Mr. Scott Ault

President/Dealer Developer

Deceleration Technologies, LLC

5515 University Drive

Grand Forks, ND 58203

Dear Mr. Ault:

This responds to your letter, in which you ask about the permissible activation of stop lamps under Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. Specifically, you asked whether it would be permissible to activate the stop lamps when the vehicle reaches a certain rate of deceleration, regardless of whether the driver intended to activate a braking or engine retardation system. Our answer is that this would not be permissible 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 approvals 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. 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.

With regard to the specific technology, called Slow-N-Tell, you are inquiring about, you state:

My technology specifically reads vehicle speed and calculates rate of deceleration, when deceleration is detected. Based on the rate of deceleration, expressed as negative mph per second, stop lamps are activated when braking threshold is reached.

As you note in your letter, deceleration can occur in a variety of situations, including upon application of the service brake, activation of an engine retarder, or simply by force of gravity if the vehicle is traveling up an incline. In the latter situation, because Slow-N-Tell works by sensing deceleration, it would activate the stop lamps even though the driver may not have intended the vehicle to decelerate. You state that it is your opinion that this does not violate paragraph S5.1.3 of FMVSS No. 108 (which states that no motor vehicle equipment shall be installed that impairs the effectiveness of lighting equipment required by this standard), because it signals to following drivers that the vehicle is slowing.

We disagree with your suggested interpretation of the standard. The SAE Recommended Practices on stop lamps that are incorporated by reference into Standard No. 108, SAE J586 (May 1984) and SAE J1398 (May 1985), define stop lamps as [l]amps which indicate the intention of the operator of a vehicle to stop or diminish speed by braking. [emphasis added] As we have stated in several letters, including the April 10, 1992 letter to Mr. Lance Watt[1] that you cite:

Activation of the stop lamps initiated by release of the accelerator pedal is permissible only when the intent of the driver is to reduce the speed of the vehicle by an immediate subsequent act of braking, whether that is achieved through his use of the service brake system, use of retarders, or a combination of the two.

However, a configuration where the stop lamps operate in the absence of service brake application or activation of a retarder system (as appears to occur when a retarder cut off switch has been activated) would be subject to S5.1.3 of the standard.

The situation you describe is analogous to the situation proscribed in the letter to Mr. Watt. If the vehicle experienced deceleration due to reasons other than the application of a braking or engine retardation system (e.g., the vehicle was traveling up an incline), it would be a violation of paragraph S5.1.3 for the stop lamps to activate.

Finally, we do not agree with your assertion that activating the stop lamps in such a situation would actually enhance the effectiveness of the lighting equipment. The signal emitted by stop lamps is to alert other drivers of the vehicle operators intent to slow down or stop. If the vehicle is decelerating due to an incline, activation of the stop lamps would send an improper signal that could be confusing to other drivers.

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

Sincerely yours,

Stephen P. Wood

Acting Chief Counsel



[1] Available at