at the wheel is

increased, slippage will occur between the

tire and the road surface. To generate

slippage, the rotational speed of the tire must

be less than the speed of the wheel center

and, therefore, the vehicle. This slippage

between the tire and road surface is the

longitudinal slip defined earlier.

Longitudinal friction properties of tires

have been measured and tabulated for

numerous combinations of tire/load/road/

environmental conditions in the form of

muX-slip curves. (This type of data is quite

prevalent in the public domain for passenger

car tires while similar data for truck tires are

sparse.)

The braking force that a tire is capable of

developing varies with wheel slip in

accordance with the typical curve shown in

Figure 2. The shape of the muX-slip curve

illustrates the classic features of longitudinal

force generation. The braking or longitudinal

force is zero when the tire is free rolling,

reaches a peak at about 10–20 percent slip

and then falls off to a somewhat lower level

when the tire is operating at 100 percent slip,

i.e., fully locked (sliding).

The initially steep increase of longitudinal

force with increasing slip reflects the

circumferential elasticity of the tire’s carcass

and tread structure. As the brakes are applied

with increasing amounts of torque, the elastic

capability of the tire in the footprint area is

exceeded and sliding begins to take place at

the rear of the footprint. Beyond the elastic

region, the force output reaches a peak as all

of the tread elements traversing the contact

patch begin to slide relative to the roadway.

Beyond peak friction, any increase in brake

torque causes sliding across the entire

footprint and the tire rapidly goes into full

lockup. In this regime, frictional coupling

between the tire and road degrades due to

rubbing speed and heating effects, hence, the

characteristically negative slope at high slip

level.

The shape of this curve (see Figure 3) is

dependent upon the tire characteristics and

the road surface properties. Typically, the

peak is relatively high on dry roads but tire

force fall-off is small. On wet roads, the peak

is lower and the fall-off as the wheel locks

is much greater.

Another form of hysteresis that affects ABS

design is related to the braking force versus

wheel slip characteristics. As both the peak

and slide coefficients of friction become

lower on more slippery road surfaces, the

time necessary for a locked (or nearly locked)

wheel to spin up to near the vehicle’s

velocity increases. This results from the

reduced force generating capability of tires

on low friction road surfaces together with

mass of the rotating components that include

the wheel. On the drive axles of heavy

vehicles, this mass, which includes the tire,

wheel, axle assembly and axle differential

components, can be great enough to require

more than one-half second for a locked wheel

to spin up to the vehicle’s speed on very

slippery road surfaces such as ice.

For pneumatic tires, the magnitude of the

braking force is dependent upon tire

construction properties, tread depth, amount

of loading, wheel speed (velocity), the type

and condition of the road surface and the

amount of slippage between the tire and the

roadway. With regard to maximum braking

capability, the pertinent features of the muXslip curve are the peak value of braking force

coefficient, the peak coefficient of friction,

and the slide value under the locked-wheel

condition at 100 percent slip, the sliding

coefficient of friction.

In the preamble of this notice, the terms

skid number and peak friction coefficient

(PFC) are used. These terms represent the

results of a test to determine the longitudinal

friction characteristics of a road surface using

a specific test procedure, the American

Society for Testing and Materials (ASTM)

Method E1337–90 procedure, a specific tire,

the ASTM E1136 SRTT tire, and a specific

test device, an ASTM traction trailer. Skid

number is the result of the ASTM test which

characterizes the slide value of the friction

coefficient between the ASTM tire and the

road surface being measured. The peak

friction coefficient, PFC, is the result of the

ASTM test which characterizes the peak

value of the friction coefficient between the

ASTM tire and the road surface being

measured.

The friction force potential of truck tires is

significantly less than that for car tires. The

difference is due primarily to the rubber

compounding used to achieve the high tread

life typically achieved with truck tires and

the higher pressures in the tires that result in

higher footprint loading. The braking

performance of any vehicle is ultimately

limited by its tire properties. Thus, given

current truck tire properties, heavy vehicles

cannot perform as well as passenger cars in

braking situations even if they have braking

systems that are 100 percent efficient (i.e., a

braking system that would utilize all of the

available tire/road friction).

b. Cornering (Lateral) Friction

In addition to braking forces, tires must

also generate lateral—or cornering—forces to

direct the vehicle in accordance with steering

inputs from the driver or in response to other

lateral forces such as crosswinds.

Tire friction characteristics in cornering are

described by the relationship between lateral

force coefficient and slip angle.

The lateral force that an unbraked tire is

capable of developing varies with slip angle

in accordance with the typical curve shown

for the free rolling tire in Figure 4. The single

most important feature of the force generating

capability of a tire, as it relates to vehicle

control and stability, is the ability of a rolling

tire to generate forces perpendicular to the

tire’s direction of travel.

c. Combined Braking/Cornering Friction

When braking a vehicle, it is necessary to

generate both braking and cornering forces at

the wheels if the vehicle is to be stopped

without deviating from its intended path.

