Interpretation ID: nht93-3.37

DATE: May 6, 1993

FROM: John Womack -- Acting Chief Counsel, U.S. Department of Transportation, NHTSA

TO: Bob Brinton -- Friction Advisory Service

TITLE: None

ATTACHMT: Attached to letter dated 3-16-93 from Bob Brinton to NHTSA (OCC 8436); Also attached to letter dated 12-9-76 from Frank A. Berndt to Leon W. Steenbock (Std. 121)

TEXT: This responds to your letter inquiring about the legality of an auxiliary parking system in addition to the spring parking brake system. According to your letter, you are familiar with certain refuse type vehicles with right hand side drive that are equipped with an I.C.C. flip switch valve or a push pull valve. These valves permit a driver to temporarily park the vehicle while the driver leaves the vehicle and picks up trash. You explained that while the auxiliary brake system is applied, the spring brakes are not applied to help the spring avoid extreme wear cycles.

You asked whether the auxiliary brake system is legal under Standard No. 121. In your letter, you indicate your view that these auxiliary systems do not comply with the parking brake requirements in S5.6.3 of Standard No. 121, AIR BRAKE SYSTEM. Based on our understanding of the brake system you describe, I am pleased to have this opportunity to explain our regulations to you.

By way of background information, the National Traffic and Motor Vehicle Safety Act ("Safety Act") requires this agency, the National Highway Traffic Safety Administration (NHTSA), to promulgate motor vehicle safety standards that specify performance requirements for new motor vehicles and items of motor vehicle equipment. One such standard is Standard No. 121, which establishes performance and equipment requirements for braking systems on vehicles equipped with air brake systems, and applies to almost all new trucks, buses, and trailers equipped with air brake systems. The purpose of the standard is to ensure safe braking performance under normal and emergency conditions.

A vehicle equipped with air brakes is required to comply with the requirements set forth in Standard No. 121. Among other things, S5.6 of the Standard requires air-braked vehicles to be equipped with a parking brake system that meets specified performance requirements. The requirements in standard No. 121, however, do not preclude the installation of a braking system in addition to the systems installed to comply with the Standard's requirements. Accordingly, the agency would not consider the requirements of S5.6 to prohibit an auxiliary parking brake system in addition to the brake systems required to comply with Standard No. 121.

Nevertheless, as an item of motor vehicle equipment subject to the requirements in sections 151-159 of the Safety Act concerning the recall and remedy of products with defects related to motor vehicle safety, an auxiliary parking brake system should be built in such a manner that the public is protected against unreasonable risk of injury that might occur as a result of its design, construction, or performance.

Please note that this interpretation is consistent with the agency's

long-standing view about the use of auxiliary parking brake systems. I am enclosing a December 9, 1976 interpretation letter to Mr. Leon Steenbock which addressed this issue.

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