Federal Motor Vehicle Safety Standards; Stability and Control of Medium and Heavy Vehicles During Braking
Federal RegisterMar 10, 1995
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SUMMARY: In response to the Intermodal Surface Transportation
Efficiency Act (ISTEA) of 1991, this final rule amends Standard No.
105, Hydraulic Brake Systems, and Standard No. 121, Air Brake Systems,
to require medium and heavy vehicles to be equipped with an antilock
brake system (ABS) to improve the directional stability and control of
these vehicles during braking. For truck tractors, the ABS requirement
is supplemented by a 30-mph braking-in-a-curve test on a low
coefficient of friction surface using a full brake application. By
improving directional stability and control, these requirements will
significantly reduce deaths and injuries caused by jackknifing and
other losses of directional stability and control during braking.
In addition, this final rule requires all powered heavy vehicles to
be equipped with an in-cab lamp to indicate ABS malfunctions. Truck
tractors and other towing trucks are required to be equipped with two
separate in-cab lamps: one indicating malfunctions in the towing truck
ABS and the other indicating malfunctions in the towed trailer or dolly
ABS. Trailers produced during an initial eight-year period must also be
equipped with an external malfunction indicator that will be visible to
the driver through the rearview mirror of the towing truck or tractor.
More specifically, the external trailer indicator will indicate an ABS
malfunction to the driver, if the trailer is being towed by an older
vehicle that is not equipped with an in-cab lamp for trailer ABS
malfunction indication. In general, the indicators will provide
valuable information about ABS malfunctioning to the driver and to
maintenance and Federal and State inspection personnel.
DATES: Effective Dates: The amendments to 49 CFR 571.105 become
effective on March 1, 1999. The amendments to 49 CFR 571.121 become
effective on March 1, 1997. Compliance to Sec. 571.121 with respect to
air-braked trailers and single unit trucks and buses will be required
as of March 1, 1998.
Petitions for Reconsideration: Any petitions for reconsideration of
this rule must be received by NHTSA no later than April 10, 1995.
ADDRESSES: Petitions for reconsideration of this rule should refer to
Docket 92-29; Notice 5 and should be submitted to: Administrator,
National Highway Traffic Safety Administration, 400 Seventh Street,
S.W., Washington, D.C. 20590.
FOR FURTHER INFORMATION CONTACT: Mr. George Soodoo, Office of Crash
Avoidance, National Highway Traffic Safety Administration, 400 Seventh
Street, SW., Washington, D.C. 20590 (202) 366-5892.
SUPPLEMENTARY INFORMATION:
I. Overview
II. Background
A. The Safety Problem: Loss of Control Crashes
B. Braking Systems, Tires, Wheel Lockup, and Loss of Control
Crashes
III. US and Foreign Activities Related to Stability and Control
During Braking Performance
A. Early US Regulatory History
B. PACCAR Case
C. US and Foreign Experience with ABS since PACCAR
IV. Advance Notice of Proposed Rulemaking (ANPRM)
V. Agency Proposal
VI. Comments on the Proposal
VII. Agency's Supplemental Proposal
VIII. Comments on the Supplemental Proposal
IX. Agency Decision
A. Requirement for and Definition of ABS
1. Legal Authority
2. Elements of the Requirement/Definition for ABS
3. Dynamic Versus Equipment Requirements
B. Independent Wheel Control
C. Braking-In-A-Curve Test
1. General Considerations
2. Test Surface
3. Test Speed
4. Type of Brake Application
5. Number of Test Stops for Certification
6. Test Weight
7. Loading Conditions
8. Initial Brake Temperature
9. Transmission Position
10. Summary of General Test Conditions
D. Reliability and Maintenance
E. Requirements for Durability, Reliability, and Maintainability
F. Alleged Safety Problems
G. ABS Malfunction Indicator Lamps
1. Number and Location; Duration of Trailer Requirement
2. Conditions for Activation
3. Activation Protocol for Malfunction Indicators
4. Signal Storage
5. Disabling Switch
6. ABS Failed System Requirements
H. Power Source
I. Applicability of Amendments
1. Trailers with Hydraulic or Electric Brakes
2. Hydraulically Braked Vehicles
J. Implementation
K. Intermediate and Final Stage Manufacturers/Trailer
Manufacturers
L. Benefits
M. Costs
IX. Rulemaking Analyses and Notices
A. Executive Order 12866 and DOT Regulatory Policies and
Procedures
B. Regulatory Flexibility Act
C. National Environmental Policy Act
D. Executive Order 12612 (Federalism)
E. Civil Justice Reform
I. Overview
As part of NHTSA's plans to improve the braking performance of
medium and heavy vehicles,1 this final rule amends the agency's
two brake standards for those vehicles by adopting requirements to
improve the directional stability and control characteristics of these
vehicles while braking. The two Federal Motor Vehicle Safety Standards
(FMVSSs) are Standard No. 105, Hydraulic Brake Systems, and Standard
No. 121, Air Brake Systems. In formulating this final rule, NHTSA has
relied on extensive fleet studies of tractor trailer combinations
equipped with antilock systems, road testing of such vehicles at the
agency's Vehicle Research Test Center (VRTC), review of its Fatal
Accident Reporting Systems (FARS) data and other crash data, the
positive experience with ABS-equipped heavy vehicles in Europe and
throughout the world, comments to the public docket about this
rulemaking, and other available information.
\1\Hereinafter referred to as ``heavy vehicles.''
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In order to fully understand the safety problem being addressed by
this rulemaking, it is necessary to examine in detail the reasons for
wheel lockup and the consequences of such lockup. Moreover, in order to
fully understand the reasons for the agency's decision to require that
heavy vehicles be equipped with a closed-loop ABS, it is necessary to
understand the general characteristics of brake systems, the force-
generating characteristics of tires, and the interactions between brake
systems and tires.
To provide the reader with a means for gaining this understanding,
NHTSA has included an Appendix in this document, which provides a
discussion of basic service brake systems, loss-of-control crashes, and
ABS characteristics. The Appendix discusses the types of heavy brake
systems that [[Page 13217]] are currently in use, how brake systems
work, and why lockup occurs. It also discusses the force-generating
characteristics of tires and how they are affected by varying levels of
wheel slip and the need to take these characteristics into account in
addressing the problem of loss-of-control crashes. Finally, the
Appendix discusses the need for ABS and describes their method of
operation. Several terms, such as ``wheel slip'' that are used
throughout this notice are discussed in detail and defined in the
Appendix. When terms whose precise meaning affects the understanding of
the agency's rationale are introduced, the reader could refer to the
Appendix for a discussion of the term.
Therefore, readers who lack a technical background and who desire a
more complete understanding of this rulemaking may wish at this point
to read the Appendix before moving on to the rest of the preamble.
NHTSA has decided to require the installation of ``closed-
loop''2 antilock systems on all heavy vehicles. The agency, in
accordance with Supreme Court precedent that required the agency to
consider mandating the installation of a particular type of automatic
restraint system (i.e., ``airbags only'') for passenger cars,3 is
adopting a rule that defines antilock brake systems, in performance
terms, as systems that ``automatically control the degree of rotational
wheel slip4 during braking'' through sensors and transmitters that
measure, transmit, and generate signals concerning the rate of wheel
angular rotation to controlling devices which adjust brake application
pressure to prevent wheel lockup. In addition, for truck tractors, the
rule prescribes a 30-mph braking-in-a-curve dynamic test on a low
coefficient of friction surface.
\2\A closed-loop (control) system is one which examines the
output of the system and adjusts the input to the system in response
to that output. This inclusion of the output (or some function of
the output) as part of the input to such a system is referred to as
feedback.
\3\(Motor Vehicle Manufacturers' Association v. State Farm
Insurance, 463 U.S. 29, (1983))
\4\See the Appendix for a discussion of this term and
directional stability.
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Although some commenters characterized NHTSA's definition as an
impermissible design standard, NHTSA has specifically sought to avoid
imposing unnecessary design restrictions or impeding the future
development of ABS, by adopting a definition that permits any antilock
brake system that ensures feedback between what is actually happening
at the tire-road surface interface and what the device is doing to
respond to excessive wheel slip. To the extent that NHTSA's definition
restricts design choices, e.g., by requiring a ``feedback'' system in
which control devices must respond to signals that monitor wheel slip,
the requirements are stated broadly and in performance terms. Such an
approach is consistent with that adopted in numerous other Federal
Motor Vehicle Safety Standards, including Standard No. 108 which
requires vehicles to be equipped with specified lamps and reflective
devices, Standard No. 111 which requires that vehicles be equipped with
rearview mirrors, and Standard No. 208 which requires vehicles be
equipped with safety belts.
Moreover, the United States Court of Appeals for the Sixth Circuit
has upheld a dimensional restriction on rectangular headlamps,
reasoning that ``uniformity of headlamp size is an element of headlamp
performance.''5 Accordingly, NHTSA has decided to reject the
conceptual objections to ``closed-loop'' ABS systems expressed by
commenters whose economic self-interest militates against the
requirement, including manufacturers of alternative, non-electronic
braking systems that are incapable of sensing and adjusting braking
pressures to control that wheel slip, and an association of fleet
owners that may wish to avoid incurring the added expense of purchasing
vehicles that are equipped with electronic ABS systems.
\5\Chrysler Corp. v. DOT, 515 F.2d 1053, 1058-59 (1975).
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Currently, all powered6 heavy vehicles equipped with ABS are
required to be equipped with an in-cab ABS malfunction indicator lamp
indicating malfunctions in the powered vehicle's ABS. Today's final
rule requires trucks (including truck tractors) equipped to tow another
air-braked vehicle to be equipped with another, separate in-cab lamp
indicating malfunctions in the ABS(s) of the towed vehicle(s). For an
eight-year period, the amendment requires trailers to be equipped with
an external ABS malfunction indicator that will be visible to the
driver of the towing truck or truck tractor through the rearview
mirror. In particular, the external trailer indicator lamp will provide
information to the driver, if the trailer is being towed by an older
vehicle that is not equipped with an in-cab lamp indicating trailer ABS
malfunctions. In general, the indicators will provide valuable
information about ABS malfunctioning to the driver and to maintenance
and Federal and State inspection personnel.
\6\By powered vehicle, the agency means a vehicle equipped with
an engine that propels the vehicle. In contrast, a non-powered
vehicle, such as a trailer, is towed by another vehicle.
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In separate, related documents published elsewhere in today's
Federal Register, NHTSA announces its decision to reinstate stopping
distance requirements for air-braked heavy vehicles and to establish
such requirements for hydraulically-braked heavy vehicles. In addition,
to carry out the antilock requirement, the Federal Highway
Administration (FHWA) is announcing its intent to require such systems
on heavy vehicles to be operational.
NHTSA is issuing this final rule on directional stability and
control pursuant to the Motor Carrier Act of 1991, a part of the
Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991.
Section 4012 directs the Secretary of Transportation to initiate
rulemaking concerning methods for improving braking performance of new
commercial motor vehicles,7 including truck tractors, trailers,
and their dollies. Congress specifically directed that such a
rulemaking examine antilock systems, means of improving brake
compatibility, and methods of ensuring effectiveness of brake timing.
The Act requires that the rulemaking be consistent with the Motor
Carrier Safety Act of 1984 (49 U.S.C. Sec. 31147) and be carried out
pursuant to, and in accordance with, the National Traffic and Motor
Vehicle Safety Act of 1966 (Safety Act) (49 U.S.C. 30101 et seq.).
\7\Vehicles with a gross vehicle weight rating (GVWR) of 26,001
or more pounds.
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NHTSA notes that, in the mid-1970's, Standard No. 121 was amended
to include stringent stopping distance requirements, coupled with a
``no lockup'' requirement, which had the effect of requiring heavy
vehicles to be equipped with antilock brake systems. In response to a
legal challenge, the U.S. Court of Appeals for the 9th Circuit
invalidated the stopping distance and ``no lockup'' requirements in
Standard No. 121, along with certain other provisions, holding that the
standard was ``neither reasonable nor practicable at the time it was
put into effect.''8
\8\PACCAR v. NHTSA, 573 F.2d 632 (9th Cir. 1978), cert. denied,
439 U.S. 862 (1978)
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As explained throughout this document, the underlying conditions
related to equipping heavy vehicles with antilock brake systems differ
markedly from 20 years ago when the petitioners challenged the agency
in PACCAR. First, antilock brake technology has advanced dramatically
since the mid-1970's, and antilock brake systems are now in widespread,
everyday use, both in this country and [[Page 13218]] throughout the
world. Second, NHTSA's extensive fleet study about heavy vehicle
antilock systems demonstrates that these systems are reliable when
placed in use. Third, the agency's testing of truck tractors equipped
with antilock systems indicates that they provide significantly
improved directional stability and control compared to vehicles without
antilock systems. Fourth, while the antilock systems used in the mid-
1970s also incorporated significantly larger, more aggressive
foundation brakes, which were sometimes incompatible with less
aggressive systems on existing vehicles when the antilock system
malfunctioned, the requirements being adopted today do not necessitate
such aggressive brakes. Therefore, they do not have the potential for
creating a more dangerous highway environment. Fifth, the performance
requirements adopted in today's final rule do not raise practicability
concerns. Based on these and other considerations discussed throughout
this document, NHTSA believes that today's final rule satisfies the
concerns raised by the PACCAR court.
II. Background
A. The Safety Problem: Loss of Control Crashes
Crashes involving heavy vehicles result in a significant number of
fatalities and injuries, and a significant amount of property damage
each year. Based on available statistics, NHTSA has estimated the
number of crashes in 1992 for several different groups of heavy
vehicles. For heavy combination vehicles, the agency estimates that
there were about 168,000 crashes. These crashes resulted in about
13,600 injuries and 387 fatalities to the occupants of heavy
combination vehicles and about 51,500 injuries and 2,452 fatalities to
the occupants of the other vehicles involved. For truck tractors
operating without a trailer, also known as ``bobtail'' truck tractors,
the agency estimates that there were about 8,400 crashes, resulting in
about 1,200 injuries and 39 fatalities to truck tractor occupants and
about 2,600 injuries and 178 fatalities to occupants of other involved
vehicles. For heavy single-unit trucks and school buses, the agency
estimates that there were about 192,600 crashes, resulting in about
15,700 injuries and 165 fatalities to truck and school bus occupants
and about 48,300 injuries and 891 fatalities to occupants of other
involved vehicles. For transit and intercity buses, the agency
estimates that there were about 49,500 crashes, resulting in about
19,500 injuries and 28 fatalities to bus occupants and about 9,100
injuries and 230 fatalities to occupants of other involved vehicles.
Based on analyses of both national and state accident data, NHTSA
estimates that between 10 percent and 15 percent of the crashes
involving heavy combination vehicles (including bobtail truck tractors)
involved in a jackknife or other braking-induced instability or loss of
control. For a more detailed discussion of the injury statistics, the
reader should refer to the Final Economic Assessment (FEA) for this
rulemaking.
This rulemaking focuses on crashes involving loss-of-control. Such
incidents result from braking-induced wheel lockup with subsequent loss
of the ability of the vehicle's tires to generate ``stabilizing
forces.''9 This loss of tire stabilizing forces can result in
either vehicle directional instability if it occurs at the vehicle's
rear wheels or loss of steering control if it occurs at the vehicle's
steering (front) wheels.
\9\See the Appendix which defines and discusses this term.
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B. Braking Systems, Tires, Wheel Lockup, and Loss of Control Crashes
When a vehicle driver makes a brake application that is too
``hard'' for conditions, the driver is likely to lock some or all of
the vehicle's wheels (i.e., the wheels will be ``sliding'' rather than
``rolling''). Locking up wheels is more likely to occur under
conditions where the maximum forces that can be generated by the
vehicle's tires are reduced, i.e., when the vehicle is lightly loaded
or empty and/or when the road is slippery. When wheel lockup occurs,
vehicle loss-of-control can result. Incorporation of an ABS decreases
the likelihood of wheel lockup, and increases the driver's ability to
maintain control during severe braking maneuvers, that would otherwise
lead to wheel lockup and resultant loss of directional stability and
control, if the vehicle is not equipped with an ABS.
