Federal Motor Vehicle Safety Standards; Air Brake Systems; Air Applied, Mechanically Held Brake Systems

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 93-17; Notice 2]

RIN 2127-AE77

Federal Motor Vehicle Safety Standards; Air Brake Systems; Air

Applied, Mechanically Held Brake Systems

AGENCY: National Highway Traffic Safety Administration (NHTSA),

Department of Transportation.

ACTION: Final rule.

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SUMMARY: This rule amends Standard No. 121, Air Brake Systems, with

respect to the requirements related to the application and holding of

parking brake systems and the requirements related to the supply line

pressure retention for trailer brakes. NHTSA initiated rulemaking to

respond to concerns raised by International Transquip Industries (ITI)

which manufactures air-applied, mechanically held parking brakes. These

amendments provide regulatory relief by removing unnecessary

restrictions to facilitate the use of alternative brake systems,

without adversely affecting safety.

DATES: Effective Date: The amendments in this notice become effective

March 16, 1994.

Petitions for Reconsideration: Any petitions for reconsideration of

this rule must be received by NHTSA no later than March 16, 1994.

ADDRESSES: Petitions for reconsideration of this rule should refer to

Docket 93-17; Notice 2 and should be submitted to: Administrator,

National Highway Traffic Safety Administration, 400 Seventh Street,

SW., Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT:

Mr. Richard Carter, Office of Vehicle Safety Standards, National

Highway Traffic Safety Administration, 400 Seventh Street, SW.,

Washington, DC 20590 (202-366-5274).

SUPPLEMENTARY INFORMATION:

I. Introduction

II. Notice Of Proposed Rulemaking And Comments On The Proposal

III. Agency Decision

A. Grade Holding Requirements

1. Background Considerations

2. Diaphragm Failure Modes

3. Test Procedure

B. Supply Line Pressure Requirements for Trailers

IV. Leadtime

V. Rulemaking Analyses and Notices

1. Executive Order 12688 (Federal Regulation) and DOT Regulatory

Policies and Procedures

2. Regulatory Flexibility Act

3. Executive Order 12612 (Federalism)

4. National Environmental Policy Act

5. Civil Justice Reform

I. Introduction

Manufacturers typically comply with the parking brake requirements

in Federal Motor Vehicle Safety Standard No. 121, Air Brake Systems, by

equipping their air-braked vehicles with spring brake systems. With

these brake systems, air pressure holds the spring in the released

position when a vehicle is being driven. Upon parking, the air pressure

is vented, allowing the springs to apply the parking brakes. Consistent

with NHTSA's policy to issue Federal safety standards that are not

unnecessarily design restrictive, the agency has conducted a number of

rulemakings to ensure that the standard does not unnecessarily prevent

the manufacture of parking brake systems other than conventional spring

brake systems (e.g., air-applied, mechanically held parking brake

systems). See 44 FR 46850, August 9, 1979; 51 FR 10641, March 28, 1986;

56 FR 26927, June 12, 1991.

In 1992, International Transquip Industries, Inc. (ITI), a

manufacturer of an air-applied, mechanically held parking brake system,

informed NHTSA that it believed two of Standard No. 121's current

requirements are unnecessarily design restrictive or otherwise

inappropriate for its brake system design. One of these requirements

specifies that a vehicle must meet parking brake grade holding

requirements on a 20 percent grade (or other equivalent requirements),

with ``any single leakage-type failure'' of certain parts, including a

failed diaphragm. See S5.6 of Standard No. 121. ITI argued that this

requirement is unnecessarily restrictive with respect to its air-

applied, mechanically held single diaphragm brake system. That company

argued that its brake system is designed so that the diaphragm will

never experience a major failure, and that vehicles equipped with its

brake system can be parked on a 20 percent grade in the presence of the

types of diaphragm failures that typically occur.

The other requirement that ITI believed is inappropriate for its

brake design is the supply line pressure requirement for trailers. See

S5.8.2. This requirement addresses brake drag. According to ITI, it is

inappropriate for its brake system, which is designed so that its

brakes are either fully applied or fully released.

II. Notice of Proposed Rulemaking and Comments on the Proposal

After considering ITI's arguments, NHTSA issued a notice of

proposed rulemaking (NPRM) that proposed certain changes to Standard

No. 121. (58 FR 13437, March 11, 1993). Specifically, the agency

proposed to amend the requirements related to the application and

holding of parking brake systems and the requirements related to the

supply line pressure retention for trailer brakes. In that notice, the

agency tentatively concluded that these amendments would remove

unnecessary restrictions, thus facilitating the use of air-applied,

mechanically held parking brake systems. The agency further explained

that the Standard should not unnecessarily prevent parking brake

systems that are different than conventional spring brake systems. The

agency believed that this proposal would provide regulatory relief by

removing a restriction affecting the use of non-spring brake systems,

while continuing to ensure appropriate grade holding performance of air

braked heavy vehicles.

