Interpretation ID: 7855-2
Equipment Coordinator
Transportation Services
Salt River Project
P.O. Box 52025
Phoenix, AZ 85072-2025
Dear Mr. Gayer:
This responds to your letter asking whether certain trailers, manufactured in 1989, were required to comply with Federal Motor Vehicle Safety Standard No. 121, Air Brake Systems. (49 CFR 571.121). You explained that you disagree with statements by the trailers' manufacturer that "these trailers do not need to comply with `121,' because they are `Heavy Haul Trailers.'" You further stated that the trailers may not comply with certain provisions in Standard No. 121, including the reservoir requirements in S5.2.1.1 and S5.2.1.5.
I note that we previously responded to a similar letter from Salt River Project concerning certain trailers manufactured in 1987. Our letter (copy enclosed) was sent to Mr. Derral T. Crance on April 3, 1989. We explained that heavy hauler trailers are not excepted from Standard No. 121 unless they have a GVWR of more than 120,000 pounds. Since you indicated that the trailers of current concern have a GVWR of 68,000 pounds, they would not be excepted from the standard as heavy hauler trailers. Moreover, the trailers do not appear to come within any of the other exceptions to Standard No. 121.
Standard No. 121 does, however, include a number of special provisions for heavy hauler trailers, including exceptions from certain requirements. Of particular note, S5.6 sets forth a number of specific parking brake requirements but permits heavy hauler trailers to meet the requirements of either that section, or, at the option of the manufacturer, the requirements of 49 CFR 393.43. Part 393 requires commercial motor vehicles to be equipped with various types of equipment, including brakes. Specifically, section 393.43 addresses brake requirements in breakaway and emergency braking situations.
Heavy hauler trailers manufactured in 1989 were generally subject to sections S5.2.1.1 and S5.2.1.5 of Standard No. 121, the provisions about which you specifically asked. Under S5.2.1.1, a reservoir was required to be provided that is capable of releasing the vehicle's parking brakes at least once and that is unaffected by a loss of air pressure in the service brake system. Under S5.2.1.5, each service reservoir was required to be protected against loss of air pressure due to failure or leakage in the system between the service reservoir and its source of air pressure by check valves or equivalent devices.
Notwithstanding the general applicability of S5.2.1.1, certain heavy hauler trailers which complied with the requirements of 49 CFR 393.43 instead of the specific parking brake requirements set forth in S5.6 would not have had to comply with S5.2.1.1. This is so because the vehicle is not required to have parking brakes. However, a braking system is required which applies automatically and promptly upon breakaway from a towing vehicle. Such a vehicle would also be required to carry sufficient chocking blocks to prevent movement when parked, as required by 393.41.
Since your letter suggests that you purchased trailers that may not have complied with Standard No. 121, I have referred the matter to our Office of Vehicle Safety Compliance for appropriate action.
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
ref:121 d.12/14/92