The situation is identical when a driver must

brake severely while negotiating a curve or

lane change where cornering forces are

required to keep the vehicle from sliding

towards the outside of the turn while the

braking forces decelerate the vehicle.

In braking-in-a-curve maneuvers, tire

friction properties are determined primarily

by the peak and slide values of the resultant

braking-cornering coefficients. Figure 4

shows the lateral force coefficient versus slip

angle relationships for a free rolling tire and

for a braked tire at different amounts of

wheel slip, including 100 percent (locked

wheel condition). All of the curves converge

at a slip angle of 90° as expected, since the

tire is perpendicular to the direction of

travel.

At small slip angles, the lateral force

capability under locked wheel conditions is

much lower than that of a free-rolling wheel.

It should be noted that although this figure

shows that the tire is capable of generating

lateral force in the locked wheel, 100 percent

wheel slip condition, this force is ‘‘lateral’’ in

relation to the tire itself. In this situation, the

only force generated by the tire is opposite

to its direction of travel, and its ‘‘lateral’’

component results from the tire’s being

steered away from its direction of travel. This

locked wheel, ‘‘lateral’’ force is basically

equal to the sliding coefficient of friction of

the tire times the vertical load on the tire

times the sine of the slip angle.

Lateral is a relative term whose meaning

depends upon the object or direction to

which it relates, i.e., lateral in relation to the

vehicle is not the same as lateral in relation

to a tire steered relative to the vehicle, and

is also not the same as lateral with respect

to the vehicle’s direction of travel.12 Earlier

in this notice and in the previous notices

related to this Final Rule, the phrase lateral

stability has been used to describe whether

or not a vehicle can resist yawing or spinning

in response to some external lateral force

acting on the vehicle. As long as the vehicle’s

direction of travel is the same as or very close

to the direction in which the vehicle is

pointed no significant confusion results.

However, once a vehicle has begun to yaw or

spin and its direction of travel is significantly

different than the direction in which the

vehicle is pointed, confusion can result

regarding the meaning of lateral stability and

lateral tire forces. To eliminate any

confusion, the term directional stability (or

directional stability and control) will be used

throughout the remainder of this notice in

place of lateral stability (or lateral stability

and steering control).

With respect to the tire forces related to a

vehicle’s directional stability and control, the

phrase, ‘‘stabilizing tire forces’’ will be used

to describe tire forces that act perpendicular

to the vehicle’s direction of travel, instead of
13262 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

13A low mu surface is one that is relatively

slippery and thus provides lower levels of braking

force and poorer directional stability and control

during braking. These surfaces, which are typical

on wet roads, are also referred to as low coefficient

of friction surfaces.

the phrase ‘‘lateral tire forces’’ the meaning

of which can be unclear relative to the

vehicle’s direction of travel. As indicated

earlier, a tire’s ability to generate such

‘‘stabilizing tire forces’’ is the single most

important feature of the force generating

capability of a tire, as it relates to vehicle

directional control and stability.

The graph in Figure 4 can be used to

illustrate how tire traction characteristics

influence vehicle directional stability. For

example, if a single-unit vehicle negotiates a

cornering maneuver with the front wheels at

4° slip angle and the rear wheel at 3° slip

angle, and the application of braking pressure

results in 20 percent slip at the front tires

while the rear tires become locked, the data

indicate that the lateral force coefficient at

the front would decrease from 0.55 to 0.25

while the corresponding decrease at the rear

would be from 0.45 to 0.03. In this case, the

lateral force capability at the front would be

eight times greater than at the rear. Because

of the greatly reduced stabilizing forces on

the rear tires, they would no longer be

capable of resisting the vehicle yaw induced

by the forces on the front tires, and the

vehicle would spin out.

Tire loading also affects the amount of slip

which occurs at the various wheels on a

vehicle. For example, weight is transferred

from the inside to the outside wheels of a

vehicle when it is driven around a corner.

Therefore, the wheels on the inside of the

vehicle will operate at a lighter tire load and

hence, when generating the same braking

force, will operate at a higher percentage of

wheel slip than their counterparts on the

outside of the vehicle. In tractor-trailer

combinations, improper load distribution can

produce unequal axle loadings between the

tractor and trailer. If both the tractor and

trailer brakes are applied equally, increased

wheel slip will occur at the wheels which are

carrying the lightest load. If the improper

load distribution is severe enough, wheel

lockup and skidding can occur at otherwise

normally acceptable deceleration rates.

4. Vehicle Loss of Control

Heavy vehicles are likely to experience

wheel lockups in maximum braking

situations because of the friction properties

of their tires and the less than optimal force

distributions of their brake systems. Lockup

of all of the wheels on one or more of a

vehicle’s axles, if not responded to by the

driver, will usually result in either a loss of

steering control or loss of the vehicle’s

directional stability.

a. Single-Unit Trucks

A single-unit truck behaves much like a

passenger car when wheel lockup occurs.

Figure 5 shows a simple single unit vehicle

(car or truck) with only its front wheels

locked. Such a vehicle, with only the front

wheels locked and the rear wheels rolling,

will experience a loss of steering control. The

vehicle cannot be steered, but it is stable due

to the stabilizing forces provided by the

rolling rear wheels and does not tend to yaw

or spin out.

