[Federal Register Volume 63, Number 50 (Monday, March 16, 1998)]
[Rules and Regulations]
[Pages 12660-12664]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-6522]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-98-3387]
RIN 2127-AF96


Federal Motor Vehicle Safety Standards; Stability and Control of 
Medium and Heavy Vehicles During Braking

AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION: Final rule; petitions for reconsideration.

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SUMMARY: This document responds to petitions for reconsideration of 
final rules that amended Standard No. 105, Hydraulic Brake Systems, to 
require medium and heavy vehicles to be equipped with an antilock brake 
system (ABS). In response to the petitions, this document permits 
hydraulically-braked vehicles with a gross vehicle weight rating (GVWR) 
greater than 10,000 pounds but less than 19,501 pounds to be equipped 
with a single wheel speed sensor in the driveline to control wheel

[[Page 12661]]

slip at the drive axle and permits rear tag axles to lock up. 
Additionally, this document allows motor homes with a GVWR of 22,500 
pounds or less to use a single rear drive axle wheel speed sensor if 
they are manufactured before March 1, 2001, after which date new motor 
homes must meet the same ABS requirements as other hydraulically-braked 
trucks and buses.

DATES: Effective Dates: The amendments to 49 CFR 571.105 are effective 
March 1, 1999. Petitions for Reconsideration: Any petition for 
reconsideration of this rule must be received by NHTSA no later than 
April 30, 1998.

ADDRESSES: Petitions for reconsideration of this rule should refer to 
the above referenced docket numbers 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. Samuel Daniel, Jr., Office of 
Crash Avoidance Standards, National Highway Traffic Safety 
Administration, 400 Seventh Street, SW., Washington, D.C. 20590; 
Telephone (202) 366-4921, Fax (202) 366-4329.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Background
II. Petitions for Reconsideration of the December 1995 Final Rule
III. NHTSA's Response to Petitions for Reconsideration Related to 
Standard No. 105
    A. Control of Rear Wheel Slip
    B. Application of ABS to Non-Powered, Rear Tag Axles
    C. ABS Malfunction Lamp Activation Protocol

I. Background

    Section 4012 of the Motor Carrier Act of 1991 1 directed 
the Secretary of Transportation to initiate rulemaking concerning 
methods for improving the braking performance of new commercial motor 
vehicles, including trucks, tractors, trailers, and 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 required that the rulemaking be 
consistent with the Motor Carrier Safety Act of 1984 (49 U.S.C. 31136) 
and be carried out pursuant to, and in accordance with the National 
Traffic and Motor Vehicle Safety Act of 1966.2
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    \1\ The Motor Carrier Act is part of the Intermodal Surface 
Transportation Efficiency Act (ISTEA) of 1991, Pub. L. 102-240.
    \2\ Now codified as 49 U.S.C 30101 et seq. (Safety Act)
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    On March 10, 1995, NHTSA issued final rules requiring medium and 
heavy vehicles 3 to be equipped with an antilock brake 
system (ABS) to improve their directional stability and control during 
braking. (60 FR 13216, 60 FR 13297) These final rules also reinstated 
stopping distance requirements for air-braked heavy vehicles and 
established stopping distance requirements for hydraulically-braked 
heavy vehicles. In addition to the ABS requirement, the March 1995 
final rule specified requirements about the electrical powering of 
trailer ABS and ABS malfunction indicators. In response to petitions 
for reconsideration of these requirements, NHTSA published a final rule 
that affirmed its decision to require these features. (60 FR 63965, 
December 13, 1995).
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    \3\ The document uses the term heavy vehicles to refer to medium 
and heavy vehicles.
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II. Petitions for Reconsideration of the December 1995 Final Rule

