Interpretation ID: 20696.ogm
Mr. Tom Brunson
Trailer Component Innovations
111 Park Drive
Forsyth, GA 31029
Dear Mr. Brunson:
This is in response to your letter requesting information regarding the regulations applicable to the use of hydraulic brakes on trailers with axle capacities of 3500 to 8000 pounds per axle. I apologize for the delay in our response. Specifically, you wish to know if trailers of this type would be required to be equipped with an antilock braking system (ABS).
Your letter states that the trailers would be equipped with hydraulic axle brakes controlled by an electric brake controller. This electric brake controller, similar in design to the type usually used for electric trailer brakes, would draw electric power from the tow vehicle. In addition, electric power from the tow vehicle would be used to power an air compressor mounted on the trailer. You then ask if ABS would be required for a non-commercial trailer with a gross vehicle weight rating of less than 26,000 pounds under the following two scenarios:
- An electric brake controller is mounted on the tow vehicle with the force used to apply the trailer brakes being supplied by compressed air from an air tank and air compressor mounted on the trailer. Application of the hydraulic trailer brakes would be controlled by the electric brake controller. The controller would, when it sensed the tow vehicle decelerating or accelerating or when activated by an electric control available to the driver, electrically activate valves modulating the air pressure supplied to the mechanism used to apply or release the hydraulic trailer brakes.
- An electric brake controller is mounted on the tow vehicle. A spring mechanism would be used to supply the force used to apply the trailer brakes. The amount of force applied to actuate the hydraulic brakes by the spring mechanism would be controlled by air pressure supplied by an air tank and air compressor mounted on the trailer. Application of the hydraulic trailer brakes would be controlled by the electric brake controller when it sensed deceleration or acceleration of the tow vehicle or when activated by an electric control available to the driver. The controller would, as required, electrically activate valves modulating the air pressure supplied to counteract the force applied to the hydraulic brakes by the spring mechanism.
I am pleased to have this opportunity to explain our regulations to you. 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 ("Safety Act"), it is the responsibility of the manufacturer to ensure that its vehicles or equipment comply with applicable standards issued by this agency. A manufacturer then certifies that its vehicles or equipment comply with applicable standards.
NHTSA has issued several standards applicable to brake systems: Standard No. 105, Hydraulic Brake Systems; Standard No. 121, Air Brake Systems; and Standard No. 135, Passenger Car Brake Systems. Standard No. 105 specifies requirements for hydraulic service brake and associated parking brake systems, and applies to new passenger cars, multipurpose passenger vehicles, trucks, and buses equipped with hydraulic brake systems. Standard No. 121 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. Standard No. 135 specifies requirements for hydraulic service brake and associated parking brake systems for new passenger cars built after September 1, 2000 and for new multipurpose passenger vehicles, trucks and buses with a gross vehicle weight rating of 3,500 kilograms (7,716 pounds) or less built after September 1, 2002. Of these three standards, Standard No. 121 is the only standard which applies to trailers.
Standard No. 121 (49 CFR 571.121) specifies performance requirements for trucks, buses and trailers equipped with air brake systems. The purpose of the standard is to insure safe braking performance of vehicles under normal and emergency conditions. S5.1.6 of Standard No. 121 requires that truck tractors equipped with air brake systems manufactured on and after March 1, 1997 and single-unit trucks, buses, trailers, and trailer converter dollies equipped with air brake systems manufactured on and after March 1, 1998 must be equipped with antilock brake systems (ABS) in order to operate in the United States (U.S.).
We note, however, that Standard No. 121 only applies to vehicles with air brake systems. An air brake system is defined in S4 of the Standard as follows:
Air brake system means a system that uses air as a medium for transmitting pressure or force from the driver control to the service brake, including an air-over-hydraulic brake subsystem, but does not include a system that uses compressed air or vacuum only to assist the driver in applying muscular force to hydraulic or mechanical components.
The devices described in your letter appear to use compressed air as a means to actuate or control the hydraulic service brakes of a trailer. The application of this compressed air is controlled not by the driver, but by the electric brake controller. While the driver may, in some applications, have the ability to activate the electric brake controller through a dash mounted switch, air is not used as a medium for transmitting pressure or force from the driver control to the service brake on the trailer. Accordingly, the system you describe is not, under Standard No. 121, an air brake system and is not subject to the ABS requirements of that Standard.
You should, however, also be aware of the requirements of Standard No. 106, Brake Hoses, which specifies requirements for motor vehicle brake hose, brake hose assemblies, and brake hose end fittings. That standard applies to new motor vehicle equipment as well as to new motor vehicles. You should check to see if any parts of your devices are subject to the requirements of Standard No. 106. In addition, Standard No. 116, Motor Vehicle Brake Fluids, sets forth the requirements for all fluid for use in motor vehicle hydraulic brake systems. Any fluid used in a hydraulic brake system must meet the requirements of Standard No. 116.
I hope this information is helpful. If you have any further questions about NHTSA's safety standards, please feel free to contact Otto Matheke of my staff at this address or by telephone at (202) 366-2992.
Sincerely,
Frank Seales, Jr.
Chief Counsel
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d.5/4/00