NHTSA received twelve comments on the proposal. Among the

commenters were ITI, which commented twice; the Motor Equipment

Manufacturers Association (MEMA), a trade association that represents

heavy duty brake manufacturers; spring brake manufacturers and spring

brake rebuilders, including Midland-Grau, MGM Brakes, Neway Anchorlok,

Allied Signal, TSE Brakes, and Ferodo America; heavy vehicle

manufacturers including GM/Volvo White and Freightliner; and the

American Trucking Associations (ATA). There was no consensus among the

commenters about whether the proposal should be adopted. While ITI

favored the proposal which it believed would eliminate an unnecessary

design restriction, the manufacturers of spring brake systems opposed

it. The spring brake manufacturers would experience increased

competition from the additional use of air-applied, mechanically held

systems, which, according to ITI currently represent 2 percent of the

air brake chamber market. The ITI system would provide weight savings

but would cost an additional $28 more per axle than spring brake

chambers. The spring brake manufacturers argued that the proposal poses

significant safety problems since they believe that brake diaphragms

can and do experience rapid catastrophic failures. The commenters also

addressed specific issues about the proposed test procedure for air-

applied, mechanically held parking brake systems and the need to retain

the supply line pressure requirement for vehicles equipped with these

systems. The agency has analyzed the comments and responds to the

significant ones below.

III. Agency Decision

A. Grade Holding Requirements

1. Background Considerations

Standard No. 121 currently requires an air-braked vehicle to have a

parking brake system that enables it to meet certain grade holding

requirements. Manufacturers have the option of complying with either a

20 percent grade holding test or an equivalent static drawbar pull

test. The purpose of the parking brake requirement is to ensure that an

air-braked vehicle has adequate parking brake performance on a grade.

The standard provides that the parking brake grade holding

requirements must be met with ``any'' single leakage-type failure of

certain parts, including service brake diaphragms. The purpose of this

provision is to ensure that a driver can safely park a vehicle in the

event of a leakage-type failure in the service brake system. The

standard specifies ``any'' failure because leakage-type failures of

many types, sizes, and locations can occur in vehicle brake systems. To

ensure that a vehicle has adequate grade holding performance regardless

of the specific nature or extent of a leakage-type failure, the agency

intentionally did not limit the size or location of such failures.

In the NPRM, NHTSA explained that most brake systems are designed

with two diaphragms, one for the service brake function and one for the

parking brake function. Further, most brake systems incorporate a

spring brake for parking. These brake systems can easily meet the

parking brake holding requirements with a failure in the service brake

diaphragm, because a failure in that diaphragm does not adversely

affect parking brake performance. In contrast, the ITI air-applied,

mechanically held brake system has only one diaphragm that provides

both the parking brake and service brake functions. A hole in that

diaphragm can therefore affect both parking brake and service brake

performance.

According to ITI, it is inappropriate to require vehicles to meet

grade holding requirements with ``any'' failure in the common diaphragm

of its brake system, because its system is designed so that a hole in

the diaphragm with not get any larger than \1/8\ inch during real-world

use. ITI further stated that a vehicle equipped with its brake system

will hold on a 20 percent grade and can never be driven with a failure

larger than \1/8\ inch. This is because, according to ITI, diaphragm

failures begin as very small holes, develop very slowly, and its brakes

will not release once the hole gets larger than \1/8\ inch. Thus, once

a hole gets that large and the driver parks the vehicle at the end of

the day, it will not be possible to drive the vehicle without repairing

the brakes.

As explained in the NPRM, NHTSA evaluated the issues raised by ITI

through tests of the air-applied, mechanically held system conducted at

the agency's Vehicle Research and Test Center (VRTC). (See, Evaluation

of Mini-Max Parking Forces with Chamber Diaphragm Failures, December

17, 1992, which has been placed in Docket No. 93-17, Notice 1.) That

testing confirmed that vehicles equipped with the ITI system could not

be unparked in the presence of a relatively small failure.

In the NPRM, NHTSA sought comment on two primary issues related to

air-applied, mechanically held brake systems: (1) Whether the current

requirement is appropriate for an air-applied, mechanically held brake

system like ITI's system and (2) whether it is possible to develop a

test procedure that will identify the ``worst case'' diaphragm failure

that might be experienced in the real world.

2. Diaphragm Failure Modes

In the NPRM, NHTSA discussed whether air-applied, mechanically held

brake systems only experience small, gradual failures or whether they

can experience catastrophic failures.\1\ If diaphragms do in fact

experience catastrophic failures, then the proposed requirement would

not ensure the safety of air-braked vehicles. However, based on

information provided by ITI and the agency's analysis of that

information, NHTSA assumed, for purposes of this rulemaking, that

diaphragm failures begin small and develop very slowly. Accordingly,

the proposed test procedure was designed to evaluate the small, gradual

leakage-type failures that, according to ITI, occur with its system.

Notwithstanding NHTSA's decision to propose requirements that would be

appropriate only if diaphragms only experience small, gradual leakage-

type failures, the agency sought comment about whether catastrophic

diaphragm failures occur in the real world.

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\1\By ``catastrophic failure,'' the agency means one in which a

service brake application is made and the diaphragm fails, for any

reason, to an extent that the brake chamber will not generate

sufficient torque to add significantly to the vehicle's braking.

Types of catastrophic failures include puncturing the diaphragm with

a broken spring, pulling the diaphragm loose from the air brake

chamber clamp ring, or blowing a large hole in the diaphragm.