    NHTSA received petitions for reconsideration of the December 1995 
amendments to the final rule from the American Trucking Associations 
(ATA), which represents trucking fleets, the National Private Truck 
Council (NPTC), which represents private trucking fleets, the Truck 
Manufacturers Association (TMA) 4, which represents truck 
manufacturers, the Truck Trailer Manufacturers Association (TTMA), 
which represents trailer manufacturers, the Heavy Duty Brake 
Manufacturers Council (HDBMC) 5, which represents heavy duty 
brake component manufacturers, Midland-Grau, Kelsey-Hayes, Rockwell 
WABCO, Vehicle Enhancement Systems (VES), AlliedSignal, General Motors 
(GM), Ford, and the Recreational Vehicle Industry Association (RVIA).
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    \4\ TMA member companies include Ford, Freightliner, General 
Motors, Mack Trucks, Navistar International, PACCAR, and Volvo GM 
Heavy Truck.
    \5\ HDBMC member companies include Abex, AlliedSignal, Eaton, 
Midland-Grau, Ferodo America, Haldex, Lucas, MGM Brakes, Motion 
Control/Carlisle, Rockwell, Rockwell WABCO, and Spicer/Dana.
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    Most of the petitions focused on issues associated with Standard 
No. 121's requirements on the electrical powering of trailer ABS and 
the in-cab display of trailer ABS malfunctions. Those issues were 
addressed in a final rule published on February 15, 1996. (61 FR 5949)
    Petitions submitted by Ford, GM, Kelsey-Hayes, and RVIA addressed 
issues associated with Standard No. 105, including the control of rear 
wheel slip, the application of ABS to non-powered rear tag axles, and 
the ABS malfunction lamp protocol. The February 1996 final rule stated 
that it was deferring a response to these petitions because they 
addressed issues associated with Standard No. 105. Today's notice 
addresses the concerns raised by those petitioners.

III. NHTSA's Response to Petitions for Reconsideration Related to 
Standard No. 105

A. Control of Rear Wheel Slip

    In the March 1995 final rule, NHTSA required that each 
hydraulically-braked vehicle with a GVWR greater than 10,000 pounds be 
``equipped with an antilock brake system that directly controls the 
wheels of at least one front axle and the wheels of at least one rear 
axle of the vehicle.''
    In the December 1995 final rule that responded to petitions for 
reconsideration from Chrysler, Kelsey-Hayes, and the American 
Automobile Manufacturers Association (AAMA), NHTSA amended Section 
S5.5.1 by adding the following provision: ``On each vehicle with a GVWR 
greater than 10,000 pounds but not greater than 12,000 pounds, the 
antilock brake system may also directly control the wheels of the drive 
axle by means of a single sensor in the driveline.'' Chrysler stated 
that all its pickup trucks in the 10,000-12,000 pound GVWR class had 
successfully used the driveline wheel speed sensor arrangement. 
Notwithstanding NHTSA's decision to allow this sensing arrangement on 
hydraulically-braked trucks up to 12,000 pounds, the agency emphasized 
that such an arrangement would not be appropriate for heavier air-
braked trucks, because greater braking efficiency is typically required 
at the rear wheels of such air-braked vehicles than on medium vehicles. 
This is because air-braked vehicles typically are heavier and have 
greater load carrying capacity.
    In response to the December 1995 final rule, GM, Ford, and Kelsey-
Hayes asked NHTSA to revise section S5.5.1 of Standard No. 105. Ford 
first requested that the 12,000-pound limit allowing driveline wheel 
speed sensors be raised to 17,500 pounds and then to 20,500 pounds. 
Kelsey-Hayes requested a 17,500-pound limit for driveline sensors. GM 
requested a 16,500-pound limit; that company also cited the April 1995 
AAMA petition for reconsideration requesting that the agency either 
exempt all hydraulically-braked vehicles from the requirement for two 
independent rear wheel sensors, or exempt all hydraulically-braked 
vehicles under

[[Page 12662]]