III. US and Foreign Activities Related to Stability and Control During
Braking Performance
A. Early US Regulatory History
NHTSA has been concerned about the safety of heavy vehicle braking
systems since the agency's inception. On October 11, 1967, the
predecessor of NHTSA, the FHWA's National Highway Safety Bureau,
published a notice of its intention to promulgate brake standards for
hydraulic and air-braked trucks and buses, and air-braked trailers. (32
FR 14279.) The initial notice of proposed rulemaking (NPRM) for air-
braked systems proposed various requirements, including requiring
vehicles equipped with such systems to stop within certain distances,
from certain speeds, without leaving a 12-foot wide lane and without
lockup of any wheel ``more than momentarily.'' (35 FR 10368, June 25,
1970.) A companion NPRM for hydraulic brake systems proposed
essentially identical performance requirements for heavy vehicles
equipped with those systems. (35 FR 17345, November 11, 1970.) These
notices proposed that heavy vehicles would have to stop from 60-mph
within 216 feet on a surface with a skid number of 75.\10\ The ``no
lockup'' provision was intended to minimize skidding, spinning, and
jackknifing due to wheel lockup and loss of directional stability.
\10\A skid number describes the friction properties of pavement.
A skid number of 75 is representative of a dry surface with a
relatively high coefficient of friction. See the Appendix for a
discussion of this term.
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In the final rule establishing Standard No. 121, the agency decided
to increase the 60-mph stopping distance from 216 feet to 245 feet. (36
FR 3817, February 27, 1971.) The final rule amending Standard No. 105
to extend its applicability to heavy vehicles, also increased the 60-
mph stopping distance for those vehicles to 245 feet. (37 FR 17970,
September 2, 1972.) The requirements for air-braked vehicles were to
become effective on September 1, 1973, and those for hydraulic-braked
vehicles, on September 1, 1974.
Although neither standard specifically required antilock, NHTSA
anticipated that manufacturers would equip heavy vehicles with antilock
brake systems to comply with these requirements. The agency explained
that the less stringent stopping distance was being required to reflect
more accurately the vehicle performance given the test track road
surface's friction characteristics.
Since the required stopping distances were shorter than the
stopping performance achieved by certain heavy vehicles, new, more
aggressive foundation braking systems were necessary for those
vehicles. In particular, vehicles with short wheelbases needed to have
considerably more aggressive front axle brakes to meet the shorter
stopping distance requirements. If not kept properly adjusted, these
more aggressive front brakes might produce a brake ``pull'' to one
side, which was disconcerting to drivers, particularly on vehicles
without power steering. In addition, drivers were concerned about loss
of steering control caused by wheel lockup on the
[[Page 13219]] steering axle. At the time, most manufacturers equipped
their vehicles with antilock devices because the standards required
stops to be made without more than momentary lockup of the wheels.
These devices served to prevent steering axle lockup problems as well,
but there was concern that safety problems could result on short-
wheelbase, high-center-of-gravity vehicles, in the event that the
antilock system should malfunction.
NHTSA extended the effective dates for the stopping distance
requirements in Standard No. 105 and Standard No. 121. (37 FR 3905,
February 24, 1972; 38 FR 3047, February 1, 1973; 39 FR 17550, 17563,
May 17, 1974.) Prior to the final effective date for Standard No. 105,
the amendments pertaining to heavy vehicles were withdrawn, so the
requirements for heavy hydraulic-braked trucks and buses never went
into effect. (40 FR 18411, April 28, 1975.) Standard No. 121 became
effective on January 1, 1975, for trailers, and on March 1, 1975, for
trucks and buses. At that time, the 60-mph stopping distance
requirement remained at 245 feet. However, after several revisions to
the stopping distance requirements, NHTSA amended the standard by
extending the 60-mph stopping distance requirement to 293 feet, as
requested by Freightliner in a petition for reconsideration. (41 FR
8783, March 1, 1976.)
B. PACCAR Case
In January 1975, PACCAR (a truck manufacturer), the American
Trucking Associations (ATA), and the Truck Equipment and Body
Distributors Association (TEBDA) sued the agency, challenging the
stopping distance requirements in Standard No. 121, which they believed
required the use of antilock brake systems.
Specifically, the petitioners challenged the 245-foot stopping
distance. The subsequent increase to 293 feet, a distance that did not
necessitate such aggressive front brakes, occurred after the suit was
filed. The petitioners argued that the agency failed to demonstrate a
safety need for the standard and that the testing procedures were not
objective, impracticable, and unreasonable. TEBDA objected to the
standard's certification requirements.
In response to the suit, the stopping distance and ``no lockup''
requirements in Standard No. 121, along with certain other provisions,
were invalidated by the United States Court of Appeals for the 9th
Circuit in PACCAR. The court held that NHTSA was justified in
promulgating a standard requiring improved air brake systems and
stability mechanisms. However, after reviewing the record about
reliability problems with antilock brake systems then in use, the court
further held that the standard was ``neither reasonable nor practicable
at the time it was put into effect.'' Id. at 640. Among the court's
other findings were that the agency had a responsibility (1) to examine
the results of its rulemakings by investigating more fully the safety
of vehicles in use, (2) to assure that the new systems it requires are
reliable when placed in use, and (3) to determine that its regulations
do not produce a more dangerous highway environment than that which
existed prior to government intervention. Based on these findings, the
court stated that
* * * those parts of the Standard requiring heavier axles and
the antilock device should be suspended. The evidence indicates that
this can be accomplished if we hold, as we do, that the stopping
distance requirements from 60 mph are invalid * * * We hold only
that more probative and convincing data evidencing the reliability
and safety of vehicles that are equipped with antilock and in use
must be available before the agency can enforce a standard requiring
its installation.
Id. at 643.
The court also ruled on the objectivity and practicability of the
testing procedures in Standard No. 121. First, the court stated that
road surface skid numbers used for testing certified vehicles were
``ill-chosen'' where they assumed the use of a particular tire no
longer in production. Id. at 644. Second, the skid number method of
testing was not objective. Id. at 644. Third, the testing procedure was
not practicable because fluctuations in skid numbers on a given road
surface made it impracticable for manufacturers to conduct tests that
assure that their vehicles will exactly meet the objective standard
when tested by NHTSA. Id. at 644. Fourth, manufacturers are entitled to
testing criteria that they can rely on with certainty. Id. at 644.
Fifth, the standard failed to specify formal and reasonably specific
testing criteria about the time intervals between tests, the duration
of permissible wheel lockup during tests, and the amount of curving in
testing track roadways. Id. at 645. Sixth, the agency's suggestions of
alternative methods of satisfying the Safety Act's ``due care''
provision were inadequate since such alternatives were not set forth in
the regulations. Id. at 645.
The court remanded the matter to NHTSA to clarify certain
provisions in Standard No. 121. In response to PACCAR, the agency
issued several notices amending the standard to be consistent with the
decision. (43 FR 39390, September 5, 1978; 43 FR 48646, October 19,
1978; 43 FR 58820, December 18, 1978; 44 FR 46849, August 9, 1979.) In
the September 1978 notice, the agency amended the standard to specify
test procedures and conditions for frictional characteristics of the
test track surface, duration of time intervals between road tests,
duration of permissible wheel lockup during road tests, the amount of
curving in the test track, and the means for establishing the
frictional resistance of the road test surface. In the October 1978
notice, the agency set forth its interpretation of PACCAR to guide
continuing compliance with the standard. Specifically, the notice
explained that the court had invalidated the ``no lockup'' provisions
in S5.3.1 and S5.3.2 as they apply to trucks and trailers, along with
the related stopping distances established for 60-mph stopping tests
for heavy vehicles. That notice also amended the requirements to
provide for ``due care certification.'' In the December 1978 notice,
NHTSA responded to petitions for reconsideration of certain aspects of
the September 1978 notice, including vehicle exclusions and road test
procedures. The agency withdrew the changes to specification of initial
brake temperatures, skid number ranges, and duration of wheel lockup
that were made in the September notice. In the August 1979 notice, the
agency further clarified its interpretation of certain findings of
PACCAR.
C. US and Foreign Experience With ABS Since PACCAR
As a result of the 1978 PACCAR decision, U.S. manufacturers chose
to halt development and production of ABS for heavy vehicles. For
instance, before the 1978 ruling, A-C Sparkplug, a domestic
manufacturer of ABS, produced about 180,000 ABS units per year. By
1984, it was producing only about 500 units annually.
NHTSA continued to study the effectiveness of heavy truck antilock
brake systems. Among other things, the agency studied the in-use
experience with ABS in other countries, conducted performance testing
of ABS equipped heavy vehicles, and conducted an extensive domestic
fleet in-use test of ABS equipped heavy vehicles.
In response to section 9107 of the Truck and Bus Regulatory Reform
Act of 1988, NHTSA submitted a report to Congress titled ``Improved
Brake Systems for Commercial Vehicles'' (Report No. DOT HS 807 706).
(April 1991) After discussing crash data concerning heavy vehicle brake
systems, the report examined factors related to braking effectiveness,
stability and [[Page 13220]] control during braking, and braking system
compatibility of heavy combination vehicles. Among other things, the
report indicated that the stopping distances and directional stability
of heavy vehicles could be improved by equipping those vehicles with
ABS.
With respect to the in-use experience with ABS in other countries,
NHTSA conducted a study of the performance, reliability, and
maintainability of in-service commercial air-braked vehicles equipped
with ABS in Europe and Australia.\11\ At the time of the study in 1987,
there were approximately 1.5 million ABS-equipped trucks and tractors,
and 0.9 million ABS-equipped trailers in use in Western Europe, and
92,000 trucks and tractors and 80,000 trailers in Australia. ABS market
penetration, at that time, in Western Europe was estimated to be 4.5
percent for trucks and tractors and 5.6 percent for trailers, while in
Australia the comparable figures were 1.3 percent for trucks and
tractors, and less than 1 percent for trailers. Based on data derived
from interviews with fleets which were using ABS and surveys conducted
by ABS and vehicle manufacturers, the reliability of ABS when equipped
on European vehicles was estimated to be 1 to 2 ABS component failures
per 1000 vehicles per month. Based on those data, it was predicted that
between 4 and 20 malfunctions would occur with the 200 ABS-equipped
truck tractors involved in the NHTSA-sponsored two-year in-service
fleet study, which was subsequently performed between 1989-91. In fact,
nineteen ABS components failed, which is within the range predicted by
the European study.
\11\``European/Australian Experience with Antilock Braking
Systems in Fleet Service,'' U.S. Department of Transportation,
NHTSA, DOT HS 807 269, March 1988.
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Among the study's other findings were that maintenance was done
only when a malfunction indicator activated; malfunction indications
did not cause drivers to disrupt their operations and stop en route; no
special maintenance was performed on the ABS beyond routine periodic
inspections; no problems with electronic and radio frequency
interference (RFI) were reported; with proper maintenance, ABS life was
expected to equal that of the vehicle; and carriers reported that
drivers liked driving ABS-equipped vehicles. Although some problems
were encountered with wiring and connector failures, ABS manufacturers
believed that their systems were generally reliable and expected future
improvements.
Since the completion of NHTSA's study, several European countries
have issued regulations requiring heavy vehicles to be equipped with
antilock brake systems. Specifically, the Economic Commission for
Europe\12\ (ECE) Regulation No. 13 includes technical requirements for
antilock systems in Annex 13 of its regulation.\13\ Annex 13 sets forth
definitions of antilock brake systems and component parts, various
``types'' of antilock systems, and test procedures. ECE's Annex 13
specifies a design requirement and dynamic performance requirements.
The European Economic Community (EEC Common Market) directive has
identical requirements. As a result, since October 1, 1991, all heavy
trucks (with GVWR greater than 16 metric tons), interurban buses (with
GVWR greater than 12 metric tons), and heavy trailers (with GVWR
greater than 10 metric tons) submitted for new type approvals in
European countries adopting the standard have been required to be
equipped with ABS. Accordingly, ABS have been installed on tens of
thousands of European heavy vehicles that have traveled millions of
miles over the last few years. All vehicles for which ABS is mandatory
under Annex 13 are required to have a Category 1 system. Such systems
are essentially the same as those required by today's final rule.
\12\The Economic Commission for Europe (ECE) is a United Nations
organization comprised of European countries plus the United States
and Canada, which establishes requirements applicable to the type
approval of motor vehicles and other products for sale in those
nations that choose to apply the requirements.
\13\Annex 13 is titled ``Requirements Applicable to Tests for
Braking Systems Equipped with Anti-Lock Devices (Wheel-Lock
Preventers).'' It is Annex 13 of ECE Regulation No. 13, which is
titled ``Uniform Provisions Concerning the Approval of Vehicles with
Regard to Braking.'' Regulation No. 13 is Addendum 12 of the
``United Nations Agreement Concerning the Adoption of Uniform
Conditions of Approval and Reciprocal Recognition of Approval for
Motor Vehicle Equipment and Parts,'' done at Geneva on March 20,
1958, which is commonly known as the ``1958 Agreement.''
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With respect to performance testing, NHTSA has issued two reports
on the stopping distance capability of several different types of heavy
air-braked vehicles at various loading conditions.\14\ The agency also
tested some vehicles equipped with ABS, thus allowing comparisons about
stopping distances with and without these devices. At the beginning of
each test series, these vehicles were equipped with new tires and with
new original equipment brake system components to provide consistency
in test results. At the beginning of each testing series, the tests
were conducted on various vehicles (school buses, transit buses, single
unit trucks, tractor trailers) at the loaded and empty conditions and
with various equipment (with ABS activated and deactivated). All the
tests were straight line stops from 60 mph on a dry concrete surface.
The test results indicated that: (1) All stops made with ABS were
stable, regardless of whether the vehicle was operating fully loaded or
empty, and (2) stopping distance improvements with ABS (compared to no
ABS) were greatest in the bobtail configuration (+47 percent in one
case), were significant with an empty trailer (+29 percent in one case)
and were smallest (+4 percent) in the fully loaded condition.\15\
\14\``NHTSA Heavy Duty Vehicle Brake Research Program Report No.
9, Stopping Distances of 1988 Heavy Vehicles,'' (DOT HS 807 531,
February 1990)
\15\DOT HS 807 531, Table 4, page 19; Table 5, page 23; Table 6,
page 25)
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NHTSA's fleet testing program of ABS-equipped truck tractors
evaluated the reliability, maintainability, and durability of 200 truck
tractors equipped with ABS. The fleet study found that current
generation ABSs are reliable and can be successfully installed on
commercial motor vehicles.16 The agency added trailers to the
fleet study program in 1990-1991 and found similar results. A copy of
that study has been submitted to the public docket.17 The findings
of the fleet testing program are discussed later in this preamble.
\16\``An In-Service Evaluation of the Reliability,
Maintainability, and Durability of Antilock Braking Systems (ABS)
for Heavy Truck Tractors,'' (DOT HS 807 846, Final Report, March
1992.)
\17\``An In-Service Evaluation of the Performance, Reliability,
Maintainability, and Durability of Antilock Braking Systems (ABSs)
for Semitrailers'' (DOT HS 808 059, Final Report, October 1993.)
---------------------------------------------------------------------------
IV. Advance Notice of Proposed Rulemaking (ANPRM)
On June 8, 1992, NHTSA responded to Congress' 1991 mandate in ISTEA
by publishing an advance notice of proposed rulemaking (ANPRM)
announcing the agency's interest in measures to improve the directional
stability and control of heavy vehicles during braking. (57 FR 24212.)
The advance notice stated the agency's tentative conclusion that ABS
represents the best available and most reliable technology to reduce
jackknifing and other loss-of-control crashes during braking. The
notice posed questions about such matters as the occurrence of loss-of-
control crashes; the availability and performance of systems to improve
directional stability and control under all conditions of braking and
vehicle [[Page 13221]] load; potential regulatory approaches to improve
the directional stability and control of heavy vehicles during braking,
including anticipated performance requirements, test procedures, and
equipment requirements; a schedule for implementing requirements;
diagnostic equipment to ensure in-use functioning of the systems; and
anticipated costs of such requirements.
