Interpretation ID: 77-5.7

TYPE: INTERPRETATION-NHTSA

DATE: 12/20/77

FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA

TO: General Motors Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. David Martin Director of Automotive Safety Engineering General Motors Technical Center Warren, Michigan 48090

Dear Mr. Martin:

Please find enclosed a copy of a recent interpretation of Standard No. 121, Air Brake Systems, that may be relevant to your company's compliance efforts. The interpretation clarifies that service brake control modulation by the driver is permissible in evaluating compliance of a vehicle with S5.3.1 of the standard.

Joseph J. Levin, Jr. Chief Counsel

cc: Mr. W. E. Whitner

1-3-78 - LCL,RAR,DAM,RLL,DPD,GSB, RJD,MRB,CTT,JWS,RAW,WLW,JLM,WCC,DPR

DEC 20, 1977

Mr. Donald P. Weiher Chief Project Engineer - Safety AM General Corporation 32500 Van Born Road Wayne, Michigan 48184

Dear Mr. Weiher:

This responds to AM General's December 12, 1977, request to know whether modulation of the service brake control is permissible during stopping distance tests of an air-braked vehicle's compliance with S5.3.1 of Standard No. 121, Air Brake Systems. Modulation would be employed to prevent lockup of wheels above 10 mph, as required by S5.3.1. The other questions in your letter will be answered separately.

Section 5.3.1 does not limit the type of brake application that may be employed. When a test procedure or condition is not specified, the manufacturer is free to conduct that aspect of the test in any reasonable manner.

In this case, the standard requires compliance in one out of six attempts, which is intended to increase the test driver's familiarity with the vehicle for test purposes. Driver modulation occurs in the real world and is, in the agency's view, a reasonable procedure by which to demonstrate compliance. The normal skill of a test driver is anticipated in compliance testing.

Joseph J. Levin, Jr. Chief Counsel