16,500 pounds GVWR from the ABS mandate.
    Each petitioner stated that the 12,000-pound limit for allowing 
driveline sensors was not high enough to include their medium trucks 
that have the same type of driveline sensor as Chrysler's sensor. Ford 
stated that its F-Series chassis, including the F-350, the E-350, and 
the E-Super duty vehicles have GVWRs up to 11,000, 12,500, and 14,050 
pounds, respectively. GM stated that its GMC Sierra 3500 HD chassis cab 
and the Chevrolet 3500 HD chassis cab can be configured to GVWRs up to 
15,000 pounds, while its P-30 forward control chassis will soon be 
available up to 16,500 pounds GVWR. Kelsey-Hayes stated that it has 
supplied a single driveline sensor to GM since 1992 for use on trucks 
with GVWRs up to 17,500 pounds.
    In June 1996, GM and Ford 6 supplemented their January 
1996 petitions for reconsideration, with additional information about 
driveline sensors. They asked that the upper GVWR limit be eliminated 
completely and that all ABS-equipped hydraulically-braked vehicles, 
regardless of GVWR, be allowed to have a single sensor in the driveline 
to control wheel slip at both rear wheels. In support of their 
position, GM and Ford tested a light duty truck that was configured and 
equipped to have a 20,500 pound GVWR. The truck was fitted with a 
three-sensor, three-modulator (3S/3M) ABS that uses a single driveline 
rear wheel speed sensor. The vehicle was lightly loaded to 8838 pounds 
(the worst case condition) and subjected to a 30-mph brake-in-a-curve 
test similar to, but more stringent than Standard No. 121's brake-in-a-
curve test for air-braked truck tractors. The petitioner's testing was 
more stringent given that it was conducted on a curve with a lower 
radius of curvature ( a 420-foot radius curve rather than a 500-foot 
one), and on a slippier road surface (a surface with a 0.39 peak 
friction coefficient (PFC) rather than a 0.50 PFC one). The testing 
indicated that the single driveline sensor provided an acceptable 
reading of the individual rear wheel speeds, resulting in the vehicle 
remaining stable and within the lane throughout the test.
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    \6\ Kelsey-Hayes and RVIA have stated their concurrence with 
this position.
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    NHTSA agrees with the petitioners that these test results 
demonstrate that a 3S ABS with a single rear driveline sensor provides 
satisfactory safety performance for medium duty hydraulically-braked 
vehicles. The agency has added the term ``rear'' to the sentence in 
S5.5.1 addressing ABS requirements to assure that a single drive axle 
sensor is not installed on a front driveline axle. However, the agency 
is not willing to eliminate the GVWR limit since there are 
hydraulically-braked trucks with a GVWR in excess of 26,000 pounds and 
the petitioners provided no 3S ABS braking stability and control test 
data to support the allowance of 3S ABS for these trucks. The 
petitioners' test results indicate that the braking stability and 
control of hydraulically-braked trucks with relatively high GVWRs, up 
to 20,500 pounds, is not compromised if a manufacturer uses an ABS 
control strategy that employs a single rear driveline wheel speed 
sensor in lieu of a control strategy employing direct control of each 
individual rear wheel.
    Accordingly, this rule permits 3S ABS on hydraulically-braked 
vehicles up to 19,500 pounds GVWR, a breakpoint in the existing vehicle 
weight class system used by State vehicle inspectors and the trucking 
industry generally. A GVWR of 19,500 pounds, the upper limit of Class 
5, will avoid introducing a unique breakpoint for this 3S ABS 
requirement that differs from the breakpoints used for other regulatory 
requirements. The 19,500-pound GVWR limit chosen for this requirement 
is also slightly less than the test weight of the vehicle used in 
braking stability and control tests cited by the petitioners.
    By allowing 3S ABS on hydraulically-braked vehicles up to 19,500 
pounds GVWR, NHTSA has addressed almost all the concerns expressed by 
the petitioners. However, the American Automobile Manufacturers 
Association (AAMA) provided additional information in a letter and 
videotape forwarded to the agency on July 29, 1997. The tape shows a 
motor home with a GVWR of 22,500 pounds ballasted to 26,000 pounds (the 
breakpoint for Class 6 vehicles) successfully completing braking-in-a-
curve testing similar to the braking stability and control testing 
required in Standard No. 121 for truck tractors. This testing was 
performed on dry asphalt and wet jennite by Kelsey-Hayes at its vehicle 
development center. NHTSA staff followed this up by attending a 
supplementary demonstration of motor home stability and control during 
braking at General Motors' test track in November 1997.
    The AAMA originally asked that these test results be used to permit 
extending 3S ABS to all Class 6 hydraulically-braked vehicles (GVWR of 
up to 26,000 pounds). However, when NHTSA asked for information about 
what difficulties were posed by using the generally-required 4S ABS for 
Class 6 vehicles, AAMA responded that the problems were for motor homes 
only, not other Class 6 vehicles. GM provided information for its P-
chassis, which is used for 9,000 to 10,000 motor homes annually. The P-
chassis, which currently uses a 3S ABS, can be used to manufacture a 
completed motor home with a 22,500-pound GVWR. GM will modify this 
chassis to use a 4S ABS system, but the modifications won't be ready 
for production chassis for a few years. In the meantime, GM would have 
to stop offering this chassis for use by the motor home industry. Since 
there are no substitute motor home chassis in this GVWR range that 
offer 4S ABS, these vehicles would in effect be temporarily forced out 
of the market. RVIA argued that this would be an unfair burden, because 
these motor homes are produced in very limited quantities (9,000-10,000 
per year) by small businesses. RVIA also argued that these vehicles are 
generally driven only for vacationing and camping.
    In response to these arguments and information, NHTSA believes it 
is appropriate to allow motor homes with a GVWR greater than 19,500 
pounds to use a 3S ABS system. To prevent the economic hardship of 
forcing motor home manufacturers to discontinue production for a few 
years until appropriate 4S ABS chassis are available, the agency will 
allow 3S ABS motor homes for a limited period of time. However, NHTSA 
has no information indicating any difficulties for vehicles other than 
motor homes in the 19,500 to 26,000 pound GVWR range (Class 6 vehicles) 
in meeting the 4S ABS requirements. Hence, all Class 6 vehicles other 
than motor homes will be required to provide 4S ABS.
    For the purposes of this 3S ABS rulemaking, NHTSA is defining the 
term ``motor home'' the same way that term has been defined in Standard 
No. 208. Thus, a ``motor home'' for purposes of Standard No. 105 will 
mean ``a motor vehicle with motive power that is designed to provide 
temporary residential accommodations, as evidenced by the presence of 
at least four of the following facilities: cooking; refrigeration or 
ice box; self-contained toilet; heating and/or air conditioning; a 
potable water supply system including a faucet and a sink; and a 
separate 110-125 volt electric power supply and/or an LP gas supply.''
    NHTSA believes it can accommodate the needs of motor home 
manufacturers while assuring that these vehicles will transition 
quickly to the same braking systems as other vehicles in their GVWR

