Interpretation ID: aiam1857
United States Senate
Washington
DC 20510;
Dear Senator Hartke: Thank you for your letter of March 7, 1975, asking for detaile consideration of Mr. David L. Daugherty's concern that final-stage manufacturers will be unable to fulfill their certification responsibilities on air-braked trucks built after March 1, 1975. As you know, Standard No. 121, *Air brake systems*, became effective for trucks and buses on March 1, 1975.; Mr. Daugherty has raised one of the most critical aspects of truc manufacturing in assuring a minimum brake performance level. Unlike passenger cars, the vast majority of heavy trucks are manufactured by adding specialized bodies or equipment to a chassis-cab. These additions affect the center of gravity, dynamic load transferral, and other characteristics of the truck which determine in large part its stopping capability.; As a practical matter, meaningful dynamic brake performance standard cannot be developed without regulating the truck as it is completed and sold.; The National Highway Traffic Safety Administration (NHTSA) recognize that Standard No. 121, as the first comprehensive performance requirement for trucks, will limit somewhat the freedom of manufacturers to modify brake systems and mount bodies without regard for their effect on braking. We consider the increased care exercised by final-stage manufacturers to be one of the most significant benefits of the standard.; Mr. Daugherty correctly points out that chassis-cab manufacturer released the necessary information on their chassis only a short time before March 1, 1975. The two trade associations for final-stage manufacturers petitioned for delay of the standard for this reason. After careful consideration of possible relief, NHTSA denied those petitions. It was concluded that every form of relief had obvious drawbacks and would not achieve the objective of final-stage manufacturers to receive 121-type chassis to use in re-engineering their body and equipment installations. It was concluded that if the standard for completed vehicles were suspended, chassis manufacturers would no longer have to provide incomplete vehicles with the necessary equipment and final-stage manufacturers would be unable to develop solutions for their engineering problems. Even if incomplete vehicles could be certified and completed vehicles could be exempt, serious danger would exist when modifications of the new systems were undertaken without consideration of the handling consequences.; I would like to point out that the March 1, 1975, effective date doe not require an instantaneous ('one day') change for final-stage manufacturers. Part 568 of our regulations (49 CFR Part 568) permits a final-stage manufacturer to use the date of completion of the chassis as the date of certification of the completed vehicle. This means that the chassis manufactured prior to March 1 may be completed at any later period without meeting Standard No. 121. It is not until final-stage manufacturers begin to receive the chassis which have just started to be produced that they will have to complete vehicles in conformity with the standard. They now have data on the new chassis, and thus have a period in which to make modifications. Several manufacturers have large inventories of pre-121 chassis and it should be several months before all trucks will be completed in conformity with Standard No. 121.; Thank you for your continuing interest in motor vehicle safety. Sincerely, James B. Gregory, Administrator