Interpretation ID: aiam1941
Manager
Product Safety & Quality
Volvo of America Corporation
Rockleigh
NJ 07647;
Dear Mr. Taylor: This responds to Volvo of America Corporation's May 9, 1975, reques for reconsideration of the NHTSA's March 31, 1975, determination that a Volvo brake system that employs air pressure modulated by the vehicle operator to provide the energy used to actuate the brakes is an air brake system subject to Standard No. 121, *Air brake systems*.; Having reviewed all of the data submitted with your letter, it i concluded that the Volvo system is an air brake system subject to Standard No. 121. In the development of separate air brake and hydraulic brake system standards, the NHTSA had to make a determination of the status of brake systems which employ both air and hydraulic fluid as a means of transmitting force to the vehicle brakes. The agency decided that use of air as a means of power and transmission of the brake force would qualify the system as an air brake system. This decision permits manufacturers to determine with certainty whether a standard applies to their products.; Since the withdrawal of applicability to trucks of Standard No. 105-75 *Hydraulic brake systems*, our decision has had the beneficial effect of ensuring that 'air over hydraulic' systems are subject to a braking standard. If you are aware of any adverse safety consequences of our decision, I would appreciate hearing from you.; Sincerely, Robert L. Carter, Associate Administrator, Motor Vehicl Programs;