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The commenters expressed conflicting views about the nature of

diaphragm failures. On the one hand, ITI reiterated its view that

diaphragm failures begin small and develop very slowly because the

diaphragms use a rip stop nylon fabric. This led ITI to conclude that

long before a hole becomes large enough to affect parking capabilities,

it is no longer possible to release the parking brakes. ITI accordingly

requested that diaphragms be excluded from failure testing. On the

other hand, the spring brake manufacturers (Midland-Grau, MGM Brakes,

Neway Anchorlok, Allied Signal, MEMA, and Ferodo) stated that

diaphragms can and do experience rapid massive failure in addition to

the gradual failure discussed by ITI. The spring brake manufacturers

alleged that there were several catastrophic failure modes, including:

(1) The piston plate wearing a hole through the diaphragm, (2) air

permeating between the rubber or neoprene compound causing it to

balloon out and then blow, (3) the effects of exposing the diaphragm to

oil which causes the compound to delaminate from the fabric, (4) broken

springs or piston plates cutting into the diaphragm, (5) and

manufacturing defects in the nylon fabric. Neway Anchorlok believed

that because these catastrophic failure modes can occur between parking

brake applications, they may significantly and suddenly impair the

service brake's capabilities. The potential for catastrophic failures

led the spring brake manufacturers to recommend that the agency retain

the ``any leakage'' requirements.

After reviewing the conflicting comments, NHTSA decided to examine

further the failure modes experienced by diaphragms. To this end, the

agency visually inspected failed diaphragms submitted by Bendix,

Ferodo, and MGM. In addition, the agency contacted diaphragm

manufacturers. In its examination of diaphragms submitted by various

manufacturers, NHTSA found no evidence of catastrophic failure; rather,

the agency found that failures typically involved slow deterioration

through extended use. The only time the agency found a catastrophic

failure was when there was a rapid air loss resulting from a spring

puncture or a pull-out from the clamp band area. Spring puncture

failures are not relevant to the present rulemaking about air-applied,

mechanically held systems which do not have springs. With respect to

possible pull-out, ITI has stated that if, in servicing its units, the

diaphragm is installed improperly, the brakes cannot be released upon

air-up of the system. The agency has placed the findings of its

inspection of failed diaphragms in the docket.

In response to agency inquiries, Longwood Elastomers and Goodyear,

two large diaphragm manufacturers, stated that diaphragms do not fail

catastrophically. While they acknowledge that some failure modes

mentioned by the spring brake manufacturers do occur (e.g., spring

puncture, plate chaff, unseating, flex cracking in the bead area,

accelerated degradation caused by exposure to oil), they contended that

such failures either happen so infrequently that they do not raise

safety concerns or would not happen with an air-applied, mechanically

held brake system (e.g., a single diaphragm brake system has no heavy

spring brake that can pierce the diaphragm after failing from fatigue).

With respect to failure rates, one diaphragm manufacturer informed the

agency that it had returns of about 20 units from an annual production

of between 2,000,000 to 2,500,000 units. This failure rate translates

to a reliability of about 99.999 percent. These reliability figures are

for the useful lifecycle before wearout begins. All diaphragms would

eventually wear out. Therefore, diaphragms in air-applied, mechanically

held systems and in the service side of spring brake systems are

typically replaced after between four and five years of service. The

diaphragm manufacturers further stated that they have never encountered

a catastrophic failure during cycle testing of their production runs.

Based on NHTSA's review of the failed diaphragms, contacts with

diaphragm manufacturers and other available information, the agency has

concluded that diaphragms used with air-applied, mechanically held

parking brake systems do not fail catastrophically. Rather, the typical

failure mode with these systems is a gradual deterioration through

extended use. The agency further notes that GM/Volvo White and

Freightliner, which use ITI air brake chambers as original equipment on

their vehicles when ordered by a customer, have not experienced any

catastrophic failures with these systems. Accordingly, the agency

concludes that the current requirement to require vehicles to meet the

parking brake requirements with ``any'' single leakage type failure is

unnecessarily design-restrictive with respect to air-applied,

mechanically held air brake systems.

ITI requested that NHTSA exclude diaphragms entirely from failure

testing with respect to the parking brake requirements. However, NHTSA

has decided that an exclusion would be inappropriate. A diaphragm is an

integral part of the parking brake system, and the failure of a

diaphragm can have adverse safety consequences. Therefore, excluding

diaphragms from such testing would be inconsistent with the safety

purposes of the standard. Such an exclusion would be inconsistent with

the underlying purpose of the parking brake requirements which serve to

ensure that a driver can safely park a vehicle in the event of a

leakage-type failure in the service brake system. Because diaphragms do

fail, as ITI readily admits, it would be inconsistent with the parking

brake requirements to exclude such an important component in the brake

system from the relevant test requirements.

3. Test Procedure

In the NPRM, NHTSA proposed a test procedure that it tentatively

concluded would identify the ``worst case'' leakage-type diaphragm

failure that is likely to occur with brake systems using common

diaphragms. Under the proposed procedure, the first step would be to

determine the threshold level of diaphragm leakage-type failure (or

equivalent level of leakage from the air chamber containing that

diaphragm) at which the vehicle's parking brakes become unreleasable. A

measurement would then be taken of the leakage rate associated with

that level of failure. The proposal explained that the ``threshold

maximum reservoir leakage rate'' is the rate of reservoir air pressure

decrease, for whichever of the vehicle's reservoirs that is

experiencing the most rapid decrease in pressure level, that results

from that threshold level of leakage. The agency proposed that a

vehicle would be required to meet grade holding requirements with a

level of diaphragm leakage-type failure that results in a reservoir

leakage rate that is three times the threshold maximum reservoir

leakage rate. This ``three times'' safety factor was included to

account for the possibility that a small diaphragm failure could grow

larger between parking brake applications.