Figure 6 shows a simple single unit vehicle

(car or truck) with only its rear wheels

locked. In this case, the vehicle will

experience a loss of directional stability. It is

very unstable and the slightest side force

disturbance (i.e., lateral force due to steering,

side slope or road crown, crosswind, unequal

front axle braking, etc.) results in the vehicle

yawing significantly or spinning out.

If all wheels are locked, the vehicle cannot

be steered but is not as likely to spin.

b. Combination-Unit Vehicles

With combination-unit vehicles, the effect

of wheel lockup is more complex but can

easily be inferred from the simple single-unit

vehicle case by treating each vehicle in the

combination as a single-unit vehicle.

If the wheels on the steering axle lock, the

vehicle, experiencing a loss of steering

control, will travel essentially in a straight

path, stable but unsteerable, as illustrated in

Figure 7. Usually a driver immediately senses

this condition and, if conditions permit, can

modulate the brakes to allow the steering

axle wheels to spin up and regain

steerability.

If the trailer wheels lock, the trailer will

experience a loss of directional stability and

(if side force disturbances are present) will

swing to the outside of the vehicle path, as

shown in Figure 8. However, because trailer

wheelbases are long in comparison to the

tractor, this unstable yawing response is

slower. Thus, a driver again, if conditions

permit and if the driver is aware of the

condition soon enough, may have time to

modulate the brakes to spin up the trailer

wheels and bring the trailer back in line. As

a trailer becomes shorter, this possibility of

correction becomes less likely.

If the tractor’s drive axle wheels lock, the

truck tractor will experience a loss of

directional stability and the combination

vehicle will begin to jackknife if a side force

disturbance exists, as shown in Figure 9.

When this occurs, the process usually

becomes irreversible as the driver is unable

to react fast enough to prevent total loss of

vehicle control, particularly when the tractor

has a short wheelbase. This instability

condition is the one which a driver is least

likely to be able to control.

As more units (and more articulation

points) are added to the combination, the

situation becomes more complex and the

modes of instability increase in number.

5. The Need for Antilock

As mentioned earlier, the only means by

which a driver is able to control the

direction, velocity, and path of a vehicle is

to apply steering, braking, and/or accelerator

inputs to the vehicle which in turn result in

forces and moments being generated by the

vehicle’s tires. A tire can only generate a

limited amount of frictional force. As the tire

is required to generate more force for braking,

its capability to generate stabilizing force is

reduced. Since the capability of a tire to

generate both braking (longitudinal) and

stabilizing (lateral) forces is determined by

the amount of wheel slip at which the tire

is operating, controlling wheel slip is the

only means by which it is possible to have

a tire generate a significant amount of

longitudinal force to decelerate a vehicle

while still maintaining the capability to also

produce sufficient amounts of stabilizing

force to steer the vehicle and to retain

directional stability.

As illustrated earlier, when the wheel slip

goes beyond the point at which maximum

(peak) braking force occurs, the tire’s

stabilizing force capability drops

dramatically, leading to a situation that can

result in loss of vehicle control. By sensing

and controlling wheel slip, an antilock

system automatically reduces the amount of

brake application pressure to prevent

prolonged, excessive wheel slip which would

compromise the vehicle’s directional stability

by reducing the stabilizing force capabilities

of the vehicle’s tires. An antilock system

which operates in such a manner is referred

to as a closed-loop system. The basic closedloop control algorithm for an ABS is as

follows:

1. The driver actuates the brake pedal (or

treadle valve) resulting in an application of

brake pressure to the vehicle’s foundation

brakes,

2. this generates brake torque at the

vehicle’s wheels that creates braking forces at

the tire/road interface,

3. this results in wheel slip (as discussed

above), the level of which is determined by

the ABS by sensing the rotational speed of

the vehicle’s wheels,

4. if the amount of wheel slip is not within

an ‘‘acceptable’’ range (which is determined

by the ECU, based on a predetermined set of

logic) the brake application pressure is

adjusted to return the level of wheel slip to

the acceptable range; i.e., if the level of wheel

slip is excessive, the brake application

pressure is reduced and if the level of wheel

slip is too low, the brake application pressure

is increased, but never to a level higher than

that which results from the driver’s actuation

of the brake pedal (or treadle valve).

Vehicles equipped with ABS, operating in

such a manner, usually have shorter stopping

distances compared to the same vehicle

without ABS, particularly on low mu

surfaces.13 An antilock system which

controls the wheel slip at the level that

results in the maximum amount of braking

force at the tire/road interface maximizes a

vehicle’s stopping capability and also

provides some directional stability

enhancement. On the other hand, antilock

systems which control wheel slip at levels

below that which results in peak braking

force generation will result in a greater

degree of directional stability but provide

lower levels of braking force resulting in

longer stopping distances.

6. General Antilock System Operation

The following discussion addresses three

different aspects of ABS operation. The first

aspect discussed is the control strategies used

by an ABS to monitor wheel rotational speed

and adjust brake application pressure to

control wheel slip at an individual wheel.

