[Code of Federal Regulations]

[Title 49, Volume 6]

[Revised as of October 1, 2005]

From the U.S. Government Printing Office via GPO Access

[CITE: 49CFR571.121]



[Page 432-454]

 

                        TITLE 49--TRANSPORTATION

 

                            OF TRANSPORTATION

 

PART 571_FEDERAL MOTOR VEHICLE SAFETY STANDARDS--Table of Contents

 

            Subpart B_Federal Motor Vehicle Safety Standards

 

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



    S1. Scope. This standard establishes performance and equipment 

requirements for braking systems on vehicles equipped with air brake 

systems.

    S2. Purpose. The purpose of this standard is to insure safe braking 

performance under normal and emergency conditions.

    S3. Application. This standard applies to trucks, buses, and 

trailers equipped with air brake systems. However, it does not apply to:

    (a) Any trailer that has a width of more than 102.36 inches with 

extendable equipment in the fully retracted position and is equipped 

with two short track axles in a line across the width of the trailer.

    (b) Any vehicle equipped with an axle that has a gross axle weight 

rating (GAWR) of 29,000 pounds or more;

    (c) Any truck or bus that has a speed attainable in 2 miles of not 

more than 33 mph;

    (d) Any truck that has a speed attainable in 2 miles of not more 

than 45 mph, an unloaded vehicle weight that is not less than 95 percent 

of its gross vehicle weight rating (GVWR), and no capacity to carry 

occupants other than the driver and operating crew;

    (e) Any trailer that has a GVWR of more than 120,000 pounds and 

whose body conforms to that described in the definition of heavy hauler 

trailer set forth in S4;

    (f) Any trailer that has an unloaded vehicle weight which is not 

less than 95 percent of its GVWR; and

    (g) Any load divider dolly.

    S4. Definitions.

    Agricultural commodity trailer means a trailer that is designed to 

transport bulk agricultural commodities in off-road harvesting sites and 

to a processing plant or storage location, as evidenced by skeletal 

construction that accommodates harvest containers, a maximum length of 

28 feet, and an arrangement of air control lines and reservoirs that 

minimizes damage in field operations.

    Air brake system means a system that uses air as a medium for 

transmitting pressure or force from the driver control to the service 

brake, including an air-over-hydraulic brake subsystem, but does not 

include a system that uses compressed air or vacuum only to assist the 

driver in applying muscular force to hydraulic or mechanical components.

    Air-over-hydraulic brake subsystem means a subsystem of the air 

brake system that uses compressed air to transmit a force from the 

driver control to a hydraulic brake system to actuate the service 

brakes.

    Antilock brake system or ABS 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



[[Page 433]]



one or more controlling devices which interpret those signals and 

generate responsive controlling output signals; and

    (3) Transmitting those controlling signals to one or more modulators 

which adjust brake actuating forces in response to those signals.

    Auto transporter means a truck and a trailer designed for use in 

combination to transport motor vehicles, in that the towing vehicle is 

designed to carry cargo at a location other than the fifth wheel and to 

load this cargo only by means of the towed vehicle.

    Common diaphragm means a single brake chamber diaphragm which is a 

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

    Container chassis trailer means a semitrailer of skeleton 

construction limited to a bottom frame, one or more axles, specially 

built and fitted with locking devices for the transport of intermodal 

shipping containers, so that when the chassis and container are 

assembled, the units serve the same function as an over the road 

trailer.

    Directly controlled wheel means a wheel for which the degree of 

rotational wheel slip is sensed, either at that wheel or on the axle 

shaft for that wheel and corresponding signals are transmitted to one or 

more modulators that adjust the brake actuating forces at that wheel. 

Each modulator may also adjust the brake actuating forces at other 

wheels that are on the same axle or in the same axle set in response to 

the same signal or signals.

    Effective projected luminous lens area means that area of the 

projection on a plane perpendicular to the lamp axis of that portion of 

the light-emitting surface that directs light to the photometric test 

pattern, and does not include mounting hole bosses, reflex reflector 

area, beads or rims that may glow or produce small areas of increased 

intensity as a result of uncontrolled light from small areas (\1/2\ 

degree radius around the test point).

    Full-treadle brake application means a brake application in which 

the treadle valve pressure in any of the valve's output circuits reaches 

85 pounds per square inch (psi) within 0.2 seconds after the application 

is initiated, or in which maximum treadle travel is achieved within 0.2 

seconds after the application is initiated.

    Heavy hauler trailer means a trailer which has one or more of the 

following characteristics, but which is not a container chassis trailer:

    (1) Its brake lines are designed to adapt to separation or extension 

of the vehicle frame; or

    (2) Its body consists only of a platform whose primary cargo-

carrying surface is not more than 40 inches above the ground in an 

unloaded condition, except that it may include sides that are designed 

to be easily removable and a permanent ``front end structure'' as that 

term is used in Sec. 393.106 of this title.

    Independently controlled wheel means a directly controlled wheel for 

which the modulator does not adjust the brake actuating forces at any 

other wheel on the same axle.

    Indirectly controlled wheel means a wheel at which the degree of 

rotational wheel slip is not sensed, but at which the modulator of an 

antilock braking system adjusts its brake actuating forces in response 

to signals from one or more sensed wheel(s).

    Initial brake temperature means the average temperature of the 

service brakes on the hottest axle of the vehicle 0.2 mile before any 

brake application in the case of road tests, or 18 seconds before any 

brake application in the case of dynamometer testing.

    Intermodal shipping container means a reusable, transportable 

enclosure that is especially designed with integral locking devices for 

securing the container to the trailer to facilitate the efficient and 

bulk shipping and transfer of goods by, or between various modes of 

transport, such as highway, rail, sea and air.

    Load divider dolly means a trailer composed of a trailer chassis and 

one or more axles, with no solid bed, body, or container attached, and 

which is designed exclusively to support a portion of the load on a 

trailer or truck excluded from all the requirements of this standard.

    Maximum drive-through speed means the highest possible constant 

speed at which the vehicle can be driven through 200 feet of a 500-foot 

radius



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curve arc without leaving the 12-foot lane.

    Maximum treadle travel means the distance that the treadle moves 

from its position when no force is applied to its position when the 

treadle reaches a full stop.

    Peak friction coefficient or PFC means the ratio of the maximum 

value of braking test wheel longitudinal force to the simultaneous 

vertical force occurring prior to wheel lockup, as the braking torque is 

progressively increased.

    Pulpwood trailer means a trailer that is designed exclusively for 

harvesting logs or pulpwood and constructed with a skeletal frame with 

no means for attachment of a solid bed, body, or container, and with an 

arrangement of air control lines and reservoirs designed to minimize 

damage in off-road operations.

    Tandem axle means a group or set of two or more axles placed in a 

close arrangement, one behind the other, with the centerlines of 

adjacent axles not more than 72 inches apart.

    Straddle trailer means a trailer that is designed to transport bulk 

agricultural commodities from the harvesting location as evidenced by a 

framework that is driven over the cargo and lifting arms that suspend 

the cargo for transit.

    Wheel lockup means 100 percent wheel slip.

    S5. Requirements. Each vehicle shall meet the following requirements 

under the conditions specified in S6.

    S5.1 Required equipment for trucks and buses. Each truck and bus 

shall have the following equipment:

    S5.1.1 Air compressor. An air compressor of sufficient capacity to 

increase air pressure in the supply and service reservoirs from 85 psi 

to 100 psi when the engine is operating at the vehicle manufacturer's 

maximum recommended r.p.m. within a time, in seconds, determined by the 

quotient (Actual reservoir capacityx25)/Required reservoir capacity.

    S5.1.1.1 Air compressor cut-in pressure. The air compressor governor 

cut-in pressure for each bus shall be 85 p.s.i. or greater. The air 

compressor governor cut-in pressure for each truck shall be 100 p.s.i. 

or greater.

    S5.1.2 Reservoirs. One or more service reservoir systems, from which 

air is delivered to the brake chambers, and either an automatic 

condensate drain valve for each service reservoir or a supply reservoir 

between the service reservoir system and the source of air pressure.

