Interpretation ID: NCC-200810-001-HMSL Hazard Lamp - Rostra

March 5, 2024

Mr. Peter Kallgren

Vice President, Sales & Marketing

Rostra Precision Controls, Inc.

2519 Dana Drive

Laurinburg, NC 28352

Dear Mr. Kallgren, 

This responds to your company’s request for interpretation regarding whether a replacement center high mounted stop lamp (CHMSL) intended to be installed on a truck cap is permitted to flash when a vehicle’s hazard lamps are activated. As we explain below, it is our view that it would not be permissible for the CHMSL to flash as a supplemental hazard warning lamp because our regulations require that a CHMSL be steady burning when activated. We respond to your question in more detail below. 

By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue Federal motor vehicle safety standards (FMVSS) 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, and NHTSA does not determine compliance of a vehicle or item of motor vehicle equipment outside the context of an actual enforcement proceeding. 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. The following represents NHTSA’s opinion regarding the applicability of FMVSS No. 108 requirements to your proposed CHMSL, based on the information you have provided. 

Under 49 U.S.C. 30122, a vehicle manufacturer, distributor, dealer, rental company, or repair business generally may not knowingly “make inoperative” any part of a device or element of design installed in or on a motor vehicle in compliance with an applicable FMVSS. You ask specifically about a CHMSL that would be a supplement to the existing one. This additional lamp is made necessary because, without one, a truck cap installed by your company would “make inoperative” the existing CHMSL by creating an obstruction or blockage. 

FMVSS No. 108 specifies requirements for original and replacement lamps, reflective devices, and associated equipment. The standard contains a number of specific requirements for certain lamps, such as headlamps, turn signal lamps, and high-mounted stop lamps, among others. In order to not “make inoperative” the required CHMSL, the lamp you propose to mount on the truck cap to avoid the obstruction would need to meet all the requirements of FMVSS No. 108 that apply to the original CHMSL. A CHMSL, by definition under paragraph S4, is expected to be steady burning, and it is also expressly required to be steady burning by paragraph S6.1.5, Activation, which states in relevant part that “Each lamp must be activated as specified … in response to the inputs specified in Table I ….” Table I-A, in turn, requires high mounted stop lamps to be “steady burning” and to “be activated only upon application of the service brakes or [ ] be activated by a device designed to retard the motion of the vehicle.” 

You describe a situation in which a CHMSL mounted on a truck cap is wired into a vehicle’s signal lighting system in a manner that causes the CHMSL to flash with the turn signals when the vehicle’s hazard warning system is activated. Accordingly, you ask whether it is permissible for the CHMSL to be considered a supplemental hazard lamp that flashes when the vehicle’s hazard warning system is activated. 

Because FMVSS No. 108 requires a CHMSL to be steady burning, as explained above, a CHMSL that flashes would not comply and would fail to prevent the cap obstruction from rendering inoperative the CHMSL required by FMVSS No. 108. The fact that hazard warning lamps have been activated does not change the requirement that the CHMSL be steady burning, and FMVSS No. 108 does not permit a CHMSL to cease to function as a CHMSL and begin to function as a supplemental hazard warning lamp simply because the hazard warning system is activated. This is consistent with past NHTSA interpretations, where the agency stated that “causing the center high-mounted stop lamp to flash would not change the center lamp into a ‘hazard warning lamp’ within the meaning of Standard No. 108.”1 

If you have further questions, please contact Eli Wachtel of my staff at (202) 366-2992. 

Sincerely, 

John Donaldson 

Acting Chief Counsel

1 Letter to Randy I. McClanahan (April 2, 1996), available at https://www.nhtsa.gov/interpretations/11610ztv.

Dated: 3/5/24

Ref: Standard No. 108