Interpretation ID: nht92-4.27

DATE: August 21, 1992

FROM: Paul Jackson Rice -- Chief Counsel, NHTSA

TO: S. Watanabe -- Manager, Automotive Equipment Legal and Homologation Sect., Stanley Electric Co. Ltd.

TITLE: None

ATTACHMT: Attached to letter dated 8/7/92 from S. Watanabe (signature by P.P. F. Nakayama) to Paul J. Rice

TEXT:

This responds to your letter of August 7, 1992, with respect to the legality under Federal Motor Vehicle Safety Standard No. 108 of two configurations of rear stop/taillamps and center highmounted stop lamps (CHMSL) on passenger cars.

In your Figure 1, the stop/taillamps are mounted at 72 inches height above the road surface, while the CHMSL is mounted 3 inches below the rear window. In your Figure 2, the stop/taillamps are again mounted at 72 inches while the CHMSL is mounted above the rear window and between the stop/taillamps. You believe that both Figures depict a conforming rear lighting scheme under Standard No. 108.

You are correct. Standard NO. 108 does not specify any spatial relationship between the CHMSL and stop lamps or taillamps. It permits the CHMSL to be mounted anywhere on the vertical centerline of the passenger car, but not lower than 3 inches below the rear window. Standard No. 108 also permits stop and taillamps to be mounted not higher than 72 inches above the road surface. Your two Figures do not exceed these regulatory parameters, and thus, each is permitted by Standard No. 108.

However, the research that proved the efficacy of the CHMSL in addressing the problem of rear end collisions was based upon a triangular configuration of stop lamps in which the CHMSL was the apex. We note that the CHMSL in Figure 1 is at the apex of an inverted triangle, while in Figure 2 the CHMSL is simply a lamp in a horizontal array. It is possible that the benefits of the CHMSL would not be realized through use of the configurations depicted in Figures 1 and 2, even if they are permitted by Standard No. 108.