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

American Government Special Collections Reference Desk

American Government Topics:  National Highway Traffic Safety Administration, Federal Motor Vehicle Safety Standards

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

Howard M. Smolkin
Federal Register
February 14, 1994

[Federal Register: February 14, 1994]


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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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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




    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

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