The second relates to the various component

configurations that are used to control the

wheels on an axle or a tandem axle set. The

third is the control strategies used to control

the wheels on an axle or tandem axle set.
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13263

14The following discussion, which is largely

based on the previously referenced Leasure and

Williams SAE, paper specifically addresses ABS

control modes for air brake systems. Similar control

strategies are used in hydraulic ABSs with the

specific parameters of the control modes differing

due to differences in the brake torque versus brake

pressure application characteristics of air and

hydraulic brake systems.

a. ABS Wheel Slip Control Strategies

The goal of an antilock system is to prevent

wheel slip on the controlled wheels from

exceeding that which provides a good

compromise between providing near

maximum levels of braking force and

providing sufficient levels of stabilizing

forces to assure that the vehicle will remain

directionally stable without reducing the

wheel slip below that which produces

braking force which utilizes most of the

friction (adhesion) that is available at the

tire/road interface. Once wheel slip goes

beyond the point which provides peak

braking traction, both braking and cornering

traction are reduced, as shown in Figure 10

for a truck tire cornering at an 8° slip angle.

Early mechanical antilock systems

controlled slip by the use of an assembly at

the wheel which contained an inertia disc

that rotated freely with the wheel when

brakes were not applied. Braking the wheel

caused it to decelerate while the inertia disc

tried to continue to rotate at the original

speed, but was restrained by a triggering

mechanism. This triggering mechanism

controlled an air valve (modulator valve)

which when activated, shut off air pressure

to the foundation brake air chambers and

exhausted pressure already in the chambers.

When deceleration of the wheel exceeded

about ‘‘1g,’’ the inertia of the disc generated

enough force to trip the mechanism

activating the modulator valve. As braking

force decreased and the wheel speeded up,

the force exerted by the inertia disc

decreased, allowing the trip mechanism to

deactivate the modulator valve, thus,

reapplying the brakes.

Electronic antilock systems act in a manner

similar to the early mechanical systems

except they are more sophisticated as a result

of their computational capability. With

electronic systems, the mechanical wheel

assembly is replaced by a wheel speed sensor

and an electronic control module (ECU).

Wheel speed sensors, which are located at

the wheels or within the axle housings,

constantly monitor wheel speed (or a

component whose speed is proportional to

the wheel speed) sending electrical signals to

the ECU which are proportional to the wheel

speed. The ECU determines wheel speed and

changes in wheel speed (acceleration and

deceleration) based on these signals.

The following discusses two basic control

modes 14 used by electronic ABSs to control

brake applications at a wheel in response to

wheel speed sensor signals.

In the acceleration/deceleration threshold

mode of operation, the ECU recognizes the

rapid wheel deceleration that occurs as

wheel slip exceeds the peak friction wheel

slip (Figure 11), and electrically commands

the modulator valve to reduce brake

application pressure and, thus, brake torque.

When brake torque decreases enough to

cause braking force to be less than the

friction force at the tire/road interface, the

wheel stops decelerating and begins to

accelerate. The rate of acceleration increases

with the increasing friction associated with a

reduction in wheel slip. When wheel slip

falls to the level corresponding to peak

braking force, the acceleration rate peaks and

starts to decrease with wheel slip. The ECU

senses this change in acceleration rate and

commands the modulator valve to start

increasing brake application pressure and the

cycle repeats.

In the reference speed mode of operation,

the ECU tracks wheel speed information

which it uses to estimate vehicle speed. The

antilock system uses this estimated speed to

compute a ‘‘reference speed’’ which is less

than the estimated speed by a

preprogrammed factor. The reference speed

is updated throughout a stop as illustrated in

Figure 12. This figure also illustrates how the

ECU in one manufacturer’s 1970’s system

uses this reference speed as a cue to

modulate the brake application pressure.

When the brakes are applied as shown in the

figure, the wheel starts decelerating. As

wheel speed falls below the reference speed

(point ‘‘G–1’’), the antilock system acts to

reduce brake pressure. After brake pressure

has been reduced long enough to allow the

wheel speed to roll up to that of the reference

speed (point ‘‘G–2’’), the antilock system acts

to increase brake pressure. This cycle

continues until the vehicle is stopped.

Today’s antilock systems usually combine

acceleration/deceleration threshold logic and

speed reference logic in some fashion. Both

are believed necessary to improve the

efficiency of antilock systems to account for

the variance of tractor performance with

surface (Figure 13), slip angle (Figure 14,

vehicle speed (Figure 15), etc.

If an antilock system waits for the

threshold deceleration associated with peak

braking friction under some conditions, the

ability of the wheel to provide cornering

friction will have been compromised

severely. Therefore, a threshold reference

speed needs to be established around 30

percent to prevent excessive wheel slip.

Figure 16 shows a typical control cycle for

one manufacturer’s antilock system which

uses a ‘‘hold’’ pressure phase, as well as a

release pressure phase. This ECU uses two

wheel slip thresholds (K1 and K2) and two

deceleration thresholds (¥b and b) in making

decisions regarding control of the modulator.