    S5.1.2.1 The combined volume of all service reservoirs and supply 

reservoirs shall be at least 12 times the combined volume of all service 

brake chambers. For each brake chamber type having a full stroke at 

least as great as the first number in Column 1 of Table V, but no more 

than the second number in Column 1 of Table V, the volume of each brake 

chamber for purposes of calculating the required combined service and 

supply reservoir volume shall be either that specified in Column 2 of 

Table V or the actual volume of the brake chamber at maximum travel of 

the brake piston or pushrod, whichever is lower. The volume of a brake 

chamber not listed in Table V is the volume of the brake chamber at 

maximum travel of the brake piston or pushrod. The reservoirs of the 

truck portion of an auto transporter need not meet this requirement for 

reservoir volume.

    S5.1.2.2 Each reservoir shall be capable of withstanding an internal 

hydrostatic pressure of five times the compressor cutout pressure or 500 

psi, whichever is greater, for 10 minutes.

    S5.1.2.3 Each service reservoir system shall be protected against 

loss of air pressure due to failure or leakage in the system between the 

service reservoir and the source of air pressure, by check valves or 

equivalent devices whose proper functioning can be checked without 

disconnecting any air line or fitting.

    S5.1.2.4 Each reservoir shall have a condensate drain valve that can 

be manually operated.

    S5.1.3 Towing vehicle protection system. If the vehicle is intended 

to tow another vehicle equipped with air brakes, a system to protect the 

air pressure in the towing vehicle from the effects of a loss of air 

pressure in the towed vehicle.

    S5.1.4 Pressure gauge. A pressure gauge in each service brake 

system, readily visible to a person seated in the normal driving 

position, that indicates



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the service reservoir system air pressure. The accuracy of the gauge 

shall be within plus or minus 7 percent of the compressor cut-out 

pressure.

    S5.1.5 Warning signal. A signal, other than a pressure gauge, that 

gives a continuous warning to a person in the normal driving position 

when the ignition is in the ``on'' (``run'') position and the air 

pressure in the service reservoir system is below 60 psi. The signal 

shall be either visible within the driver's forward field of view, or 

both audible and visible.

    S5.1.6 Antilock brake system.

    S5.1.6.1(a) Each single-unit vehicle manufactured on or after March 

1, 1998, 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. Wheels on other axles of the vehicle 

may be indirectly controlled by the antilock brake system.

    (b) Each truck tractor manufactured on or after March 1, 1997, 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, with the wheels of at least one axle being 

independently controlled. Wheels on other axles of the vehicle may be 

indirectly controlled by the antilock brake system. A truck tractor 

shall have no more than three wheels controlled by one modulator.

    S5.1.6.2 Antilock malfunction signal and circuit.

    (a) Each truck tractor manufactured on or after March 1, 1997, and 

each single unit vehicle manufactured on or after March 1, 1998, shall 

be equipped with an indicator lamp, mounted in front of and in clear 

view of the driver, which is activated whenever there is a malfunction 

that affects the generation or transmission of response or control 

signals in the vehicle's antilock brake system. The indicator lamp shall 

remain activated as long as such a malfunction exists, whenever the 

ignition (start) switch is in the ``on'' (``run'') position, whether or 

not the engine is running. Each message about the existence of such a 

malfunction shall be stored in the antilock brake system after the 

ignition switch is turned to the ``off'' position and automatically 

reactivated when the ignition switch is again turned to the ``on'' 

(``run'') position. The indicator lamp shall also be activated as a 

check of lamp function whenever the ignition is turned to the ``on'' 

(``run'') position. The indicator lamp shall be deactivated at the end 

of the check of lamp function unless there is a malfunction or a message 

about a malfunction that existed when the key switch was last turned to 

the ``off'' position.

    (b) Each truck tractor manufactured on or after March 1, 2001, and 

each single unit vehicle manufactured on or after March 1, 2001, that is 

equipped to tow another air-braked vehicle, shall be equipped with an 

electrical circuit that is capable of transmitting a malfunction signal 

from the antilock brake system(s) on one or more towed vehicle(s) (e.g., 

trailer(s) and dolly(ies)) to the trailer ABS malfunction lamp in the 

cab of the towing vehicle, and shall have the means for connection of 

this electrical circuit to the towed vehicle. Each such truck tractor 

and single unit vehicle shall also be equipped with an indicator lamp, 

separate from the lamp required in S5.1.6.2(a), mounted in front of and 

in clear view of the driver, which is activated whenever the malfunction 

signal circuit described above receives a signal indicating an ABS 

malfunction on one or more towed vehicle(s). The indicator lamp shall 

remain activated as long as an ABS malfunction signal from one or more 

towed vehicle(s) is present, whenever the ignition (start) switch is in 

the ``on'' (``run'') position, whether or not the engine is running. The 

indicator lamp shall also be activated as a check of lamp function 

whenever the ignition is turned to the ``on'' (``run'') position. The 

indicator lamp shall be deactivated at the end of the check of lamp 

function unless a trailer ABS malfunction signal is present.

    (c) [Reserved]

    S5.1.6.3 Antilock power circuit for towed vehicles. Each truck 

tractor manufactured on or after March 1, 1997, and each single unit 

vehicle manufactured on or after March 1, 1998, that is equipped to tow 

another air-braked vehicle shall be equipped with one or more electrical 

circuits that provide



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continuous power to the antilock system on the towed vehicle or vehicles 

whenever the ignition (start) switch is in the ``on'' (``run'') 

position. Such a circuit shall be adequate to enable the antilock system 

on each towed vehicle to be fully operable.

    S5.1.7 Service brake stop lamp switch. A switch that lights the stop 

lamps when the service brake control is statically depressed to a point 

that produces a pressure of 6 psi or less in the service brake chambers.

    S5.1.8 Brake distribution and automatic adjustment. Each vehicle 

shall be equipped with a service brake system acting on all wheels.

    (a) Brake adjuster. Wear of the service brakes shall be compensated 

for by means of a system of automatic adjustment. When inspected 

pursuant to S5.9, the adjustment of the service brakes shall be within 

the limits recommended by the vehicle manufacturer.

    (b) Brake indicator. For each brake equipped with an external 

automatic adjustment mechanism and having an exposed pushrod, the 

condition of service brake under-adjustment shall be displayed by a 

brake adjustment indicator that is discernible when viewed with 20/40 

vision from a location adjacent to or underneath the vehicle, when 

inspected pursuant to S5.9.

    S5.2 Required equipment for trailers. Each trailer shall have the 

following equipment:

    S5.2.1 Reservoirs. One or more reservoirs to which the air is 

delivered from the towing vehicle.

    S5.2.1.1 The total volume of each service reservoir shall be at 

least eight times the combined volume of all service brake chambers 

serviced by that reservoir. For each brake chamber type having a full 

stroke at least as great as the first number in Column 1 of Table V, but 

no more than the second number in column 1, the volume of each brake 

chamber for purposes of calculating the required total service reservoir 

volume shall be either the number specified in Column 2 of Table V or 

the actual volume of the brake chamber at maximum travel of the brake 

piston or pushrod, whichever is lower. The volume of a brake chamber not 

listed in Table V is the volume of the brake chamber at maximum travel 

of the brake piston or pushrod. The reservoirs on a heavy hauler trailer 

and the trailer portion of an auto transporter need not meet this 

requirement for reservoir volume.

    S5.2.1.2 Each reservoir shall be capable of withstanding an internal 

hydrostatic pressure of 500 psi for 10 minutes.

    S5.2.1.3 Each reservoir shall have a condensate drain valve that can 

be manually operated.

    S5.2.1.4 Each service reservoir shall be protected against loss of 

air pressure due to failure or leakage in the system between the service 

reservoir and its source of air pressure by check valves or equivalent 

devices.

    S5.2.2 Brake distribution and automatic adjustment. Each vehicle 

shall be equipped with a service brake system acting on all wheels.

    (a) Brake adjuster. Wear of the service brakes shall be compensated 

for by means of a system of automatic adjustment. When inspected 

pursuant to S5.9, the adjustment of the service brakes shall be within 

the limits recommended by the vehicle manufacturer.

    (b) Brake indicator. For each brake equipped with an external 

automatic adjustment mechanism and having an exposed pushrod, the 

condition of service brake under-adjustment shall be displayed by a 

brake adjustment indicator in a manner that is discernible when viewed 

with 20/40 vision from a location adjacent to or underneath the vehicle, 

when inspected pursuant to S5.9.

    S5.2.3 Antilock brake system.

    S5.2.3.1(a) Each semitrailer (including a trailer converter dolly) 

manufactured on or after March 1, 1998, shall be equipped with an 

antilock brake system that directly controls the wheels of at least one 

axle of the vehicle. Wheels on other axles of the vehicle may be 

indirectly controlled by the antilock brake system.

