Interpretation ID: nht90-1.23

TYPE: Interpretation-NHTSA

DATE: January 25, 1990

FROM: James R. Mitzenberg -- Project Engineer, The Flxible Corporation

TO: Steven P. Wood -- Chief Counsel, NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 9-26-90 from P.J. Rice to J.R. Mitzenberg (A36; Std. 108)

TEXT:

The Flxible Corporation is a city transit bus manufacturer and requests an interpretation concerning FMVSS 108, "Lamps, reflective devices, and associated equipment".

An air brake system is used on our bus. As the driver starts to apply the service brake pedal to stop the bus, a service brake stop lamp switch is activated. The stop lamp switch is installed to comply with Section S5.1.7 of FMVSS 121, "Air brake syste ms". The stop lights are activated by the stop lamp switch.

The Flxible Corporation offers an optional transmission retarder for supplemental braking, to increase brake lining life. This retardation is over and above the normal service brake system. The transmission retarder is electrically operated during the initial travel of the service brake pedal. As the service brake pedal is further depressed, air is emitted from the brake valve and the service brakes are activated.

A ruling is requested on whether a non-compliance with Section S4.5.4 of FMVSS 108 would result, if the stop lamps were activated by engagement of the retarder, prior to the activation of the service brakes. Section S4.5.4 states: "The stop lamps on eac h vehicle shall be activated upon application of the service brakes". The driver is depressing the service brake pedal to stop or slow down the vehicle. However, if the stop lights are activated by the retarder, the stop lights could be illuminated wit hout the service brakes actually being applied during that initial travel of the service brake pedal, and up until the point in time air is actually emitted from the brake pedal and into the service brake system.