Kim D. Mann, Esq.

Scopelitis, Garvin, Light & Hanson

1850 M Street, NW

Washington, DC 20036

Dear Mr. Mann:

This responds to your letter asking about the permissibility of certain auxiliary lighting equipment under Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. You asked about this in connection with a product of one of your clients. Specifically, your letter requested our opinion as to the permissibility of a row of eleven lamps that function as identification lamps, stop lamps, supplemental stop lamps, and turn signals. Based on the information about the product that you provided and the analysis below, it is our opinion that the auxiliary stop lamps and turn signal lamps would impair the effectiveness of the identification lamps, and thus be impermissible under the standard.

By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). NHTSA does not provide approval of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. FMVSS No. 108 specifies requirements for original and replacement lamps, reflective devices, and associated equipment. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs. If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action.

Paragraph S5.1.3 of Standard No. 108 specifies that no additional lamp, reflective device or other motor vehicle equipment shall be installed that impairs the effectiveness of lighting equipment required by this standard. As you are aware, identification lamps are required
equipment on trailers (as specified in Table II, which states that identification lamps on trailers should be located on the rear 3 lamps as close as practicable to the top of the vehicle at the same height). It is our opinion that the product you ask about would impair the effectiveness of the identification lamps by obscuring the three-lamp cluster pattern required by the Standard, rendering it unrecognizable by turning it into an eleven-lamp cluster.

You present a variety of arguments that you believe support the permissibility of your clients product, and we will address them here. In your first argument, you state that NHTSA issued an interpretation in 1999[1] stating that a set of brake lights, functioning as supplemental stop lights when brakes are applied, may be installed adjacent to compliant three-lamp cluster rear identification lamps. [emphasis added] This reading is somewhat inaccurate. In that letter, the product addressed was a light bar which contained the required cluster of three identification lamps. Those same three bulbs also acted as supplemental stop lamps by increasing in intensity when the brakes were applied. In addressing the increased brightness, we stated that the effectiveness of [the identification lamps] would not be impaired by an increase in the intensity of the lamps when the brake pedal is applied. [emphasis added] The distinguishing difference between this product and the one you ask about is that the product addressed in the 1999 letter maintained the characteristic three-lamp cluster indicative of identification lamps even when acting as a supplemental stop lamp, whereas the additional eight lamps of your clients design would effectively mask the three-lamp cluster, turning it into an eleven-lamp cluster. Table II of Standard No. 108, which lays out in detail the location and many characteristics of required lighting equipment for truck trailers, is specific that three lamps are to be used, as well as to their required configuration.

In your second argument, you noted a letter sent by this agency in 2005,[2] which stated that auxiliary lamps should be located sufficiently distant from the three-lamp ID cluster so as not to impair its effectiveness. You then proceed to state that:

It is not the precise number of lights, three, that indicates the presence of a large vehicle in the roadway. It is the presence of a series of high-mounted lights across the rear of the trailer.

This logic deviates from the logic that NHTSA has used for some time in creating a standardized system for lighting symbols on the highways. In a 1999 letter of interpretation, we summarized our position as follows:

Intuitively, it may seem to you that providing additional stop lamp, turn signal, and taillamp functions can only enhance motor vehicle safety. However, we are convinced that our current standardized approach to motor vehicle lighting has positive safety benefits by virtue of its broad public and international acceptance, and that lighting equipment that is required by Standard No. 108 for a specific purpose ought not to be used for a different purpose. A driver, when confronted

with a signal, must not be confused and must react to it as quickly as possible. The use of the outer lamps of the identification lamp cluster as supplementary turn signals, carry the potential for confusion and hence impairment of the lamps[3]

Thus, we believe that the three-lamp cluster, by virtue of the standardization ensured by Standard No. 108, is inherently safer than other, non-conforming patterns of lamps such as an eleven-lamp cluster. This is also why we reject the argument you make that the additional high-mounted turn lights would, when activated, make the trailers presence even more pronounced. While the additional lamps would perhaps make it brighter, the obscuring of the highway-standard three-lamp cluster would outweigh that benefit.

You also argue that with regard to an identification lamp cluster, three bulbs is a minimum according to paragraph S5.1.1. You state that the number of identification lamps may be any number exceeding two (including 11). We disagree that this is a correct interpretation of the language in that paragraph. The relevant language of paragraph S5.1.1 reads:

Each vehicle shall be equipped with at least the number of lamps, reflective devices, and associated equipment specified in Tables I and III and S7, as applicable

This language simply indicates that FMVSS No. 108 specifies requirements for a minimum number of lamps, reflective devices, and associated equipment. We note that it does not permit additional lamps that interfere with the functioning of the required lighting equipment, or alter established lighting systems, contrary to paragraph S5.1.3.

NHTSA has previously stated that the identification lamp system must consist of no more than three lamps. For example, in 2003, NHTSA made the following statement:

[A]n identification lamp system complying with Standard No. 108 cannot have more than three lamps. You have correctly interpreted Standard No. 108 to your prospective customers who have expressed an interest in having an array of more than three such lamps.[4]

Finally, you point to a 1991 letter of interpretation to J.C. Brown,[5] which stated that an auxiliary high mounted stop light and turn signal complied with the requirements of FMVSS No. 108 as lending support to the argument that your clients product would be compliant. The 1991 interpretation concerns an auxiliary center high mounted stop lamp/turn signal that was to be installed on trailers in close proximity to the three-lamp identification cluster. In that letter, the agency concluded that the auxiliary lamps were permitted despite concern that they could mask the light from the identification cluster when activated. The agency reasoned that because of the presence of clearance lamps, which also serve the purpose of identifying the vehicle, the fact that the light from the identification cluster might be temporarily masked did not impair its effectiveness for purposes of section S5.1.3.

In the instant matter, our concern is not that the auxiliary stop and turn signal lamps could mask the light, but rather that they necessarily will obscure the standard three-lamp cluster that NHTSA has determined to be the standard for identification lamps, by turning it into an unrecognizable eleven-lamp cluster. We note that while you stated the eleven-lamp cluster would significantly enhance safety, no engineering data were provided to support this assertion.

If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.

Sincerely yours,

Anthony M. Cooke

Chief Counsel



[1] 6/23/99 letter to a confidential recipient, available at

[2] 7/28/05 letter to Robert Clarke, available at

[3] 10/26/99 letter to Michael Lafon, available at

[4] 3/7/03 letter to Randy McGuire, available at

[5] 3/7/91 letter to J.C. Brown, available at