V. Agency Proposal
On September 28, 1993, NHTSA proposed to amend Standard No. 105 and
Standard No. 121, to add requirements that would improve the
directional stability and control of heavy vehicles during braking. (58
FR 50738.) NHTSA decided to propose that each heavy vehicle must be
equipped with an antilock braking system that satisfies the agency's
proposed definition of ABS. In addition, as a verification of the
performance of the ABS, the agency proposed that a heavy vehicle comply
with a braking-in-a-curve test.
NHTSA stated that, in proposing these amendments, its overriding
goal was to ensure the directional stability and control of heavy
vehicles during braking. The agency stated that, to ensure adequate ABS
performance by means of dynamic test requirements, it would need to
establish a broad array of performance requirements that would test the
directional stability and control of vehicles under a number of loading
conditions, travel speeds, and deceleration rates, and on a wide
variety of road surfaces, including roads that are dry, wet, icy, and
``split mu.'' In addition, to ensure that directional stability and
control are not provided at the expense of stopping distance, each of
these tests would need to require the vehicle to stop within a
specified distance.
NHTSA explained, however, that an approach that relied exclusively
on dynamic test requirements would raise serious practicability
concerns, given the inherent variability of stopping distance
performance on low coefficient of friction surfaces and the costs
associated with requiring such an extensive array of dynamic
performance test requirements. NHTSA, therefore, focused its efforts on
expressly requiring that heavy vehicles be equipped with ABS, and on
supplementing that requirement with feasible and practicable dynamic
tests that check the directional stability and control, and stopping
distance of vehicles under a limited set of circumstances that may be
experienced in the real world.
The proposal that heavy vehicles be equipped with antilock systems
would have required that the front axle and at least one rear axle of
each heavy vehicle be equipped with an ABS that would automatically
control rotational wheel slip during braking by (1) sensing the rate of
angular rotation of the wheels, (2) transmitting signals regarding the
rate of wheel angular rotation to one or more devices which interpret
those signals and generate controlling output signals, and (3)
transmitting those controlling signals to one or more devices which
adjust brake actuating forces in response to those signals. The agency
stated its belief that these characteristics, specified in the
definition of ABS, would permit the installation of any antilock
braking system, provided that it is a ``closed-loop'' system that
ensures feedback between what is actually happening at the tire-road
surface interface and what the device is doing to respond to excessive
wheel slip. NHTSA tentatively concluded that these criteria were
necessary to ensure the introduction of systems that control wheel slip
and sustained wheel lockup under a wide variety of real world
conditions and thus would significantly improve safety.
In addition, the NPRM contained a detailed discussion of the
braking-in-a-curve test, including the test track's configuration, lane
width, and test surface, the vehicle's test speed, the type and number
of brake applications, loading conditions, control trailer
requirements, and the initial brake temperature.
NHTSA also proposed requirements for the ABS malfunction lamps and
the power source for trailer antilock systems. The agency also
addressed such considerations as requirements for diagnostic systems,
the types of vehicles to be covered by the rulemaking, the
implementation schedule for the proposed requirements, the rulemaking's
potential effects on intermediate and final stage manufacturers and
trailer manufacturers, and its costs and benefits.
VI. Comments on the Proposal
NHTSA received over 60 comments in response to the NPRM. Commenters
included heavy vehicle manufacturers, brake manufacturers, safety
advocacy groups, heavy vehicle users, trade associations, State
entities, and other individuals.
Most commenters agreed that the agency should issue requirements to
improve the stability and control of heavy vehicles during braking,
thereby reducing the number of loss-of-control crashes. Advocates for
Highway and Auto Safety (Advocates), the Heavy Duty Brake Manufacturers
Council (HDBMC), the Insurance Institute for Highway Safety (IIHS), and
Rockwell WABCO generally supported the agency's proposal to require
heavy vehicles to be equipped with an ABS. These commenters stated that
ABS will improve vehicle safety by providing improved braking
performance and vehicle stability and control during braking.
The American Automobile Manufacturers Association (AAMA)\18\, the
American Trucking Associations (ATA), and fleet operators expressed
mixed support for the rulemaking. AAMA stated that it ``reluctantly
accepts the design specific proposal,'' given its concerns about the
proposed braking-in-a-curve test procedure. ATA stated that it supports
the use of ABS, but is concerned that the proposed effective dates
would require universal use of ABS too soon to assure safety and
reliability. AAMA and ATA stated that they would fully support the
rulemaking, if the agency revised various aspects of the proposals.
AAMA was primarily concerned about the practicability of the braking-
in-a-curve test. ATA was primarily concerned about the ABS equipment
requirement and alleged problems with the reliability of separate
tractor-to-trailer electrical cables/connecters. The agency notes that
some of ATA's requested revisions would be major departures from the
original proposal.
\18\AAMA submitted joint comments on behalf of eight major
domestic manufacturers of heavy vehicles: Chrysler, Ford,
Freightliner, General Motors (GM), Mack Trucks, Navistar, PACCAR,
and Volvo-GM).
---------------------------------------------------------------------------
The National Private Truck Council (NPTC), the National Truck
Equipment Association (NTEA), the National Association of Fleet
Administrators (NAFA), and the National Association of Trailer
Manufacturers (NATM) opposed requiring heavy vehicles to be equipped
with ABSs. These commenters were primarily concerned about the costs
that an ABS requirement would impose on fleets, final stage
manufacturers of vehicles produced in multiple stages, and small
trailer manufacturers. NTEA stated that it would be impracticable for
final stage manufacturers to certify compliance with the braking-in-a-
curve test.
Commenters also addressed specific issues raised in the NPRM,
including the proposal to require vehicles to be equipped with ABS, the
type of and definition for ABS, the braking-in-a-curve test procedure,
the implementation schedule for the [[Page 13222]] requirements, the
malfunction indicator requirements, the power requirement, and the
rulemaking's cost. A more specific discussion of the comments, and the
agency's responses, are set forth below.
VII. Agency's Supplemental Proposal
Based on its analysis of comments on the NPRM and other available
information, NHTSA issued a supplemental notice of proposed rulemaking
(SNPRM) proposing a modified implementation schedule for the
requirements in the agency's September 1993 NPRM and a requirement for
independent wheel control on at least one axle. (59 FR 17326, April 12,
1994.)
With respect to leadtime, the agency proposed concurrent effective
dates for the heavy vehicle stability and control requirements and for
the heavy vehicle stopping distance requirements. Specifically, the
agency proposed the following implementation schedule for both sets of
requirements:
Truck tractors--2 years after final rule (1996)
Trailers--3 years after final rule (1997)
Air-braked single unit Trucks and buses--3 years after final rule
(1997) Hydraulic-braked single unit trucks and buses--4 years after
final rule (1998)
With respect to independent wheel control, NHTSA proposed to
require heavy vehicles to be equipped with an ABS that controls the
wheels on at least one front and one rear axle, and independently
controls the wheels on at least one of these two axles. The agency
tentatively concluded that this would provide a necessary level of
stopping distance performance on low mu and split mu surfaces. The
agency posed a number of questions about the need for independent wheel
control.
VIII. Comments on the Supplemental Proposal
NHTSA received comments from AAMA, other vehicle manufacturers,
brake manufacturers, safety advocacy groups, ATA, and others.19
Aside from ATA, almost all the commenters favored the proposed
implementation schedule. Several commenters, including AAMA, Ford,
Bendix, and Midland-Grau were concerned that the proposed requirements
addressing independent wheel control were unreasonably design
restrictive.
\19\Comments on the SNPRM will be specifically labeled as such.
Other comments will be assumed to be in response to the NPRM.
---------------------------------------------------------------------------
Among the other issues raised by commenters were whether the
proposal is a performance requirement, alleged reliability and
maintenance problems with ABS, alleged safety problems caused by ABS,
the regulation's benefits and costs, its applicability to hydraulic
systems, and the possible need for a phased-in implementation schedule
and a separate power circuit for operating the ABS.
IX. Agency Decision
A. Requirement for and Definition of ABS20
\20\The reader may wish to review the Appendix which provides a
technical explanation of how antilock brakes work, including various
methods of wheel control.
---------------------------------------------------------------------------
In developing the proposal for this rulemaking, NHTSA considered
what requirements are necessary to ensure improved stability and
control for heavy vehicles. Among other things, the agency considered
whether adequate performance relating to stability and control could be
ensured solely by means of dynamic vehicle performance test
requirements.
The agency stated in the NPRM its belief that, in order for an
approach relying solely on dynamic tests to be successful, it would be
necessary to establish a broad array of dynamic performance
requirements that would test the directional stability and control of
vehicles under a variety of loading conditions, travel speeds, and
deceleration rates, and on a variety of road surfaces, including ones
that have coefficients of friction that are low, high, and split mu. In
addition, in order to ensure that stopping distance performance is not
compromised in the attempt to improve directional stability and control
during braking, it would be necessary for these performance
requirements to specify maximum stopping distances.
NHTSA explained, however, that the poor correlation between
stopping distance performance and the peak friction coefficient21
(PFC) of low coefficient of friction surfaces, combined with the costs
associated with such an extensive array of dynamic performance
requirements, would, at this time, raise serious practicability
concerns about any approach that included such an array of dynamic test
requirements.22 NHTSA therefore focused its efforts on a single
provision expressly requiring that heavy vehicles be equipped with
antilock systems, and on identifying feasible and practicable dynamic
tests that could supplement that provision by directly assessing the
directional stability, control and stopping distance of vehicles under
some of the wide variety of circumstances that may be experienced in
the real world.
\21\See the Appendix for a discussion of this term.
\22\``MVMA/NHTSA/SAE Round Robin Brake Test,'' Transportation
Research Center of Ohio, Report No. 091194, August 26, 1991.
---------------------------------------------------------------------------
This section discusses the proposed provision expressly requiring
that heavy vehicles be equipped with antilock systems. More
specifically, NHTSA proposed to require that each heavy vehicle be
equipped with an ABS that satisfies the following definition:
``Antilock braking system'' means a portion of a service brake
system that automatically controls the degree of rotational wheel
slip during braking by:
(1) sensing the rate of angular rotation of the wheels;
(2) transmitting signals regarding the rate of wheel angular
rotation to one or more devices which interpret those signals and
generate responsive controlling output signals; and
(3) transmitting those controlling signals to one or more
devices which adjust brake actuating forces in response to those
signals.
In developing this definition, the agency specifically sought to
avoid unnecessary design restrictions or impede the future development
of ABS. NHTSA stated in the NPRM that it believed that the proposed
requirement would permit any ABS, provided that it was a closed-loop
system that ensures feedback between what is actually happening at the
tire-road surface interface and what the device is doing to respond to
changes in wheel slip.
For a number of reasons discussed in the NPRM (and below), NHTSA
tentatively concluded that a device that satisfies these criteria is
necessary in order to prevent wheel lockup under a wide variety of real
world conditions, thereby significantly improving safety.
A number of commenters, including vehicle manufacturers and brake
manufacturers, recognized the practicability problems currently
associated with some dynamic performance requirements and accordingly
supported the agency's proposal to require heavy vehicles to be
equipped with ABSs. AAMA stated that despite its strong preference for
what it termed ``performance requirements,'' it would accept an
explicit ABS requirement, provided that the braking-in-a-curve test is
not adopted and the effective date for the proposed stopping distance
requirement is made concurrent with the other effective dates for this
rulemaking.23 That organization stated that, in general,
manufacturers ``much prefer performance over design specifications
because performance [[Page 13223]] requirements allow new, improved and
more cost-efficient technological means to achieve desired safety
ends.'' Nevertheless, AAMA indicated that it was willing to accept an
ABS equipment requirement because it believes there are significant
practicability problems associated with various dynamic tests that the
agency has considered, including the braking-in-a-curve test.
\23\AAMA's specific concerns about the braking-in-a-curve test
are discussed in a later section of this document.
---------------------------------------------------------------------------
Similarly, Rockwell WABCO stated that it ``reluctantly accepts the
proposal for an ABS equipment standard rather than a performance
standard.'' That commenter stated that it normally opposes equipment
standards since they have the potential of restricting the
implementation of new technology. However, it stated that, in this
case, ``the current difficulty in formulating valid, repeatable
performance criteria prohibit a true performance standard at this
time.'' Rockwell WABCO concluded that ``the proposed combination of an
equipment specification and a performance test is both understandable
and acceptable'' for now.
Advocates stated that it is convinced that:
The agency's resolve to mandate a basic level of ABS as required
equipment on all tractors, trucks, trailers, and buses with
verification of desirable safety performance gained through a single
major operating test, is the most appropriate way to ensure that the
substantial safety benefits of heavy vehicle ABS are realized
quickly.
Midland-Grau stated that the characteristics specified in the
proposed definition will permit any antilock brake system, provided
that it is a ``closed-loop'' system that ensures feedback between what
is actually happening at the tire-road surface interface and what the
device is doing to respond to changes in wheel slip.
Mr. John Kourik, a brake engineer, stated that the proposed
definition:
1. Selects the proper technology to assure optimum stability and
control, [and]
2. Supplements the intent of the original definition with a high
degree of sophistication. This should eliminate the inferior
mechanisms and devices that have been offered by `toying' with the
brevity of the original definition while making representations and
distorted claims to suggest equivalency to ABS. Thus, the new
definition should end the ``smoke and mirrors'' promotions of
alleged substitutes for ABS.
According to Mr. Kourik, the proposed definition would preclude the
use of unsophisticated equipment that does not sense changes in the
wheel rotation rate, e.g., equipment such as mechanical devices,
pneumatic dampeners, hydraulic dampeners, hydro/mechanical units, and
electro/mechanical units.
Other commenters strongly opposed the proposed ABS requirement. ATA
argued that NHTSA had proposed a ``design standard for ABS'' that is
``unlawful because it is contrary to the agency's statutory mandate to
issue only performance standards.'' Citing the statutory definition of
``motor vehicle safety standard,'' that organization stated that, under
the Safety Act, the requirements in Federal motor vehicle safety
standards must prescribe performance, not design obligations.
ATA claimed that, despite the statutory mandate, much of the
agency's proposal represents design requirements. Specifically, ATA
stated that there were additional impermissible design aspects to the
proposal, including the definition of ABS, and the requirements for
trailer electrical power to be transmitted by a separate circuit
specifically provided for that purpose and for warning systems to be
electrical.
ATA also argued that the proposed definition for ABSs is
unnecessarily design-restrictive, and would stifle innovation and
require continual updating of the standard. ATA stated that the
requirements would preclude anything but electronic systems, thereby
prohibiting mechanical systems. That organization also argued that the
requirements would impair efforts to develop new electronic
technologies.
Several small companies which manufacture or sell brake products
also argued that the proposed requirements are inappropriately design-
restrictive. They argued that NHTSA should change the proposed
definition of ABS so that devices other than computerized ABS can be
used to meet the requirements. Trade International Corporation (TIC)
argued that the proposed definition for ABS is fundamentally flawed
because it does not specify what the system is supposed to accomplish
but rather specifies how the system is supposed to work. It argued that
a system could satisfy the definition but not accomplish the desired
function.
After carefully considering the comments, NHTSA has decided to
adopt the proposed requirement for and definition of ABS. The agency's
response to the comments, including a more detailed discussion of some
of the comments summarized above, is presented in the sections which
follow.
1. Legal Authority
NHTSA disagrees with ATA's allegation that the agency does not have
the statutory authority to issue a ``design standard.'' NHTSA's
longstanding position24 on this subject, which is presented in the
form of a hypothetical discussion concerning the agency's authority to
regulate the width of motor vehicles, is set forth below:
\24\This discussion has been presented in past NHTSA letters,
including a May 2, 1979 letter to the Insurance Institute for
Highway Safety.
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We believe that the National Traffic and Motor Vehicle Safety
Act * * * would permit issuance of a safety standard that regulated
or limited vehicle width, if it were found that such a regulation
``meets the need for motor vehicle safety'' (Sec. 103(a), 15 U.S.C.
1392(a)). As is true with every motor vehicle safety standard,
however, it would be necessary to establish a reasonable, objective
basis for the conclusion that this regulation can be justified by
safety benefits obtainable, to avoid a judicial conclusion that the
action is ``arbitrary, capricious, [or] an abuse of discretion.'' (5
U.S.C. 706). The issue, in other words, would not be one of basic
authority, but of justification.