Midland-Grau, ITI, and Allied Signal believed that the proposed

test procedure was unnecessarily complex. Midland-Grau stated that the

procedures were difficult to follow and could be interpreted in many

ways. Midland-Grau requested that NHTSA modify the test procedure so

that it could be easily followed. Moreover, it stated its preference

for testing parameters that are concise, and lead to consistent test

results that allow easy assessment of whether the system passes or

fails. ITI requested that the agency simplify the test to make it less

complicated. Allied Signal criticized the proposal for being overly

complex, claiming that multiple attempts would be necessary to

establish the size of diaphragm failure for both release and

application.

After reviewing the proposal in light of the comments, NHTSA

believes that the proposed test procedure, with minor adjustments, is

appropriate to evaluate brake systems that incorporate a common

diaphragm. The agency further believes that the test procedure is not

unreasonably complicated. In particular, the agency's experience at

VRTC in running the tests indicates that the tests are not overly

burdensome and that with a valving meter in place, various pressure

levels of leakage can be obtained relatively quickly and without much

difficulty. The agency notes that to simplify testing, it could have

specified a fixed orifice size to be used for all systems. However,

such an approach would have prevented certain parking brake systems and

thus have been unnecessarily design restrictive, since the size of leak

at which sufficient force is generated to park the vehicle varies for

different systems. In contrast, the variable leak rate procedure that

the agency is adopting in this final rule may be used to evaluate any

brake system regardless of its design.

In response to specific comments and further analysis of the

regulatory text, NHTSA has made some minor changes to the proposed test

procedures applicable to air-applied, mechanically held brake systems.

For instance, in response to criticisms by Midland-Grau of terminology

that it believed was ambiguous, NHTSA has deleted reference to

``certain level'' of failure as proposed in S5.6(b). In addition, as

explained below, the agency has modified the terminology related to the

concept of parking brake ``release.''

Nevertheless, NHTSA has decided to retain the following terms that

Midland-Grau criticized: ``Increasing or decreasing,'' ``threshold

level of diaphragm leakage,'' ``threshold maximum reservoir leakage

associated with that level of failure,'' and ``threshold of allowable

leakage.'' With respect to finding the leakage rate at which the

parking brake system becomes unreleasable, the agency believes it is

necessary for the test evaluator to find the appropriate threshold

level with ``progressively increasing or decreasing levels'' of failure

because each brake configuration is different. While this procedure

will require some searching for the leakage rate at which the system

becomes unreleasable, the agency believes the appropriate level of

failure can be ascertained without too much difficulty by using

metering valves. NHTSA notes that in VRTC's testing to develop this

rule's requirements and procedures, the agency installed an adjustable

metering valve in the brake chamber housing to simulate a leak in the

brake chamber diaphragm. The ``threshold level of common diaphragm

leakage type failure'' at which the parking brakes become unreleasable

was determined by increasing the leakage rate, by ``opening'' the

metering valve, from one test to the next in relatively large

increments until the parking brakes would not release. Then, the

metering valve was ``closed,'' to decrease the leakage rate, in smaller

increments until the parking brakes would release. The leakage rate was

then increased by even smaller increments until the parking brakes were

again unreleasable. The precision with which the final determination of

the ``threshold level of common diaphragm leakage-type failure'' at

which the parking brakes become unreleasable is determined by the

number of times the direction of leakage rate change, e.g., from

increasing to decreasing and vice versa, and the magnitude of the

increments by which the leakage rate is increased or decreased.

With respect to various references to the concept of the

``threshold,'' the agency has modified these provisions slightly to use

just two terms: ``Threshold level of common diaphragm leakage-type

failure'' in S5.6.7.1.1 and S5.6.7.2.1 and the ``threshold maximum

reservoir leakage rate'' in S5.6.7.1.2 and S5.6.7.2.2. NHTSA,

nevertheless, disagrees with Midland-Grau's more general concern that

the term ``threshold'' is ambiguous. The agency notes that the

dictionary defines ``threshold'' to mean ``a level, point, or value

above which something is true or will take place and below which it is

not or will not.''\2\ Applying this definition to the parking brake

test for systems with common diaphragms, the agency believes that

``threshold level of common diaphragm leakage-type failure'' is an

objective term that means the initial level at which the parking brake

can no longer be released. Similarly, the meaning of the phrase

``threshold maximum reservoir leakage rate'' was discussed in the NPRM

and means the rate of reservoir air pressure decrease that results at

that threshold level of leakage.

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\2\Webster's Ninth New Collegiate Dictionary, 1986.

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With respect to the concept of ``release,'' NHTSA has decided to

clarify the term so that it covers brake applications that involve a

vehicle being parked on a grade or a drawbar pull test. NHTSA notes

that in addressing a similar issue in an earlier rulemaking about what

was meant by ``release,'' the agency stated that ``NHTSA considers a

brake to be released at the point where it no longer exerts any

torque.'' (37 FR 12495, June 24, 1972). The agency believes that this

discussion of release is pertinent to the procedure set forth in

S5.6(b). Accordingly, in the final rule, the agency has specified that

the relevant consideration is when the parking brakes ``become

unreleasable.'' Since the final rule specifies the criteria in terms of

``becom(ing) unreleasable,'' Midland-Grau's concerns about when the

released condition exists or about the status of a partial release are

no longer relevant.

Midland-Grau requested that the agency provide an acceptable

leakage value for each brake component. It further stated that

statements about ``compressor shut-off points'' and ``air flow'' should

be pinned down to definitive values.

