Interpretation ID: nht75-6.23

DATE: 01/01/75 EST

FROM: RICHARD B. DYSON -- NHTSA ASSISTANT CHIEF COUNSEL

TO: ALLAN B. FREDHOLD -- GENERAL MANAGER K-B AXLE CO., INC.

TITLE: N40-30 (TWH)

ATTACHMT: LETTER DATED 4/16/75 FROM RICHARD B. DYSON -- NHTSA CHIEF COUNSEL TO GEOFFREY R. MYERS OF HALL AND MYERS; UNDATED LETTER FROM RICHARD B. DYSON -- NHTSA CHIEF COUNSEL TO ADDRESSEE UNKNOWN

TEXT: Dear Mr. Fredhold:

This responds to K-B Axle Company's March 4, 1975, request for guidance in assisting K-B's customers in meeting their certification responsibilities under Standard No. 121, Air brake systems.

Standard No. 121 specifies air brake performance requirements (and some equipment requirements) which newly-manufactured trucks, buses, and trailers must be capable of meeting. For example, the standard specifies that if a truck or bus, in the loaded and unloaded condition, is stopped six times from 60 mph on certain test surfaces, it must be capable of stopping at least once in 258 feet without leaving a 12-foot wide lane and without uncontrolled wheel lockup.

Many manufacturers incorrectly assume that this requirement means that, in order to certify that it has this capability, each vehicle produced must actually be tested from 60 mph on a test track. In fact the National Traffic and Motor Vehicle Safety Act of 1966 (15 U.S.C. 1391, et. seq.) specifies the manufacturer's certification responsibility, which is to exercise "due care" that the vehicle or item of equipment is capable of meeting all requirements.

NHTSA has made clear in the past, and has emphasized in its implementation of Standard No. 121, that a manufacturer is free to use whatever method is reasonably calculated to fulfill his responsibility to exercise due care. To cite a simple example, if a safety standard specifies that a certain safety device be no less than 8 inches above the ground, it would not be necessary to measure the height of each safety device on each vehicle produced to assure in the exercise of due care that it complies.

Standard No. 121, of course, establishes more complex performance requirements, and they would be affected by the addition of your "tag" or "pusher" axles. Most final-stage manufacturers and alterers feel confident that they can meet such requirements as minimum air tank volume when they add a third axle. In more complex areas, however, they require some reasonable basis on which to certify, in the exercise of due care, that the vehicle still is capable of stopping within the required distance, and that the brake actuation and release times still meet the minimum performance levels of the standard.

As noted earlier, the standard and our statute do not require road testing as the basis of certification. NHTSA, in a preamble to Standard No. 121 recognized:

What constitutes due care in a particular case depends on all relevant facts, including such things as the time to elapse before a new effective date, the availability of test equipment, the limitations of current technology, and above all the diligence evidenced by the manufacturer.

Road testing would be one method of exercising due care. Your customers, of course, may not have the capability to conduct road testing.

As a supplier of the added component, you are in a good position to develop engineering data on the effect your axle has when added to a 121 vehicle. For example, you could add your axle to a 121 chassis with a representative body and conduct a road test to see that the vehicle with the added axle and gross vehicle weight would still meet the stopping distance requirements. You might also test the actuation and release times on this vehicle to see that the axle addition does not cause non-conformity. This experimentation would permit you to make general statements about the conditions under which your axle could be added to a 121-type chassis without causing non-conformity.

Although retardation force is not a requirement for a vehicle other than a trailer, you suggest use of dynamometer data as a basis of certification. Such information would be a valid basis of certification if it is shown that a reasonable correlation exists between the retardation forces you specify and the actual ability of the modified truck to stop.

Yours truly,