Federal Motor Vehicle Safety Standards; Air Over Hydraulic Brake Systems

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 94-56; Notice 2]

RIN 2127-AF01

Federal Motor Vehicle Safety Standards; Air Over Hydraulic Brake

Systems

AGENCY: National Highway Traffic Safety Administration (NHTSA),

Department of Transportation.

ACTION: Final rule.

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SUMMARY: In response to a petition submitted by Mr. John Kourik, this

final rule amends Standard No. 121, Air Brake Systems, to include a

definition of air-over-hydraulic brake subsystems. The agency believes

that this definition will clarify the classification of vehicles

equipped with these subsystems and thus eliminate the need for

manufacturers to request, and the agency to provide interpretations

about those vehicles.

DATES: Effective date. The amendments in this final rule become

effective August 17, 1995.

Petitions for reconsideration. Any petitions for reconsideration of

this final rule must be received by NHTSA no later than August 17,

1995.

ADDRESSES: Petitions for reconsideration of this rule should refer to

Docket 94-56; Notice 2 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. Richard Carter, Office of Vehicle

Safety Standards, National Highway Traffic Safety Administration, 400

Seventh Street, S.W., Washington, D.C. 20590 (202-366-5274).

SUPPLEMENTARY INFORMATION:

I. Background

Air-over-hydraulic brake systems typically consist of an air brake

system from the treadle valve to an air brake chamber that provides the

mechanical force to actuate a hydraulic-operated master cylinder. In

turn, the hydraulic pressure from the master cylinder actuates the

brake shoes or pads. The air brake chamber unit combined with the

hydraulic-operated master cylinder is called the ``power cluster'' and

generally serves as the separating point between the air- and

hydraulic-actuated portions of the air-over-hydraulic brake system.

Air-over-hydraulic brake systems are installed on slightly more

than one percent of medium and heavy trucks sold in the United States.

This percentage represents about 5,000 vehicles, most of which are

Class 6 vehicles with gross vehicle weight ratings (GVWRs) between

19,501 and 26,000 pounds.

Federal motor vehicle safety standard No. 121, Air brake systems,

currently defines ``air brake system'' to mean

A system that uses air as a medium for transmitting pressure or

force from the driver control to the service brake, but does not

include a system that uses compressed air or vacuum only to assist

the driver in applying muscular force to hydraulic or mechanical

components.

(49 CFR Sec. 571.121) Part 570, Vehicle In Use Inspection Standards,

defines ``Air-over-hydraulic brake system'' to mean

A subsystem of the air brake that uses compressed air to

transmit a force from the driver control to a hydraulic brake system

to actuate the service brakes.

(49 CFR Part 570, emphasis added) The underlined portion of the

definition of air-over-hydraulic subsystem explicitly states that an

air-over-hydraulic brake subsystem means a subsystem of the air brake

system.

In initially issuing Standard No. 121, NHTSA stated that

It should be noted that the term ``air brake system'' as defined

in the standard applies to the brake configuration commonly referred

to as ``air-over-hydraulic,'' in which failure of either medium can

result in complete loss of braking ability.

(36 FR 3817, February 27, 1971). The agency reiterated that an air-

over-hydraulic brake system is subject to Standard No. 121, stating

that ``Standard No. 105a [Hydraulic Brake Systems] does not apply to

vehicles equipped with `air-over-hydraulic' systems, which remain

within the purview of Standard No. 121 * * *. '' (37 FR 17970,

September 2, 1972.) Moreover, NHTSA has issued several interpretations

stating that a vehicle equipped with an air-over-hydraulic brake system

must comply with the requirements in Standard No. 121.

NHTSA received a petition from Mr. John Kourik, requesting that the

agency amend Standard No. 121 to specify that an air-over-hydraulic

brake subsystem is subject to that Standard. The petitioner stated that

such an amendment would avoid the need for manufacturers to request

interpretations about air-over-hydraulic brake systems.

II. Notice of Proposed Rulemaking and Public Comments

In response to Mr. Kourik's petition, NHTSA proposed amending

Standard No. 121 by expanding the current definition of air brake

system to incorporate the definition of air-over- hydraulic brake

subsystem. (59 FR 35298, July 11, 1994) The agency stated that even

though the definition of an air brake system currently includes a

description of an air-over-hydraulic subsystem, it is not explicitly

clear on the face of the standard that such a subsystem is classified

as an air-braked system and that a vehicle equipped with such a

subsystem would thus have to comply with the requirements in Standard

No. 121. NHTSA further stated that it would be appropriate to clarify

the classification of air-over-hydraulic brake systems. The agency

reasoned that amending the definition of an air brake system to state

explicitly that an air-over-hydraulic brake subsystem is classified as

an air brake system would eliminate the need felt by some manufacturers

to request interpretations regarding the standard's applicability to

vehicles equipped with air-over- hydraulic brake subsystems.

NHTSA received comments from Advocates for Highway and Auto Safety

(Advocates), the Heavy Duty Brake Manufacturers Council (HDBMC),

WhiteGMC Volvo (WhiteGMC), Freightliner, AlliedSignal, and Mr. Robert

Crail, a brake engineer. The commenters generally agreed with the

proposed amendment. Some commenters raised additional questions to

which the agency responds below.

III. Agency Determination

After reviewing the comments, NHTSA has decided to amend the

current definition of air brake system in Standard No. 121 to

incorporate the definition of air-over-hydraulic brake subsystem. The

agency believes that this amendment will clarify the agency's

requirements, as they apply to air-over-hydraulic brake systems. The

agency is making a minor modification to the definition consistent with

WhiteGMC's comment that the word ``system'' should follow ``air brake''

in the definition of air-over-hydraulic brake subsystem. NHTSA believes

that adding the word ``system'' is appropriate since Standard No. 121

defines ``air brake system'' and not ``air brake.''