NHTSA disagrees with Midland-Grau's request to provide a specific

level of leakage for each brake component. The agency's goal in this

rulemaking is to establish a performance test for the entire brake

system, because the agency's concern is to test for and prohibit

system-wide failures that may pose safety problems. The agency

therefore is not concerned with the leakage level of any particular

component. Nor does the agency believe it is necessary or appropriate

to specify definitive values for the compressor shut-off points. Such

an action might be unnecessarily design restrictive and serve to

prohibit some manufacturers from selecting a higher cut off value than

would be appropriate for its system.

Allied and Midland-Grau expressed concern that the rate of

reservoir pressure drop is influenced by valving, plumbing, and air

supply capability. NHTSA acknowledges that these variables exist;

however, the agency believes that they are not large enough to

adversely affect the test results. Specifically, as long as testing is

done at three times the leak rate, the actual numerical value of the

leak rate is not overly important, because the value for the safety

factor is measured in the same way, which results in factoring out most

of the variability. The agency further notes that these variables are

part of the manufacturing process and thus, if necessary, they can be

controlled by the brake system manufacturer. Moreover, alternative

methods of testing would have necessitated using expensive flow meters

that would not significantly reduce the level of variability or

otherwise improve the test results. NHTSA notes that while the rate of

air flow through the system may be affected by slight variations in air

hose lengths from vehicle to vehicle, internal size variations in the

castings used in the hose fittings, and differences in valve

tolerances; the leak rates at issue are not sufficiently large to be

significantly affected by this type of variability from vehicle to

vehicle. Internal drag on air flow does not become a factor until the

flow rates become substantially higher than those being measured here.

In the NPRM, NHTSA proposed that a vehicle would be required to

meet grade holding requirements with the level of diaphragm leakage

failure of three times the threshold maximum reservoir leakage rate.

The agency reasoned that a safety factor was necessary to address the

situation when a small diaphragm failure grows larger between parking

brake applications, prior to the time the vehicle is parked (at which

point the parking brakes would be unreleasable.

Midland-Grau, ITI, and Allied objected to including a safety factor

``three times the threshold maximum reservoir leakage.'' Midland-Grau

stated that the rationale for this test is not easily visualized and is

questionable as to why it was selected as a test parameter. ITI stated

that the safety factor should be eliminated to avoid additional time

and cost in compliance testing. Allied stated that it was not aware of

any information or data that the agency used to establish the three

times reservoir pressure drop rate as being a ``worst case'' type of

failure for a brake chamber diaphragm.

After reviewing the comments, NHTSA continues to believe that it is

necessary to include a safety factor in the application and holding

requirements for air-applied, mechanically held parking brake systems.

The agency notes that including the provision for grade holding at

``three times the failure rate'' is essential to ensure the brake

system's safety since the hole associated with a diaphragm failure

grows larger during the day. In addition, including a safety factor

serves to prevent marginal systems from being manufactured. The agency

selected a safety factor of three based on general engineering

principles and the agency's testing at VRTC. In general, a safety

factor needs to be as large as possible to ensure safety, while not be

too large to make it unreasonable, impracticable, and unaffordable. In

agency tests at VRTC, NHTSA determined that the ITI system would still

produce sufficient parking force with a diaphragm leak over ten times

larger than the system would detect and still not release the parking

brakes. Based on its understanding of diaphragm failures associated

with air-applied, mechanically held braking systems, NHTSA determined

that a safety factor of three was the most appropriate level of safety

for inclusion in a FMVSS. The agency believes that this level of safety

will not require manufacturers to ``over-design'' their parking brake

systems, but will ensure appropriate brake system performance. NHTSA

disagrees with ITI's comment that inclusion of a safety factor would

add needless complexity to the requirement. Agency testing at VRTC

indicates that inclusion of a safety factor will not significantly add

to the time and cost of compliance testing. Essentially, as a result of

the safety factor, a test evaluator needs to establish the threshold

value for the maximum reservoir leakage rate and then triple it. Based

on its experience at VRTC, the agency believes that this will add only

five to ten minutes to the compliance testing (at only nominal

additional cost.)

B. Supply Line Pressure Requirements for Trailers

Section S5.8.2 of Standard No. 121 currently requires that any

single leakage type failure in the service brake system must not result

in the pressure in the supply line falling below 70 p.s.i., measured at

the forward trailer supply coupling. (See 56 FR 50666, October 8,

1991). The purpose of this provision is to prevent brake drag caused by

the automatic application of trailer parking brakes while the minimum

trailer supply line pressure is maintained.

In a June 5, 1992 letter to the agency, ITI requested that the

agency ``exempt'' its brake system from S5.8.2. It argued that this

provision relates to problems caused by brake drag, a situation that it

contends is not applicable to ITI's brake system, which, by design, can

only be in the fully applied or fully released positions.

After considering ITI's arguments, NHTSA, in the NPRM, tentatively

concluded that no safety purpose would be served to apply this

provision to non-towing trailers using air-applied, mechanically held

parking brakes that use a common diaphragm. The agency noted that these

vehicles do not use spring brakes and thus the requirement which

addresses the safety problem of brake drag is not relevant to them.

Accordingly, the agency proposed to amend section S5.8.2 to clarify

that this provision would not apply to non-towing trailers equipped

with air-applied, mechanically held parking brakes that use a common

diaphragm. Nevertheless, NHTSA emphasized that section S5.8.2 would

continue to apply to towing trailers, since the 70 psi requirements may

be necessary for other vehicles in the train.

