Federal Motor Vehicle Safety Standards; Air Brake Systems; Air Applied, Mechanically Held Brake Systems |
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Topics: National Highway Traffic Safety Administration, Federal Motor Vehicle Safety Standards
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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.
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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
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