Interpretation ID: 1985-04.3

TYPE: INTERPRETATION-NHTSA

DATE: 10/22/85

FROM: AUTHOR UNAVAILABLE; Jeffrey R. Miller; NHTSA

TO: Kenneth E. Deane -- Application Engineer, Mallory Timers Company

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Kenneth E. Deane Application Engineer Mallory Timers Company P.O. Box 986 Indianapolis, IN 46206

This is in reply to your letter of July 25, 1985, to Mr. Vinson of this office asking for an interpretation of Motor Vehicle Safety Standard No. 108.

With reference to the center high-mounted stop lamp and the acceptability of a switch you have designed, you have asked whether the new lamp and the vehicle's primary stop lamps "must be energized simultaneously, or that the low mount light must come on first, followed by the high mount light within 35 milliseconds." You have designed a switch which would energize these lamps within 80 milliseconds of each other.

Paragraph S4.5.4 requires that the stop lamps on a vehicle be activated upon application of the service brakes, and, further, that the center high-mounted stop lamp shall only be activated upon application of the service brakes. We interpret this as meaning that all stop lamps on a vehicle must be activated simultaneously. Lawrence J. Fogel's "Human Information Processing" (Prentice-Hall, Inc. (1967), p. 101) indicates that the eye cannot discern delays of 50 milliseconds or less. Therefore, we believe that an observer would not be able to detect a 35 millisecond delay but would be able to detect an 80 millisecond delay. Accordingly, a 35 millisecond delay would be considered to be "simultaneous," but an 80 millisecond delay would not.

You have also asked whether "slow 'teasing' of the brake pedal must not cause intermittent 'blip' flashing of the high mount light when the hazard warning signal is employed." A center high-mounted stop lamp is allowed to flash with the hazard warning system on passenger cars manufactured before September 1, 1986, but it must be steady burning at all times on passenger cars manufactured on or after that date.

I hope that this answers your questions. Sincerely, Jeffrey R. Miller Chief Counsel

July 25, 1985 Mr. Taylor Vinson SMVSS108 NHTSA Room 5219 U.S. Department of Transportation 400 7th Street, SW Washington, DC 20024

Dear Mr. Vinson:

I have been referred to you by Mr. Kevin Cavey of the NHTSA for a clarification of one of the requirements for the High Mounted Brake Light on passenger cars.

We have designed and tooled a brake switch for this application in which the low mount brake lights and the high mount brake lights are energized within 80 milliseconds of each other. (This is at a brake lever actuation speed of 5mm/second.) To further clarify, either light could come on first, followed by the other light within 80 milliseconds.

Recent inputs from our customer, B-O-C Detroit, indicate that both lights must be energized simultaneously or that the low mount light must come on first, followed by the high mount light within 35 milliseconds. Also that slow "teasing" of the brake pedal must not cause any intermittent "blip" flashing of the high mount light when the hazard warning system is employed. In conversation with B-O-C engineering they indicated that they "think" this is the NHTSA requirement.

A complete redesign of our already tooled product would be necessary to meet these new requirements at considerable cost and subsequent program delay. For this reason, we request your input and interpretation of the NHTSA's intentions in this area.

Thank you for your early consideration. Respectfully, Kenneth E. Deane Application Engineer KED/s cc: Messrs. E. Eaton P. Johnson J. Smith R. Stafford J. Wiser