1516                             Laws of Maryland                       Ch. 534

vehicle, the towing vehicle will be capable of being stopped by the
use of its service brakes.

(f)    Trailer air reservoirs safeguarded. Air brake systems in-
stalled on trailers manufactured or assembled after June 1, 1970,
shall be so designed that the supply reservoir used to provide air
for the brakes shall be safeguarded against backflow of air from the
reservoir through the supply line.

(g)    Two means of emergency brake operation.

(1)    Air brakes. After June 1, 1971, every towing vehicle, when
used to tow another vehicle equipped with air controlled brakes, in
other than driveway or towaway operations, shall be equipped with
two means for emergency application of the trailer brakes. One of
these means shall apply the brakes automatically in the event of a
reduction of the towing vehicle air supply to a fixed pressure which
shall be not lower than 20 pounds per square inch nor higher than
45 pounds per square inch. The other means shall be a manually
controlled device for applying and releasing the brakes, readily oper-
able by a person seated in the driving seat, and its emergency posi-
tion or method of operation shall be clearly indicated. In no instance
may the manual arrangement be arranged to permit its use to pre-
vent operation of the automatic means. The automatic and the man-
ual means required by this section may be, but are not required
to be, separate.

(2)    Vacuum brakes. After June 1, 1970, every towing vehicle
used to tow other vehicles equipped with vacuum brakes, in opera-
tions other than driveaway or towaway operations, shall have, in
addition to the single control device required by subsection (h), a
second control device which can be used to operate the brakes on
towed vehicles in emergencies. The second control shall be in-
dependent of brake air, hydraulic, and other pressure, and inde-
pendent of other controls, unless the braking system be so arranged
that failure of the pressure upon which the second control depends
will cause the towed vehicle brakes to be applied automatically. The
second control is not required to provide modulated braking.

(h) Single control to operate all brakes. After June 1, 1971,
every motor vehicle, trailer, semitrailer, and pole trailer, and every
combination of such vehicles, except motorcycles, equipped with
brakes shall have the braking system so arranged that one control
device can be used to operate all service brakes. This requirement
does not prohibit vehicles from being equipped with an additional
control device to be used to operate brakes on the towed vehicles.
This regulation does not apply to driveaway or towaway operations
unless the brakes on the individual vehicles are designed to be oper-
ated by a single control on the towing vehicle, NOR DOES IT APPLY
TO THE OPERATION OF ELECTRIC TRAILER BRAKES.

(i) Reservoir capacity and check valve.

(1) Air brakes. Every bus, truck, or truck tractor with air oper-
ated brakes shall be equipped with at least one reservoir sufficient
to insure that, when fully charged to the maximum pressure as
regulated by the air compressor governor cut-out setting, a full serv-
ice brake application may be made without lowering the reservoir
pressure by more than 20 per cent. Each reservoir shall be provided
with means for readily draining accumulated oil or water.