    (b) Each full trailer manufactured on or after March 1, 1998, shall 

be equipped with an antilock brake system that directly controls the 

wheels of at least one front axle of the vehicle and at least one rear 

axle of the vehicle. Wheels on other axles of the vehicle may be 

indirectly controlled by the antilock brake system.



[[Page 437]]



    S5.2.3.2 Antilock malfunction signal. Each trailer (including a 

trailer converter dolly) manufactured on or after March 1, 2001, that is 

equipped with an antilock brake system shall be equipped with an 

electrical circuit that is capable of signaling a malfunction in the 

trailer's antilock brake system, and shall have the means for connection 

of this antilock brake system malfunction signal circuit to the towing 

vehicle. The electrical circuit need not be separate or dedicated 

exclusively to this malfunction signaling function. The signal shall be 

present whenever there is a malfunction that affects the generation or 

transmission of response or control signals in the trailer's antilock 

brake system. The signal shall remain present as long as the malfunction 

exists, whenever power is supplied to the antilock brake system. Each 

message about the existence of such a malfunction shall be stored in the 

antilock brake system whenever power is no longer supplied to the 

system, and the malfunction signal shall be automatically reactivated 

whenever power is again supplied to the trailer's antilock brake system. 

In addition, each trailer manufactured on or after March 1, 2001, that 

is designed to tow other air-brake equipped trailers shall be capable of 

transmitting a malfunction signal from the antilock brake systems of 

additional trailers it tows to the vehicle towing it.

    S5.2.3.3 Antilock malfunction indicator.

    (a) In addition to the requirements of S5.2.3.2, each trailer and 

trailer converter dolly manufactured on or after March 1, 1998, and 

before March 1, 2009, shall be equipped with an external antilock 

malfunction indicator lamp that meets the requirements of S5.2.3.3 (b) 

through (d).

    (b)(1) The lamp shall be designed to conform to the performance 

requirements of Society of Automotive Engineers (SAE) Recommended 

Practice J592 JUN92, or J592e, July 1972, Clearance, Side Marker, and 

Identification Lamps, for combination, clearance, and side marker lamps, 

which are marked with a ``PC'' or ``P2'' on the lens or housing, in 

accordance with SAE J759 Jan 95, Lighting Identification Code. SAE J592 

June 92, SAE J592e July 1972, and SAE J759 January 1995, are 

incorporated by reference and thereby are made part of this standard. 

The Director of the Federal Register approved the material incorporated 

by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. 

Copies of the material may be inspected at NHTSA's Docket Section, 400 

Seventh Street, SW., room 5109, Washington, DC, or at the National 

Archives and Records Administration (NARA). For information on the 

availability of this material at NARA, call 202-741-6030, or go to: 

http://www.archives.gov/federal--register/code--of--federal--

regulations/ibr--locations.html.

    (2) The color of the lamp shall be yellow.

    (3) The letters ``ABS'' shall be permanently molded, stamped, or 

otherwise marked or labeled in letters not less than 10 mm (0.4 inches) 

high on the lamp lens or its housing to identify the function of the 

lamp. Alternatively, the letters ``ABS'' may be painted on the trailer 

body or dolly or a plaque with the letters ``ABS'' may be affixed to the 

trailer body or converter dolly; the letters ``ABS'' shall be not less 

than 25 mm (1 inch) high. A portion of one of the letters in the 

alternative identification shall be not more than 150 mm (5.9 inches) 

from the edge of the lamp lens.

    (c) Location requirements. (1) Each trailer that is not a trailer 

converter dolly shall be equipped with a lamp mounted on a permanent 

structure on the left side of the trailer as viewed from the rear, no 

closer than 150 mm (5.9 inches), and no farther than 600 mm (23.6 

inches) from the red rear side marker lamp, when measured between the 

closest edge of the effective projected luminous lens area of each lamp.

    (2) Each trailer converter dolly shall be equipped with a lamp 

mounted on a permanent structure of the dolly so that the lamp is not 

less than 375 mm (14.8 inches) above the road surface when measured from 

the center of the lamp with the dolly at curb weight. When a person, 

standing 3 meters (9.8 feet) from the lamp, views the lamp from a 

perspective perpendicular to the vehicle's centerline, no portion of the 

lamp shall be obscured by any structure on the dolly.



[[Page 438]]



    (3) Each trailer that is not a trailer converter dolly and on which 

the malfunction indicator lamp cannot be placed within the location 

specified in S5.2.3.3(c)(1) shall be equipped with a lamp mounted on a 

permanent structure on the left side of the trailer as viewed from the 

rear, near the red rear side marker lamp or on the front face of the 

left rear fender of a trailer equipped with fenders.

    (d) The lamp shall be illuminated whenever power is supplied to the 

antilock brake system and there is a malfunction that affects the 

generation or transmission of response or control signals in the 

trailer's antilock brake system. The lamp shall remain illuminated as 

long as such a malfunction exists and power is supplied to the antilock 

brake system. Each message about the existence of such a malfunction 

shall be stored in the antilock brake system whenever power is no longer 

supplied to the system. The lamp shall be automatically reactivated when 

power is again supplied to the trailer's antilock brake system. The lamp 

shall also be activated as a check of lamp function whenever power is 

first supplied to the antilock brake system and the vehicle is 

stationary. The lamp shall be deactivated at the end of the check of 

lamp function, unless there is a malfunction or a message about a 

malfunction that existed when power was last supplied to the antilock 

brake system.

    S5.3 Service brakes--road tests. The service brake system on each 

truck tractor shall, under the conditions of S6, meet the requirements 

of S5.3.1, S5.3.3, S5.3.4, and S5.3.6, when tested without adjustments 

other than those specified in this standard. The service brake system on 

each bus and truck (other than a truck tractor shall) manufactured 

before July 1, 2005 and each bus and truck (other than a truck tractor) 

manufactured in two or more stages shall, under the conditions of S6, 

meet the requirements of S5.3.1, S5.3.3, and S5.3.4 when tested without 

adjustments other than those specified in this standard. The service 

brake system on each bus and truck (other than a truck tractor) 

manufactured on or after July 1, 2005 and each bus and truck (other than 

a truck tractor) manufactured in two or more stages on or after July 1, 

2006 shall, under the conditions of S6, meet the requirements of S5.3.1, 

S5.3.3, S5.3.4, and S5.3.6, when tested without adjustments other than 

those specified in this standard. The service brake system on each 

trailer shall, under the conditions of S6, meet the requirements of 

S5.3.3, S5.3.4, and S5.3.5 when tested without adjustments other than 

those specified in this standard. However, a heavy hauler trailer and 

the truck and trailer portions of an auto transporter need not met the 

requirements of S5.3.

    S5.3.1 Stopping distance--trucks and buses. When stopped six times 

for each combination of vehicle type, weight, and speed specified in 

S5.3.1.1, in the sequence specified in Table I, each truck tractor 

manufactured on or after March 1, 1997, and each single unit vehicle 

manufactured on or after March 1, 1998, shall stop at least once in not 

more than the distance specified in Table II, measured from the point at 

which movement of the service brake control begins, without any part of 

the vehicle leaving the roadway, and with wheel lockup permitted only as 

follows:

    (a) At vehicle speeds above 20 mph, any wheel on a nonsteerable axle 

other than the two rearmost nonliftable, nonsteerable axles may lock up, 

for any duration. The wheels on the two rearmost nonliftable, 

nonsteerable axles may lock up according to S5.3.1(b).

    (b) At vehicle speeds above 20 mph, one wheel on any axle or two 

wheels on any tandem may lock up for any duration.

    (c) At vehicle speeds above 20 mph, any wheel not permitted to lock 

in S5.3.1 (a) or (b) may lock up repeatedly, with each lockup occurring 

for a duration of one second or less.

    (d) At vehicle speeds of 20 mph or less, any wheel may lock up for 

any duration.

    S5.3.1.1 Stop the vehicle from 60 mph on a surface with a peak 

friction coefficient of 0.9 with the vehicle loaded as follows:

    (a) Loaded to its GVWR so that the load on each axle, measured at 

the tire-



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ground interface, is most nearly proportional to the axles' respective 

GAWRs, without exceeding the GAWR of any axle.

    (b) In the truck tractor only configuration plus up to 500 lbs. or, 

at the manufacturer's option, at its unloaded weight plus up to 500 lbs. 

