Sealco Commercial Vehicle Products

CFR49 571.121
From the U.S. Code Of Federal Regulations. Check current code for latest revisions.


[Code of Federal Regulations]
[Title 49, Volume 5]
[Revised as of October 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR571.121]

[Page 374-396]
 
                        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 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 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 capacity x 25) / 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 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 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.
    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 Office of the 
Federal Register, 800 North Capitol Street, NW., Washington, DC.
    (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.
    (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 manufactured before March 1, 1997, shall, under the 
conditions of S6, meet the requirements of S5.3.3 and S5.3.4, when 
tested without adjustments other than those specified in this standard. 
The service brake system on each truck tractor manufactured on or after 
March 1, 1997, 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) manufactured before March 1, 1998, shall, under 
the conditions of S6, meet the requirements of 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 March 1, 1998, 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 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 meet 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-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 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--truck tractors. 
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 manufactured on or after March 1, 1997, 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, 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.
    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 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/in^2  for 
a brake not subject to the control of an antilock system, or 12 lb/
in^2  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/in^2  for a brake not subject to the control of an 
antilock system or 12 lb/in^2  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 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 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.
    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, 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 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 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.
    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 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.
    S6.2  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 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.


[GRAPHIC] [TIFF OMITTED] TC01AU91.051
[GRAPHIC] [TIFF OMITTED] TC01AU91.053
[GRAPHIC] [TIFF OMITTED] TC01AU91.054

                       Table I--Stopping Sequence

1. Burnish.
2. Stops on a peak friction coefficient surface of 0.5:
(a) With the vehicle at gross vehicle weight rating (GVWR), stop the 
vehicle from 30 mph using the service brake, for a truck tractor with a 
loaded unbraked control trailer.
(b) With the vehicle at unloaded weight plus up to 1500 lbs., stop the 
vehicle from 30 mph using the service brake, for a truck tractor.
3. Manual adjustment of the service brakes allowed for truck tractors, 
within the limits recommended by the vehicle manufacturer.
4. Other stops with vehicle at GVWR:
(a) 60 mph service brake stops on a peak friction coefficient surface of 
0.9, for a truck tractor with a loaded unbraked control trailer, or for 
a single-unit vehicle.
(b) 60 mph emergency brake stops on a peak friction coefficient of 0.9, 
for a single-unit vehicle. Truck tractors are not required to be tested 
in the loaded condition.
5. Parking brake test with the vehicle loaded to GVWR.
6. Manual adjustment of the service brakes allowed for truck tractors 
and single-unit vehicles, within the limits recommended by the vehicle 
manufacturer.
7. Other stops with the vehicle at unloaded weight plus up to 1500 lbs.:
(a) 60 mph service brake stops on a peak friction coefficient surface of 
0.9, for a truck tractor or for a single-unit vehicle.
(b) 60 mph emergency brake stops on a peak friction coefficient of 0.9, 
for a truck tractor or for a single-unit vehicle.
8. Parking brake test with the vehicle at unloaded weight plus up to 
1500 lbs.
9. Final inspection of service brake system for condition of adjustment.

                                       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]
U.S. Federal Regulations