Although it may be argued that such a safety standard would be a
regulation of ``design, and not performance'', for reasons set forth
below we feel that this argument is insubstantial and reflects an
inadequate understanding of the Act and the safety standards * * *.
Section 102(2) of the Act (15 U.S.C. 1391) defines a motor
vehicle safety standard as ``a minimum standard for motor vehicle
performance, or motor vehicle equipment performance, which is
practicable, which meets the need for motor vehicle safety and which
provides objective criteria.'' Section 103(f) of the Act also
requires the standards to be ``reasonable, practicable and
appropriate for the particular type of motor vehicle * * * for which
it is prescribed.''
It has sometimes been suggested that the inclusion of the word
``performance'' in this definition suggests the existence of a
dichotomy between vehicle design and performance. We do not,
however, consider that there is a dividing line between standards
that regulate performance and standards that affect design. Senator
Magnuson recognized the absence of any dichotomy when he said that
some safety standards would necessarily determine the configuration
of some vehicle components. (112 C.R. 20600 (Aug. 31, 1966.)). In
fact, all safety standards have a strong effect on vehicle or
equipment design, in spite of their being phrased in ``performance''
terms. This is necessarily so since the design of vehicles and
equipment determines the quality of their performance. (Some
confusion over ``design'' may arise from the common use of the word
to mean appearance or shape. In our work, however, the word means
the sum of all of the characteristics that a product is intended to
have, e.g., size, weight, interrelationship of components,
materials, and markings.)
Each of our safety standards meets the need for motor vehicle
safety by specifying requirements for the performance of a
particular vehicle or item of equipment. Any design that will
satisfy the requirements may be used for the system or item of
equipment. The extent to which the choice of a design
[[Page 13224]] is restricted by a particular standard is purely a
matter of degree, depending on the specificity of the requirement.
We try, in carrying out the congressional mandate, to make the
requirements as broad as the safety need allows. We will probably
never have to reach the level of a true ``design specification'' as
an engineer would use the term, i.e., a detailed description of
every significant aspect of a product including the materials and
manufacturing processes used. This is true because the standards
deal only with the safety-related characteristics of the regulated
items, e.g., the height, width, and strength of a head restraint and
the light output of a headlamp.
In some cases, the configuration of a vehicle component or item
of equipment is the characteristic that relates to safety. A good
example of this is our standard on transmission shift levers (No.
102), which standardizes the position of Park, Reverse, etc., on all
our passenger cars today. There, standardization of at least some
external aspects of the component is needed for safety's sake. A
second example is our standard on control identification (No. 101),
where again an enforced similarity in the words and symbols used to
identify vehicle controls is the heart of the safety requirement * *
*.
Thus, if the width of a vehicle is, in fact, the characteristic
that is found to require regulation for safety purposes (analogously
to the spacing of headlamps in Standard 108 or the width of a head
restraint in Standard 202), there should be no doubt of NHTSA's
authority to regulate it.
NHTSA's requirements for specified safety equipment are at the
heart of many of the Federal motor vehicle safety standards. Indeed,
thousands of the lives saved and the injuries reduced or prevented by
Federally-mandated safety features are the direct result of
requirements for specific types of equipment. Most prominent among
these requirements is the 25-year-old requirement in Standard No. 208,
Occupant Crash Protection, for the installation of specific types of
safety belts. This is the most heavily judicially and Congressionally
scrutinized safety standard, and no question has ever been raised about
the agency's authority to issue such a standard.
Equipment requirements are critical for helping to ensure that
vehicles have many of the items necessary to guarantee safety. For
example, it is critical for drivers to be able to see where they are
going, and for their vehicle to be seen by other drivers. The safety
standards therefore require items that are critical for driver
visibility and vehicle conspicuity in the rain and at night. Standard
No. 104 requires vehicles to have a windshield wiping system, Standard
No. 108 requires vehicles to be equipped with specified lamps and
reflective devices, Standard No. 111 requires that vehicles be equipped
with rearview mirrors, and Standard No. 205 specifies the types of
glazing which may be used in various locations.
Many other safety standards, including the existing brake
standards, specify equipment requirements that meet equally important
safety needs. Thus, the extremely narrow reading of the word
``performance'' advocated by ATA is inconsistent with the entire
history of the Federal program for motor vehicle safety standards, and
indeed with a majority of the existing standards.
The case law addressing this issue has clearly upheld NHTSA's
authority to issue safety standards that directly affect design. In
Chrysler v. DOT, 515 F.2d 1053 (6th Cir. 1975), for example, the court
upheld a dimensional restriction on rectangular headlamps. That court
reasoned that:
Uniformity of headlamp size is an element of headlamp
performance. Design freedom would inhibit safety, and certainly the
congressional purpose of encouraging safety-related competition
among manufacturers is meaningless in this context.
We conclude that the dimension restriction at issue here
essentially serves to ensure proper headlamp performance and lies
within the regulatory authority granted by Congress to the NHTSA.
515 F.2d at 1058, 1059.
Moreover, in Motor Vehicle Manufacturers Association v. State Farm,
463 U.S. 29 (1983), the United States Supreme Court held that, before
rescinding a general requirement for automatic restraints because one
type of automatic restraint (e.g., the detachable automatic safety
belt) might be ineffective, NHTSA must consider establishing an airbag-
only requirement. The Court further stated that the agency could
prohibit detachable automatic safety belts if the agency determined
that they would not provide effective passenger protection. Therefore,
the Supreme Court clearly recognized NHTSA's authority both to require
specific safety equipment deemed to provide superior safety protection
and to prohibit specific equipment that the agency deemed to provide
inferior safety protection.
NHTSA therefore rejects ATA's argument concerning the agency's
authority to require specified safety equipment. However, as indicated
above, the agency does, in carrying out its statutory mandate, attempt
to make its safety requirements as broad as the safety need allows. The
relevant issue for this rulemaking is thus not whether the agency
proposed an unlawful ``design standard,'' but instead whether the
proposed requirement/definition for ABS is unnecessarily design-
restrictive. For the reasons discussed below, NHTSA has concluded that
each element of the proposed requirement/definition for ABS is
necessary to meet the safety need for improved stability and control.
2. Elements of the Requirement/Definition for ABS
Far from proposing a detailed ``design requirement,'' NHTSA simply
proposed to require vehicles to be equipped with an ABS consistent with
the generally understood meaning of that term among brake engineers.
The agency used this approach precisely to avoid imposing unnecessary
design restrictions or impeding the future development of ABS. As
discussed in the NPRM, the definition is sufficiently broad to permit
the installation of any antilock braking system, provided that it is a
``closed-loop'' system that ensures feedback between what is actually
happening at the tire-road surface interface and what the device is
doing to respond to changes in wheel slip.
In developing the proposed definition, the agency relied on the
Society of Automotive Engineers25 (SAE) J656 (Apr88) ``Automotive
Brake Definitions and Nomenclature'' and the Economic Commission for
Europe's Regulation 13, Annex 13 (1988). SAE J656 refers to ABSs as
``wheel slip brake control systems'' that automatically control
rotational wheel slip during braking. Among the terms related to ABS
that are defined in SAE J656 are ``modulator'' and ``wheel slip
sensor.'' These terms are used in SAE's test procedure for antilock
systems, as specified in SAE J46 (JUN80) ``Wheel Slip Brake Control
System Road Test Code.'' Similarly, Annex 13 of ECE Regulation 13
refers to ``anti-lock devices'' as systems which automatically control
the degree of slip, in the direction of rotation of the wheel(s). The
Annex 13 definition of ABS also states that such devices include ``a
sensor or sensors, a controller or controllers and actuating valves.''
The agency's proposed definition of ABS incorporated the terms set
forth in SAE J656 and ECE Regulation 13 to reflect the attributes of
antilock systems as commonly understood by the automotive engineering
industry.
\25\The Society of Automotive Engineers is a voluntary
professional organization that establishes recommended practices
related to various aspects of motor vehicles.
---------------------------------------------------------------------------
The proposed equipment requirement specifies simply that vehicles
must be equipped with an ABS which is defined [[Page 13225]] as a
system that automatically controls the degree of rotational wheel slip
during braking, by (1) sensing the rate of wheel rotation, (2)
transmitting signals regarding the rate of wheel rotation to a device
which interprets those signals and generates responsive controlling
signals, and (3) transmitting those controlling signals to a device
which adjusts brake actuating forces in response to those signals. For
reasons discussed below, each of these elements is necessary to meet
the need for safety. In addition, the definition only states the
performance required of the ABS components, not how the components must
detect wheel rotation, etc.
As discussed earlier in this preamble, the safety problem being
addressed by this rulemaking is that whenever the driver applies the
brakes with too much force relative to extant tire and road conditions,
sustained wheel lockup occurs. This usually results in loss of vehicle
directional stability and/or steering control; i.e., a jackknife, spin-
out or skid, and often a crash. Such sustained lockup most often occurs
when the road is slippery or when the vehicle is lightly loaded or has
no cargo. This is because drivers are likely to make a hard brake
application in a panic situation, and the resulting braking forces
easily cause lockup when the road is slippery or when the vehicle is
lightly loaded or empty. Moreover, drivers are unable to sense lockup
quickly enough to control it.26
\26\``Improved Brake Systems for Commercial Motor Vehicles,''
DOT 807 706 Section 3.2.2; pages 3-5.
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In order to address this safety problem, NHTSA has determined that
it is necessary to prevent the brake system from generating forces that
result in uncontrolled lockup. This need is addressed in part by the
first element of the requirement/definition: each ABS must
automatically control the degree of rotational wheel slip during
braking.27 Automatic control is necessary since drivers cannot
control lockup in an emergency situation. By the time a driver can
sense that lockup has occurred, it is often too late to prevent the
sustained lockup that results in loss of directional stability or
control.
\27\As discussed in the Appendix, wheel slip refers to the
proportional amount of wheel/tire skidding relative to vehicle
forward motion, and lockup is simply the condition of 100 percent
wheel slip.
---------------------------------------------------------------------------
The second element of the requirement/definition (sensing rate of
wheel rotation and transmitting signals about the rate to a device that
generates responsive control signals) is necessary to ensure that
lockup will be prevented or controlled for all road surfaces and under
all load conditions, and also to ensure that stability is not provided
at the expense of stopping distance. The prevention of sustained
lockup, and resulting loss of directional stability and control, should
not be accomplished simply by putting weak brakes on the vehicle or
lowering braking forces under all conditions. Thus, in addressing this
safety problem, the agency must consider the twin goals of preventing/
controlling lockup and ensuring good stopping distance under all road
surface and load conditions.
In a braking situation, the more the driver depresses the brake
pedal, and thereby increases braking forces, the more quickly the
vehicle will stop, so long as the braking force is not so high that it
causes wheel lockup. Thus, if stopping distances are to be minimized
during braking, it is necessary to permit the hydraulic or air pressure
to rise to a point just below the point where lockup would occur.
Moreover, the amount of pressure that causes lockup will vary
dramatically depending on the road surface and vehicle loading. In
order to ensure that braking force rises to a point just below the
point where lockup would occur, it is necessary for an ABS to sense
either each of the factors on which lockup is dependent, i.e., road
surface friction, vehicle loading, dynamic weight transfer during
braking, condition of brake linings, etc., or the product of all of
those factors, i.e., the rate of wheel rotation from which wheel slip
can be determined. Since it may not be technologically feasible for an
ABS to sense all of the factors which may lead to lockup, the
definition specifies that an ABS must sense the product of those
factors, i.e., the rate of wheel rotation.
The rest of the second element of the definition is necessary to
ensure that an ABS uses the relevant information, i.e., rate of wheel
rotation, to control wheel slip and prevent lockup. The relevant
information must be transmitted to a device which interprets the
information and generates responsive controlling signals. Those
controlling signals must then be transmitted to a device which adjusts
brake actuating forces in response to those signals.
NHTSA has determined, based on all available information, that a
device that lacks any one of the elements specified in the definition
could not meet the need for safety addressed by this rulemaking, since,
for the reasons discussed above, its operation would not be dependent
on factors that are relevant to the desired safety performance.
The agency notes that while several commenters asserted that the
proposed definition is unnecessarily design restrictive, none attempted
to explain how a device not meeting one or more of the elements could
ensure stability and control for heavy vehicles for a wide range of
test surfaces and loading conditions.
Most of the commenters arguing that the proposed definition is
unnecessarily design restrictive were small companies which manufacture
or sell brake products. In essence, they wished the agency to change
the proposed definition of ABS so that their devices can be used to
meet the requirements. These companies are, of course, free to develop
and sell products that meet the definition. Also, to the extent that
these companies produce products that do not meet the definition, they
are free to sell them as supplemental equipment, so long as the
products do not create compliance problems or contain safety defects.
However, for the reasons discussed above, and expanded on below in the
context of these comments, products which do not meet the definition
would not prevent sustained wheel lockup.
Strait-Stop, a company which manufactures what it calls a
``noncomputerized ABS,'' argued that the proposed ABS definition is
discriminatory and excessively design-restrictive because it
necessitates the use of electronic computerized systems with wheel
speed sensors. It argued that the agency's tests ``(do) not prove,
conclusively, that the computerized ABS is the only alternative to
accomplish stability and control.'' Strait-Stop also stated that
NHTSA's fleet study indicated that computerized ABS activated very
rarely, only 1.4 times per 10,000 brake applications or 1.1 times per
10,000 miles driven, and that it is a tool with which drivers will not
gain familiarity. In contrast, Strait-Stop stated that its device
activates approximately 98 percent of the time that the driver applies
the brakes, thereby enabling drivers to become familiar with the
system. While Strait-Stop did not describe how its ``non- computerized
ABS'' works or precisely what it does, that company stated that its
device uses ``modulation but not reduction of braking pressure.''
Moreover, literature about its system indicates that the air flow from
the foot (treadle) valve to the relay valve is interrupted through the
Strait-Stop system and pulsates the brake chambers. The ``system
intermittently repeats the on and off cycle at a pre-set rate.''
Jenflo Brake-Aid (Jenflo) also argued that the proposed ABS
definition is discriminatory, and that the definition should be revised
to permit braking devices other than the ones tested by the
[[Page 13226]] agency. Jenflo manufactures a device for air brake
systems which causes a ``pulsing (or air pressure to) the brake
actuators hundreds of times per minute, (that will) cause the tires to
approach lock-up, then the brakes are off for a `small' fraction of a
second and are just as rapidly reapplied.'' As a result, the air
pressure is continually released and reapplied on all the controlled
wheels during all but ``normal'' braking.
Trade International Corporation (TIC) stated that the proposed ABS
definition is unnecessarily narrow and could preclude the use of
available, beneficial products and technologies, and also impede the
development of other useful products and technologies. TIC argued that
a system which continuously modulates the braking force applied to
every wheel whenever braking force is applied would not satisfy the
definition because it lacks the specified sensing and transmitting
functions, regardless of its ability to prevent wheel lockup and/or
enhance braking effectiveness.
The devices referred to by Strait-Stop, Jenflo Brake-Aid, and TIC
all ``pulse'' the air pressure for essentially all but normal brake
applications. These commenters did not explain in detail how these
products work. However, based on the available information, they
provide the same ``pulsing'' of air pressure at a fixed pulsation rate
for all brake applications above some braking or turning threshold.
Regardless of how they work, however, the devices cannot ensure the
twin goals of preventing/controlling lockup and ensuring good stopping
distance under all road surface and load conditions, if they do not
meet the proposed definition. This is because, for the reasons
explained above, their operation would not be dependent on the factors
that are relevant to the desired safety performance. Only by
continuously sensing and responding to what is actually happening at
the tire/road surface interface can an ABS system optimize the braking
pressure so as to both prevent lockup and minimize stopping distances.