The ECU tracks the information from all of

the vehicle’s wheel speed sensors (even

when the brakes are not applied) and uses

this information to compute a reference

speed which it continually updates. In the

panic stop in Figure 16, the wheel

decelerates until the wheel speed sensors

indicate a deceleration which the vehicle

cannot physically attain (point 1). At this

point, the reference speed, which until this

instant has corresponded to the wheel speed,

now separates from the wheel speed and

decreases according to an empirically

determined rate of deceleration.

At point 2, the deceleration threshold ¥b

is reached and the wheel runs into the

unstable range of the traction curve. The

wheel has exceeded the maximum braking

force and any further increase in braking

torque only increases wheel deceleration.

Brake pressure is, therefore, quickly reduced

and wheel deceleration falls after a short

time. This deceleration time is determined by

the hysteresis time lag between the time the

modulator valve actuates to release the air

pressure to the time that the air pressure in

the air brake chamber, the hysteresis of the

foundation brakes and the hysteresis related

to the time needed for the wheel (and its

associated rotating components) to spin up

after it has been locked. Only after this delay

does a further pressure fall also lead to

reduction of wheel deceleration.

The deceleration signal ¥b is traversed at

point 3 and brake pressure is held constant

for a fixed time T1. Normally wheel

acceleration will rise above the threshold +b

at a point 4 within this holding time T1.

Provided this happens, brake pressure will

continue to be held constant. (Were the +b

signal not produced within the time T1, as

with very low friction surfaces, then brake

pressure would be again reduced in response

to the slip signal. The time constant, T1, is

determined for each vehicle/brake system

based on the influences of the various kinds

of hysteresis previously discussed).

During the constant pressure phase, the

wheel accelerates in the stable slip range, the

+b signal being traversed again at point 5 at

which time utilized adhesion is just below

the maximum on the traction curve. The +b

threshold is used this time to signal a rapid

pressure increase over time T2 to overcome

brake hysteresis.

The time T2 is preprogrammed for the first

control cycle and then recalculated for each

subsequent control operation depending

upon the response of the wheels. After this

rapid pressure increase stage, brake pressure

is raised again but at a lesser gradient by

alternate pressure increase and hold pulses.

As a rule, the deceleration threshold ¥b is

again reached during the pulsing phase at

point 9, and brake pressure falls. The

procedure repeats itself as long as the brake

pedal is depressed too forcefully for the

existing road conditions or until the vehicle

speed drops below a specified value.

The logic presented here in principle is not

fixed, but, matched by microcomputers to the

dynamic response of the wheel under

differing adhesion conditions. Not only are

ABSs capable of ‘‘adapting’’ to various

conditions by employing complex algorithms

to control wheel slip, but they are also able

to ‘‘adapt’’ the parameters of those

algorithms, as with the T2 parameter

discussed above, to improve the system’s

ability to control wheel slip over the broad

range of road surface and vehicle load

conditions under which heavy vehicles

operate. One obvious result of this

adaptability is the range of ABS cycle times,

or controlling frequencies, that result when

controlling wheel slip under various road

surface and vehicle load conditions.

Figures 17 and 18 illustrate the effects of

two very different situations of load and road

surface conditions on the ABS cycle times

and how an air brake ABS adapts its control

of wheel slip. Figure 17 shows treadle valve

pressure, and brake chamber pressure, wheel

speed and ABS modulator solenoid activity
13264 Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations

for the left wheel of the intermediate drive

axle for a full treadle application stop of a

Freightliner 6×4 conventional truck tractor

with a WABCO 6S/6M ABS in a lightly

loaded condition on a very low friction

surface, ice. The figure shows the first five

ABS cycles for that stop. To characterize ABS

cycle time, the ABS cycle is assumed to begin

when brake pressure begins to rise in the

brake chamber and that rising brake chamber

pressure leads to excessive wheel slip or

wheel lockup. This excessive wheel slip is

sensed by the ECU which actuates the

modulator valve to decrease brake chamber

pressure to reduce wheel slip to an

acceptable level. This ‘‘initial’’ rise in brake

chamber pressure can result from an increase

in the driver’s level of brake application, i.e.,

rising treadle valve pressure, or from an

increase resulting from the ECU signaling the

modulator valve to increase brake chamber

pressure. The ABS cycle ends when, after the

reduction in brake chamber pressure

resulting from actuation of the modulator

valve, the brake chamber pressure begins to

again rise in response to the ECU signaling

the modulator valve to increase brake

chamber pressure. For the five ‘‘ABS cycles’’

shown in Figure 17–a, the ABS cycle times

range from 0.72 seconds to 0.80 seconds, i.e.,

an ABS controlling frequency of from about

1.2 to 1.4 cycles per second.