HDBMC expressed concern about how the recent amendment requiring

antilock brake systems (ABS) would affect air-over-hydraulic

subsystems. Specifically, HDBMC stated that if the agency required

individual wheel

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control,1 two air to hydraulic converters would be needed on the

axle providing individual wheel control. The commenter continued that

this would result in ``brake pull'' which would reduce vehicle

stability and cause uneven brake lining wear.

\1\ The ABS final rule did not define ``individual wheel

control.'' (60 FR 13216, March 10, 1995) However, that rule defined

``Independently Controlled Wheel'' to mean a directly controlled

wheel for which the modulator does not adjust the brake actuating

forces at any other wheel on the same axle.

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NHTSA notes that the ABS final rule does not require single unit

vehicles to have independent wheel control. Instead, it requires only

certain axles on truck tractors to have independent wheel control.

Since air-over-hydraulic brake systems are only installed on single

unit vehicles, the problem referenced by HDBMC will not affect air-

over-hydraulic vehicles equipped with ABS. Therefore, no changes are

necessary to satisfy HDBMC's concerns.

AlliedSignal stated that it does not consider an air-over-hydraulic

brake system to be a subsystem of an air brake system. It recommended

that the agency reconsider the proposed definition of air-over-

hydraulic to be ``more `in tune' with the industry accepted

terminology.'' Specifically, it requested including wording to define

the lack of mechanical push-through and/or the definition contained in

ISO 611. The ISO definition states that an ``air-over-hydraulic

system'' means

A braking system in which the energy necessary to produce the

braking force arises exclusively from compressed air. This energy is

transformed to hydraulic energy by one or more air-hydraulic

converter(s). The hydraulic fluid actuates the brakes.

NHTSA has determined that the suggested ISO definition would add

nothing useful to the definition already proposed by the agency.

AlliedSignal's concern over the phrase ``no mechanical push-through''

is addressed in the definition of ``Air Brake System,'' which clarifies

that ``air-over-hydraulic'' is not the type of system which has

mechanical push-through. In an ``air-assisted'' brake system, if the

air or vacuum boost fails, there is still a means available to transmit

force to the brakes through the brake pedal. With regard to

AlliedSignal's comment on the word ``subsystem,'' Webster's Dictionary

states that it is a ``secondary or subordinate system,'' which is

consistent with the definition being adopted. Based on the above

considerations, no change in the definition is necessary.

AlliedSignal also recommended amending the standard to require that

the hydraulic master cylinders of an air-over-hydraulic brake system

comply with S5.3 (Brake System Indicator Lamp) and S5.4 (Reservoirs) of

Standard No. 105.

NHTSA has decided not to amend S5.3 and S5.4 of Standard 105 at

this time, since it has not proposed these modifications. The agency

may consider these modifications in future rulemakings.

IV. Rulemaking Analyses and Notices

1. Executive Order 12866 (Federal Regulation Planning and Review) and

DOT Regulatory Policies and Procedures

This rulemaking was not reviewed under E.O. 12866. NHTSA has

analyzed this rulemaking and determined that it is not ``significant''

within the meaning of the Department of Transportation's regulatory

policies and procedures. A full regulatory evaluation is not required

because the rule will have no mandatory effects. Instead, the rule will

only codify a longstanding agency interpretation of existing

requirements. Therefore, this rulemaking will not have any cost

impacts.

2. Regulatory Flexibility Act

In accordance with the Regulatory Flexibility Act, NHTSA has

evaluated the effects of this action on small entities. Based upon this

evaluation, I certify that the amendment will not have a significant

economic impact on a substantial number of small entities. Vehicle and

brake manufacturers typically do not qualify as small entities.

Accordingly, no regulatory flexibility analysis has been prepared.

3. Executive Order 12612 (Federalism)

This action has been analyzed in accordance with the principles and

criteria contained in Executive Order 12612, and it has been determined

that the rulemaking will not have sufficient Federalism implications to

warrant preparation of a Federalism Assessment. No State laws will be

affected.

4. National Environmental Policy Act

Finally, the agency has considered the environmental implications

of this rule in accordance with the National Environmental Policy Act

of 1969 and determined that the rulemaking will not significantly

affect the human environment.

5. 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, Motor vehicle safety, Motor vehicles, Rubber and rubber

products, Tires.

In consideration of the foregoing, the agency amends Standard No.

121, Air Brake Systems, part 571 of Title 49 of the Code of Federal

Regulations as follows:

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

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. In Sec. 571.121, S4 is amended by revising the definition of

``Air brake system'' and by adding the definition of ``Air-over-

hydraulic brake subsystem'' in alphabetical order to read as follows:

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

* * * * *

S4. Definitions.

* * * * *

Air brake system means a system that uses air as a medium for

transmitting pressure or force from the driver control to the service

brake, including an air-over-hydraulic brake subsystem, but does not

include a system that uses compressed air or vacuum only to assist the

driver in applying muscular force to hydraulic or mechanical

components.

Air-over-hydraulic brake subsystem means a subsystem of the air

brake system that uses compressed air to transmit a force from the

driver control to a hydraulic brake system to actuate the service

brakes.

* * * * *

Issued on: July 10, 1995.

Ricardo Martinez,

Administrator.

[FR Doc. 95-17453 Filed 7-17-95; 8:45 am]

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