As discussed in the ABS Wheel Slip Control Strategies section of the
Appendix, one effect of varying road surface and vehicle load
conditions on the operation of ABSs is the varying controlling
frequencies that are needed to adapt to these varying conditions. The
fact that these other devices incorporate a fixed pulsation rate
demonstrates their lack of adaptability to varying road surface and
vehicle load conditions. As shown in Figures 17 and 18 in the Appendix,
the ABS controlling frequency needs to be relatively slow, between 1
and 2 cycles per second, in order to prevent sustained excessive wheel
slip on very low friction surfaces and needs to be much faster,
approaching 10 cycles per second, in order to achieve very short
stopping distances on high friction surfaces. The increase in stopping
distance on high friction road surfaces that would result from a system
which exhibited a slower than optimum ABS controlling frequency may not
be great. However, the impact of a much faster than optimum ABS
controlling frequency on a very low friction surface would be sustained
and excessive wheel lockup. As shown in Figure 17 in the Appendix,
wheel lockup can occur very rapidly. Figure 17 also shows that from the
time that the ABS solenoid is activated to reduce brake pressure it
takes about 0.25 seconds before the wheel even begins to spin up, about
0.35 seconds for the wheel to reach one-half of the vehicle's speed and
more than 0.6 seconds for the wheel to reach the vehicle's speed. If
the devices referred to by Strait-Stop and Jenflo Brake-Aid pulse the
brakes several times a second, the ``off'' portion of pulsation cycle
would not be sufficiently long to allow the locked wheel to spin up
prior to the next ``on'' portion of the cycle which would result in
sustained wheel lockup.
The basic problem with devices that do not incorporate feedback on
what is happening at the tire/road surface interface (as required by
the definition of ABS mandated by this amendment) such as those
described by Strait-Stop, Jenflo and TIC, is that they are ``blind'' to
the road and surface conditions on which the vehicle is operating and
thus make the same response each time, regardless of whether that
response is appropriate for the existing circumstances. In other words,
the systems cannot appropriately adjust their cycle rate or the degree
of pressure variation to compensate for the effects that load condition
and road surface friction can have on the lockup and spinup times of a
vehicle's wheels. This lack of ``adaptability'' to changes in load and
road surface conditions results either in sustained wheel lockup (and
resultant loss of stability and control) or in stopping distances that
are much longer than the vehicle would otherwise be able to achieve
under those conditions for which the system was not optimized. As a
result, even if these systems enhanced vehicle stability on one type of
surface, they would provide inferior braking on a different surface.
For instance, the relatively high brake pressure required for short
stopping distance on a high coefficient of friction surface would lock
the wheels on a slippery surface because wheel lockup occurs when the
braking force at the tire/road surface interface, needed to resist the
torque generated by the brake, is greater than that which can be
generated from the available surface friction. Because wet surfaces
have lower friction levels, vehicles on these roads will lock up at
lower levels of brake pressure. Conversely, if the pulsating mechanical
system were designed so that brake pressure was reduced in a manner
that ensured that lockup would not occur during hard braking on a
slippery surface, stopping distances would be very long when braking on
high coefficient of friction surfaces.
NHTSA also notes that in order to optimize stopping distance and
maintain vehicle stability, an antilock system must be capable of
reducing, holding, and reapplying braking pressure to each controlled
wheel. The wheel speed sensor monitors the rotational speed of the
wheel. When a monitored wheel approaches a lockup condition, there is a
sharp rise in peripheral wheel deceleration and in wheel slip. If this
rise exceeds the designed threshold levels, the ECU sends signals to
the modulator device to hold or reduce the build-up of wheel brake
pressure until the danger of wheel lockup has passed. The brake
pressure must then be increased again to ensure that the wheel is not
underbraked for the road surface conditions. During automatic brake
control, it is important for the wheel speed to be constantly monitored
so that the maximum braking force for the conditions could be achieved
by a succession of pressure-reduction, pressure-holding, and pressure-
reapplication phases. The agency notes that the systems described by
Strait-Stop, Jenflo and TIC reduce and reapply pressure, without
reference to road conditions, brake forces, or impending wheel lockup.
With respect to Strait-Stop's argument that drivers will not gain
familiarity with the kinds of ABS systems tested by NHTSA because the
systems activate only rarely, the agency notes that no special
familiarity is necessary to operate the system properly. ABS is a
safety device which operates automatically in emergency situations.
Strait-Stop also alleged that the system defined and tested by
NHTSA does not prevent lockup. While that company did not explain this
comment, the agency assumes that Strait-Stop is distinguishing between
momentary lockup and sustained lockup. All of the systems tested by
NHTSA prevent sustained lockup.
Strait-Stop argued that the inference that the screened-out systems
would not [[Page 13227]] meet the braking-in-a-curve test requirement
is unsupported since the agency has not tested and, in some cases has
refused to provide testing for them. As discussed above, it is possible
that a system not meeting the proposed definition could be optimized to
provide enhanced stability for a particular test on a particular test
surface. However, such a system would provide inferior braking
performance on other surfaces and/or under different test conditions.
There is no requirement or reason for the agency to test every
invention identified by commenters in a rulemaking proceeding. The
agency can use its technical and engineering analysis to determine what
performance attributes are necessary to meet the need for safety, and
it can also often make determinations about whether particular devices
would provide safety benefits by the same means.
NHTSA has also analyzed another type of device, from Emergency
Brake Technologies, described by Dr. Barry Wells. This is an emergency
braking device that is manually activated by the driver through a dash-
mounted switch that activates arms that drop polyurethane wedges and
rubber flaps under the vehicle's wheels. After the device is activated,
the vehicle must be stopped and reversed so that the wedges can be
removed from beneath the wheels. Emergency Brake Technologies claims
that this device ``could stop a fully loaded vehicle in the same
distance as an automobile and completely eliminate jackknifing.'' While
NHTSA does not have any opinion concerning whether this device might
provide benefits in some emergency stopping situations, the device
would not meet the need for safety being addressed by this rulemaking,
i.e., ensuring stability and control during braking. In fact, the
dropping of polyurethane wedges and rubber flaps under the wheels would
create essentially the same condition as fully-locked wheels, and
therefore could result in a loss of control. Once the driver activated
this system, the driver would be committed to a quick, sliding stop.
The driver would have no capability to release the device once applied,
and could also have difficulty steering around a problem. While such a
device could provide short stopping distances under dry-road
conditions, it would do so by sacrificing vehicle stability and
control.
ATA and Strait-Stop commented that the proposed definition would
preclude anything but electronic systems, thereby prohibiting
mechanical systems. NHTSA notes that this is incorrect, since the
definition does not require electronics for the sensing of the wheel
rotation, or transmission of wheel rotation or controlling signals.
Such functions could be performed using pneumatic, hydraulic, optic, or
other mechanical means. The agency notes that it is likely that
electronic systems will be used, given currently available
technologies. All ABSs currently marketed in the United States are
electronic in nature.
In the case of an ABS that does not require electrical power for
operation, the only mandatory electrical requirement in this rulemaking
(addressed later in this document) is for malfunction indicator lamps
used to signal a problem in the ABS.
ATA also argued that the requirements would impair efforts to
develop new electronic technologies. ATA stated that the restrictions
would limit engineers' abilities to develop electronic braking (brake-
by-wire) systems (EBS) by forcing the logic for such systems to be
based on existing ABS designs. According to ATA, EBS is designed to
handle all braking functions: compatibility, load sensing/brake
proportioning, balance, timing, ABS, traction control, and failure
control. ATA stated that successful development of these systems may
require that designers not be tied to a rotational slip view of wheel
lockup.
NHTSA disagrees that the proposed ABS requirements will impair
efforts to develop EBS. The agency notes that Robert Bosch GmbH
currently markets the Bosch-ELB Electronically Controlled Commercial
Vehicle Brake, in Europe. This system includes ABS, traction control,
and electronic service braking (with pneumatic backup) functions, and
uses the same wheel speed sensor arrangement as does Bosch's ABS sold
without EBS. This indicates that EBS is fully compatible with current
ABS technology, including wheel speed sensors. Furthermore, a
combination-unit vehicle with good brake balance, compatibility, and
timing may still be capable of being over-braked by the driver,
especially when operated lightly-loaded or on slippery road surfaces,
and such a vehicle would still require ABS to prevent wheel lockup when
operated under these conditions. The development of the Bosch
electronic braking system proves that the rotational slip view of wheel
lockup does not hinder the development of successful EBS.
ATA also stated that the requirements could ``hold back'' disc
brake technology since disc brakes are ``virtually incompatible'' when
used together with drum brakes on a combination vehicle. ATA appears to
believe that because EBS can make the ``decisions'' to compensate for
those major differences, it is needed for disc brake technology to come
into general use. The agency notes that, according to product
literature, the Bosch-ELB system measures wheel speeds and brake
actuator pressures at each wheel position, and microcomputers in the
electronic control unit store and process these data and transmit the
correcting commands accordingly. This system could, therefore,
compensate for incompatibilities in brake force balance on a vehicle,
and would permit safe introduction of disc brakes on vehicles. This
system incorporates ABS technology that complies with the agency's
proposed ABS requirements, as well as ECE Regulation 13. Therefore,
NHTSA disagrees with ATA's argument that ABS requirements will hold
back disc brake technology.
In a somewhat different vein, TIC argued that a system could
satisfy the proposed definition but not accomplish the desired function
of preventing lockup. As part of this argument, TIC stated that the
proposed definition for ABS is fundamentally flawed because it does not
specify what the system is supposed to accomplish but rather specifies
how the system is supposed to work. TIC's comment in essence raises the
issue of whether the definition is sufficient, by itself or with other
requirements, to meet the need for safety.
As indicated at the beginning of this section, the agency developed
a broad definition precisely to avoid imposing unnecessary design
restrictions or impeding the future development of ABS. The ABS
definition is based on the premise that wheel lockup is the source of a
vehicle's loss of directional stability and steering control during
braking, and that any device designed to improve such stability during
braking must control the source of that instability. Hence, the
definition establishes a linkage between the input, signals that sense
wheel lockup, and the output, modulated brake pressure to prevent wheel
lockup. This is essentially the extent of the design constraints
established by the agency, and it gives the industry considerable
latitude to design and develop individual components, ranging from
sensor design and placement, to the ECU control algorithm and to brake
pressure modulation frequency.
NHTSA rejects TIC's argument that the definition does not specify
what the system is supposed to accomplish but rather how the system is
supposed to work. Modulating brake pressure in [[Page 13228]] response
to information about rate of angular rotation is part of what is
supposed to be accomplished. As discussed above, the rate of angular
rotation reflects what is happening at the tire/surface interface.
NHTSA further concludes that the requirement/definition for ABS is
sufficient at this time to meet the need for safety. In arguing that a
system can satisfy the definition but not accomplish the desired
function, TIC provided the following ``extreme example'':
Consider the following system: (1) a set of angular rate of
rotation sensors, one on every wheel; which (2) transmit signals
whose level is proportional to the rate of angular wheel rotation to
a device which compares the signals and generates control signals;
and (3) transmits those control signals to devices which increase
the braking force applied to any wheel which has an angular rotation
rate higher than the wheel which has the lowest angular rotation
rate. Such a system satisfies every element of the proposed
definition, however, the result of implementing such a system would
be that if any wheel locked up during braking all wheels would lock
up!
While TIC itself acknowledged that its example was ``extreme,''
NHTSA notes that its basic premise also is silly, since it assumes that
a manufacturer would deliberately build a brake system that could not
work. In considering the impacts of its standards, NHTSA must assess
how manufacturers are likely to respond, not unrealistic hypothetical
situations. The basic premise underlying this rulemaking is that
manufacturers will respond to the definition/requirement for ABS by
providing systems that will prevent wheel lockup. This view is
confirmed by the comments of the vehicle and brake manufacturers. There
is no evidence that manufacturers would respond by deliberately
building systems that do not prevent lockup but instead cause lockup.
Moreover, the definition for ABS does not stand in a theoretical
vacuum. Manufacturers must design their brake systems to meet other
safety requirements (including stopping distance requirements and, for
some vehicles, the braking-in-a-curve test). It might not be possible
to meet those requirements with systems that did not prevent lockup but
instead caused lockup. Manufacturers are also subject to Federal
requirements concerning safety-related defects. And, of course,
manufacturers must ensure customer satisfaction.
The agency also notes that there is absolutely no incentive for
manufacturers to provide ABS systems that do not function as they
intended. TIC's comment essentially raises the possibility that a
manufacturer might spend all the money necessary to meet the definition
of ABS and then include a faulty ECU control algorithm. However, there
is no basis to believe that this would happen. The agency only
addresses unreasonable safety risks in developing safety standards and
need not address unrealistic hypothetical possibilities.
3. Dynamic Versus Equipment Requirements
As discussed in the NPRM and above, NHTSA considered whether
adequate performance relating to directional stability and control
could be ensured solely by means of dynamic test requirements, but
concluded that, at this time, there would be practicability problems
associated with the broad array of dynamic test requirements that would
be associated with such an approach. The agency therefore decided to
propose a single provision expressly requiring that heavy vehicles be
equipped with antilock systems, and on identifying feasible and
practicable dynamic tests that could supplement that provision by
directly assessing the directional stability, control and stopping
distance of vehicles under some of the wide variety of circumstances
that may be experienced in the real world.
ATA commented that the desired result from mandating the
installation of ABS is ensuring that a vehicle can be controlled during
a stop, and asserted that the proposed braking-in-a-curve performance
requirement, with certain changes, would accomplish this conceptually.
However, ATA did not substantiate its assertion about the efficacy of
such a requirement, standing by itself. ATA did not address the
practicability problems of adopting a set of dynamic performance
requirements, or even the practicability problems associated with
applying the braking-in- a-curve requirement to all affected vehicles.
ATA did, however, suggest that the agency initiate additional research
and development for what it called ``true performance tests.''
While NHTSA plans to continue research on dynamic performance tests
for trucks, buses and trailers, it has concluded that the desired
safety benefits of ABSs could be achieved now by means of a specific
equipment requirement for ABS and (as discussed below) a dynamic
performance test requirement applicable to truck tractors only. NHTSA
is charged by the Safety Act with promulgating safety standards that
meet the need for safety. Moreover, Congress was sufficiently concerned
about the directional stability and control problems associated with
heavy vehicles that it specifically required NHTSA to conduct a
rulemaking that examines and could result in requiring the installation
of ABSs in these vehicles. The agency has concluded that large safety
benefits can be obtained by requiring ABSs on heavy vehicles, and has
developed requirements that will ensure installation of this safety
equipment.
NHTSA disagrees with the suggestion that it delay implementation of
this life-saving rule while it conducts further research in search of
the type of rule ATA desires. The overall history of agency rulemaking
is one of gradual progression, when and where practicable and
beneficial to safety, toward increasingly sophisticated and
increasingly more dynamic performance standards. However, relying
exclusively on dynamic performance requirements has never been a
statutorily mandated requirement. Were it so, there would be many fewer
Federal motor vehicle safety standards today--and many thousands more
deaths and injuries, occurring annually.
B. Independent Wheel Control
In the NPRM, NHTSA proposed to require that the antilock brake
system monitor and control the wheels of the front axle (i.e., steering
axle) and the wheels of at least one rear axle. NHTSA believed that
this would ensure that the wheels on the steering axle and the wheels
on the selected rear axle were directly controlled by the ABS. By
``directly controlled,'' the agency meant that the signal provided at
the wheel or on the axle of the wheel would directly modulate the
braking forces of that wheel or axle. The agency tentatively concluded
that it is necessary to specify that the ABS directly control the
steering axle because some ABSs control only a vehicle's drive-axle,
which could result in the loss of steering control if the front wheels
locked during braking.
Several commenters addressed the need for front wheel control. ATA
strongly opposed mandating ABS for the steering axle of single-unit
trucks and suggested that the agency reconsider the requirement for
tractors. In contrast, Rockwell, WABCO, Freightliner, AAMA, Advocates,
and IIHS favored requiring that an ABS be installed on front axles.
AAMA favored equipping each vehicle with an ABS that has at least one
independent channel of control for the wheels on a front axle and at
least one independent channel of control for the wheels on a rear axle.