Midland-Grau, ITI, ATA, and Allied Signal addressed the issue of

whether the 70 psi supply line pressure requirement should be retained

for trailers, particularly towing trailers, equipped with air-applied,

mechanically held parking brakes. Midland-Grau stated that making the

70 psi requirement optional for towing trailers with air-applied

mechanically hold brake systems introduces a detriment to the couple

vehicles in the event of system failure. This led Midland-Grau to

conclude that it is necessary to apply failure. This led Midland-Grau

to conclude that it is necessary to apply the supply line pressure

requirements to trailers since a towing trailer will experience brake

degradation if it is not properly protected from towed trailer system

failures.

In contrast, ITI stated that this requirement should not be applied

to either towing or non-towing vehicles equipped with air-applied,

mechanically held vehicles since they do not experience brake drag.

This led ITI to state that S5.8.4 was not necessary, because it claimed

that partial application or brake drag is not an issue with its brake

systems. Thus, it requested that towing trailers with air-applied,

mechanically held systems be permitted without the 70 psi supply line

protection feature, even though it acknowledge that this may result in

some mismatches. In response to Midland-Grau's comment, ITI stated that

trailers equipped with spring brakes manufactured before and after the

October 1992 rule that specified these requirements (56 FR 50666,

October 8, 1991) will experience compatibility problems. Therefore, ITI

believed that the problem raised by Midland-Grau will exist with spring

brake equipped trailers as well as trailers equipped with air-applied,

mechanically held equipped trailers.

ATA commented that the existing 70 psi supply line requirement is

inappropriate and prevents tractor low air pressure warning systems

from warning drivers of the loss of service pressure in trailers.

Therefore, it requested that the agency either exempt all trailers from

the 70 psi supply line requirement or modify the requirement. Allied

Signal similarly stated that the 70 psi requirement has undermined the

effectiveness of the low pressure warning system, especially for

doubles and triples.

After reviewing the comments, NHTSA has decided not to apply the

supply lone pressure requirements to single trailers equipped with air-

applied, mechanically held brake systems. Such trailers, which do not

experience brake drag, also do not affect the braking of any other

vehicle because they are not connected to other trailers. Therefore, as

discussed in the NPRM, this requirement would not benefit this type of

trailer.

Nevertheless, the agency has decided that the supply line pressure

requirements are relevant to air-applied, mechanically held brake

systems on towing trailers used in double and triple trailer

combinations.\3\ The agency is not convinced by ITI's argument that

trailers equipped with their system should not have to comply with the

70 psi requirement because there are older spring brake-equipped

trailers that will pose similar compatibility problems. The agency

believes that there would be a safety problem if it were to apply the

supply line pressure requirements to certain vehicles in double or

triple combinations but not others. Specifically, if ITI's request were

adopted, a trailer being towed by a trailer equipped with air-applied,

mechanically held brakes would not necessarily receive adequate air

pressure and therefore could experience brake drag. The agency's

decision to apply these requirements to towing trailers is consistent

with recent legislation and the efforts of the agency, manufacturers,

and end-users to standardize operating conditions to improve

compatibility. Specifically, section 4012 of the Intermodal Surface

Transportation Efficiency Act (ISTEA) directs the agency to initiate

rulemaking to improve compatibility of truck tractors, trailers, and

their dollies. The agency further notes that a specialized trailer

protection valve could be developed for ITI's system that would permit

compliance with the requirements of S5.8.2 and S5.8.3.

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\3\A towing trailer is one that is equipped with a pintle hook

and air line connections at the rear to tow another air braked

trailer. In doubles and triples operations, nearly all trailers are

so equipped, regardless of the position they may occupy in any

particular trailer train.

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With respect to concerns expressed by ATA and Allied about the 70

psi supply line pressure requirement, NHTSA notes that it is reviewing

this provision in the context of a rulemaking petition submitted by the

California Highway Patrol. The agency anticipates issuing another

notice addressing the supply line pressure requirements in 1994.

IV. Leadtime

Section 103(c) of the Vehicle Safety Act requires that each order

shall take effect no sooner than 180 days from the date the order is

issued unless ``good cause'' is shown that an earlier effective date is

in the public interest. NHTSA has determined that there would be ``good

cause'' not to provide the 180 day lead-in period given that this

amendment will not impose any mandatory requirements on manufacturers.

The public interest will also be served by not delaying the

introduction of the requirement. Based on the above, the agency has

determined that there is good cause to have an effective date 30 days

after publication in the final rule.

V. Rulemaking Analyses and Notices

1. Executive Order 12688 (Federal Regulation) and DOT Regulatory

Policies and Procedures

NHTSA has analyzed this rulemaking and determined that it is

neither ``significant'' within the meaning of the Department of

Transportation's regulatory policies and procedures nor ``significant''

within the meaning of Executive Order 12688. This rulemaking document

was not reviewed under E.O. 12688, ``Regulatory Planning, and Review.''

A full regulatory evaluation is not required because the rule will have

no mandatory effects. Rather, the rule will provide regulatory relief

to facilitate the introduction of alternative brake systems. Therefore,

the agency does not believe that this rulemaking will result in

significant additional costs or cost savings.

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 amendments will not have a significant

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

brake manufacturers typically will not qualify as small entities. This

amendment will also affect small businesses, small organizations, and

small governmental units to the extent that these entities purchase

air-braked vehicles. As discussed above, the agency's assessment is

that this amendment will have no significant cost impact to the

industry. For these reasons, vehicle manufacturers, small businesses,

small organizations, and small governmental units which purchase motor

vehicles will not be significantly affected by the requirements.

