Interpretation ID: GF002551.3

Mr. Robert M. Clarke
President, Truck Manufacturers Association
1225 New York Avenue, NW
Suite 300
Washington, DC 20005-6156

Dear Mr. Clarke:

This responds to your March 11, 2005, letter regarding installation of certain auxiliary lighting on heavy-duty trucks and truck tractors. Specifically, you ask about installing auxiliary lamps in the vicinity of the front identification and clearance lamps. You also ask about installing auxiliary lamps above or below the surface occupied by front identification and clearance lamps.

The standard relevant to your question is Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, reflective devices and associated equipment. For vehicles of 80 or more inches in overall width (such as the trucks and the truck tractors described in your letter), Table II of FMVSS No. 108 requires that 3 amber identification lamps (three-lamp cluster) be located as close as practicable to the top center of the vehicle or the cab, with lamps placed 6 to 12 inches apart. The function of this three-lamp cluster is to indicate the presence of a large vehicle on the roadway. Table II also, requires that two amber clearance lamps be located "to indicate the overall width of the vehicle . . . and as near the top thereof as practicable."

Before addressing the auxiliary lamp configurations discussed in your letter, we note that S5.1.3 of FMVSS No. 108 prohibits installation of lamps that would impair the effectiveness of the required lighting, including the identification lamp cluster. The agency has long maintained that highway traffic safety is enhanced by the familiarity of drivers with established lighting schemes, which facilitates their ability to instantly recognize the meaning the lamps convey and respond accordingly. Therefore, the agency previously explained that auxiliary lamps must be located such that they would not interfere or be confused with the lamps required by our standards. For example, in a January 21, 2004, interpretation letter to a confidential party, the agency explained that auxiliary lamps must be located far enough away from the three-lamp cluster, so that they do not impair their effectiveness. In an October 18, 2002, letter to Mr. Weidman, we indicated that two auxiliary lamps located next to the three-lamp cluster would detract from the purpose of the cluster. With this background in mind, we turn to auxiliary lamp configurations described in your letter.

You provided descriptions and illustrations showing several different lamp configurations and asked whether these configurations would be permitted under FMVSS No. 108. Specifically, you describe three configurations consisting of the three-lamp identification cluster, two clearance lamps, and one or more sets of auxiliary lamps located between the clearance lamps and the three-lamp cluster. You ask if all three configurations would comply with FMVSS No. 108. In alternative, you ask that the agency confirm that the auxiliary lamps are permissible, if the distance between the three-lamp cluster and the auxiliary lamps is at least twice the distance that separates each lamp in the cluster.

First, we note that auxiliary lamps located immediately adjacent to the three-lamp cluster would not be permitted by FMVSS No. 108 because they would impair the effectiveness of identification lamps. The purpose of the three-lamp cluster requirement is to signal the presence of a large vehicle to other drivers. The number of lamps, three, is a part of the signal, and additional lamps could make the signal less recognizable.

Second, while we would generally prefer to establish distance requirements through rulemaking, we recognize the need for guidance with respect to the permissible positioning of auxiliary lamps located between the clearance lamps and the three-lamp cluster. We believe that positioning auxiliary lamps at a distance that is at least twice the distance that separates each lamp in the required three-lamp cluster provides sufficient separation not to impair the effectiveness of the three-lamp cluster (see diagram below).

Third, you also asked about installing auxiliary lamps above or below the surface occupied by the three-lamp cluster and the clearance lamps. We note that FMVSS No. 108 does not prohibit auxiliary lamps that are located on a different surface from the three-lamp cluster and the clearance lamps. Specifically, auxiliary lamps may be located on the roof of the truck cab, if the required lamps are located on the sleeper roof above the cab roof. The reverse arrangement is also permissible. In either configuration, the auxiliary lamps are located at a sufficient distance from the required lamps that they would not impair their effectiveness.

Finally, we note that the auxiliary lamps must have the same photometric output and be of the same color as the lamps specified in Table II to avoid impairment. We believe that maintaining color and photometric output consistency is important because, for example, the presence of red auxiliary lamps located next to amber clearance lamps could confuse drivers as to the traveling direction of the vehicle.

If you need further assistance, please contact George Feygin of my staff at this address or at (202) 366-2992.

Sincerely,

Jacqueline Glassman
Chief Counsel

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