[Code of Federal Regulations]

[Title 49, Volume 5]

[Revised as of October 1, 2005]

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

[CITE: 49CFR393.43]



[Page 398-399]

 

                        TITLE 49--TRANSPORTATION

 

                      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) Towing vehicle protection system. Every motor vehicle, if used 

to tow a trailer equipped with brakes, shall be equipped with a means 

for providing that in the case of a breakaway of the trailer, the 

service brakes on the towing vehicle will be capable of stopping the 

towing vehicle. For air braked towing units, the tractor protection 

valve or similar device shall operate automatically when the air 

pressure on the towing vehicle is between 138 kPa and 310 kPa (20 psi 

and 45 psi).

    (b) Emergency brake requirements, air brakes. 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



[[Page 399]]



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) Emergency brake requirements, vacuum brakes. 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 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) Breakaway braking requirements for trailers. Every trailer 

required to be equipped with brakes shall have brakes which apply 

automatically and immediately upon breakaway from the towing vehicle. 

With the exception of trailers having three or more axles, all brakes 

with which the trailer is required to be equipped must be applied upon 

breakaway from the towing vehicle. The brakes must remain in the applied 

position for at least 15 minutes.

    (e) Emergency valves. 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) Exception. The requirements of paragraphs (b), (c) and (d) of 

this section shall not be applicable to commercial motor vehicles being 

transported in driveaway-towaway operations.



[53 FR 49384, Dec. 7, 1988, as amended at 70 FR 48050, Aug. 15, 2005]