Source: https://cms.fmcsa.dot.gov/print/regulations/title49/section/393.11
Timestamp: 2019-04-25 22:49:46+00:00

Document:
Guidance: §393.26(b)  cross references Federal Motor Vehicle Safety Standards (developed and issued by the NationalHighway Traffic Safety Administration) (FMVSS) 108 (49 Code of Federal Regulations (CFR) 571.108, S5.1.1.4) which allows reflective material to be used for side reflex reflectors under the conditions described below. Retro-reflective tape conforming to Federal specification L-S-300, "Sheeting and Tape, Reflective; Non-exposed Lens, Adhesive Backing," September 7, 1965, may be used in place of side reflex reflectors if this material as used on the vehicle, meets the performance standards in either Table I or Table IA of Society of Automotive Engineers J594f, Reflex Reflectors, January 1977.
Question 3: §393.11 , Footnote 5, requires that each converter dolly be equipped with turn signals at the rear if the converter dolly obscures the turn signals at the rear of the towing vehicle when towed singly by another vehicle. Are turn signals required on the rear of the converter dolly when the towing of the unladen dolly prevents other motorists from seeing only a portion of the lenses of the turn signals on the towing vehicle?
Question 4: Does a Commercial Motor Vehicle (CMV) equipped with amber tail lamps in addition to the red tail lamps required to designate the rear of a Commercial Motor Vehicle CMV meet the lighting requirements of §393.11 ?
No. §393.11  requires that lighting devices on Commercial Motor Vehicle CMVs placed in operation after March 7, 1989, meet the requirements of FMVSS No. 108 in effect at the time of manufacture. The National Highway Traffic Safety Administration (NHTSA) has issued interpretations which indicate that the use of amber tail lamps impairs the effectiveness of the required lighting equipment and as such is prohibited by Federal Motor Vehicle Safety Standards (developed and issued by the NationalHighway Traffic Safety Administration) (FMVSS) No. 108 (S5.1.3). Since National Highway Traffic Safety Administration (NHTSA) does not allow vehicle manufacturers to install amber tail lamps, the Federal Highway Administration (FHWA) has concluded that the use of amber tail lamps on vehicles placed in operation after March 7, 1989, is prohibited by §393.11 .
In the case of vehicles placed in operation on or before March 7, 1989, §393.11  requires that vehicles meet either the lighting requirements of part 393  or Federal Motor Vehicle Safety Standards (developed and issued by the NationalHighway Traffic Safety Administration) (FMVSS) No. 108 in effect at the time of manufacture. Prior to the December 7, 1988, final rule on part 393  (53 FR 49397), amber tail lamps were prohibited by §393.25 . §393.25(e)(3) (in the October 1, 1988 edition of the Code of Federal Regulations) required all rear lamps, with certain exceptions, to be red. Since tail lamps were not included in the exceptions, the use of amber tail lamps was implicitly prohibited. Therefore, a vehicle placed in operation on or before March 7, 1989, must not be equipped with amber tail lamps because the use of such lamps meets neither the lighting requirements of part 393  nor FMVSS No. 108 in effect at the time of manufacture.

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