[[Page 12663]]

range for the following reasons. First, the GM P-chassis, with a GVWR 
of 22,500 pounds, is the largest hydraulically-braked motor home 
chassis to use a 3S ABS. Any greater capacity motor home chassis would 
be newly designed. NHTSA believes it is reasonable to require newly 
designed Class 6 chassis to use a 4S ABS system. Second, the motor home 
industry needs a transition period to move from 3S ABS on Class 6 
vehicles to 4S ABS on those vehicles. GM, the manufacturer of the P-
chassis, has stated to NHTSA that GM will move to install 4S ABS on 
this vehicle in the next few years. Given these circumstances, NHTSA 
will permit motor homes with a GVWR between 19,501 pounds and 22,500 
pounds to use a 3S ABS system on vehicles manufactured before March 1, 
2001. This will give GM and other motor home chassis manufacturers 
three years to develop and install 4S ABS, thus minimizing the burden 
on both vehicle chassis and motor home manufacturers. All new motor 
homes manufactured on or after March 1, 2001 with a GVWR of more than 
19,500 pounds will be required to provide the 4S ABS system required on 
other vehicles.
    Since 3S ABS will be allowed on motor homes with a GVWR between 
19,500 pounds and 22,500 pounds, it is important that the incomplete 
vehicle manufacturer of a chassis equipped with 3S ABS include in the 
statement of specific conditions of final manufacturer (Part 
568.4(a)(7)(ii)) that only if the completed vehicle is a motor home, 
will it conform to the standard. Completed vehicles in the specified 
GVWR range, other than motor homes, will not conform to the standard, 
if the incomplete chassis is equipped with a 3S ABS.