Two things shown in Figure 17–b are of

note. The first is the time required for the

wheel to lock after the initial brake

application which is very short, about 0.04

seconds. The second is the time required for

the wheel’s speed to increase to that of the

vehicle after the wheel has locked, i.e., the

wheel’s spin up time. The spin up times

shown in Figure 17–b range from 0.20

seconds for the fourth ABS cycle (wheel spin

up begins at about 3 seconds on the time

scale) to 0.34 seconds for the first ABS cycle

(wheel spin up begins at about 0.5 seconds

on the time scale). The rate of wheel spin up

can be characterized by the acceleration of

the outer surface of the tire, i.e., the tread of

the tire, relative to the wheel center. In the

case of the wheel spin up during the first

ABS cycle, the spin up time is 0.34 seconds

and the change in wheel speed over that time

is 11.3 mph; the wheel’s acceleration is

therefore 33.2 mph per second or 48.8 feet

per second per second.

In contrast to the ABS cycle time and

wheel spin up rates shown in Figure 17,

Figure 18 illustrates a situation where the

ABS cycle times are much shorter and the

wheel spin up rates are much faster. Figure

18 shows treadle valve pressure, and brake

chamber pressure, wheel speed and ABS

modulator solenoid activity for the left

wheels of the tandem drive axles for a full

treadle application stop of a Volvo-GM 6×4

conventional truck tractor with a Bosch 6S/

4M ABS in a lightly loaded or bobtail

condition on what is believed to be a high

friction surface. The reason for the

uncertainty of the conditions under which

this stop took place is that this data resulted

from the monitoring and recording of ABS

event occurrences during the agency’s truck

tractor fleet study and no details are available

regarding the exact circumstances of this

stop. However, given the high average

deceleration rate of this stop, more than 16

feet per second per second which if sustained

during a stop from 60 mph would result in

a stopping distance of less than 240 feet, it

is reasonable to assume that the surface had

a rather high coefficient of friction. Given

this and the low level of brake chamber

pressure at which excessive wheel slip

occurs, between 15 and 30 psi, it is

reasonable to assume that the vehicle was

lightly loaded and may even have been a

bobtail situation.

It should be noted that the various data

traces shown in Figure 18 are rough

‘‘stairsteps’’ during the first second of data.

The reason for this is that the data

monitoring/recording equipment used in the

truck tractor fleet study used a data sampling

rate of 10 samples per second while

monitoring ABS activity. When an ‘‘ABS

braking event’’ was detected the equipment

began to use a data sampling rate of 50

samples per second. The equipment then

stored the data for the one second prior to the

‘‘ABS braking event’’ at a 10 sample per

second rate and for the entire ‘‘event’’ at a 50

sample per second rate.

With regard to the ABS controlling

frequency shown in Figure 18, unlike the

situation shown in Figure 17, the ABS cycles

are not discrete cycles where the wheel goes

to complete lockup and then the brake

application pressure is reduced to zero. To

estimate the ABS controlling frequency in

this situation, an ABS cycle is characterized

by a decrease in brake chamber pressure

followed by an increase in brake chamber

pressure where these pressures are less than

the treadle valve pressure so as to be sure

that the brake chamber pressure is being

controlled by the ABS. Using this criteria,

Figure 18–a shows that between two and

three seconds on the time scale the brake

chamber pressure goes through about 9 such

‘‘cycles’’, i.e., an ABS controlling frequency

of about 9 cycles per second. This is more

than 6 times faster than the fastest ABS

controlling frequency shown in Figure 17–a

for the stop on an ice surface.

With regard to the wheel spin up time for

the stop shown in Figure 18–b, just after time

equals 3 seconds, there is a large decrease in

wheel speed for left rear drive wheel

followed by a steep increase in speed of that

wheel. This wheel speed increase is 7.3 mph

and occurs over 0.06 seconds, i.e., a wheel

acceleration of 121.7 mph per second or

178.4 feet per second per second. This is

more than 3.5 times higher than the wheel

acceleration rate for the ‘‘ice’’ stop shown in

Figure 17–b. Since, as indicated earlier,

hydraulic brake systems generally have much

lower levels of hysteresis than air brake

systems, everything tends to happen faster in

hydraulic brake systems and, as such, the

controlling frequency for hydraulic brake

ABS can be significantly higher. The logic

used in different systems also varies with the

control strategy utilized and the number of

wheel speed sensors.

A difficult task for air brake antilock

systems, with regard to controlling slip, is the

prevention of wheels going into ‘‘deep

cycles’’ (wheel slips in the high wheel slip

part of the friction curve where both braking

and cornering friction are reduced). Deep

cycles are particularly undesirable in the first

cycle of an antilock system operation where

the demand for cornering friction can be the

highest because of the speed of the vehicle.

The extent to which an antilock system goes

into a deep cycle depends on how effectively

the modulator controls air into and out of the

air chambers. Figure 19 shows how a 1970’s

antilock system was not able to reduce the air

pressure fast enough in a panic application

to prevent some wheel lockup. The electronic

antilock systems of today, because of the

versatility of digital technology (and

compatible pneumatic valving) have an

expanded control range that provides for

better air pressure control to respond to

conditions and to prevent overpressurizing

air chambers. This makes possible the

reductions in deep cycling shown in Figure

20.