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 rule will not have sufficient Federalism implications to

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

affected.

4. National Environmental Policy Act

The agency has considered the environmental implications of this

rule in accordance with the National Environmental Policy Act of 1969

and determined that the rule will not significantly affect the human

environment.

5. Civil Justice Reform

This rule will not have any retroactive effect. Under section

103(d) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C.

1392(d)), 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. Section 105 of the Act (15 U.S.C. 1394) 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, title 49 part 571 is amended as

follows:

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

1. The authority citation for part 571 continues to read as

follows:

Authority: 15 U.S.C. 1392, 1401, 1403, 1407; delegation of

authority at 49 CFR 1.50.

2. Section 571.121 is amended by revising S4 to add a new

definition; revising S5.6; removing S5.6.3.5; adding a new S5.6.7

through S5.6.7.2.3; revising S5.8.2; and adding a new S5.8.4. The

revised and added paragraphs read as follows:

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

* * * * *

S4 Definitions.

* * * * *

Common diaphragm means a single brake chamber diaphragm which is a

component of the parking, emergency, and service brake systems.

* * * * *

S5.6 Parking brake system.

(a) Except as provided in S5.6(b) and S5.6(c), each vehicle other

than a trailer converter dolly shall have a parking brake system that

under the conditions of S6.1 meets the requirements of:

(1) S5.6.1 or S5.6.2, at the manufacturer's option, and

(2) S5.6.3, S5.6.4, S5.6.5, and S5.6.6.

(b) At the option of the manufacturer, for vehicles equipped with

brake systems which incorporate a common diaphragm, the performance

requirements specified in S5.6(a) which must be met with any single

leakage-type failure in a common diaphragm may instead be met with the

level of leakage-type failure determined in S5.6.7. The election of

this option does not affect the performance requirements specified in

S5.6(a) which apply with single leakage-type failures other than

failures in a common diaphragm.

(c) At the option of the manufacturer, the trailer portion of any

agricultural commodity trailer, heavy hauler trailer, or pulpwood

trailer may meet the requirements of Sec. 393.43 of this title instead

of the requirements of S5.6(a).

* * * * *

S5.6.7 Maximum level of common diaphragm leakage-type failure/

Equivalent level of leakage from the air chamber containing that

diaphragm. In the case of vehicles for which the option in S5.6(b) has

been elected, determine the maximum level of common diaphragm leakage-

type failure (or equivalent level of leakage from the air chamber

containing that diaphragm) according to the procedures set forth in

S5.6.7.1 through S5.6.7.2.3.

S5.6.7.1 Trucks and buses.

S5.6.7.1.1 According to the following procedure, determine the

threshold level of common diaphragm leakage-type failure (or equivalent

level of leakage from the air chamber containing that diaphragm) at

which the vehicle's parking brakes become unreleasable. With an initial

reservoir system pressure of 100 psi, the engine turned off, no

application of any of the vehicle's brakes, and, if the vehicle is

designed to tow a vehicle equipped with air brakes, a 50 cubic inch

test reservoir connected to the supply line coupling, introduce a

leakage-type failure of the common diaphragm (or equivalent leakage

from the air chamber containing that diaphragm). Apply the parking

brakes by making an application actuation of the parking brake control.

Reduce the pressures in all of the vehicle's reservoirs to zero, turn

on the engine and allow it to idle, and allow the pressures in the

vehicle's reservoirs to rise until they stabilize or until the

compressor shut-off point is reached. At that time, make a release

actuation of the parking brake control, and determine whether all of

the mechanical means referred to in S5.6.3.2 continue to be actuated

and hold the parking brake applications with sufficient parking

retardation force to meet the minimum performance specified in either

S5.6.1 or S5.6.2. Repeat this procedure with progressively decreasing

or increasing levels (whichever is applicable) of leakage-type

diaphragm failures or equivalent leakages, to determine the minimum

level of common diaphragm leakage-type failure (or equivalent level of

leakage from the air chamber containing that diaphragm) at which all of

the mechanical means referred to in S5.6.3.2 continue to be actuated

and hold the parking brake applications with sufficient parking

retardation forces to meet the minimum performance specified in either

S5.6.1 or S5.6.2.

S5.6.7.1.2 At the level of common diaphragm leakage-type failure

(or equivalent level of leakage from the air chamber containing that

diaphragm) determined in S5.6.7.1.1, and using the following procedure,

determine the threshold maximum reservoir rate (in psi per minute).

With an initial reservoir system pressure of 100 psi, the engine turned

off, no application of any of the vehicle's brakes and, if the vehicle

is designed to tow a vehicle equipped with air brakes, a 50 cubic inch

test reservoir connected to the supply line coupling, make an

application actuation of the parking brake control. Determine the

maximum reservoir leakage leakage rate (in psi per minute), which is

the maximum rate of decrease in air pressure of any of the vehicle's

reservoirs that results after that parking brake application.

S5.6.7.1.3 Using the following procedure, introduce a leakage-type

failure of the common diaphragm (or equivalent leakage from the air

chamber containing that diaphragm) that results in a maximum reservoir

leakage rate that is three times the threshold maximum reservoir

leakage rate determined in S5.6.7.1.2. With an initial reservoir system

pressure of 100 psi, the engine turned off, no application of any of

the vehicle's brakes and, if the vehicle is designed to tow a vehicle

equipped with air brakes, a 50 cubic inch test reservoir connected to

the supply line coupling, make an application actuation of the parking

brake control. Determine the maximum reservoir leakage rate (in psi per

minute), which is the maximum rate of decrease in air pressure of any

of the vehicle's reservoirs that results after that parking brake

application. The level of common diaphragm leakage-type failure (or

equivalent level of leakage from the air chamber containing that

diaphragm) associated with this reservoir leakage rate is the level

that is to be used under the option set forth in S5.6(b).

