Dear Mr. Moore:
We have received your letter of September 29, 1993, with reference to the location requirements of Standard No. 108 for identification (i.d.) lamps.
Table II of the standard in pertinent part specifies the following location for i.d. lamps: "On the rear - 3 lamps as close as practicable to the top of the vehicle at the same height, as close as practicable to the vertical centerline . . . ." You reference at least two instances in the past 20 years or longer in which "NHTSA has allowed the slight misalignment of I.D. lights because of `Practical' circumstances," and have asked for copies of these interpretations.
We are unaware of these interpretations. In their absence, you have asked for an interpretation of the phrase "at the same height" that would permit the mounting height of the center lamp to deviate slightly from the height of the two lamps that flank it, as shown in your letter. You depict two other possible configurations in which the three lamps are mounted at identical heights. In one configuration, the lower edges of the outboard lamps hang below the frame "making them vulnerable to being damaged or knocked off" in your opinion. In the second configuration, the lamps are raised and protected, but the center lamp is somewhat obscured by the "typical roller or protective pad." You deem these configurations undesirable for safety reasons.
The question to be answered is whether the configuration you prefer is "as close as practicable to the top of the vehicle at the same height" (note the absence of a comma between "vehicle" and "at"). The determination of practicability is initially that of the manufacturer. Unless it is clearly erroneous, NHTSA will not question it. In the absence of a superstructure, the frame location may be regarded as being "as close as practicable to the top of the vehicle. . . ." Because "at the same height" is part of the same phrase, practicability also governs placement of the lamps at the same height. A manufacturer may determine that, for the sake of practicability, i.d. lamps may be mounted at a height sufficient to protect them from breakage (the outboard lamps) and to ensure compliance with photometric requirements (the center lamp). The configuration you depict is sufficiently close to the literal reading of the phrase "at the same height" that NHTSA would not question the manufacturer's determination of practicability with respect to the mounting height of the center i.d. lamp.
John Womack Acting Chief Counsel