Interpretation ID: nht91-6.2

DATE: September 18, 1991

FROM: Paul Jackson Rice -- Chief Counsel, NHTSA

TO: John E. Calow -- Senior Safety Engineer, Oshkosh Chassis Division

TITLE: None

ATTACHMT: Attached to letter dated 8-12-91 from John E. Calow to Taylor Vincon (OCC 6358)

TEXT:

This responds to your letter of August 12, 1991, to Taylor Vinson of this Office, asking for a verification of your understanding of certain requirements of Motor Vehicle Safety Standard No. 108.

Specifically, you ask:

"If the Brake Lights and Hazard Warning Lights are optically combined and both are activated (per federal regulations) which of the following will occur?

A) The brake lights will over-ride causing a steady light emission.

B) The hazard lights will over-ride causing a flashing light emission.

The answer to your first question is either "A" or "B" depending on how the manufacturer decided to wire the vehicle. The vehicular hazard warning signal operating unit is required to operate sufficient turn signal lamps to meet, as a minimum, the turn signal lamp photometric requirements of the standard (see S5.5.5) and function (see Table I or III) in accordance with SAE J910, January 1966. Since the vehicular hazard warning signal operating unit causes turn signal lamps to operate simultaneously, the turn signal lamps become hazard warning lamps that are optically combined with turn signal lamps. Should these hazard warning lamps also be optically combined with the brake lamps, as in your question, the standard does not provide any requirement for which, brake or hazard, should override.

You also ask:

"If the vehicle has a Center High Mounted Stop Lamp 'CHMSL' is it acceptable to have the Hazard Warning Lights over-ride the Brake Lights if the CHMSL has a steady light emitance (sic) upon brake application?"

The answer to this question is the same as the first. However, the CHMSL may not be combined, optically or otherwise, with any other lamp, and therefore it must remain operative upon brake application, even if the remaining stop lamps have been overridden.

I hope that this answers your questions.