However, AAMA objected to mandating more than two independent channels
of control. [[Page 13229]]
NHTSA did not specifically address the concept of independent
control in the NPRM, but addressed it in the SNPRM by proposing that
the wheels on at least one axle be independently controlled. The agency
in today's final rule defines an ``independently controlled wheel'' to
mean a directly controlled wheel for which the modulator device does
not modulate the brake forces at any other wheel on the same axle. This
means that a side-by-side control strategy on a tandem axle could have
the wheels on the sensed axle of the tandem being independently
controlled by a modulator, and the wheels of the other axle of the
tandem being indirectly controlled by the modulator for the wheel on
the sensed axle on the same side of the vehicle.
Rockwell, Freightliner, Advocates, and IIHS commented that the
regulatory language in the NPRM requiring each axle to be directly
controlled by an ABS would allow select low28 antilock systems on
any axle. These commenters believed that an antilock system must
provide independent control at each wheel of a heavy vehicle to ensure
good, overall ABS performance in the areas of stability and stopping
distance. Accordingly, they recommended that the equipment requirement
include language that would require ``independent control of each
wheel'' of the axles that are required to be ABS-controlled. They
believed that the inclusion of such a requirement would prevent
significant degradation in stopping performance, particularly on a
split mu surface. Bosch recommended a minimum requirement of a four-
sensor, three- modulator-valve (which is referred to as a 4S/3M system)
ABS. Freightliner favored requiring at least four independent channels
of control, i.e., two for each axle, to allow independent control of
each wheel on the front and a rear axle. Similarly, IIHS favored
requiring the brakes for each wheel on the front axle and the brakes
for each wheel on one rear axle to be independently controlled.
Advocates recommended that the ABS be functional on all axles, not just
one axle in each multiple axle set on a heavy vehicle.
28See the Appendix for a discussion of this term.
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Based on its analysis of these comments and other available
information, NHTSA issued an SNPRM proposing modifications to the NPRM
to require heavy vehicles to be equipped with systems that
independently control each wheel on at least one axle of a truck, a
truck tractor, or a bus (i.e., 4S/3M systems). As explained in the
SNPRM, the agency tentatively concluded that a minimum requirement that
ABS provide independent wheel control on at least one axle would
provide an acceptable level of stopping distance performance on low mu
and split mu surfaces. The agency believed that a vehicle with
independent ABS wheel control would stop in a shorter distance than
either a vehicle equipped with an axle-by-axle ``select low'' control
ABS, or a non-ABS equipped vehicle operated by a driver making his or
her best efforts to minimize stopping distance through manually
modulating the brake pedal. The agency also proposed to prohibit tandem
control29 by an ABS, by requiring that no more than two wheels be
controlled by one modulator valve. NHTSA requested comments about its
proposal for independent control of each wheel on at least one axle and
about prohibiting tandem control by an antilock system.
29As explained in the appendix, tandem control refers to
having two adjacent axles being controlled by the same modulator
valve. Specifically, while each axle has its own wheel speed sensor,
the brakes on two axles are controlled by one modulator valve.
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In response to the SNPRM, NHTSA received comments from Ford, AAMA,
Strait-Stop, GM, Navistar, White GMC, Bosch, PACCAR, Eaton, Midland-
Grau, Truck Trailer Manufacturers Association (TTMA), Advocates, and
ATA about the proposal to require independent control on at least one
axle. Aside from Freightliner, WABCO, Bosch, Advocates, and IIHS, most
other commenters opposed the proposal claiming that requiring
independent control would be unreasonably design-restrictive. Bosch
stated that the proposal is appropriate since at least one of the axles
that contributes most to vehicle deceleration in the loaded condition
should have the ability to have its wheels individually controlled.
Ford, AAMA, GM, Navistar, PACCAR, Eaton, and Midland-Grau stated that
the agency should specify direct control as a minimum requirement but
not require independent control. AAMA stated that the standard should
permit any control system that provides stability without substantial
degradation in stopping distance. Ford claimed that any requirement
that ABS must employ more than two channels of control would not result
in any safety advantage over its two-channel system, but would result
in substantial and unnecessary incremental costs to Ford and might
jeopardize its ability to meet early implementation dates. Midland-Grau
strongly opposed the SNPRM's approach, claiming that it presented a
major change in scope from performance requirements and minimal design
requirements. Specifically, it complained that the SNPRM changed the
rulemaking's focus from directional stability and control to stopping
distance on split mu surfaces.
Consistent with their comments on control philosophies, AAMA, GM,
White GMC, PACCAR, and Midland-Grau also opposed the proposed
definition of ``independently controlled wheels.''30 AAMA and
PACCAR claimed that the proposed definition does not accommodate widely
used ABS algorithms and control technologies. It requested that the
word ``only'' be omitted since its inclusion in the definition would
inappropriately preclude antilock systems that ``rely on wheel speed
information from both wheels on an axle to modulate brake pressure at
each of the wheels.''
30The agency proposed to define ``Independently Controlled
Wheel'' as a ``wheel at which the degree of rotational wheel slip is
sensed and corresponding signals are transmitted to one controlling
device that adjusts the brake actuating forces only at that wheel in
response to those signals.''
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Ford, AAMA, GM, Navistar, White GMC, PACCAR, Eaton, and Midland-
Grau opposed prohibiting tandem control. TTMA requested that trailers
equipped with more than three axles be excluded from the requirements,
claiming that it would be very expensive to equip these vehicles, which
account for only four percent of trailer production, with ABS.
ATA and Strait-Stop opposed specifying the type of wheel control,
claiming that doing so creates an impermissible design requirement.
Strait-Stop stated that the proposed approach prohibits creativity in
the development of other technology that may accomplish the performance
standards more effectively with greater economic efficiency.
Several commenters submitted test data about various ABS
configurations. WABCO and Freightliner submitted simulated test data
showing that 4S/2M systems on truck tractors provide very poor stopping
distance performance on split mu surfaces, compared with 4S/4M systems.
These commenters reported that the 4S/2M systems they tested took
between 316 percent and 353 percent of the norm to stop on a split mu
surface, with driver best effort being defined as the norm, or 100
percent. Ford and Bendix submitted simulated data showing that 4S/2M
systems incorporating the modified select high regulation (MSHR31)
wheel slip control strategy on truck tractors perform acceptably.
Bendix also submitted vehicle test data showing that the stopping
distance performance with [[Page 13230]] tandem control ABS
incorporating the MSHR wheel slip control strategy (2S/1M) on trailers
is comparable to the performance of a 2S/2M system.
31See the Appendix for a discussion of this term.
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As explained above, in establishing the requirements applicable to
the stability and control of heavy vehicles, NHTSA has decided that, at
a minimum, wheels on the steering axle and at least one rear axle of a
powered vehicle must be controlled by a closed-loop antilock system.
Similarly, the wheels on at least one axle of a semitrailer and dolly,
and the wheels of at least one front axle and one rear axle of a full
trailer must be controlled by a closed-loop antilock system. The agency
has decided that requiring a closed-loop antilock system is necessary
to ensure the directional stability and control of heavy vehicles
during braking.
NHTSA emphasizes that requiring a closed-loop antilock system is a
minimum requirement that the agency believes will ensure the safety of
heavy vehicles. The agency has also decided to establish supplementary
requirements beyond these minimum requirements that address the type of
wheel control for various types of vehicles. In establishing these
supplementary requirements, the agency has sought an approach that is
responsive to the many and oftentimes disparate views of the commenters
and that ensures safety performance objectives, while considering
practicability, costs and, to the extent possible, stated industry
practice.
The supplementary equipment requirements, which specify the type of
wheel control, are based on the philosophy that, for the reasons set
forth below, an incrementally higher level of stability performance
during braking is warranted for truck tractors compared to that which
is appropriate and needed for trailers, single-unit trucks, and buses.
First, truck tractors, when used in a combination vehicle, are
articulated and therefore are more likely to lose control than single-
unit vehicles. Second, truck tractors typically have shorter wheelbases
than single-unit trucks, trailers and buses and therefore are more
susceptible to locked wheel-induced, unrecoverable loss of control than
are any of these other vehicle types. This loss of control typically
manifests itself as a jackknife when tractors are coupled to
semitrailers. Third, truck tractors typically travel approximately five
times more annual miles than single-unit trucks, three times more miles
than trailers (since there are proportionally three times as many
trailers in use than there are tractors which tow them), and
approximately seven times as many miles as buses. This substantially
larger use proportionally increases a truck tractor's exposure to risk.
Fourth, truck tractors typically operate on roads (i.e., interstate
highways and rural State and U.S. routes) that have comparatively
higher posted speed limits and vehicle operating speeds than the roads
on which single-unit trucks and many buses generally operate. A higher
operating speed exacerbates the consequences of braking-induced wheel
lockup and loss-of-control. This is a significant contributing factor
to the high proportion of heavy vehicle braking instability-related
crashes, fatalities and injuries that involve combination-unit trucks.
Based on the above considerations, NHTSA has decided that the
requirements for truck tractors must be more stringent than those for
the other vehicle types. Specifically, on at least one of the truck
tractors's axles, each wheel must be independently controlled by an ABS
modulator. With respect to a given wheel, ``independently controlled''
means a wheel at which the degree of rotational wheel slip is sensed
and corresponding signals are transmitted to a modulator that adjusts
the brake actuating forces at that wheel on the axle or at other wheels
on other axles. The agency has decided to revise the definition in
response to AAMA's comment on the definition of independently
controlled, since its inclusion might inadvertently prohibit acceptable
systems. Requiring independent control ensures that a wheel provides
optimal braking forces on all surfaces, enabling the vehicle to achieve
near optimal braking on all surfaces, especially split mu ones.
In most cases, the axle with independent wheel control will likely
be the tractor's drive axle(s). Commenters, including AAMA, Midland-
Grau, and Bendix, submitted to the agency road testing data about how
certain antilock systems improved the braking efficiency and
directional control and stability of various vehicle configurations.
Based on these data, the agency believes that independently controlling
the drive axle(s) will result in incrementally better braking
performance on split mu road surfaces than the other ABS equipment
configurations that are permitted on the other vehicle types covered by
this rule.
Rockwell WABCO correctly stated that allowing select low ABS on all
axles will result in substantially longer stopping distances on split
mu surfaces, particularly when the differences between the coefficients
of friction on the two surfaces is large. Notwithstanding this
shortcoming, the agency believes that a select low system is
appropriate for the front axle for the following reasons. First, since
the front axle brakes typically provide about 25 percent of the braking
on a truck tractor, the stopping distance degradation with select low
on the front axle will be small. Second, having equal braking forces at
each wheel alleviate steering wheel ``pull'' that would occur on a
split mu surface with ABS independently controlled front brakes. Third,
current antilock systems installed on the front axle of heavy vehicles
tend to use SLR, MSHR, or MIR wheel slip control strategies.32 No
vehicle manufacturer uses a system in which front axle control is
purely independent wheel control. Accordingly, the agency has
determined that it would be inappropriate and impracticable to prohibit
the use of select low control on front axles.
32SLR, MSHR, MIR and other wheel slip control strategies
are discussed in the Appendix.
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NHTSA has also decided that it is necessary to prohibit tandem
control on tractors to further ensure the safe braking performance for
tractor trailers. This decision is based on test data33 which
indicate that tandem control does not provide an acceptable level of
stopping distance performance for truck tractors, even though it may
ensure a heavy vehicle's stability and control.
33``Improved Brake Systems for Commercial Motor
Vehicles,'' DOT HS 807 706, April 1991,
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Notwithstanding its decision to prohibit tandem control on truck
tractors, NHTSA has decided that tandem control is appropriate for
vehicles other than truck tractors, such as trailers and single unit
vehicles. Vehicle test data submitted by Ford, Bendix, and Midland
showed comparable vehicle stopping distance performance, and in some
cases superior performance, of tandem control (2S/1M) systems compared
with side-by-side control (2S/2M) systems, without any difference in
vehicle stability performance. Vehicle test data also showed comparable
ABS performance with MSHR tandem control on trailer axles. Accordingly,
today's requirements permit direct control 2S/1M systems for converter
dollies, semitrailers, and the front axles of full trailers. The agency
further notes that single unit vehicles equipped with 4S/2M systems
have been approved for use in Europe as ``Category 1'' systems.
C. Braking-In-A-Curve Test
1. General Considerations
As explained in the previous section on equipment requirements,
NHTSA proposed requiring heavy vehicles to be [[Page 13231]] equipped
with antilock systems, and supplementing that requirement with dynamic
performance requirements to check the directional stability, control
and stopping distance of such vehicles. The agency proposed only those
dynamic performance requirements that it believed would be feasible and
practicable for checking the directional stability of a vehicle when it
is maximally braked. Specifically, in its September 1993 NPRM, the
agency proposed a ``braking-in-a-curve requirement'' on a low
coefficient of friction surface without a stopping distance
requirement. Under this proposed requirement, heavy vehicles would have
to be capable of stopping without loss of directional stability or
control, while turning on a slippery surface during an aggressive or
``hard'' stop. Separately, in its February 1993 NPRM, the agency
proposed braking effectiveness requirements through the use of high
speed (60 mph) stopping distance requirements on a high coefficient of
friction road surface.
NHTSA explained, in the September 1993 NPRM, its tentative
conclusion that the braking-in-a-curve test on a low mu surface is an
objective, repeatable, and practicable procedure for evaluating a heavy
vehicle's directional stability and directional control. The agency
further explained that the proposed braking-in-a-curve test is
consistent with industry's views, since the Antilock Test Procedure
Task Force of the Motor Vehicle Safety Research Advisory Committee
(MVSRAC) recommended this procedure and the SAE has proposed it in
Recommended Practice J1626, Braking, Stability, and Control Performance
Test Procedures for Air-Brake-Equipped Truck Tractors.
In response to the NPRM, Advocates stated that the agency's
proposal to specify both an equipment and dynamic performance
requirement was the most appropriate way to ensure that the substantial
safety benefits of heavy vehicle ABS are realized quickly. Rockwell
WABCO reluctantly supported the proposed combination of an equipment
specification and a dynamic performance test, given the current
difficulty in formulating valid additional, repeatable performance
criteria. Midland-Grau favored this approach for truck tractors since
it believed that merely issuing an ABS requirement, without an
accompanying performance requirement, would allow ineffective systems
in the marketplace.
Allied Signal supported the braking-in-a-curve test for truck
tractors, but opposed the test for other vehicles, stating that
vehicles other than truck tractors have not been tested using this
maneuver. Midland-Grau was also concerned that very little test data
have been collected on vehicle types other than truck tractors. Volvo-
GM stated that the test is unsafe for many vehicles, and that a dynamic
performance requirement is not necessary, given the provision requiring
ABSs. AAMA stated that although it generally favors performance-based
dynamic requirements for Federal Motor Vehicle Safety Standards, it
opposes the braking-in-a-curve test given what it perceives as its
``overwhelming practicability and objectivity problems.'' Among AAMA's
concerns were that (1) there has been no test program by NHTSA to
decide whether the test is suitable for single-unit trucks, buses, and
trailers, (2) the braking-in-a-curve test alone cannot evaluate the
effectiveness of an ABS, (3) there is a lack of repeatability of the
braking-in-a-curve test procedure, and (4) no suitable test facilities
exist for vehicle manufacturers to conduct compliance testing. Given
these concerns, AAMA favored adopting, on an interim basis, an
equipment requirement only.
ATA, Strait-Stop, and several other commenters supported a dynamic
performance-based requirement instead of an equipment requirement. They
believed that this approach would encourage further development of
antilock technology and would enable users to find the system that best
suits their operation. ATA was concerned that an equipment requirement
would preclude the development of more effective systems for different
applications.
TTMA believed that the braking-in-a-curve test is inappropriate for
trailers. It stated that trailer manufacturers, many of which are small
entities, do not have the financial resources or the facilities to
conduct road testing.
After reviewing the comments and other available information, NHTSA
has decided to amend the Standard to include the braking-in-a-curve
test for certain vehicles. The agency considered requiring surface
transition tests (i.e., a test maneuver in which vehicle braking begins
on a high coefficient of friction surface and then completes the stop
on a low mu surface, and vice versa), a lane change test, and split mu
or side-to-side differential coefficient of road surface friction
tests, to achieve that objective. The tests would ideally be conducted
at various speeds with different loading conditions and test surfaces.
