Interpretation ID: nht94-6.13

DATE: April 25, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Ken Simons -- Esq.

TITLE: None

ATTACHMT: Attached to letter dated 6/25/93 from Kenneth P. Simons to Department of Transportation, Trucking Division (OCC-8877)

TEXT:

This responds to your letter asking about brake requirements for trailers used in tractor trailer combinations. I apologize for the delay in our response. You asked whether all such trailers are required to be equipped with "maxi" brakes on one or both axles. You state that a "maxi" brake is found on all road tractors and "sets the brakes automatically when the air pressure gets down to a minimum level." Please note that the term "maxi" brakes ordinarily refers to spring brakes used in parking and emergency brake applications. I further note that most, but not all, trailers are equipped with spring brakes. I am pleased to have this opportunity to explain our requirements.

By way of background information, under the National Traffic and Motor Vehicle Safety Act ("Safety Act," 15 U.S.C. S1392), the National Highway Traffic Safety Administration (NHTSA) is authorized to issue Federal motor vehicle safety standards applicable to new motor vehicles and items of motor vehicle equipment. NHTSA does not approve vehicles or equipment. Instead, manufacturers are required to certify that their vehicles or equipment meet all applicable standards.

Standard No. 121, Air Brake Systems (49 CFR S571.121, copy enclosed), specifies performance requirements for trucks, buses and trailers equipped with air brake systems. The purpose of the standard is to insure safe braking performance of vehicle under normal and emergency conditions.

While Standard No. 121 does not require manufacturers to use spring brakes or any other particular type of brake system, many manufacturers use spring brakes to comply with the standard's requirements concerning parking brake performance (truck, buses and trailers; see S5.6), emergency brake performance (trucks and buses only; see S5.7), and trailer pneumatic system failure performance (see S5.8). I note that while the requirements of S5.65 and S5.8 apply to most air-braked trailers, S3 of Standard No. 121 excludes some trailers from all of the standard's requirements. In addition, S5.6 and S5.8 specify alternative requirements for some trailers.

I hope this information is helpful. If you have any further questions about NHTSA's safety standards, please feel free to contact Marvin Shaw of my staff at this address or by telephone at (202) 366-2992.