B. Application of ABS to Non-Powered, Rear Tag Axles

    In its January 29, 1996 petition, RVIA requested that the ABS 
requirement not apply to hydraulically-braked motor homes with tag 
axles and GVWRs greater than 10,000 pounds. Tag axles are non-liftable, 
non-powered axles that are fitted, either in front of or behind the 
rear axle of the vehicle, by the second-stage vehicle manufacturer. Tag 
axles improve a vehicle's balance and increase its carrying capacity. 
RVIA stated that there is no way to apply antilock capability to tag 
axles added to a vehicle chassis by second-stage vehicle manufacturers, 
such as RVIA members. RVIA stated that less than 3000 vehicles per 
model year have a tag axle. It further stated that brake and tag axle 
manufacturers are reluctant to design, develop, and test ABS systems 
for such a limited application.
    In its June 24, 1996 supplement to its original petition, RVIA 
stated that it would support a requirement for ABS on hydraulically-
braked motor homes, provided that a single driveline rear wheel speed 
sensor is permitted and that the no-wheel-lockup requirement did not 
apply to tag axles. With respect to tag axles, RVIA cited tests 
conducted by GM and Kelsey/Hayes on a GM P-30 motor home chassis with a 
GVWR of 19,500 pounds. In the tests, the vehicle was lightly loaded 
(16,500 pounds), and driven at a speed of 25 mph (75 percent of the 
vehicle's maximum drive-through speed) through a 500-foot radius curve 
on a wetted jennite surface. The vehicle was also tested fully loaded, 
on a high to low coefficient of friction transition test (asphalt to 
ice). While the vehicle's tag axle (which was not controlled by ABS) 
locked when brakes were applied, the vehicle's ABS modulated the brakes 
and wheel speeds on the vehicle's powered drive axle and its steering 
axle. The vehicle remained stable and under control throughout both 
stops, despite the fact that the tag axle's wheels were locked.
    The agency has received many requests for clarification of the ABS 
requirements for heavy-duty, single unit vehicles with regard to the 
number of axles that require ABS sensors. For heavy-duty single unit 
vehicles, the standard requires ABS control on only one rear axle, 
regardless of the number of rear axles and regardless of whether the 
axles are installed as a tag or pusher axle by a final stage 
manufacturer. To clarify this, the agency has added a definition for 
the term ``tandem axle,'' which means an arrangement of axles, drive or 
non-drive, in close proximity to each other. Hence, if a manufacturer 
chooses to install ABS on the drive axle of a tandem but not on the 
non-drive (tag or pusher) axle, the wheel lock restrictions would still 
be able to be met without ABS on the tag or pusher axle. The current 
wheel lock restrictions allow any two wheels on a tandem axle 
(including two wheels on the tag axle) to lock-up for any duration. 
Based on the foregoing, and on the test results mentioned by RVIA, the 
agency has determined that it is not necessary to equip a tag axle with 
ABS to comply with the wheel lock restriction requirements. The agency 
notes that, even though the tag axle wheels locked when the motor 
home's brakes were applied, the vehicle remained stable within the 
travel lane throughout the stopping maneuvers. As RVIA stated, tag 
axles that are added to these type vehicles typically do not carry a 
significant portion of the vehicle's overall weight. These 
considerations indicate that there are no negative stability 
consequences if such axles lock-up.

C. ABS Malfunction Lamp Activation Protocol

    In its January 1996 petition for reconsideration, Kelsey-Hayes 
requested that NHTSA reconsider the final rule's activation protocol 
requirements for ABS malfunction warning lamps. That company requested 
that the malfunction warning lamp be allowed to remain activated (i.e., 
``on'' or lighted) during a low speed drive away to verify that the 
vehicle's wheel speed sensors were properly functioning.
    NHTSA has decided not to amend the ABS activation lamp protocol. 
The agency notes that in support of its request, Kelsey-Hayes did not 
provide any new data or reasoning, beyond that which was available to 
the agency prior to the issuance of the March 10, 1995 final rule. At 
that time, the agency noted that it had considered all the information 
available on this issue, and had concluded that standardization of the 
activation protocol was warranted for the following reasons. First, a 
standardized protocol would enable Federal and State safety inspection 
personnel to determine the operational status of ABSs without having to 
move the vehicle. Second, it would preclude confusion among heavy 
vehicle drivers relative to how this type of lamp functions. Third, 
standardization would be consistent with ECE requirements on this 
subject and would, therefore, be consistent with the goal of 
international harmonization. Given that there is no new information to 
reverse its previous decision, the agency has decided not to modify the 
activation protocol requirements.

IV. Rulemaking Analyses and Notices

A. Executive Order 12866 and DOT Regulatory Policies and Procedures

    This notice has not been reviewed under Executive Order 12866. 
NHTSA has considered the impacts of this rulemaking action and 
determined that it is not ``significant'' within the meaning of the 
Department of Transportation's regulatory policies and procedures. In 
connection with the March 1995 final rules, the agency prepared a Final 
Economic Assessment (FEA) describing the economic and other effects of 
this rulemaking action. Summary discussions of those effects were 
provided in the ABS final rule. For persons wishing to examine the full 
analysis, a copy is in the docket.

