Interpretation ID: aiam2497
3745 Winston Drive
El Monte
CA 91731;
Dear Mr. Noriega: This responds to your November 3, 1976, question whether Standard No 121, *Air Brake Systems*, prohibits the installation in a towing vehicle of a service brake control that is designed to permit separate, sequential, or simultaneous actuation of the service brake systems of the towing vehicle and any towed vehicle.; Assuming that the valve for the towing vehicle represents a 'split service brake system as specified in S5.7 of Standard No. 121, such a service brake control design would not conflict with the Standard's requirements. Of course, the actual compliance of any vehicle with Standard No. 121 depends on the actual installation and performance of the system as well as its design.; I would like to note that the agency is not endorsing the service brak control in question by the issuance of this interpretation letter. In fact, the agency is unsure about the effect the control may have on safe braking in a panic situation. Any test information that you or a vehicle manufacturer may care to provide would be appreciated.; Sincerely, Frank Berndt, Acting Chief Counsel