[Code of Federal Regulations]
[Title 49, Volume 4]
[Revised as of October 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR393.43]

[Page 1065-1066]
 
                        TITLE 49--TRANSPORTATION
 
        CHAPTER III--FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION,
                      DEPARTMENT OF TRANSPORTATION
 
PART 393--PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATION--Table of Contents
 
                            Subpart C--Brakes
 
Sec. 393.43  Breakaway and emergency braking.

    (a) Every motor vehicle, if used to tow a trailer equipped with 
brakes, shall be equipped with means for providing that in case of 
breakaway of such trailer the service brakes on the towing vehicle will 
be sufficiently operative to stop the towing vehicle.
    (b) Every truck or truck tractor equipped with air brakes, when used 
for towing other vehicles equipped with air brakes, shall be equipped 
with two means of activating the emergency features of the trailer 
brakes. One of these means shall operate automatically in the event of 
reduction of the towing vehicle air supply to a fixed pressure which 
shall not be lower than 20 pounds per square inch nor higher than 45 
pounds per square inch. The other means shall be a manually controlled 
device readily operable by a person seated in the driving seat. Its 
emergency position or method of operation shall be clearly indicated. In 
no instance may the manual means be so arranged as to permit its use to 
prevent operation of the automatic means. The automatic and manual means 
required by this section may be, but are not required to be, separate.
    (c) Every truck tractor and truck when used for towing other 
vehicles equipped with vacuum brakes, shall have, in addition to the 
single control required by Sec. 393.49 to operate all brakes of the 
combination, a second manual control device which can be

[[Page 1066]]

used to operate the brakes on the towed vehicles in emergencies. Such 
second control shall be independent of brake air, hydraulic, and other 
pressure, and independent of other controls, unless the braking system 
be so arranged that failure of the pressure on which the second control 
depends will cause the towed vehicle brakes to be applied automatically. 
The second control is not required by this rule to provide modulated or 
graduated braking.
    (d) Every trailer required to be equipped with brakes shall be 
equipped with brakes of such character as to be applied automatically 
and promptly upon breakaway from the towing vehicle, and means shall be 
provided to maintain application of the brakes on the trailer in such 
case for at least 15 minutes.
    (e) Air brake systems installed on towed vehicles shall be so 
designed, by the use of ``no-bleed-back'' relay emergency valves or 
equivalent devices, that the supply reservoir used to provide air for 
brakes shall be safeguarded against backflow of air to the towing 
vehicle upon reduction of the towing vehicle air pressure.
    (f) The requirements of paragraphs (b), (c), and (d) of this section 
shall not be applicable to motor vehicles in driveaway-towaway 
operations.