Interpretation ID: nht75-3.33
DATE: 12/15/75
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: Volvo of America Corporation
TITLE: FMVSS INTERPRETATION
TEXT: This responds to Volvo of America's October 9, 1975, question whether a truck equipped with an air-assisted hydraulic brake system with hydraulic push through capability and, in the towing vehicle configuration, a source of compressed air for air braked trailer operation, is subject to Standard No. 121, Air Brake Systems.
From your description of the system and the materials that accompanied your letter, the truck does not qualify as an air-braked vehicle to which the standard applies. The fact that it is capable of operation in combination with an air-braked vehicle and supplies the compressed air for braking that vehicle does not affect the truck's classification as an hydraulic-braked vehicle.
At the time Standard No. 121 was developed, it covered virtually all of the trucks and truck-tractors in the heaviest categories. In planning and making your decisions to introduce hydraulic-braked vehicles in these weight categories, you should be aware that this agency is planning to cover all such vehicles with the basic performance requirements presently contained in Standard No. 121.
SINCERELY,
October 9, 1975
Frank Berndt, Acting Chief Counsel National Highway Traffic Safety Administration
Re: Applicability of Brake Regulations to Vehicle Combinations Consisting of a Hydraulic Brake Equipped Tractor and an Air Brake Equipped Trailer.
Volvo of America Corporation is currently considering the importation of a hydraulic brake equipped truck with a GVWR of 29,000 pounds. The basic vehicle can be outfitted as either a straight truck or a truck tractor. Both versions employ the same brake system. Our question concerns the applicability of the requirements of FMVSS No. 121 to this truck tractor when coupled to an air brake equipped trailer.
The operating principles of the brake system employed on both versions of the truck are described in the attachments to this letter. Basically it is an air assisted hydraulic brake system with a hydraulic push through capability. In the tractor version of this truck provisions are made in the brake system for the supply of compressed air to the brake system of the attached trailer. This is accomplished in a manner which enables the truck to operate in combination with conventional air brake equipped trailers.
Our understanding of the pertinent regulations indicates that since the truck tractor is not subject to the requirements of FMVSS No. 121, being fitted with hydraulic brakes, the combination of this tractor and an air brake equipped trailer also is not subject to the requirements of FMVSS No. 121, regardless of what requirements are applicable to the trailer by itself. Your verification of this understanding is requested.
Your prompt consideration of this matter would be greatly appreciated. If you have any questions concerning the technical details of the brake system, please direct them to Mr. Bjorn Klingenberg at the address indicated below:
Volvo of America Corporation Truck Division 266 UNION STREET NORTHVALE, N.J. 07647
All other communications concerning this matter should be directed to the undersigned.
VOLVO OF AMERICA CORPORATION Product Engineering and Development
Donald W. Taylor Manager, Product Safety & Quality
CC: B. KLINGENBERG