Search Interpretations


Mr. Rolf Bergmann

Safety Affairs and Vehicle Testing

Volkswagen of America, Inc.

Auburn Hills, MI 48326

Dear Mr. Bergmann:

This responds to your letter regarding requirements related to the spacing between daytime running lights (DRLs) and turn signals in Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. Specifically, you asked whether the provision in paragraph S5.5.11(a)(4)(iv) can be met by a system in which the intensity of the DRL (located less than 100 mm from the lighted edge of a turn signal) is reduced to the photometric output of a parking lamp when the turn signal or hazard warning signal is activated. As discussed below, the answer is no. In order to come within the provision at issue, the DRLs would need to be completely deactivated when the turn signals or hazard lights are on.

FMVSS No. 108 specifies requirements for original and replacement lamps, reflective devices, and associated equipment. Among other things, the standard specifies requirements related to spacing between DRLs and turn signals to ensure that the DRLs do not have the effect of masking the turn signals.

The provision you ask about, S5.5.11(a)(4)(iv), is one of the conditions for an option that is available for DRLs located less than 100 mm from the lighted edge of a turn signal. The condition is that:

The DRL is deactivated when the turn signal or hazard warning signal lamp is activated. (Emphasis added.)

In your letter, you argue that the intent of the option in subsection (iv) does not require that the DRL be totally extinguished when the turn signal or hazard warning is activated, and that reducing the illumination of the DRL to a parking lamp mode should be viewed as deactivation.

We disagree with your suggested interpretation based on the plain language of the standard. If the agency had intended to include dimming of the DRL as part of this option, it would have used language other than deactivated and would have specified the amount of light that could be emitted under the dimmed condition.

We also note that the Federal Register notice adding the language of paragraph S5.5.11(a)(4)(iv) to Standard No. 108 also indicates that dimming the DRL is not a correct interpretation of the standard. In devising the precise requirements of the standard, NHTSA conducted testing of the turn signal masking effect in order to determine appropriate spacing and luminosity regulations. NHTSA tested the masking effect using two variables spacing and relative luminosity. The agency found that increasing the spacing between the DRL and the turn signal was a highly effective means of allowing subjects to see the turn signals while the DRLs were active. On the other hand, the agency found that increasing the intensity of the turn signals (thereby making them brighter relative to the DRLs) had almost no effect on turn signal masking.[1] In its explanation of the rule, the agency explained:

The alternative of brighter turn signals does not resolve the issue. The only effective alternative to prevent turn signal masking would be to extinguish the DRLs during signaling.[2] [Emphasis added]

If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.

Sincerely yours,

Anthony M. Cooke

Chief Counsel



[1] 58 FR 3504, January 11, 1993.

[2] Id.