(including driver and instrumentation) and plus not more than an 

additional 1,000 lbs. for a roll bar structure on the vehicle, and

    (c) At its unloaded vehicle weight (except for truck tractors) plus 

up to 500 lbs. (including driver and instrumentation) or, at the 

manufacturer's option, at its unloaded weight plus up to 500 lbs. 

(including driver and instrumentation) plus not more than an additional 

1,000 lbs. for a roll bar structure on the vehicle. If the speed 

attainable in two miles is less than 60 mph, the vehicle shall stop from 

a speed in Table II that is four to eight mph less than the speed 

attainable in two miles.

    S5.3.2 [Reserved]

    S5.3.3 Brake actuation time. Each service brake system shall meet 

the requirements of S5.3.3.1 (a) and (b).

    S5.3.3.1(a) With an initial service reservoir system air pressure of 

100 psi, the air pressure in each brake chamber shall, when measured 

from the first movement of the service brake control, reach 60 psi in 

not more than 0.45 second in the case of trucks and buses, 0.50 second 

in the case of trailers, other than trailer converter dollies, designed 

to tow another vehicle equipped with air brakes, 0.55 second in the case 

of trailer converter dollies, and 0.60 second in the case of trailers 

other than trailers designed to tow another vehicle equipped with air 

brakes. A vehicle designed to tow another vehicle equipped with air 

brakes shall meet the above actuation time requirement with a 50-cubic-

inch test reservoir connected to the control line output coupling. A 

trailer, including a trailer converter dolly, shall meet the above 

actuation time requirement with its control line input coupling 

connected to the test rig shown in Figure 1.

    (b) For a vehicle that is designed to tow another vehicle equipped 

with air brakes, the pressure in the 50-cubic-inch test reservoir 

referred to in S5.3.3.1(a) shall, when measured from the first movement 

of the service brake control, reach 60 psi not later than the time the 

fastest brake chamber on the vehicle reaches 60 psi or, at the option of 

the manufacturer, in not more than 0.35 second in the case of trucks and 

buses, 0.55 second in the case of trailer converter dollies, and 0.50 

second in the case of trailers other than trailer converter dollies.

    S5.3.4 Brake release time. Each service brake system shall meet the 

requirements of S5.3.4.1 (a) and (b).

    S5.3.4.1(a) With an initial service brake chamber air pressure of 95 

psi, the air pressure in each brake chamber shall, when measured from 

the first movement of the service brake control, fall to 5 psi in not 

more than 0.55 second in the case of trucks and buses; 1.00 second in 

the case of trailers, other than trailer converter dollies, designed to 

tow another vehicle equipped with air brakes; 1.10 seconds in the case 

of trailer converter dollies; and 1.20 seconds in the case of trailers 

other than trailers designed to tow another vehicle equipped with air 

brakes. A vehicle designated to tow another vehicle equipped with air 

brakes shall meet the above release time requirement with a 50-cubic-

inch test reservoir connected to the control line output coupling. A 

trailer, including a trailer converter dolly, shall meet the above 

release time requirement with its control line input coupling connected 

to the test rig shown in Figure 1.

    (b) For vehicles designed to tow another vehicle equipped with air 

brakes, the pressure in the 50-cubic-inch test reservoir referred to in 

S5.3.4.1(a) shall, when measured from the first movement of the service 

brake control, fall to 5 psi in not more than 0.75 seconds in the case 

of trucks and buses, 1.10 seconds in the case of trailer converter 

dollies, and 1.00 seconds in the case of trailers other than trailer 

converter dollies.

    S5.3.5 Control signal pressure differential--converter dollies and 

trailers designed to tow another vehicle equipped with air brakes.

    (a) For a trailer designed to tow another vehicle equipped with air 

brakes, the pressure differential between the control line input 

coupling and a 50-cubic-inch test reservoir attached to



[[Page 440]]



the control line output coupling shall not exceed the values specified 

in S5.3.5(a) (1), (2), and (3) under the conditions specified in 

S5.3.5(b) (1) through (4):

    (1) 1 psi at all input pressures equal to or greater than 5 psi, but 

not greater than 20 psi;

    (2) 2 psi at all input pressures equal to or greater than 20 psi but 

not greater than 40 psi; and

    (3) Not more than a 5-percent differential at any input pressure 

equal to or greater than 40 psi.

    (b) The requirements in S5.3.5(a) shall be met--

    (1) When the pressure at the input coupling is steady, increasing or 

decreasing;

    (2) When air is applied to or released from the control line input 

coupling using the trailer test rig shown in Figure 1;

    (3) With a fixed orifice consisting of a 0.0180 inch diameter hole 

(no. 77 drill bit) in a 0.032 inch thick disc installed in the control 

line between the trailer test rig coupling and the vehicle's control 

line input coupling; and

    (4) Operating the trailer test rig in the same manner and under the 

same conditions as it is operated during testing to measure brake 

actuation and release times, as specified in S5.3.3 and S5.3.4, except 

for the installation of the orifice in the control line to restrict 

airflow rate.

    S5.3.6 Stability and control during braking--trucks and buses. When 

stopped four consecutive times for each combination of weight, speed, 

and road conditions specified in S5.3.6.1 and S5.3.6.2, each truck 

tractor shall stop at least three times within the 12-foot lane, without 

any part of the vehicle leaving the roadway. When stopped four 

consecutive times for each combination of weight, speed, and road 

conditions specified in S5.3.6.1 and S5.3.6.2, each bus and truck (other 

than a truck tractor) manufactured on or after July 1, 2005, and each 

bus and truck (other than a truck tractor) manufactured in two or more 

stages on or after July 1, 2006, shall stop at least three times within 

the 12-foot lane, without any part of the vehicle leaving the roadway.

    S5.3.6.1 Using a full-treadle brake application for the duration of 

the stop, stop the vehicle from 30 mph or 75 percent of the maximum 

drive-through speed, whichever is less, on a 500-foot radius curved 

roadway with a wet level surface having a peak friction coefficient of 

0.5 when measured on a straight or curved section of the curved roadway 

using an American Society for Testing and Materials (ASTM) E1136 

standard reference tire, in accordance with ASTM Method E1337-90, at a 

speed of 40 mph, with water delivery.

    S5.3.6.2 Stop the vehicle, with the vehicle:

    (a) Loaded to its GVWR, for a truck tractor, and

    (b) At its unloaded weight plus up to 500 pounds (including driver 

and instrumentation), or at the manufacturer's option, at its unloaded 

weight plus up to 500 pounds (including driver and instrumentation) and 

plus not more than an additional 1000 pounds for a roll bar structure on 

the vehicle, for a truck, bus, or truck tractor.

    S5.4 Service brake system--dynamometer tests. When tested without 

prior road testing, under the conditions of S6.2, each brake assembly 

shall meet the requirements of S5.4.1, S5.4.2, and S5.4.3 when tested in 

sequence and without adjustments other than those specified in the 

standard. For purposes of the requirements of S5.4.2 and S5.4.3, an 

average deceleration rate is the change in velocity divided by the 

deceleration time measured from the onset of deceleration.

    S5.4.1 Brake retardation force. The sum of the retardation forces 

exerted by the brakes on each vehicle designed to be towed by another 

vehicle equipped with air brakes shall be such that the quotient sum of 

the brake retardation forces / sum of GAWR's relative to brake chamber 

air pressure, and shall have values not less than those shown in Column 

1 of Table III. Retardation force shall be determined as follows:

    S5.4.1.1 After burnishing the brake pursuant to S6.2.6, retain the 

brake assembly on the inertia dynamometer. With an initial brake 

temperature between 125 [deg]F. and 200 [deg]F., conduct a stop from 50 

m.p.h., maintaining brake chamber air pressure at a constant 20



[[Page 441]]



psi. Measure the average torque exerted by the brake from the time the 

specified air pressure is reached until the brake stops and divide by 

the static loaded tire radius specified by the tire manufacturer to 

determine the retardation force. Repeat the procedure six times, 

increasing the brake chamber air pressure by 10 psi each time. After 

each stop, rotate the brake drum or disc until the temperature of the 

brake falls to between 125 [deg]F. and 200 [deg]F.

