C. Thomas Terry, Director
Safety Affairs & Regulation
General Motors North America
Safety Center (480-111-S56)
30200 Mound
Warren, MI 48090-9010

Dear Mr. Terry:

On February 11, 2000, you wrote the Acting Administrator, requesting an interpretation of Federal Motor Vehicle Safety Standard No. 108 and petitioning for its amendment. This letter provides an interpretation of Standard No. 108. The Associate Administrator for Safety Performance Standards will inform you in due course whether he has granted your petition.

Paragraph S5.5.4 of Standard No. 108 states in pertinent part that "the stop lamps on each vehicle shall be activated upon application of the service brakes." You asked "whether brake lamp illumination is required, prohibited, or allowed under other conditions." You set forth two such conditions where the brake pedal is not employed. The first condition is:

Service brakes applied with intent of decelerating the vehicle. An example in this category would be adaptive cruise control where the service brakes may be automatically applied (without driver application of the brake pedal) to slow the vehicle in order to preserve spacing between vehicles.

We are providing an interpretation that covers only the system given as an example, an adaptive cruise control automatically applied "to slow the vehicle in order to preserve spacing between vehicles." The SAE Standards on stop lamps that are incorporated by reference in Standard No. 108, J586 MAY84 and J1398 MAY85, define stop lamps as "Lamps . . . [which] indicate the intention of the operator of a vehicle to stop or diminish speed by braking." Since you state that the intent of the brake application in this context would be "to slow the vehicle," which would "diminish speed by braking" within the meaning of the applicable SAE standards, we conclude that activation of the stop lamps would be required under these circumstances.

The second condition you set forth is:

Service brakes applied with no intent to decelerate the vehicle. The best example in this category would be traction control, where the intent is to help accelerate, rather than decelerate, the vehicle. Electronic stability control is another technology that can momentarily actuate the service brakes with minimal or no vehicle deceleration.

The intent of the brake application under the first part of the second condition is not to stop the vehicle or diminish its speed. Therefore, activation of the stop lamps, as defined in the applicable SAE Standards, would not be required. In addition, S5.1.3 of Standard No. 108 states that "No additional lamp, reflective device, or other motor vehicle equipment shall be installed that impairs the effectiveness of lighting equipment required by" Standard No. 108. In our view, activation of the stop lamps for a purpose other than to indicate stopping or slowing will create confusion for the driver following as to the meaning of the signal, with the potential of causing that driver to apply the brakes in his or her vehicle inappropriately. Thus, illumination of the stop lamp during traction control would be an impairment of the stop lamp function within the meaning of S5.1.3. We have therefore concluded that installation of traction control systems, or any other equipment, that activates the stop lamps for purposes other than to indicate that the vehicle is stopping or slowing is prohibited by S5.1.3 and would create a noncompliance with Standard No. 108.

Regarding the second part of the second condition, electronic stability control, the same interpretation would apply if the vehicle speed was not diminished by application of the service brakes (or any part). It would not apply if the application of the service brakes resulted in deceleration. In that case, the stop lamps must be illuminated.

We realize that, under some circumstances, the driver's application of the service brake system to achieve the same result, i.e. not actually achieving a reduction in speed, will cause the stop lamps to illuminate, but this is an unavoidable consequence of the technology available for driver application of the service brakes. With the advent of sophisticated electronic systems, such as those that you mention, there is no need for them to provide false signals.

Also, you have asked that we "for the near term . . . agree that FMVSS 108 allows, but does not require or prohibit, illumination of the brake lamps under the two conditions described above" because a "strict 'required' or 'prohibited' interpretation could have the effect of raising compliance issues with current production vehicles." We cannot adopt a different interpretation for the near term than for the long term. We encourage manufacturers to write us for interpretations before introducing new systems into production so that compliance issues will not arise, or to file petitions for rulemaking where appropriate. If a manufacturer constructs a noncompliant vehicle based upon a misunderstanding of what is required by a Federal motor vehicle safety standard, it must accept the consequences of its actions.

If you have any questions, you may refer them to Taylor Vinson of this Office (202-366-5263).

Frank Seales, Jr.
Chief Counsel