Interpretation ID: nht78-2.46

DATE: 01/26/78

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

TO: AM General Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your December 12, 1977, request for confirmation that an air-braked electric trackless trolley may be tested for compliance with S5.3.1 of Standard No. 121, Air Brake Systems, with its transmission selector control in the "DRIVE" position if the drive wheels and motor are permanantly mechanically connected and the motor automatically provides retardation when the service brake control is depressed. Your other requests for interpretation have been answered by separate letters.

Section S6.1.3 of Standard No. 121 specifies:

S6.1.3 Unless otherwise specified, the transmission selector control is in neutral or the clutch is disengaged during all decelerations and during static parking brake tests.

This test condition does not permit testing for compliance with the transmission selector control in the "DRIVE" position. The performance levels of the standard were established at levels intended for the foundation brakes alone, exclusive of engine braking, and it is for this reason that the selector must be in neutral or the clutch disengaged. This is true both for vehicles with manual and automatic transmissions.

It does appear that a case may be made for testing the bus you describe with the selector in "DRIVE". One important factor would be whether the field in the motor generator is permanent or electrically induced. In the event you wish to petition for an amendment of S6.3.1, information of this nature should accompany your petition.

In response to your other question, the agency's July 10, 1974, letter to Flyer Industries remains valid.