However, the agency has decided that it would be unnecessarily
burdensome and costly to impose such an array of tests on heavy vehicle
manufacturers. NHTSA has determined that the performance testing and
equipment requirements imposed in today's final rules are the most
appropriate method of ensuring directional control and stability.
NHTSA has decided at this time to apply the braking-in-a-curve test
to truck tractors, but not to other heavy vehicles. The agency believes
that opposition by AAMA, Volvo-GM, and Midland Grau to the braking-in-
a-curve test requirement is based primarily on uncertainty about
whether the test would also be required for single-unit vehicles, since
the MVSRAC ABS Task Force developed the braking-in-a-curve test
procedure for testing only truck tractors. Since neither the agency nor
the Task Force included single-unit vehicles in the test program, NHTSA
believes that AAMA and the others are concerned about whether the
braking- in-a-curve test would appropriately evaluate directional
stability and control of single-unit vehicles. Accordingly, NHTSA's
decision to apply the braking-in-a-curve test at this time only to
truck tractors should reduce the concerns of AAMA and other commenters
that opposed this dynamic performance test.
With respect to truck tractors, NHTSA has concluded that the road
tests performed by the agency and the ABS Task Force provide sufficient
justification to apply the braking-in-a-curve test to these vehicles.
The agency notes that the industry, through the MVSRAC, previously
endorsed and recommended to the agency, essentially the same dynamic
performance test that is contained in this final rule. The Task Force
test data and final report indicate that the braking-in-a-curve
procedure is safe, practicable, and repeatable for truck tractors.
Accordingly, the agency believes that this recommendation remains valid
for tractor trailers.34
34TRC of Ohio, Report No. 091194, page 4, August 26, 1991.
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NHTSA has decided not to require single unit trucks, buses, and
trailers to comply with the braking-in-a-curve test requirement at this
time. The agency's limited testing of single unit trucks to the
braking-in-a-curve maneuver revealed no specific safety problems.
However, additional testing on a wider variety of trailers, dollies,
and single-unit vehicles, including buses and trucks, would be
appropriate to ensure that these vehicles could be safely tested to the
braking-in-a-curve maneuver. Specifically, the agency is concerned that
certain vehicles, especially ones with a high center of gravity, might
be prone to roll over or otherwise lose control during such tests.
NHTSA intends to develop performance test requirements equivalent to
the braking- [[Page 13232]] in-a-curve test for the other vehicle types
covered by this rule, assuming that future research indicates it
possible to conduct the test in a safe fashion and to obtain
meaningful, repeatable results. The agency anticipates conducting
additional research and road tests to decide whether heavy vehicles
other than truck tractors should be subject to this road test.
Today's notice, including the agency's decision not to apply the
braking-in-a-curve test to vehicles other than truck tractors,
completes the comprehensive rulemaking to establish directional
stability and control requirements that was initiated by the June 1992
ANPRM. If NHTSA decides that it is in the interest of motor vehicle
safety to apply the braking-in-a-curve test to single-unit vehicles or
trailers, then it will issue a new proposal to initiate a subsequent
rulemaking on this matter.
2. Test Surface
In the NPRM, NHTSA proposed that the braking-in-a-curve test be
conducted on a test surface with a peak friction coefficient (PFC) of
0.5 to represent a low coefficient of friction surface. In formulating
the proposal, NHTSA considered whether the proposed test surface
specification raised practicability or objectivity concerns in light of
PACCAR. The agency specifically requested comments on the proposed test
surface specification.
Three commenters addressed the test surface specification. Midland-
Grau stated that since maintaining a precise PFC value is not feasible,
reasonable fluctuations of 10 percent are to be expected.
Notwithstanding these inherent fluctuations, Midland-Grau commented
that its testing shows that variability in the test surface PFC value
of less than 10 percent does not affect the braking-in-a-curve test
since no stopping distance is prescribed. AAMA stated that it is not
possible to maintain a surface at a precise PFC. It further stated that
it is not apparent whether it would be more conservative to conduct
testing at a higher PFC than the proposed PFC. AAMA stated that the
variability in the peak to slide ratio is significantly greater on wet
surfaces than on dry surfaces, and that this ratio directly affects
performance. Mr. Robert Crail, a brake engineer, stated without
elaboration that using PFC rather than skid numbers will ensure that
the test surfaces and test conditions will be reasonable and repeatable
during actual vehicle testing.
Before addressing the specific comments about the test surface, the
following discussion summarizes the PACCAR decision's findings with
respect to variability and how today's rulemaking responds to that
ruling. As a result of that case, NHTSA has considered ways to better
specify test surface adhesion. Prior to the Standard No. 135, Passenger
Car Brake Systems, rulemaking, NHTSA defined road test surfaces by
specifying skid numbers. A skid number is the frictional resistance of
a pavement measured in accordance with a test procedure defined by the
American Society for Testing and Materials (ASTM). However, given the
fluctuations of skid numbers on a given surface, the PACCAR ruling
invalidated certain aspects of Standard No. 121's reliance on this
measure based on its potential impracticability. In the rulemaking
proposing Standard No. 135, several commenters advocated specifying the
peak friction coefficient as an alternative measure of a test surface's
adhesion. The agency has concluded that PFC is more relevant for the
stopping distance tests required by the standard because, unlike a skid
number, the maximum attainable deceleration in a non-locked wheel stop
is more directly related to PFC. As discussed in the Appendix, the skid
number characterizes the slide (locked wheel) value of the coefficient
of friction of a given road surface, and the PFC characterizes the peak
(rolling wheel) value of the coefficient of friction of a given road
surface. Since the agency's brake test procedures generally prohibit or
limit wheel lockup during brake testing, specifying the peak friction
coefficient is more relevant than specifying the skid number of the
surface.
NHTSA has also conducted ``Round Robin'' testing to understand
further how fluctuations of PFC affect the stopping performance of
heavy vehicles. Based on the above, NHTSA has decided that the braking-
in-a-curve test should be performed on a test surface with a PFC of
0.5, which appropriately represents a typical low coefficient of
friction road surface. Moreover, in today's companion rule adopting
stopping distance requirements, the agency has decided it is
appropriate to perform the primary 60 mph stopping distance tests on a
test surface with a PFC of 0.9. Agency and industry testing indicate
that a PFC of 0.9 represents a typical dry road surface.
The requirement to specify test surfaces in terms of PFC rather
than skid numbers also responds to PACCAR's concern about
practicability problems caused by skid number fluctuations. Because the
PFC values of surfaces measured may also indicate some fluctuation, the
agency has considered whether the fluctuation significantly affects the
requirement's objectivity. In an earlier rulemaking about Standard No.
208, the agency explained that since some variability in any test
procedure is inherent, the agency need only be concerned about
preventing ``unreasonable'' or ``excessive'' variability to avoid
causing manufacturers to ``overdesign'' vehicles to exceed the minimum
levels of protection specified by the Federal safety standards. (49 FR
20465, May 14, 1984; 49 FR 28962, July 17, 1984.) With respect to the
braking-in-a-curve test, variability of the PFC value of the test
surface will have a negligible impact on a vehicle's ability to comply
with the requirements, which is to stay within the 12-foot lane. Since
the test speed is set at the lesser of 30 mph or 75 percent of the
maximum drive-through speed\35\ of the vehicle in the curve, any
variability in the test surface will be compensated for by an increase
or decrease of the maximum drive-through speed of the vehicle. If the
maximum drive-through speed is less than 40 mph, this will result in a
corresponding increase or decrease of the test speed, which cannot be
higher than 30 mph. As a result, the variability of the test surface is
not as critical an issue for the braking-in-a-curve test as it is for a
stopping distance test on a high coefficient of friction surface, which
includes a stopping distance measurement that is more affected by test
surface variation. Based on these considerations, the agency has
determined that the results of the braking-in-a-curve test will not be
affected by minor variations in the test surface.
\35\Maximum-drive-through-speed is defined as ``the highest
possible constant speed that the vehicle can be driven through 200
feet of a 500-foot radius curve arc without leaving the 12-foot
lane.''
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The road surface requirements comply with PACCAR's holding that
manufacturers are entitled to testing criteria that they can rely on
with certainty, since they include objective terms and requirements,
i.e., the test surface is at a PFC of 0.5. For the same reason, the
requirements also comply with PACCAR's requirement that all methods to
demonstrate compliance with the requirement be set forth in the
regulation.
In evaluating the requirement's practicability, NHTSA has
considered possible difficulties with respect to building and
maintaining test surfaces with a PFC of 0.5 for the braking-in-a-curve
test and 0.9 for the high coefficient stopping test. (Those interested
in building and maintaining a test surface should refer to NHTSA's
[[Page 13233]] ``Manual for the Construction and Maintenance of Skid
Surfaces,'' (DOT HS 800 814.) Variations in PFC for high coefficient of
friction surfaces do not affect stopping distance test results
appreciably. Moreover, while variations in PFC for low coefficient
friction surfaces may affect the distance in which a vehicle stops,
such variations are not relevant for the braking-in-a-curve test, which
requires a vehicle to remain stable while it is stopped, not that it
stop within a specified distance. After reviewing the comments and
available information, NHTSA has concluded that specified test surfaces
can be achieved and maintained. As explained above, recent ``Round
Robin'' testing related to research about heavy vehicle braking by the
agency and others on several test tracks indicates that the test
surface specification does not raise practicability or objectivity
concerns.\36\
\36\TRC Report, August 21, 1991, page 6.
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One of the PACCAR court's concerns was that the road surface skid
numbers were based on an out-of-production tire. That concern is not
relevant to today's final rule since it specifies a currently-produced
tire. The requirements comply with PACCAR's concern about the testing
method's objectivity because the peak coefficient of friction is an
objective measure.
NHTSA disagrees with AAMA's comment that it is not apparent whether
it would be more conservative to conduct testing at a higher PFC than
the proposed PFC. Data from the round-robin testing and other sources
show that the stringency of a braking-in-a-curve test increases as the
PFC of the test surface decreases, if the tests are conducted at the
same vehicle speed. Since the requirement specifies a test speed based
on the vehicle's maximum drive-through speed, which decreases as the
test sequence PFC decreases, the resulting test speed will also be
lower as the PFC decreases. Hence, the stringency of the braking-in-a-
curve test should not change with minor changes in the PFC of the test
surface.
NHTSA has decided that AAMA's other comments about the test surface
requirement are without merit. That organization did not provide any
data to substantiate its statements. Nor did it explain why it believes
that ``variability in the peak to slide ratio'' is relevant. Similarly,
AAMA's comment about ``simultaneously maintaining a given surface at a
precise PFC and sliding coefficient (i.e., skid number) [being]
completely infeasible'' is irrelevant to this rulemaking. The agency
has never proposed a test surface requirement that specifies both the
PFC and skid number values.
3. Test Speed
In the NPRM, NHTSA proposed that the braking-in-a-curve test be
conducted at 30 mph, unless the vehicle could not stay within the 12-
foot lane when driven through the curve at 30 mph. If the vehicle could
not do so, the braking-in-a-curve test would be conducted at 75 percent
of the maximum drive-through speed. NHTSA believed that the proposed
vehicle test speed was sufficiently high to test ABS performance, but
low enough so as not to pose an unsafe condition during the maneuver to
the test driver of most vehicles, based on testing conducted by the
agency\37\ and SAE J1626 Proposed Recommended Practice. The agency
requested comments about the proposed test speed.
\37\TRC Report, August 26, 1991.
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Advocates opposed any reduction in the test speed below 30 mph.
Specifically, it opposed permitting vehicles that cannot negotiate the
curve at 30 mph to be tested at the 75 percent drive-through speed
because it believed that this would be a ``free-floating criterion''
that could lead to ineffective antilock systems.
Rockwell WABCO, Allied Signal, Midland-Grau, and AAMA requested
that the test speed be clarified. Rockwell WABCO recommended that the
vehicle test speed requirement be revised to read ``stopped from 30 mph
or 75% of the maximum drive through speed, whichever is less.''
Similarly, Allied Signal suggested that the vehicle test speed be
clarified to say that testing cannot exceed 30 mph. Midland-Grau
recommended that the agency revise the requirement so that the test be
conducted at only 75 percent of the maximum drive-through speed
capability. It further stated that conducting the braking-in-a-curve
test at speeds greater than 30 mph on a low mu surface could cause
safety problems. AAMA stated that the NPRM incorrectly applied SAE
J1626, which requires testing at 75 percent of drive-through speed to a
maximum of 30 mph braking speed. It stated that under the proposal, a
vehicle with a drive-through speed of 30 mph would be tested at 30 mph,
while a vehicle with a drive-through speed of 29 mph would be tested at
less than 22 mph. In opposing the proposed requirement, AAMA further
stated that the determination of the drive-through speed is highly
sensitive to driver skill, subtle vehicle maneuvers, and environmental
conditions, and is therefore not repeatable.
ATA recommended that NHTSA establish stopping or snubbing distance
requirements for vehicles in a curve, using a braking speed which is
between 95 and 100 percent of their maximum drive through speed.
After reviewing the comments and available information, NHTSA has
decided to specify that a vehicle's test speed for the braking-in-a-
curve test is ``30 mph or 75% of the maximum drive-through speed,
whichever is less.'' This modification responds to the comments by
Rockwell WABCO, Allied Signal, and Midland-Grau that the proposal was
not consistent with SAE J1626. The agency believes that making the
speed consistent with SAE 1626 will eliminate the possibility of
discontinuities in the test's stringency for different vehicles. As
AAMA correctly stated, the proposed test speed created an anomaly that
benefitted vehicles with a maximum drive-through speed slightly below
30 mph. For example, a vehicle with a maximum drive-through speed of 29
mph would have been tested at 22 mph, while a vehicle with a maximum
drive-through speed of 30 mph would have been tested at 30 mph. This
would have meant that a 1 mph difference in maximum drive-through speed
would have resulted in a 8 mph difference in test speed. This could
have caused significant variations in test results for vehicles with
slight differences in maximum drive-through speed. By establishing a
test speed that is adjusted for differences in maximum drive-through
speed and that would be more specific and distinct for each vehicle and
test surface, the agency has minimized potential compliance testing
problems that might occur due to variability in the test speeds for
different vehicle and road test surface conditions.
NHTSA notes that ATA's requested test speed and test conditions
have not been tested by the agency or industry and therefore their
adoption would not be appropriate at this time. The agency may evaluate
ATA's proposal in future test programs.
NHTSA believes that Advocates' opposition to permitting test speeds
below 30 mph is unfounded. Similarly, the agency believes that AAMA's
concern about the drive-through speed being unrepeatable is irrelevant.
By allowing vehicles to be tested at 30 mph or 75 percent of maximum
drive-through speed, whichever is less, the effects of test surface
variation are eliminated.\38\
\38\TRC Report, page 10. [[Page 13234]]
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4. Type of Brake Application
In the NPRM, NHTSA proposed that the stops be achieved through full
brake applications in which the pressure at the treadle valve must
reach 100 psi within 0.2 seconds after the application is initiated.
The agency believed that these values properly represent full brake
applications, in terms of both the application's degree of force and
its duration. The agency stated that the stability and control
requirements should evaluate worst case braking applications in an
aggressive or ``hard'' stop and that full brake applications are more
readily repeatable than the ``driver best effort'' applications.
Midland-Grau agreed with the proposal to specify a full treadle
application of 100 psi in 0.2 seconds for air braked vehicles.
According to Midland-Grau's test data, full treadle applications at 100
psi were achieved in 0.12 to 0.18 seconds, with the measurement taken
at the treadle valve's primary output circuit located at the rear axle
brakes. However, more time is needed to reach 100 psi at the secondary
circuit located at the front axle brakes because its output supplies
air to the quick release valves and then to the front axle brake
chambers. Allied Signal stated that it is not possible to reach 100 psi
within 0.2 seconds at the front axle output circuit of the treadle
valve.
After reviewing these comments, NHTSA has decided to revise the
brake application requirement for air braked vehicles to require 100
psi in at least one of the treadle valve's output circuits within 0.2
seconds, thereby allaying Allied Signal's concern. This modification to
the test condition should eliminate potential ambiguity concerning
where the application pressure is to be measured.