The hysteresis of foundation brakes can

have significant effect on the ability of an

antilock system to prevent ‘‘deep cycles.’’

Although an antilock system may quickly

detect impending wheel lock and rapidly

actuate the modulator valve to reduce the air

pressure in the air chambers, the three types

of brake system hysteresis discussed earlier

may prevent an immediate reduction in brake

torque and rapid spin up of the wheel

causing deeper wheel cycles than desired.

Figure 19 shows an example of how the

inherent hystereses of the pneumatic

components and foundation brakes of air

brake systems, and the hysteresis related to

wheel spin up times affect how quickly an

ABS can respond to and control wheel slip.

The effect of the pneumatic hysteresis can

easily be seen in the release of chamber

pressure portions of the ABS cycles. It takes

from 0.08 to 0.22 seconds for the chamber

pressure to decrease to 3 pounds per square

inch, the chamber pressure at which wheel

spin up begins for several of the ABS cycles.

The effect of foundation brake hysteresis can

not be estimated without data on the brake

torque acting on the wheel. However, it may

not be significant since this type of hysteresis

is most significant at high brake chamber

pressures. As shown in Figure 17, the

hysteresis time lags related to wheel spin up

range from 0.20 to 0.34 seconds. The ABS

cycle times of up to 0.80 seconds shown in

Figure 17, are the result of these properties

of the foundation brakes and tires used on

heavy vehicles today.

The inherent hystereses of the pneumatic

components and foundation brakes of air

brake systems and in the tire spin up rates

of heavy vehicle wheel/tire assemblies have

to be considered in the design of antilock

systems. It also has to be recognized that

different brake types/configurations can have

different amounts of hysteresis. An antilock

system which works efficiently with one type

of brake may not work as efficiently with

another type of brake.

b. ABS Single and Tandem Axle Component

Configurations

Several types of ABS configurations are

currently available for heavy vehicles. In

order of decreasing complexity and cost, the

systems for tractors include those with: (1)

individual control of the wheels on an axle;

(2) side-to-side control of the wheels on a

tandem axle set; (3) axle-by-axle control of
Federal Register / Vol. 60, No. 47 / Friday, March 10, 1995 / Rules and Regulations 13265

15With a split mu surface, the road is divided

along its length so that the wheels on one side of

the vehicle are on a high friction surface and the

wheels on the other side are on a low friction

surface. One example of a split mu surface is when

one portion of a lane is dry and another part is

covered with ice.

16Side-by-side control ABS can have two

different wheel speed sensor configurations. Either

all of the wheels on the tandem axle set have their

own wheel speed sensors, or only the wheels on

one axle of the tandem axle set have wheel speed

sensors.

17Tandem control ABS can have two different

wheel speed sensor configurations. Either all of the

wheels on the tandem axle set have their own

wheel speed sensors, or only the wheels on one axle

of the tandem axle set have wheel speed sensors.

the wheels on a tandem axle set; and (4)

tandem control of all of the wheels on a

tandem set. With individual wheel control,

the most complicated and costly type of ABS,

each of the wheels on an axle is individually

monitored and controlled using wheel-speed

sensors and modulator control valves for

each wheel. This prevents lockup at each

wheel and thus provides optimum stability

and control, especially on a split mu

surface.15 With side-to-side control,16 all of

the wheels on one side of a tandem axle set

are controlled together by one modulator in

response to wheel speed sensor signals from

one or more of those wheels. With axle-byaxle (or simply, axle) control, the wheels on

an axle (either on a single axle or on each

axle of a tandem axle set) are controlled

together by one modulator in response to

wheel speed signals from the wheels on that

axle. With tandem control,17 all four (or in

some cases, six) wheels on a tandem (or

tridem) axle set are controlled together by

one modulator in response to wheel speed

signals from the wheels on one or more of the

axles in the tandem (or tridem) axle set.

ABS technology has improved dramatically

in recent years given the use of computerized

components. Unlike the antilock brake

systems in the 1970s that primarily relied on

an analog control technology, current

generation antilock systems use advanced

digital control technology that enhances the

systems’ efficiency. Digital logic permits the

use of more complex and sophisticated

control strategies and reduces the time lags

in the antilock computer. More generally,

digital technology applied to motor vehicles

has been significantly refined in the last

twenty years to control motor vehicle fuel

systems so that vehicles can comply with

fuel efficiency and pollution prevention

regulations.

c. ABS Single and Tandem Axle Control

Strategies

As discussed above, there are several

different component configurations used to

equip an axle or axles with ABS.

For each of the configurations for which

more than one wheel is controlled by one

modulator, different wheel slip control

strategies can be used by the ABS to control

wheel slip of those wheels. These are select

low regulation (SLR), select high regulation

(SHR), and modified select high regulation

(MSHR), also called ‘‘Select Smart’’ (Bendix)

or select low high regulation (SLHR).