S5.6.7.2 Trailers.

S5.6.7.2.1 According to the following procedure, determine the

threshold level of common diaphragm leakage-type failure (or equivalent

level of leakage from the air chamber containing that diaphragm) at

which the vehicle's parking brakes become unreleasable. With an initial

reservoir system and supply line pressure of 100 psi, no application of

any of the vehicle's brakes, and, if the vehicle is designed to tow a

vehicle equipped with air brakes, a 50 cubic inch test reservoir

connected to the supply line coupling, introduce a leakage-type failure

of the common diaphragm (or equivalent leakage from the air chamber

containing that diaphragm). Make a parking brake application by venting

the front supply line coupling to the atmosphere, and reduce the

pressures in all of the vehicle's reservoirs to zero. Pressurize the

supply line by connecting the trailer's front supply line coupling to

the supply line portion of the trailer test rig (Figure 1) with the

regulator of the trailer test rig set at 100 psi, and determine whether

all of the mechanical means referred to in S5.6.3.2 continue to be

actuated and hold the parking brake applications with sufficient

parking retardation forces to meet the minimum performance specified in

either S5.6.1 or S5.6.2. Repeat this procedure with progressively

decreasing or increasing levels (whichever is applicable) of leakage-

type diaphragm failures or equivalent leakages, to determine the

minimum level of common diaphragm leakage-type failure (or equivalent

level of leakage from the air chamber containing that diaphragm) at

which all of the mechanical means referred to in S5.6.3.2 continue to

be actuated and hold the parking brake applications with sufficient

parking retardation forces to meet the minimum performance specified in

either S5.6.1 or S5.6.2.

S5.6.7.2.2 At the level of common diaphragm leakage-type failure

(or equivalent level of leakage from the air chamber containing that

diaphragm) determined in S5.6.7.2.1, and using the following procedure,

determine the threshold maximum reservoir leakage rate (in psi per

minute). With an initial reservoir system and supply line pressure of

100 psi, no application of any of the vehicle's brakes and, if the

vehicle is designed to tow a vehicle equipped with air brakes, a 50

cubic inch test reservoir connected to the rear supply line coupling,

make a parking brake application by venting the front supply line

coupling to the atmosphere. Determine the maximum reservoir leakage

rate (in psi per minute), which is the maximum rate of decrease in air

pressure of any of the vehicle's reservoirs that results after that

parking brake application.

S5.6.7.2.3 Using the following procedure, a leakage-type failure

of the common diaphragm (or equivalent leakage from the air chamber

containing that diaphragm) that results in a maximum reservoir leakage

rate that is three times the threshold maximum reservoir leakage rate

determined in S5.6.7.2.2. With an initial reservoir system and supply

line pressure of 100 psi, no application of any of the vehicle's brakes

and, if the vehicle is designed to tow a vehicle equipped with air

brakes, a 50 cubic inch test reservoir connected to the rear supply

line coupling, make a parking brake application by venting the front

supply line coupling to the atmosphere. Determine the maximum reservoir

leakage rate (in psi per minute), which is the maximum rate of decrease

in air pressure of any of the vehicle's reservoirs that results after

that parking brake application. The level of common diaphragm leakage-

type failure (or equivalent level of leakage from the air chamber

containing that diaphragm) associated with this reservoir leakage rate

is the level that is to be used under the option set forth in S5.6(b).

* * * * *

S5.8.2 Supply Line Pressure Retention. Any single leakage type

failure in the service brake system (except for a failure of the supply

line, a valve directly connected to the supply line or a component of a

brake chamber housing) shall not result in the pressure in the supply

line falling below 70 p.s.i., measured at the forward trailer supply

coupling. A trailer shall meet the above supply line pressure retention

requirement with its brake system connected to the trailer test rig

shown in Figure 1, with the reservoirs of the trailer and test rig

initially pressurized to 100 p.s.i. and the regulator of the trailer

test rig set at 100 p.s.i.; except that a trailer equipped with an air-

applied, mechanically-held parking brake system and not designed to tow

a vehicle equipped with air brakes, at the manufacturer's option, may

meet the requirements of S5.8.4 rather than those of S5.8.2 and S5.8.3.

* * * * *

S5.8.4 Automatic Application of Air-Applied, Mechanically Held

Parking Brakes. With its brake system connected to the supply line

portion of the trailer test rig (Figure 1) and the regulator of the

trailer test rig set at 100 psi, and with any single leakage type

failure in the service brake system (except for a failure of the supply

line, a valve directly connected to the supply line or a component of a

brake chamber, but including failure of any common diaphragm), the

parking brakes shall not provide any brake retardation as a result of

complete or partial automatic application of the parking brakes.

* * * * *

3. Figure 1 of Sec. 571.121 is revised to appear as follows:

BILLING CODE 4910-59-M

TR14FE94.000

BILLING CODE 4910-59-C

Issued on: February 9, 1994.

Howard M. Smolkin,

Executive Director.

[FR Doc. 94-3364 Filed 2-9-94 3:11 pm]

BILLING CODE 4910-59-M