    S5.4.2 Brake power. When mounted on an inertia dynamometer, each 

brake shall be capable of making 10 consecutive decelerations at an 

average rate of 9 f.p.s.p.s. from 50 m.p.h. to 15 m.p.h., at equal 

intervals of 72 seconds, and shall be capable of decelerating to a stop 

from 20 m.p.h. at an average deceleration rate of 14 f.p.s.p.s. 1 minute 

after the 10th deceleration. The series of decelerations shall be 

conducted as follows:

    S5.4.2.1 With an initial brake temperature between 150 [deg]F. and 

200 [deg]F. for the first brake application, and the drum or disc 

rotating at a speed equivalent to 50 m.p.h., apply the brake and 

decelerate at an average deceleration rate of 9 f.p.s.p.s. to 15 m.p.h. 

Upon reaching 15 m.p.h., accelerate to 50 m.p.h. and apply the brake for 

a second time 72 seconds after the start of the first application. 

Repeat the cycle until 10 decelerations have been made. The service line 

air pressure shall not exceed 100 psi during any deceleration.

    S5.4.2.2 One minute after the end of the last deceleration required 

by S5.4.2.1 and with the drum or disc rotating at a speed of 20 m.p.h., 

decelerate to a stop at an average deceleration rate of 14 f.p.s.p.s.

    S5.4.3 Brake recovery. Except as provided in S5.4.3(a) and (b), 

starting two minutes after completing the tests required by S5.4.2, a 

vehicle's brake shall be capable of making 20 consecutive stops from 30 

mph at an average deceleration rate of 12 f.p.s.p.s., at equal intervals 

of one minute measured from the start of each brake application. The 

service line air pressure needed to attain a rate of 12 f.p.s.p.s. shall 

be not more than 85 lb/in\2\, and not less than 20lb/in2 for 

a brake not subject to the control of an antilock system, or 12 lb/

in2 for a brake subject to the control of an antilock system.

    (a) Notwithstanding S5.4.3, neither front axle brake of a truck-

tractor is subject to the requirements set forth in S5.4.3.

    (b) Notwithstanding S5.4.3, neither front axle brake of a bus or a 

truck other than a truck-tractor is subject to the requirement set forth 

in S5.4.3 prohibiting the service line air pressure from being less than 

20 lb/in2 for a brake not subject to the control of an 

antilock system or 12 lb/in2 for a brake subject to the 

control of an antilock system.

    S5.5 Antilock system.

    S5.5.1 Antilock system malfunction. On a truck tractor manufactured 

on or after March 1, 1997, that is equipped with an antilock brake 

system and a single unit vehicle manufactured on or after March 1, 1998, 

that is equipped with an antilock brake system, a malfunction that 

affects the generation or transmission of response or control signals of 

any part of the antilock system shall not increase the actuation and 

release times of the service brakes.

    S5.5.2 Antilock system power--trailers. On a trailer (including a 

trailer converter dolly) manufactured on or after March 1, 1998, that is 

equipped with an antilock system that requires electrical power for 

operation, the power shall be obtained from the towing vehicle through 

one or more electrical circuits which provide continuous power whenever 

the powered vehicle's ignition (start) switch is in the ``on'' (``run'') 

position. The antilock system shall automatically receive power from the 

stoplamp circuit, if the primary circuit or circuits are not 

functioning. Each trailer (including a trailer converter dolly) 

manufactured on or after March 1, 1998, that is equipped to tow another 

air-braked vehicle shall be equipped with one or more circuits which 

provide continuous power to the antilock system on the vehicle(s) it 

tows. Such circuits shall be adequate to enable the antilock system on 

each towed vehicle to be fully operable.

    S5.6 Parking brakes.

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

than a trailer converter dolly shall have a parking



[[Page 442]]



brake system that under the conditions of S6.1 meets the requirements 

of:

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

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

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

brake systems which incorporate a common diaphragm, the performance 

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

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

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

option does not affect the performance requirements specified in S5.6(a) 

which apply with single leakage-type failures other than failures in a 

common diaphragm.

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

agricultural commodity trailer, heavy hauler trailer, or pulpwood 

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

of the requirements of S5.6(a).

    S5.6.1 Static retardation force. With all other brakes made 

inoperative, during a static drawbar pull in a forward or rearward 

direction, the static retardation force produced by the application of 

the parking brakes shall be:

    (a) In the case of a vehicle other than a truck-tractor that is 

equipped with more than two axles, such that the quotient static 

retardation force/GAWR is not less than 0.28 for any axle other than a 

steerable front axle; and

    (b) In the case of a truck-tractor that is equipped with more than 

two axles, such that the quotient static retardation force/GVWR is not 

less than 0.14.

    S5.6.2 Grade holding. With all parking brakes applied, the vehicle 

shall remain stationary facing uphill and facing downhill on a smooth, 

dry portland cement concrete roadway with a 20-percent grade, both

    (a) When loaded to its GVWR, and

    (b) At its unloaded vehicle weight plus 1500 pounds (including 

driver and instrumentation and roll bar).

    S5.6.3 Application and holding. Each parking brake system shall meet 

the requirements of S5.6.3.1 through S5.6.3.4.

    S5.6.3.1 The parking brake system shall be capable of achieving the 

minimum performance specified either in S5.6.1 or S5.6.2 with any single 

leakage-type failure, in any other brake system, of a part designed to 

contain compressed air or brake fluid (excluding failure of a component 

of a brake chamber housing but including failure of any brake chamber 

diaphragm that is part of any other brake system including a diaphragm 

which is common to the parking brake system and any other brake system), 

when the pressures in the vehicle's parking brake chambers are at the 

levels determined in S5.6.3.4.

    S5.6.3.2 A mechanical means shall be provided that, after a parking 

brake application is made with the pressures in the vehicle's parking 

brake chambers at the levels determined in S5.6.3.4, and all air and 

fluid pressures in the vehicle's braking systems are then bled down to 

zero, and without using electrical power, holds the parking brake 

application with sufficient parking retardation force to meet the 

minimum performance specified in S5.6.3.1 and in either S5.6.1 or 

S5.6.2.

    S5.6.3.3 For trucks and buses, with an initial reservoir system 

pressure of 100 psi and, if designed to tow a vehicle equipped with air 

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

coupling, no later than three seconds from the time of actuation of the 

parking brake control, the mechanical means referred to in S5.6.3.2 

shall be actuated. For trailers, with the supply line initially 

pressurized to 100 psi using the supply line portion of the trailer test 

rig (Figure 1) and, if designed to tow a vehicle equipped with air 

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

line coupling, no later than three seconds from the time venting to the 

atmosphere of the front supply line coupling is initiated, the 

mechanical means referred to in S5.6.3.2 shall be actuated. This 

requirement shall be met for trucks, buses and trailers both with and 

without any single leakage-type failure, in any other brake system, of a 

part designed to contain compressed air or brake fluid (consistent with 

the parenthetical phrase specified in S5.6.3.1).

    S5.6.3.4 The parking brake chamber pressures for S5.6.3.1 and 

S5.6.3.2 are determined as follows. For trucks and



[[Page 443]]



buses, with an initial reservoir system pressure of 100 psi and, if 

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

test reservoir connected to the supply line coupling, any single leakage 

type failure, in any other brake system, of a part designed to contain 

compressed air or brake fluid (consistent with the parenthetical phrase 

specified in S5.6.3.1), is introduced in the brake system. The parking 

brake control is actuated and the pressures in the vehicle's parking 

brake chambers are measured three seconds after that actuation is 

initiated. For trailers, with the supply line initially pressurized to 

100 psi using the supply line portion of the trailer test rig (Figure 1) 

and, if designed to tow a vehicle equipped with air brakes, with a 50 

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

any single leakage type failure, in any other brake system, of a part 

designed to contain compressed air or brake fluid (consistent with the 

parenthetical phrase specified in S5.6.3.1), is introduced in the brake 

system. The front supply line coupling is vented to the atmosphere and 

the pressures in the vehicle's parking brake chambers are measured three 

seconds after that venting is initiated.

    S5.6.4 Parking brake control--trucks and buses. The parking brake 

control shall be separate from the service brake control. It shall be 

operable by a person seated in the normal driving position. The control 

shall be identified in a manner that specifies the method of control 

operation. The parking brake control shall control the parking brakes of 

the vehicle and of any air braked vehicle that it is designed to tow.

    S5.6.5 Release Performance. Each parking brake system shall meet the 

requirements specified in S5.6.5.1 through S5.6.5.4.