[[Page 12664]]

    The amendments in today's final rule do not make those effects any 
more stringent, and in some respects, they make it easier for a 
manufacturer to comply with them. Specifically, by allowing the use of 
a single driveline sensor to control rear wheel speeds and allowing 
wheels on tag axles to lock during testing, vehicle manufacturers will 
have more flexibility to comply with the requirements of this rule and, 
as a result, costs could be reduced.

B. Regulatory Flexibility Act

    NHTSA has also considered the effects of both this final rule and 
the original final rule under the Regulatory Flexibility Act. I hereby 
certify that it will not have a significant economic impact on a 
substantial number of small entities. Accordingly, the agency has not 
prepared a final regulatory flexibility analysis.
    NHTSA concluded that the March 1995 final rule had no significant 
impact on a substantial number of small entities. Thus, today's final 
rule, which could potentially reduce costs associated with the March 
1995 final rule, will not have a significant economic impact on a 
substantial number of small entities.

C. National Environmental Policy Act

    NHTSA has analyzed this rulemaking action for the purposes of the 
National Environmental Policy Act. The agency has determined that 
implementation of this action will not have any significant impact on 
the quality of the human environment.

D. Executive Order 12612 (Federalism)

    NHTSA has analyzed this action under the principles and criteria in 
Executive Order 12612. The agency has determined that this notice does 
not have sufficient Federalism implications to warrant the preparation 
of a Federalism Assessment. No State laws will be affected.

E. Civil Justice Reform

    This final rule does not have any retroactive effect. Under 49 
U.S.C. 30103, whenever a Federal motor vehicle safety standard is in 
effect, a State may not adopt or maintain a safety standard applicable 
to the same aspect of performance which is not identical to the Federal 
standard, except to the extent that the State requirement imposes a 
higher level of performance and applies only to vehicles procured for 
the State's use. 49 U.S.C. 30161 sets forth a procedure for judicial 
review of final rules establishing, amending or revoking Federal motor 
vehicle safety standards. That section does not require submission of a 
petition for reconsideration or other administrative proceedings before 
parties may file suit in court.

List of Subjects in 49 CFR Part 571

    Imports, Motor vehicle safety, Motor vehicles, Rubber and rubber 
products, Tires.

    In consideration of the foregoing, the agency is amending Standard 
No. 105, Hydraulic Brake Systems in Title 49 of the Code of Federal 
Regulations at Part 571 as follows:

PART 571--[AMENDED]

    1. The authority citation for Part 571 continues to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166, 
delegation of authority at 49 CFR 1.50. CFR 1.50.

    2. Section 571.105 is amended by adding the definitions of ``motor 
home'' and ``tandem axle'' in S4 and by revising S5.5.1, to read as 
follows:


Sec. 571.105  Standard No. 105; Hydraulic and electric brake systems.

* * * * *
S4. Definitions.
* * * * *
    Motor home means a motor vehicle with motive power that is designed 
to provide temporary residential accommodations, as evidenced by the 
presence of at least four of the following facilities: cooking; 
refrigeration or ice box; self-contained toilet; heating and/or air 
conditioning; a potable water supply system including a faucet and a 
sink; and a separate 110-125 volt electric power supply and/or an LP 
gas supply.
* * * * *
    Tandem axle means a group of two or more axles placed in close 
arrangement one behind the other with the center lines of adjacent 
axles not more than 72 inches apart.
* * * * *
    S5.5.1  Each vehicle with a GVWR greater than 10,000 pounds, except 
for any vehicle with a speed attainable in 2 miles of not more than 33 
mph, shall be equipped with an antilock brake system that directly 
controls the wheels of at least one front axle and the wheels of at 
least one rear axle of the vehicle. On each vehicle with a GVWR greater 
than 10,000 pounds but not greater than 19,500 pounds and motor homes 
with a GVWR greater than 10,000 pounds but not greater than 22,500 
pounds manufactured before March 1, 2001, the antilock brake system may 
also directly control the wheels of the rear drive axle by means of a 
single sensor in the driveline. Wheels on other axles of the vehicle 
may be indirectly controlled by the antilock brake system.
* * * * *
    Issued on: February 23, 1998.
Ricardo Martinez,
Administrator.
[FR Doc. 98-6522 Filed 3-13-98; 8:45 am]
BILLING CODE 4910-59-P