[Federal Register Volume 60, Number 137 (Tuesday, July 18, 1995)]
[Rules and Regulations]
[Pages 36740-36742]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-17453]



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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 

[[Page 36742]]
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]
BILLING CODE 4910-59-P