    S5.6.5.1 For trucks and buses, with initial conditions as specified 

in S5.6.5.2, at all times after an application actuation of the parking 

brake control, and with any subsequent level of pressure, or combination 

of levels of pressure, in the reservoirs of any of the vehicle's brake 

systems, no reduction in parking brake retardation force shall result 

from a release actuation of the parking brake control unless the parking 

brakes are capable, after such release, of being reapplied at a level 

meeting the minimum performance specified either in S5.6.1 or S5.6.2. 

This requirement shall be met both with and without the engine on, and 

with and without single leakage-type failure, in any other brake system, 

of a part designed to contain compressed air or brake fluid (consistent 

with the parenthetical phrase specified in S5.6.3.1).

    S5.6.5.2 The initial conditions for S5.6.5.1 are as follows: The 

reservoir system pressure is 100 psi. If the vehicle is designed to tow 

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

connected to the supply line coupling.

    S5.6.5.3 For trailers, with initial conditions as specified in 

S5.6.5.4, at all times after actuation of the parking brakes by venting 

the front supply line coupling to the atmosphere, and with any 

subsequent level of pressure, or combination of levels of pressure, in 

the reservoirs of any of the vehicle's brake systems, the parking brakes 

shall not be releasable by repressurizing the supply line using the 

supply line portion of the trailer test rig (Figure 1) to any pressure 

above 70 psi, unless the parking brakes are capable, after such release, 

of reapplication by subsequent venting of the front supply line coupling 

to the atmosphere, at a level meeting the minimum performance specified 

either in S5.6.1 or S5.6.2. This requirement shall be met both with and 

without any single leakage-type failure, in any other brake system, of a 

part designed to contain compressed air or brake fluid (consistent with 

the parenthetical phrase specified in S5.6.3.1).

    S5.6.5.4 The initial conditions for S5.6.5.3 are as follows: The 

reservoir system and supply line are pressurized to 100 psi, using the 

supply line portion of the trailer test rig (Figure 1). If the vehicle 

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

test reservoir is connected to the rear supply line coupling.

    S5.6.6 Accumulation of actuation energy. Each parking brake system 

shall meet the requirements specified in S5.6.6.1 through S5.6.6.6.



[[Page 444]]



    S5.6.6.1 For trucks and buses, with initial conditions as specified 

in S5.6.6.2, the parking brake system shall be capable of meeting the 

minimum performance specified either in S5.6.1 or S5.6.2, with any 

single leakage-type failure, in any other brake system, of a part 

designed to contain compressed air or brake fluid (consistent with the 

parenthetical phrase specified in S5.6.3.1) at the conclusion of the 

test sequence specified in S5.6.6.3.

    S5.6.6.2 The initial conditions for S5.6.6.1 are as follows: The 

engine is on. The reservoir system pressure is 100 psi. If the vehicle 

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

test reservoir is connected to the supply line coupling.

    S5.6.6.3 The test sequence for S5.6.6.1 is as follows: The engine is 

turned off. Any single leakage type failure, in any other brake system, 

of a part designed to contain compressed air or brake fluid (consistent 

with the parenthetical phrase specified in S5.6.3.1), is then introduced 

in the brake system. An application actuation of the parking brake 

control is then made. Thirty seconds after such actuation, a release 

actuation of the parking brake control is made. Thirty seconds after the 

release actuation, a final application actuation of the parking brake 

control is made.

    S5.6.6.4 For trailers, with initial conditions as specified in 

S5.6.6.5, the parking brake system shall be capable of meeting the 

minimum performance specified either in S5.6.1 or S5.6.2, with any 

single leakage-type failure, in any other brake system, of a part 

designed to contain compressed air or brake fluid (consistent with the 

parenthetical phrase specified in S5.6.3.1), at the conclusion of the 

test sequence specified in S5.6.6.6.

    S5.6.6.5 The initial conditions for S5.6.6.4 are as follows: The 

reservoir system and supply line are pressurized to 100 psi, using the 

supply line portion of the trailer test rig (Figure 1). If the vehicle 

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

test reservoir is connected to the rear supply line coupling.

    S5.6.6.6 The test sequence for S5.6.6.4 is as follows. Any single 

leakage type failure, in any other brake system, of a part designed to 

contain compressed air or brake fluid (consistent with the parenthetical 

phrase specified in S5.6.3.1), is introduced in the brake system. The 

front supply line coupling is vented to the atmosphere. Thirty seconds 

after the initiation of such venting, the supply line is repressurized 

with the trailer test rig (Figure 1). Thirty seconds after the 

initiation of such repressurizing of the supply line, the front supply 

line is vented to the atmosphere. This procedure is conducted either by 

connection and disconnection of the supply line coupling or by use of a 

valve installed in the supply line portion of the trailer test rig near 

the supply line coupling.

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

Equivalent level of leakage from the air chamber containing that 

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

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

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

containing that diaphragm) according to the procedures set forth in 

S5.6.7.1 through S5.6.7.2.3.

    S5.6.7.1 Trucks and buses.

    S5.6.7.1.1 According to the following procedure, determine the 

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

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

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

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

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

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

reservoir connected to the supply line coupling, introduce a leakage-

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

chamber containing that diaphragm). Apply the parking brakes by making 

an application actuation of the parking brake control. Reduce the 

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

and allow it to idle, and allow the pressures in the vehicle's 

reservoirs to rise until they stabilize or until the compressor shut-off 

point is reached. At that time, make a release actuation of the parking 

brake control,



[[Page 445]]



and determine whether all of the mechanical means referred to in 

S5.6.3.2 continue to be actuated and hold the parking brake applications 

with sufficient parking retardation force to meet the minimum 

performance specified in either S5.6.1 or S5.6.2. Repeat this procedure 

with progressively decreasing or increasing levels (whichever is 

applicable) of leakage-type diaphragm failures or equivalent leakages, 

to determine the minimum level of common diaphragm leakage-type failure 

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

diaphragm) at which all of the mechanical means referred to in S5.6.3.2 

continue to be actuated and hold the parking brake applications with 

sufficient parking retardation forces to meet the minimum performance 

specified in either S5.6.1 or S5.6.2.

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

equivalent level of leakage from the air chamber containing that 

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

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

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

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

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

reservoir connected to the supply line coupling, make an application 

actuation of the parking brake control. Determine the maximum reservoir 

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

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

that parking brake application.

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

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

chamber containing that diaphragm) that results in a maximum reservoir 

leakage rate that is three times the threshold maximum reservoir leakage 

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

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

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

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

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

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

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

the vehicle's reservoirs that results after that parking brake 

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

equivalent level of leakage from the air chamber containing that 

diaphragm) associated with this reservoir leakage rate is the level that 

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

    S5.6.7.2 Trailers.

    S5.6.7.2.1 According to the following procedure, determine the 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

actuated and hold the parking brake applications with sufficient parking 

retardation forces to meet the minimum performance specified in either 

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

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

failures or equivalent leakages, to determine the minimum level of 

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

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



[[Page 446]]



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

hold the parking brake applications with sufficient parking retardation 

forces to meet the minimum performance specified in either S5.6.1 or 

S5.6.2.

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

equivalent level of leakage from the air chamber containing that 

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

determine the threshold maximum reservoir leakage rate (in psi per 

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

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

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

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

make a parking brake application by venting the front supply line 

coupling to the atmosphere. Determine the maximum reservoir leakage rate 

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

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

parking brake application.

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

the common diaphragm (or equivalent leakage from the air chamber 

containing that diaphragm) that results in a maximum reservoir leakage 

rate that is three times the threshold maximum reservoir leakage rate 

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

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

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

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

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

line coupling to the atmosphere. Determine the maximum reservoir leakage 

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

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

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

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

that diaphragm) associated with this reservoir leakage rate is the level 

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

    S5.7 Emergency brake system for trucks and buses. Each vehicle shall 

be equipped with an emergency brake system which, under the conditions 

of S6.1, conforms to the requirements of S5.7.1 through S5.7.3. However, 

the truck portion of an auto transporter need not meet the road test 

requirements of S5.7.1 and S5.7.3.

    S5.7.1 Emergency brake system performance. When stopped six times 

for each combination of weight and speed specified in S5.3.1.1, except 

for a loaded truck tractor with an unbraked control trailer, on a road 

surface having a PFC of 0.9, with a single failure in the service brake 

system of a part designed to contain compressed air or brake fluid 

(except failure of a common valve, manifold, brake fluid housing, or 

brake chamber housing), the vehicle shall stop at least once in not more 

than the distance specified in Column 5 of Table II, measured from the 

point at which movement of the service brake control begins, except that 

a truck-tractor tested at its unloaded vehicle weight plus up to 1500 

pounds shall stop at least once in not more than the distance specified 

in Column 6 of Table II. The stop shall be made without any part of the 

vehicle leaving the roadway, and with unlimited wheel lockup permitted 

at any speed.

