Interpretation ID: aiam3344
Engineering Consultant
12814 Ashbury Drive
Tantallon
MD 20022;
Dear Mr. Madison: This responds to your June 25, 1980, letter asking whether a propose air brake system that you submitted would comply with the requirements of Standard No. 121, *Air Brake Systems*.; The National Highway Traffic Safety Administration (NHTSA) does no issue advance approval of systems constructed in compliance with safety standards. It is the responsibility of manufacturers to assure that their vehicles or equipment comply with the requirements of the safety standards. It is frequently impossible for the agency to tell from diagrams and descriptions of devices whether they will comply with the standards. Compliance is based upon testing and observation of the entire vehicle or piece of equipment as it is installed on the vehicle. Without the benefits of such tests, NHTSA cannot state whether your system would comply with Standard No. 121.; Our engineering staff has reviewed your letter and offers the followin information. First, the standard contains no requirements for tractor protection valve control pressures. However, control pressures are usually set so that the trailer brakes apply before the tractor brakes.; Second, you asked whether it is appropriate to require the release o parking brakes by pushing in both the tractor protection control valve and the park valve. The standard states that the parking brake control shall control the parking brakes of the vehicle and any vehicle it is designed to tow. The standard is silent regarding the release of those brakes.; Sincerely, Frank Berndt, Chief Counsel