Title 49, § 393.40
Required Systems
(a) General. A bus, truck, truck tractor, or a combination of motor
vehicles must have brakes adequate to control the movement of, and
to stop and hold, the vehicle or combination of vehicles.
(b) Specific systems required.
(1) A bus, truck, truck tractor, or combination of motor vehicles
must have--
(i) A service brake system that conforms to the requirements of
Sec. 393.52; and
(ii) A parking brake system that conforms to the requirements
of Sec. 393.41.
(2) A bus, truck, truck tractor, or a combination of motor vehicles
manufactured on or after July 1, 1973, must have an emergency brake
system that conforms to the requirements of Sec. 393.52(b) and consists
of either--
(i) Emergency features of the service brake system; or
(ii) A system separate from the service brake system.
A control by which the driver applies the emergency brake system
must be located so that the driver can readily operate it when he/she
is properly restrained by any seat belt assembly provided for his/her
use. The control for applying the emergency brake system may be
combined with either the control for applying the service brake
system or the control for applying the parking brake system. However,
all three controls may not be combined.
(c) Interconnected systems.
(1) If the brake systems specified in paragraph (b) of this section
are interconnected in any way, they must be designed, constructed,
and maintained so that, upon the failure of any part of the operating
mechanism of one or more of the systems (except the service brake
actuation pedal or valve)--
(i) The vehicle will have operative brakes; and
(ii) In the case of a vehicle manufactured on or after July 1,
1973, the vehicle will have operative brakes capable of performing
as specified in Sec. 393.52(b).
(2) A motor vehicle to which the emergency brake system requirements
of Federal Motor Vehicle Safety Standard No. 105 (Sec. 571.105 of
this title) applied at the time of its manufacture conforms to the
requirements of paragraph (c)(1) of this section if--
(i) It is maintained in conformity with the emergency brake requirements
of Standard No. 105 in effect on the date of its manufacture; and
(ii) It is capable of performing as specified in Sec. 393.52(b),
except upon structural failure of its brake master cylinder body
or effectiveness indicator body.
(3) A bus conforms to the requirements of paragraph (c)(1) of this
section if it meets the requirements of Sec. 393.44 and is capable
of performing as specified in Sec. 393.52(b).
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