Interpretation ID: 7170
Vice President Sales
Sealco Air Controls, Inc.
215 East Watkins Street
Phoenix, AZ 85004
Dear Mr. Mario:
This letter responds to your inquiry about recent amendments to Federal Motor Vehicle Safety Standard No. 121, Air Brake Systems, with respect to trailers. That final rule (56 FR 50666, October 8, 1991, copy enclosed) amended the standard by deleting the requirement for a separate reservoir capable of releasing the parking brake. It also added requirements for the retention of a minimum level of pressure in a trailer's supply line in the event of pneumatic failure and for the prevention of automatic application of trailer parking brakes while the minimum supply line pressure is maintained. I am pleased to have this opportunity to explain our requirements.
By way of background information, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, the manufacturer is responsible for certifying that its vehicles or equipment comply with applicable standards.
NHTSA promulgates safety standards that specify performance requirements for motor vehicles and motor vehicle equipment.
One such safety standard, Standard No. 121, specifies performance requirements for braking systems on vehicles equipped with air brake systems, including most trailers. Any air brake system that complies with the performance requirements set forth in Standard No. 121 would be permissible.
You first asked whether a trailer could be equipped with a protected separate reservoir after the amendment becomes effective on October 8, 1992. The answer is yes. While the amendment deletes a provision requiring a protected service reservoir, nothing in the amendment would prohibit a trailer from being equipped with this device. Your next two questions asked which air brake system would be required on certain axles for different types of trailers. As indicated above, any air brake system that complies with the performance requirements set forth in Standard No. 121 would be permissible. I note that while the standard does include certain specific requirements for braking at particular axles, all of the requirements amended or adopted in the October 1991 final rule are written in terms of overall vehicle braking performance. Therefore, in order to ensure compliance with these requirements, manufacturers must assess how the selection of brake designs at each axle will affect overall braking performance.
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. Sincerely,
Paul Jackson Rice Chief Counsel Enclosure
ref:121 d:5/21/92