The select low regulation strategy

modulates the brake pressure application at

both wheels of an axle at the same level

based on the wheel speed signals from the

wheel that experiences the higher level of

wheel slip. On split mu surfaces, this control

strategy results in near peak braking force on

the wheel that experiences the higher level

of wheel slip (the wheel that is on the lower

friction side of the road) and less than peak

braking force on the wheel with the lower

level of wheel slip (the wheel on the higher

friction side of the road). One wheel

operating at a lower level of wheel slip and

on a surface with a higher friction level

means that wheel has a greater capability to

provide additional stabilizing force;

therefore, providing a higher level of

directional stability and control for the

vehicle. However, on split mu surfaces with

the coefficient of friction on one side of the

road surface being very different than on the

other side, this can result in extended

stopping distances since the wheel on the

high coefficient of friction side is providing

much less than the maximum level of braking

force than can be provided by that surface.

The select high regulation strategy

modulates the brake pressure application at

both wheels of an axle at the same level

based on the wheel speed signals from the

wheel that experiences the lower level of

wheel slip. On split mu surfaces, this control

strategy results in lockup of the wheel that

experiences the higher level of wheel slip,

which results in that wheel providing less

than peak braking force and near peak

braking force on the wheel with the lower

level of wheel slip. One wheel operating at

a locked wheel condition means that wheel

has essentially no capability to provide any

stabilizing force, and the other wheel

operating at a higher level of braking force

(near the maximum available on the high

friction side of the road) means that wheel

would have a reduced capability to provide

stabilizing force. This results in a reduced

level of directional stability and control for

the vehicle compared to the SLR strategy.

However, on split mu surfaces with the

coefficient of friction on one side of the road

surface being very different than on the other

side, SHR results in shorter stopping

distances compared to the SLR strategy since

the wheel on the high coefficient of friction

side is providing near peak braking force.

The modified select high regulation

strategy combines the SLR and SHR control

strategies. At the beginning of a stop which

results in excessive wheel slip at one wheel,

the ABS controls wheel slip using the SLR

strategy. While doing so, the ECU monitors

the level of wheel slip on the wheel which

has the lower level of wheel slip (the wheel

on the high friction side of the road), and

from that information, the ECU estimates the

ratio of the coefficient of friction on the high

friction side of the road to that on the low

friction side. If this ratio exceeds a preset

threshold and the vehicle speed is above a

preset threshold, the ECU increases the brake

application pressure to the wheels which

increases the braking force provided by the

wheel with the lower level of wheel slip (the

wheel on the high friction side of the road)

and which locks the wheel with the higher

level of wheel slip (the wheel on the low

friction side of the road). The ECU then

begins to control wheel slip using the SHR

strategy which results in a higher level of

vehicle deceleration (shorter stopping

distance) than would result from the use of

the SLR strategy. However, as noted above,

this results in a reduced capability of the

both wheels to provide stabilizing forces,

therefore reducing the vehicle’s overall level

of directional control and stability. Another

feature of the MSHR strategy is that even

when the vehicle velocity and ratio of

coefficients of friction of the split mu surface

thresholds are exceeded, the ECU does not

immediately switch to the SHR control

strategy to reduce the risk that the driver will

be surprised by an unexpected steering wheel

‘‘pull’’ that can result in that control mode.

Instead, the time period over which the

system transitions from SLR to SHR control

is adjusted based on the vehicle’s velocity.

For the individual wheel control

configuration in which each wheel is

controlled by its own modulator, there are

two wheel slip control strategies:

independent regulation (IR) and modified

independent regulation (MIR). As its name

implies, the independent regulation control

strategy controls the wheel slip of each wheel

on the axle independently, allowing each

wheel’s ABS to modulate the brake

application pressure to each wheel in

response to the signals from the wheel speed

sensor at that wheel to maximize braking

forces while maintaining sufficient capability

to produce stabilizing forces to ensure

vehicle directional stability. Although this

control strategy is the most effective at both

minimizing stopping distance as well as

ensuring vehicle stability, when used on the

steering axle of trucks, truck tractors and

buses, this can lead to significant steering

wheel ‘‘pull’’ on split mu surfaces which can

be difficult for the driver to control.

Therefore, ABS manufacturers have

developed the MIR control strategy in which

the wheel slip is controlled using the SLR

strategy at the beginning of the stop. This

results in equal braking forces at each wheel

which alleviates steering wheel ‘‘pull’’ that

would occur on a split mu surface with IR

control of the steering axle brakes. After a

short period of time, the ECU smoothly

transitions to true IR control so that the

buildup of any steering wheel pull is gradual

so that it can easily be controlled by the

driver. NHTSA understands that MIR control

strategy is used exclusively by all vehicle

manufacturers on vehicles which have

independent sensor/modulator ABS on the

steering axle. It should be noted that the SLR

strategy also eliminates the problem of

steering wheel ‘‘pull’’ on split mu surfaces,

but as indicated above does not provide as

effective use of the friction available on the

high friction side of such surfaces, resulting

in longer stopping distances.

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[FR Doc. 95–5410 Filed 3–7–95; 8:45 am]

BILLING CODE 4910–59–C