Interpretation ID: nht92-9.14

DATE: February 11, 1992

FROM: Lance Watt -- Director of Engineering, The Flxible Corporation

TO: Paul Jackson Rice -- Office of Chief Counsel, NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 4/10/92 from Paul J. Rice to Lance Watt (A39; Std. 108)

TEXT:

The Flxible Corporation is a major domestic manufacturer of city transit buses and requests an interpretation concerning FMVSS 108, "Lamps Reflective Devices, and Associated Equipment," while also referencing FMVSS 121 "Air Brake Systems."

An air brake system is used on our vehicles. As the driver starts to apply the service brake pedal to slow or stop the vehicle, 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 Systems." The stop lamps are in turn activated by the stop lamp switch.

The Flxible Corporation offers optional transmissions which have internal hydraulic retarders for supplemental braking as a means to increase brake lining life. This retardation deceleration would be over and above that obtained by the normal service brake system. In our current design, the transmission retarder is electrically operated during the initial travel of the service brake pedal. As the service brake pedal is further depressed, the service brakes are activated, and this in turn triggers the stop lamp switch which in turn illuminates the stop lamps.

The Flxible Corporation has received requests from customers to activate the transmission retarder when the ACCELERATOR pedal is released. In this scenario, the service BRAKE pedal would not be used to activate the transmission retarder. However, if required, the driver could also depress the brake pedal to in turn activate the service brakes in order to achieve an even higher rate of vehicle deceleration over and above that obtained by the transmission retarder itself.

If the brake pedal were not depressed however, and with the vehicle deceleration caused solely by transmission retardation, the stop lamps would not be illuminated and therefore, following vehicles may be unaware of this sudden reduction in vehicle speed.

Some of our customers have also requested to have the transmission retarder activate the stop lamps to provide following vehicles with a warning that a sudden reduction in vehicle speed was in progress, even though it was caused by the transmission retarder as opposed to a service brake application. Again, this application of the stop lamps would be achieved by release of the accelerator and without depressing the brake pedal, and potentially without any intent to apply the service brakes on the part of the driver.

Section S5.5.4 states: "The stop lamps on each vehicle shall be activated upon application of the service brakes." This is interpreted by Flxible to mean the brake pedal would activate the service brakes which would activate the stop

lamp switch which in turn would activate the stop lights. By virtue of our customer's requests, the stop lamps would already be activated when the driver released the accelerator pedal and without any application of the brake pedal.

Flxible has in the past requested a NHTSA ruling on a further scenario outside of that, but somewhat related to that which is described here-in. Please find attached a copy of that request along with a copy of your response for reference.

Additionally, some of our customers, especially those in locations likely to experience icy or slippery road conditions, request a retarder cut off switch in order to disable the retarder and reduce the possibility of uncontrolled drive axle wheel lock-up. In cases such as this, without a dual system that would then allow stop light switch and stop light activation to be caused by application of the brake pedal as in our standard system today, a stop light activation would occur at the time of accelerator release with minimal if any change in vehicle forward speed, and again, potentially with no intent on the part of the driver to use the service brakes.

Flxible to date has resisted the customer requests as noted, however, these customers, without a specific NHTSA ruling on the request as stated above, threaten to declare Flxible a non responsive bidder on transit bus procurements. The basis of their complaints or requests in this regard stem from the fact that they require operating standardization across their various manufacturer fleets to prevent operator error or confusion.

A ruling is requested on whether a non-compliance with Section S5.5.4 of FMVSS 108 would result, if the stop lamps were activated without depressing the brake pedal as requested by our customers.

Flxible appreciates the opportunity to petition for a ruling in this complex matter so that we may use your response accordingly in responding, to our customer's requests.

Should you desire any further clarification or information on this subject, please feel free to contact the writer at (614) 362-2730.