5. Number of Test Stops for Certification
In the NPRM, NHTSA proposed that a vehicle comply with the proposed
braking-in-a-curve test in each of three consecutive stops for each
combination of weight and road conditions. In contrast, the vehicle
stopping performance tests in Standard No. 105 and Standard No. 121
specify that the vehicle must meet the requirements at least once in
six attempts through a best effort brake application. The agency
tentatively concluded that six stops should not be needed to achieve
the required performance in the braking-in-a-curve test, given the
presence of an antilock brake system. The agency requested comments
about the number of brake applications that should be required.
Advocates, Midland-Grau, and Mr. Crail stated that three stops are
sufficient for a vehicle with an antilock brake system to display
compliance with the braking-in-a-curve test. They stated that without
stopping distance requirements, this test procedure entails a simple
performance test for the vehicle to maintain control in the 12-foot
lane. Midland-Grau added that it uses three stops when conducting ABS
performance tests, and that this number of brake applications is
consistent with the SAE J1626 Recommended Practice and with the MVSRAC
Antilock Brake System Task Force's final recommendations.
AAMA argued that specifying three passes in three consecutive stops
places an unrealistic burden on the driver to control the vehicle
immediately with no opportunity to become familiar with the vehicle or
test surface. AAMA recommended that manufacturers be given the option
of conducting ten or more stops and certifying that the vehicle stayed
within the 12-foot lane for any three consecutive stops.
After reviewing the comments and the available information, NHTSA
has decided that requiring compliance with the braking-in-a-curve
requirements during three consecutive stops is appropriate. The agency
notes that specifying three consecutive full treadle test stops is
consistent with both the agency's own testing at VRTC and its testing
in conjunction with the motor vehicle industry through the MVSRAC ABS
Task Force. The use of full treadle brake applications to test an ABS-
equipped vehicle to the braking-in-a-curve maneuver requires less
driver skill than the use of a driver's-best-effort modulated brake
application (i.e., the type of application used in stopping distance
performance tests) because the ABS automatically modulates the brakes.
Further, more than three stops are unnecessary since the braking-in-a-
curve test requirement is not coupled with a stopping distance
requirement. Therefore, NHTSA has decided not to adopt AAMA's
suggestion that manufacturers be given the option of complying with
only three of ten stops. Adopting that suggestion would make the
braking-in-a-curve requirement unreasonably lenient.
6. Test Weight
In the NPRM, NHTSA proposed that single unit trucks, buses and
bobtail truck tractors be tested at their curb weight (including full
fuel tanks) plus 500 pounds to account for the driver and
instrumentation. The agency also proposed to allow a manufacturer to
conduct the braking-in-a-curve test with a roll bar structure weighing
up to an additional 1,000 pounds to protect the driver, based on a
recommendation by the MVSRAC ABS Task Force. The agency requested
comments about the appropriate unloaded test weight.
Rockwell WABCO recommended that unloaded heavy vehicles be allowed
to have less than 500 pounds added in the unloaded condition.
After reviewing Rockwell WABCO's comment, NHTSA has decided to
amend the test condition in the braking-in-a-curve test to specify the
weight in the unloaded condition to be ``up to 500 pounds'' for driver
and instrumentation.\39\ The agency notes that instrumentation hardware
has been getting more compact and lightweight. Using the regulatory
language ``up to 500 pounds'' will simplify the test condition since
manufacturers will not have to add ballast to ensure that the weight is
500 pounds. This change provides manufacturers with greater incentive
to use the newer, lighter hardware. The agency believes that this
modification will have no measurable effect on a vehicle's performance
during the braking-in-a-curve test since a weight range of a few
hundred pounds is of little significance in relation to a tractor's
typical empty weight of more than 26,000 pounds.
\39\The final rule also adopts the 1,000 pound allowance for a
roll bar.
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7. Loading Conditions
In the NPRM, NHTSA proposed that braking-in-a-curve tests be
performed in both the empty and loaded conditions, since a vehicle's
braking performance varies depending on the amount of load that it is
carrying. With respect to testing truck tractors in the loaded
condition, the agency proposed two alternatives regarding the use of
control trailers: (1) use a braked control trailer and (2) use an
unbraked control trailer.
Most commenters, including AAMA, Rockwell WABCO, and Midland-Grau,
supported the unbraked control trailer alternative. These commenters
believed that using an unbraked control trailer instead of a braked
control trailer would eliminate many sources of variability and would
provide more consistent and repeatable test data. AAMA stated that if
the braked control trailer alternative were adopted, every aspect of
the control trailer brake system would have to be precisely specified
because the tractor's performance is directly affected by the
performance of the control trailer. Midland-Grau stated that using an
unbraked control trailer is consistent with SAE J1626 and the testing
[[Page 13235]] performed by the MVSRAC ABS Task Force.
Similarly, commenters on the February 1993 stopping distance NPRM
strongly supported the unbraked control trailer alternative. Those
commenters believed that the agency would have great difficulty
defining the required performance of a braked control trailer and its
ABS if the braked control trailer alternative were adopted.
Mr. Crail and Strait-Stop stated that a truck tractor should be
tested with an ABS-equipped control trailer because it is not normal
for a combination vehicle to be operated with an unbraked control
trailer. They believed that a braked control trailer would more closely
reflect real world braking. Mr. Crail also stated that an unbraked
control trailer could result in instability during testing.
After reviewing the comments and other available information, NHTSA
has decided to specify that truck tractors be tested with an unbraked
control trailer for the braking-in-a-curve test. As the agency
explained in the NPRM, the unbraked control trailer eliminates certain
types of variability and provides more repeatable test data. Moreover,
this approach eliminates the need for the agency to specify and vehicle
manufacturers to comply with detailed foundation brake design
requirements for the control trailer. Accordingly, the unbraked control
trailer will provide more readily comparable test data among vehicles
and more repeatable test parameters for manufacturers.
NHTSA acknowledges that an unbraked control trailer does not
represent a typical operating condition for a combination vehicle. As a
result, real world combination vehicles will stop more effectively than
a test combination vehicle that has brakes on its tractor but not on
its trailer. Nevertheless, as most commenters stated, the unbraked
control trailer provides significant benefits for testing a loaded
truck tractor. Further, using the unbraked control trailer is
consistent with SAE J1626 and the testing performed by the MVSRAC Task
Force.
As for Mr. Crail's concern about stability problems during testing,
NHTSA does not agree that the use of an unbraked control trailer will
result in such problems. It is true that using an unbraked control
trailer will result in the kingpin receiving additional forces, since
the trailer will still be pushing on the kingpin while the tractor is
braking. However, the agency and industry conducted several braking-in-
a-curve tests with unbraked control trailers that indicated that these
additional kingpin forces will not increase a vehicle's instability
during testing.\40\
\40\TRC Report #091194, page 4.
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8. Initial Brake Temperature
In invalidating parts of Standard No. 121, the court in PACCAR
stated that the standard failed to specify formal and reasonably
specific testing criteria about the time intervals between tests. The
time interval between tests is important because it may affect brake
temperature and thus brake lining performance. In response to PACCAR,
the agency amended the standard to specify that the average brake
lining temperature of the hottest axle be between 150 deg. and 200
deg.F before performance tests could be conducted.
In the February 1993 NPRM on stopping distance and the September
1993 NPRM on stability during braking, NHTSA proposed that the average
brake lining temperature of the hottest axle be between 250 deg. and
300 deg. F before performance tests could be initiated. This range was
based on testing conducted by VRTC41. The agency believed that
compared to current requirements, this provision would allow tests on
heavy vehicles to be conducted within a shorter time between
measurements at temperatures representative of in-service conditions,
without affecting brake performance.
\41\``Heavy Duty Vehicle Brake Research Program--Report No. 1,''
April 1985.
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Only Advocates commented on the proposal in the stability and
control NPRM to increase the initial brake temperature from 150-200
deg.F to 250-300 deg.F. Advocates supported the higher temperature
range, stating that it is reasonable and representative of in-service
temperature conditions. However, NHTSA received numerous comments about
this issue in response to the stopping distance NPRMs. All commenters
addressing the issue of initial brake temperature in those rulemakings
strongly opposed the proposed change in temperature from 150-200 deg.F
to 250-300 deg.F. Lucas argued that the higher initial brake
temperature would be detrimental to drum brake performance. Lucas,
HDBMC, and Rockwell WABCO stated that the proposed initial brake
temperature would invalidate the vehicle manufacturer's data bank from
Standard No. 121 testing at 150-200 deg.F, which has been accumulating
since the 1970s. Midland-Grau commented that, among other things, the
higher initial brake temperature would lead to more aggressive lining
materials and vehicle compatibility problems.
Abex, AAMA, and HDBMC stated that the proposed higher initial brake
temperature would shorten testing time between 5 and 10 hours. However,
they believed that problems associated with brake fade resulting from
the higher initial brake temperature would far outweigh the nominal
cost savings obtained by having a shorter test time. Test data provided
by AAMA showed that while the higher initial brake temperature has a
slight adverse effect (a 7-28 foot increase) on full service brake
stopping distance, it has a significant adverse effect (a 25-98 foot
increase) on emergency brake stopping distance.
Rockwell WABCO stated that the perceived benefits of the higher
initial brake temperature do not justify the increased vehicle testing
and redesign that would be required to meet the proposed initial brake
temperature.
After reviewing the comments, the test data, and other available
information, NHTSA has decided that an initial brake temperature in the
150 deg.F to 200 deg.F range is more appropriate than the proposed
temperature range. As the commenters stated, testing using the 150
deg.F to 200 deg.F temperature range is more repeatable and results in
less variation between runs, compared to testing conducted using an
initial brake temperature of 250 deg.F to 300 deg.F, particularly for
the emergency brake stops. The agency further notes that an initial
brake temperature of 150 deg.F to 200 deg.F is within the 150 deg.F
to 300 deg.F range recommended by the VRTC test report. The agency is
aware that the lower temperature range increases the total test time by
5 to 10 hours. Nevertheless, because the other advantages to the lower
temperature range outweigh this concern, NHTSA has decided not to
change the specification that the initial brake temperature be between
150 to 200 deg.F.
9. Transmission Position
In the NPRM, NHTSA proposed that the transmission be in neutral or
the clutch pedal be depressed (clutch disengaged).
ATA commented that, in real world panic stops, drivers will neither
put the transmission in neutral nor depress the clutch pedal before
making a brake application. Nevertheless, ATA acknowledged that
retardation by the drivetrain could cause vehicle instabilities that
would necessitate testing at speeds lower than the drive through speed.
NHTSA has concluded that testing with the transmission in neutral
or the clutch disengaged is appropriate to ensure that engine
retardation does not affect a test which is intended to
[[Page 13236]] evaluate the influence of brake systems on vehicle
dynamic stability. Engine and drivetrain retardation forces vary from
vehicle to vehicle and can affect vehicle stability on low coefficient
of friction surfaces. Nevertheless, this is not the purpose of this
test. By requiring that the transmission be placed in neutral for brake
testing, the standard attempts to reduce these drive-train related
braking influences on the service brake performance. Therefore, testing
with the transmission in neutral or the clutch disengaged will
eliminate influences that engine or drivetrain retardation would have
on braking performance. This test condition therefore helps to ensure
test repeatability and reproducibility.
10. Summary of General Test Conditions
For the convenience of the reader, this section summarizes the
general test conditions being adopted in this notice, as follows:
Vehicle Position--Centered in the test lane at the
initiation of braking.
Steering--Driver to steer as necessary during braking to
maintain vehicle control.
Initial Brake Temperature--The average brake lining
temperature of the hottest axle between 150 to 200 deg.F.
Transmission--Neutral (or clutch pedal depressed).
Loading for Truck Tractors
Empty (Bobtail): Curb Weight (including full fuel tanks) plus up to
500 pounds for driver and instrumentation, and, at the manufacturer's
option, a roll bar weighing up to 1,000 pounds.
Loaded: Tractor is loaded with an unbraked control trailer, loaded
above the kingpin only, so that the tractor is at GVWR and the trailer
axle is at 4500 pounds. Tractor weight is distributed in accordance
with the Gross Axle Weight Ratings (GAWRs). If the tractor's fifth
wheel is fixed, preventing such loading, then the trailer is loaded
until any one tractor axle reaches its GAWR.
Brake Burnish--Follow procedures in S6.1.8(b) of Standard
No. 121.
Low Mu Braking-In-A-Curve Test
Run vehicle, empty and loaded.
Test Surface--PFC of 0.5, as determined with the ASTM
E1136 SRTT tire on ASTM traction trailer using ASTM E1337-90 procedure.
Track Configuration--500 foot radius at lane center line.
Test Speed--30 mph or 75 percent of the maximum drive-
through speed, whichever is less. Maximum drive-through speed is the
highest constant speed at which the vehicle can be driven through 200
feet of curve arc without any part of the vehicle leaving the 12-foot
lane.
Brake Application--Three full-treadle applications (i.e.,
air pressure of 100 psi at any treadle valve output circuit within 0.2
second) for each loading condition.
Test Failure Condition--Vehicle must stay within the 12-
foot lane during all three stops in order to comply with requirement.
D. Reliability and Maintenance
In response to the SNPRM, ATA, United Parcel Service (UPS), and
Tramec expressed concern about the durability, reliability, and
maintenance of ABSs. ATA stated that the rule, if adopted, would result
in significant maintenance problems, especially with respect to
failures of electrical circuits and of the power source. It claimed
that ABS components fail too often and that real world failure rates
are higher than those in NHTSA's demonstration program. ATA further
stated that it is inappropriate to compare the failure rates of ABS
components that are not subject to wear with the rates for components,
like brake linings and tires, that are subject to wear. ATA stated that
existing connectors fail in large numbers and that what it mistakenly
termed a ``separate connector requirement'' would double the failure
rate, resulting in unreasonable costs.42 It also stated that there
have been many problems resulting from inadequate installation of ABSs,
since malfunctions are frequently due to design problems, faulty
installation, and lack of knowledge about ABS maintenance. ATA also
stated that NHTSA did not take seriously enough malfunctions noted
during the agency-sponsored in-service fleet study, which were
rectified with only the expenditure of labor, namely corrections that
involved inspections or minor adjustments.
\42\The agency notes that it is requiring powering through a
separate circuit, not a separate connector.
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ATA and UPS stated that new ABS equipped heavy vehicles have a high
percentage of ``direct from factory'' ABS failures. UPS stated that
``these systems are still plagued by incidents of failure that far
exceed the normal level of problems encountered with other components
of heavy duty trucks.'' ATA also stated that NHTSA did not take labor
only failures (i.e., malfunctions that can be fully corrected through
the use of labor without the need for new parts) seriously enough. ATA
believes that they are a costly and serious problem that takes vehicles
out of service.
To evaluate the reliability of current-generation ABSs, NHTSA has
conducted extensive field studies of ABS-equipped heavy truck tractors
and semitrailers in developing this final rule. In response to the
PACCAR decision, these studies were structured to assess whether
current-generation heavy vehicle antilock brake systems were reliable
and fail-safe, whether they inordinately increased vehicle maintenance
costs, and whether they could be successfully maintained and would
remain functioning in typical U.S. heavy truck operating environments.
Between 1988 and 1993, NHTSA tracked the maintenance performance
histories of 200 truck tractors and 50 semitrailers equipped with ABS,
as well as the histories of a comparison group of 88 truck tractors and
35 semitrailers not equipped with ABS, to determine the incremental
maintenance costs and patterns associated with installing ABS on these
heavy vehicles. Additionally, special on-board vehicle recorders were
used to monitor the functioning and performance of the ABSs. Finally,
drivers and mechanics at the participating test fleets were
periodically interviewed to ascertain their views about the ABS test
vehicles' performance and ease of maintenance. This multimillion dollar
program was the largest of its kind that has ever been conducted by the
agency or throughout the world. The study's authors concluded that,
based on the data collected during the fleet study, currently available
antilock braking systems are reliable, durable and maintainable.
While ABS is not a zero-cost maintenance item, its presence on a
vehicle did not substantially increase maintenance costs (less than 1
percent for t
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