    S5.7.2 Emergency brake system operation. The emergency brake system 

shall be applied and released, and be capable of modulation, by means of 

the service brake control.

    S5.7.3 Towing vehicle emergency brake requirements. In addition to 

meeting the other requirements of S5.7, a vehicle designed to tow 

another vehicle equipped with air brakes shall--

    (a) In the case of a truck-tractor in the unloaded condition and a 

single unit truck which is capable of towing an airbrake equipped 

vehicle and is loaded to GVWR, be capable of meeting the requirements of 

S5.7.1 by operation of the service brake control only, with the trailer 

air supply line and air control line from the towing vehicle vented to 

the atmosphere in accordance with S6.1.14;

    (b) Be capable of modulating the air in the supply or control line 

to the trailer by means of the service brake



[[Page 447]]



control with a single failure in the towing vehicle service brake system 

as specified in S5.7.1.

    (c) [Reserved]

    S5.8 Emergency brakes for trailers. Each trailer shall meet the 

requirements of S5.8.1 through S5.8.3.

    S5.8.1 Emergency braking capability. Each trailer other than a 

trailer converter dolly shall have a parking brake system that conforms 

to S5.6 and that applies with the force specified in S5.6.1 or S5.6.2 

when the air pressure in the supply line is at atmospheric pressure. A 

trailer converter dolly shall have, at the manufacturer's option--

    (a) A parking brake system that conforms to S5.6 and that applies 

with the force specified in S5.6.1 or S5.6.2 when the air pressure in 

the supply line is at atmospheric pressure, or

    (b) An emergency system that automatically applies the service 

brakes when the service reservoir is at any pressure above 20 lb/in\2\ 

and the supply line is at atmospheric pressure. However, any 

agricultural commodity trailer, heavy hauler trailer, or pulpwood 

trailer shall meet the requirements of S5.8.1 or, at the option of the 

manufacturer, the requirements of Sec. 393.43 of this title.

    S5.8.2 Supply line pressure retention. Any single leakage type 

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

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

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

line falling below 70 psi, measured at the forward trailer supply 

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

requirement with its brake system connected to the trailer test rig 

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

initially pressurized to 100 psi and the regulator of the trailer test 

rig set at 100 psi; except that a trailer equipped with an air-applied, 

mechanically-held parking brake system and not designed to tow a vehicle 

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

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

    S5.8.3 Automatic application of parking brakes. With an initial 

reservoir system pressure of 100 psi and initial supply line pressure of 

100 psi, and if designed to tow a vehicle equipped with air brakes, with 

a 50 cubic inch test reservoir connected to the rear supply line 

coupling, and with any subsequent single leakage type failure in any 

other brake system, of a part designed to contain compressed air or 

brake fluid (consistent with the parenthetical phrase specified in 

S5.6.3.1), whenever the air pressure in the supply line is 70 psi or 

higher, the parking brakes shall not provide any brake retardation as a 

result of complete or partial automatic application of the parking 

brakes.

    S5.8.4 Automatic application of air-applied, mechanically held 

parking brakes. With its brake system connected to the supply line 

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

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

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

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

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

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

complete or partial automatic application of the parking brakes.

    S5.9 Final inspection. Inspect the service brake system for the 

condition of adjustment and for the brake indicator display in 

accordance with S5.1.8 and S5.2.2.

    S6. Conditions. The requirements of S5 shall be met by a vehicle 

when it is tested according to the conditions set in this S6, without 

replacing any brake system part or making any adjustments to the brake 

system except as specified. Unless otherwise specified, where a range of 

conditions is specified, the vehicle must be capable of meeting the 

requirements at all points within the range. On vehicles equipped with 

automatic brake adjusters, the automatic brake adjusters must remain 

activated at all times. Compliance of vehicles manufactured in two or 

more stages may, at the option of the final-stage manufacturer, be 

demonstrated to comply with this standard by adherence to the 

instructions of the incomplete vehicle manufacturer provided with the 

vehicle in accordance with Sec. 568.4(a)(7)(ii) and Sec. 568.5 of 

title 49 of the Code of Federal Regulations.



[[Page 448]]



    S6.1 Road test conditions.

    S6.1.1 Except as otherwise specified, the vehicle is loaded to its 

GVWR, distributed proportionally to its GAWRs. During the burnish 

procedure specified in S6.1.8, truck tractors shall be loaded to their 

GVWR, by coupling them to an unbraked flatbed semitrailer, which 

semitrailer shall be loaded so that the weight of the tractor-trailer 

combination equals the GVWR of the truck tractor. The load on the 

unbraked flatbed semitrailer shall be located so that the truck 

tractor's wheels do not lock during burnish.

    S6.1.2 The inflation pressure is as specified by the vehicle 

manufacturer for the GVWR.

    S6.1.3 Unless otherwise specified, the transmission selector control 

is in neutral or the clutch is disengaged during all decelerations and 

during static parking brake tests.

    S6.1.4 All vehicle openings (doors, windows, hood, trunk, cargo 

doors, etc.) are in a closed position except as required for 

instrumentation purposes.

    S6.1.5 The ambient temperature is between 32 [deg]F. and 100 [deg]F.

    S6.1.6 The wind velocity is zero.

    S6.1.7 Unless otherwise specified, stopping tests are conducted on a 

12-foot wide level, straight roadway having a peak friction coefficient 

of 0.9. For road tests in S5.3, the vehicle is aligned in the center of 

the roadway at the beginning of a stop. Peak friction coefficient is 

measured using an ASTM E1136 standard reference test tire in accordance 

with ASTM method E1337-90, at a speed of 40 mph, without water delivery 

for the surface with PFC of 0.9, and with water delivery for the surface 

with PFC of 0.5.

    S6.1.8 For vehicles with parking brake systems not utilizing the 

service brake friction elements, burnish the friction elements of such 

systems prior to the parking brake test according to the manufacturer's 

recommendations. For vehicles with parking brake systems utilizing the 

service brake friction elements, burnish the brakes as follows: With the 

transmission in the highest gear appropriate for a speed of 40 mph, make 

500 snubs between 40 mph and 20 mph at a deceleration rate of 10 

f.p.s.p.s., or at the vehicle's maximum deceleration rate if less than 

10 f.p.s.p.s. Except where an adjustment is specified, after each brake 

application accelerate to 40 mph and maintain that speed until making 

the next brake application at a point 1 mile from the initial point of 

the previous brake application. If the vehicle cannot attain a speed of 

40 mph in 1 mile, continue to accelerate until the vehicle reaches 40 

mph or until the vehicle has traveled 1.5 miles from the initial point 

of the previous brake application, whichever occurs first. Any automatic 

pressure limiting valve is in use to limit pressure as designed. The 

brakes may be adjusted up to three times during the burnish procedure, 

at intervals specified by the vehicle manufacturer, and may be adjusted 

at the conclusion of the burnishing, in accordance with the vehicle 

manufacturer's recommendation.

    S6.1.9 Static parking brake tests for a semitrailer are conducted 

with the front-end supported by an unbraked dolly. The weight of the 

dolly is included as part of the trailer load.

    S6.1.10 In a test other than a static parking test, a truck tractor 

is tested at its GVWR by coupling it to an unbraked flatbed semi-trailer 

(hereafter, control trailer) as specified in S6.1.10.2 to S6.1.10.4.

    S6.1.10.1 [Reserved]

    S6.1.10.2 The center of gravity height of the ballast on the loaded 

control trailer shall be less than 24 inches above the top of the 

tractor's fifth wheel.

    S6.1.10.3 The control trailer has a single axle with a GAWR of 

18,000 pounds and a length, measured from the transverse centerline of 

the axle to the centerline of the kingpin, of 258 6 inches.

    S6.1.10.4 The control trailer is loaded so that its axle is loaded 

at 4,500 pounds and the tractor is loaded to its GVWR, loaded above the 

kingpin only, with the tractor's fifth wheel adjusted so that the load 

on each axle measured at the tire-ground interface is most nearly 

proportional to the axles' respective GAWRs, without exceeding the GAWR 

of the tractor's axle or axles or control trailer's axle.

