Interpretation ID: nht69-2.38
DATE: 09/05/69
FROM: AUTHOR UNAVAILABLE; Robert Brenner; NHTSA
TO: International Harvester Company
COPYEE: SUBJ. FILE OAA; CHRON. FILE OAA; CHRON. FILE MVSPS; SUBJ. FILE 409; CHRON. FILE 409; SCHNEIDER, RM. 512, DONOHOE; FISTE, RM. 302A, DONOHOE; FHWA EX. SEO.(2); FHWA CONTROL #55
TITLE: FMVSS INTERPRETATION
TEXT: Thank you for your letter of June 26, 1969, to the Administrator, Federal Highway Administration, concerning the activation of stop lamps and hazard warning signal lamps.
Your letter poses three basic questions as follows:
1. Are spring brakes, which backup a primary air brake system, considered "emergency" brakes within the meaning of paragraph S3.4.4 of Federal Motor Vehicle Safety Standard No. 1087
2. Under Standard No. 108, does the Bureau prefer (a) a wiring system whereby the stop lamps override the hazard warning lamps, or (b) a wiring system whereby the hazard warning lamps override the stop lamps?
3. Are both of the above wiring systems permissible?
In answer to the first question, spring brakes, which back-up a primary air brake system, are not considered "emergency" brakes within the meaning of paragraph S3.4.4 of Standard No. 108. The basis for this opinion is the same as that contained in Mr. Fay's letter of April 25, 1968, to the Blue Bird Body Company. The Bureau now has under development a proposed standard for brakes which will be applicable to trucks. If under this standard, spring brakes are defined as emergency brakes, then the requirement of paragraph S3.4.4 of Standard No. 108 will be applicable.
In answer to the second and third questions, the Bureau has no well-founded research data to prove or disprove the effectiveness of the two different wiring systems for all vehicles covered by Standard No. 108. Use of either of the systems is permitted under Standard No. 108.
However, the regulations of the Federal Highway Administration's Bureau of Motor Carrier Safety (49 CFR 392.22(a) and 392.23(a)) require flashing of the turn signal lamps as a vehicular traffic hazard warning signal whenever a vehicle is stopped under certain conditions. These regulations therefore do not allow overriding of the warning signal by the stop lamps. It is our belief that a flashing light, rather than a steady-burning light, conveys a more effective warning of a stopped vehicle. Consequently, trucks, buses, and trailers which after sale may be subject to Bureau of Motor Carrier Safety regulations should be manufactured so that the stop lamps will not override the hazard warning signal. Consideration is being given to rule making(Illegible Word) which would make this mandatory for all trucks, buses, and trailers.