Interpretation ID: nht79-3.1

DATE: 01/24/79

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

TO: Volkswagen of America

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of January 3, 1979, asking for confirmation of your interpretation of Federal Motor Vehicle Safety Standard No. 108 as it applies to a braking system that Volkswagen proposes to use on its 1980 Dasher model.

Specifically, the Dasher will employ a single "pressure switch on each vehicle, meaning that the stop lamp will be activated by only one of the [two, split] service brake systems." You asked whether this is consistent with S4.5.4 of Standard No. 108 which requires that "the stop lamps on each vehicle shall be activated upon application of the service brakes." You argued that it meets the standard because:

"Neither FMVSS 571.105-75 nor 575.108 (sic) clearly specify the conditions under which the stop lights have to operate. Specifically the regulations do not specify that the stop lamps must illuminate upon application of the service brake control if one of the circuits of a dual circuit hydraulic braking system failed."

We do not concur with your interpretation. S4.5.4 quite clearly specifies the conditions under which the stop lamps must operate--"upon application of the service brakes," and it is immaterial which circuit of a dual circuit hydraulic braking system is braking the vehicle. Therefore, your proposed system would constitute an apparent noncompliance with Standard No. 108.

Sincerely,

ATTACH.

VOLKSWAGEN OF AMERICA

JANUARY 3, 1979

Joseph J. Levin -- Office of the Chief Counsel, National Highway Traffic Safety Adm.

Subject: Stop Lamp Switch Requirements - FMVSS 108

Dear Mr. Levin:

The Federal Motor Vehicle Safety Standard 108 specifies that a vehicle stop lamp shall be activated upon application of the service brakes. Volkswagen is currently considering a manufacturing decision regarding brake light switches, and because this would fall under the spectrum of the standard, we are requesting NHTSA's opinion of our contemplated course of action as it relates to the standard.

Volkswagen's current product line uses two pressure sensing switches in the master cylinder to activate both the stop lamps and the brake failure warning light. For the 1980 model year, Volkswagen is replacing these switches in the master cylinder with a float-type fluid level indicator switch to activate the brake failure warning light, and a pedal-activated switch to activate the stop lights. Together these changes will result in a cost saving. However, because of certain manufacturing considerations we are unable to employ the brake pedal switch on Dasher models. For these models we will need an alternate method to activate the stop lamps, specifically an in-line pressure sensing switch.

The proposed system uses only one pressure switch on each vehicle, meaning that the stop lamps will be activated by only one of the service brake subsystems. Our question is then whether the NHTSA believes that this strategy (the single switch) is consistent with the standard.

It is Volkswagen's position that our proposal meets the requirements of all applicable standards. Neither FMVSS 571.105-75 nor 575.108 clearly specify the conditions under which the stop lights have to operate. Specifically, the regulations do not specify that the stop lamps must illuminate upon application of the service brake control if one of the circuits of a dual circuit hydraulic braking system failed.

Volkswagen recognizes that the NHTSA may be concerned about the situation in which, with one hydraulic circuit inoperative, service brake operation is possible (at a reduced level) without stop lamp activation. However, this is a situation which has a small likelihood for occurrence, and a smaller likelihood for sustained existence.

The alternative to our proposal is the installation of a second pressure sensing switch on each vehicle such that one switch is employed in each service brake subsystem. This system would insure that, unless the switches themselves failed, stop lamp activation would continue as long as hydraulic pressure is maintained in any one of the two subsystems. However, the in-plant cost of the second switch is substantial, DM 1.80 per vehicle.

Your prompt consideration of the request for interpretation would be greatly appreciated. If you need any further information, or if you would like to discuss this topic, please contact Mr. Preuss of my staff. He can be reached at (313) 574-3784.

Sincerely

D. K. Haenchen Administrator Vehicle Regulations