    S6.1.11 Special drive conditions. A vehicle equipped with an 

interlocking



[[Page 449]]



axle system or a front wheel drive system that is engaged and disengaged 

by the driver is tested with the system disengaged.

    S6.1.12 Liftable axles. A vehicle with a liftable axle is tested at 

GVWR with the liftable axle down and at unloaded vehicle weight with the 

liftable axle up.

    S6.1.13 Trailer test rig.

    The trailer test rig shown in Figure 1 is calibrated in accordance 

with the calibration curves shown in Figure 3. For the requirements of 

S5.3.3.1 and S5.3.4.1, the pressure in the trailer test rig reservoir is 

initially set at 100 psi for actuation tests and 95 psi for release 

tests.

    S6.1.14 In testing the emergency braking system of towing vehicles 

under S5.7.3(a), the hose(s) is vented to the atmosphere at any time not 

less than 1 second and not more than 1 minute before the emergency stop 

begins, while the vehicle is moving at the speed from which the stop is 

to be made and any manual control for the towing vehicle protection 

system is in the position to supply air and brake control signals to the 

vehicle being towed. No brake application is made from the time the 

line(s) is vented until the emergency stop begins and no manual 

operation of the parking brake system or towing vehicle protection 

system occurs from the time the line(s) is vented until the stop is 

completed.

    S6.1.15 Initial brake temperature. Unless otherwise specified, the 

initial brake temperature is not less than 150[deg] F and not more than 

200[deg] F.

    S6.1.16 Thermocouples.

    The brake temperature is measured by plug-type thermocouples 

installed in the approximate center of the facing length and width of 

the most heavily loaded shoe or disc pad, one per brake, as shown in 

Figure 2. A second thermocouple may be installed at the beginning of the 

test sequence if the lining wear is expected to reach a point causing 

the first thermocouple to contact the rubbing surface of a drum or 

rotor. The second thermocouple shall be installed at a depth of .080 

inch and located within 1 inch circumferentially of the thermocouple 

installed at .040 inch depth. For centergrooved shoes or pads, 

thermocouples are installed within one-eighth of an inch to one-quarter 

of an inch of the groove and as close to the center as possible.

    S6.1.17 Selection of compliance options. Where manufacturer options 

are specified, the manufacturer shall select the option by the time it 

certifies the vehicle and may not thereafter select a different option 

for the vehicle. Each manufacturer shall, upon request from the National 

Highway Traffic Safety Administration, provide information regarding 

which of the compliance options it has selected for a particular vehicle 

or make/model.

    S6.2 Dynamometer test conditions.

    S6.2.1 The dynamometer inertia for each wheel is equivalent to the 

load on the wheel with the axle loaded to its GAWR. For a vehicle having 

additional GAWRs specified for operation at reduced speeds, the GAWR 

used is that specified for a speed of 50 mph, or, at the option of the 

manufacturer, any speed greater than 50 mph.

    S6.2.2 The ambient temperature is between 75[deg] F. and 100[deg] F.

    S6.2.3 Air at ambient temperature is directed uniformly and 

continuously over the brake drum or disc at a velocity of 2,200 feet per 

minute.

    S6.2.4 The temperature of each brake is measured by a single plug-

type thermocouple installed in the center of the lining surface of the 

most heavily loaded shoe or pad as shown in Figure 2. The thermocouple 

is outside any center groove.

    S6.2.5 The rate of brake drum or disc rotation on a dynamometer 

corresponding to the rate of rotation on a vehicle at a given speed is 

calculated by assuming a tire radius equal to the static loaded radius 

specified by the tire manufacturer.

    S6.2.6 Brakes are burnished before testing as follows: place the 

brake assembly on an inertia dynamometer and adjust the brake as 

recommended by the vehicle manufacturer. Make 200 stops from 40 mph at a 

deceleration of 10 f.p.s.p.s., with an initial brake temperature on each 

stop of not less than 315[deg] F and not more than 385[deg] F. Make 200 

additional stops from 40 mph at a deceleration of 10 f.p.s.p.s. with an 

initial brake temperature on each stop of not less than 450[deg] F and 

not more than 550[deg] F. The brakes may be adjusted up



[[Page 450]]



to three times during the burnish procedure, at intervals specified by 

the vehicle manufacturer, and may be adjusted at the conclusion of the 

burnishing, in accordance with the vehicle manufacturer's 

recommendation.

    S6.2.7 The brake temperature is increased to a specified level by 

conducting one or more stops from 40 m.p.h. at a deceleration of 10 

f.p.s.p.s. The brake temperature is decreased to a specified level by 

rotating the drum or disc at a constant 30 m.p.h.



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[[Page 454]]







                       Table I.--Stopping Sequence

------------------------------------------------------------------------

                                                                 Single

                                                      Truck       unit

                                                     tractors    trucks

                                                               and buses

------------------------------------------------------------------------

Burnish...........................................          1          1

Stability and Control at GVWR (PFC 0.5)...........          2        N/A

Stability and Control at LLVW (PFC 0.5)...........          3          5

Manual Adjustment of Brakes.......................          4        N/A

60 mph Service Brake Stops at GVWR (PFC 0.9)......          5          2

60 mph Emergency Service Brake Stops at GVWR (PFC         N/A          3

 0.9).............................................

Parking Brake Test at GVWR........................          6          4

Manual Adjustment of Brakes.......................          7          6

60 mph Service Brake Stops at LLVW (PFC 0.9)......          8          7

60 mph Emergency Service Brake Stops at LLVW (PFC           9          8

 0.9).............................................

Parking Brake Test at LLVW........................         10          9

Final Inspection..................................         11         10

------------------------------------------------------------------------





                                       Table II--Stopping Distance in Feet

----------------------------------------------------------------------------------------------------------------

                                                                       Service brake             Emergency brake

                                                           -----------------------------------------------------

              Vehicle speed in miles per hour                 PFC      PFC      PFC      PFC      PFC      PFC

                                                              0.9      0.9      0.9      0.9      0.9      0.9

----------------------------------------------------------------------------------------------------------------

                                                                (1)      (2)      (3)      (4)      (5)      (6)

                                                           ----------

20........................................................       32       35       38       40       83       85

25........................................................       49       54       59       62      123      131

30........................................................       70       78       84       89      170      186

35........................................................       96      106      114      121      225      250

40........................................................      125      138      149      158      288      325

45........................................................      158      175      189      200      358      409

50........................................................      195      216      233      247      435      504

55........................................................      236      261      281      299      520      608

60........................................................      280      310      335      355      613      720

----------------------------------------------------------------------------------------------------------------

Note: (1) Loaded and unloaded buses; (2) Loaded single unit trucks; (3) Unloaded truck tractors and single unit

  trucks; (4) Loaded truck tractors tested with an unbraked control trailer; (5) All vehicles except truck

  tractors; (6) Unloaded truck tractors.





                   Table III--Brake Retardation Force

------------------------------------------------------------------------

                                                               Column 2

                                                                brake

           Column 1 brake retardation force/GAWR               chamber

                                                              pressure,

                                                                 PSI

------------------------------------------------------------------------

0.05.......................................................           20

0.12.......................................................           30

0.18.......................................................           40

0.25.......................................................           50

0.31.......................................................           60

0.37.......................................................           70

0.41.......................................................           80

------------------------------------------------------------------------





                           Table IV [Reserved]









                  Table V--Brake Chamber Rated Volumes

------------------------------------------------------------------------

                                                                Column 2

                                                    Column 1     rated

 Brake Chamber type  (nominal area of piston or   full stroke    volume

           diaphragm in square inches)              (inches)     (cubic

                                                                inches)

------------------------------------------------------------------------

Type 9..........................................    1.75/2.10         25

Type 12.........................................    1.75/2.10         30

Type 14.........................................    2.25/2.70         40

Type 16.........................................    2.25/2.70         46

Type 18.........................................    2.25/2.70         50

Type 20.........................................    2.25/2.70         54

Type 24.........................................    2.50/3.20         67

Type 30.........................................    2.50/3.20         89

Type 36.........................................    3.00/3.60        135

------------------------------------------------------------------------





[61 FR 27290, May 31, 1996, as amended at 61 FR 49695, Sept. 23, 1996; 

61 FR 60636, Nov. 29, 1996; 63 FR 7727, Feb. 17, 1998; 66 FR 64158, Dec. 

12, 2001; 67 FR 36820, May 28, 2002; 68 FR 47497, Aug. 11, 2003]