Interpretation ID: NCC-241023-001TSEI-TIMA Letter of Interpretation 571.108 Flashing Amber Lights 12-13-2024.signed.

December 13, 2024

Mr. Chuck Polley

Transportation Safety Equipment Institute

c/o Grote Industries LLC

2600 Lanier Drive

Madison, IN 47250

Mr. John Freiler

Truck Trailer Manufacturers Association

7001 Heritage Village Plaza

Suite 220

Gainesville, VA 20155-3094

Dear Messrs. Polley and Freiler:

This responds to your letter requesting clarification of Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, reflective devices, and associated equipment, regarding flashing “emergency warning lights.” I apologize for the delay in responding. As used in your letter, the term “emergency warning lights” generically refers to a category of vehicle lighting equipment that consists of one or more amber-colored flashing or strobing lamps that is typically installed on certain types of slow-moving vehicles and utility vehicles (such as tow trucks, repair vehicles, or vehicles transporting oversized loads) to call the attention of other drivers to the presence of these vehicles. 

You ask that the National Highway Traffic Safety Administration (NHTSA) provide clarification of its longstanding interpretations of FMVSS No. 108 and permit original equipment installation of “emergency warning lights.” Alternatively, you ask that NHTSA issue guidance regarding the circumstances under which such lighting may be installed by vehicle manufacturers or repair businesses without violating the “make inoperative” provision of the National Traffic and Motor Vehicle Safety Act (Safety Act) (49 U.S.C. §§ 30101 et seq.). 

In responding to this request, NHTSA notes that the contents of this letter do not have the force and effect of law and are not meant to bind the public in any way. This letter is only intended to provide clarity regarding existing requirements under the law at the time of signature. 

After carefully considering your letter, we reaffirm our previous interpretations that, under current law, “emergency warning lights” may not be installed as original equipment and that persons subject to the make inoperative provision of the Safety Act may not legally install the lamps as original or aftermarket equipment. We explain our reasoning below, based on our understanding of the information you present. 

Background 

FMVSS No. 108 specifies requirements for original and replacement lamps, reflective devices, and associated equipment. For auxiliary lamps, the primary restriction imposed by FMVSS No. 108 is in S6.2.1, which states that “[n]o additional lamp, reflective device, or other motor vehicle equipment is permitted to be installed that impairs the effectiveness of lighting equipment required by this standard.” Additionally, both original equipment and aftermarket lighting can run afoul of the “make inoperative” provision, and NHTSA considers the installation of an aftermarket lamp to violate the “make inoperative” provision if the installation of the same lamp as original equipment would violate FMVSS No. 108.1 Whether there is an impairment is determined in the first instance by the manufacturer of the vehicle (or the entity installing the aftermarket lighting) when it is certified as compliant with FMVSS No. 108. NHTSA may contest such a determination if it is clearly erroneous.2 These prohibitions bar installation by a manufacturer, distributor, dealer, rental company, or motor vehicle repair business of lamps that would impair the effectiveness of required lighting, but do not apply to the owner of a vehicle. 

Typically, the impairment determination is made on a case-by-case basis and considers several characteristics of the auxiliary lamp, such as the brightness, color, location, and activation pattern of the lamp, to analyze whether it impairs the effectiveness of required lighting. This list of characteristics is not exhaustive and other considerations may be relevant to the analysis. NHTSA has long maintained that highway traffic safety is enhanced by the drivers’ familiarity with established lighting schemes, which enables them to instantly recognize the meaning the lamps convey and respond accordingly. NHTSA has long interpreted FMVSS No. 108 to require that all auxiliary lamps be “steady burning,” with the sole exception of auxiliary lamps that supplement required lamps that flash, such as turn signals.3 

Discussion 

NHTSA’s longstanding interpretation of FMVSS No. 108 is that the standard does not permit the “emergency warning lights” to be installed as original equipment because they are auxiliary lighting that is not steady burning and would impair the effectiveness of required lamps by causing confusion among other drivers about the meaning of required lighting or distracting drivers from required lighting.4 Further, because “emergency warning lights” would impair the effectiveness of required lamps, NHTSA has also determined that entities listed in § 30122 of the Safety Act that install “emergency warning lights” on new or used vehicles would violate the “make inoperative” provision of the Act. 

Notwithstanding those interpretations, you provide various reasons why you believe that “current regulations permit manufacturers to install such supplemental lighting as original equipment.” We respond to your reasons below. 

1 E.g., Letter to Timothy C. Murphy (Nov. 1, 2004), available at https://www.nhtsa.gov/interpretations/gf006332.
2 Letter from John Womack to Larry Grabsky (Nov. 16, 1993), available at https://www.nhtsa.gov/interpretations/9251.
3 See, e.g., Letter to Richard Seoane (June 27, 2024), available at https://www.nhtsa.gov/interpretations/ncc-231121- 001-autoliv-veoneer-spotlight-interpretation-1; and Letter to Paul Schaye (Sept. 9, 2019), available at https://www.nhtsa.gov/interpretations/571108-ama-schaye-front-color-changing-light.
4 Letter to J. Adam Krugh IV (May 22, 2003), available at https://www.nhtsa.gov/interpretations/002769drn (explaining that a flashing or strobing lamp on top of a school bus would impair the effectiveness of required signal lamps by diverting other drivers’ attention and causing confusion). 

Administrative Rewrite of FMVSS No. 108. First, you state that in an administrative rewrite of FMVSS No. 108, NHTSA removed explicit language in the standard that had contained a provision requiring that all lamps be steady burning unless otherwise indicated. You argue that the removal of this provision indicated an intention to loosen the restriction that auxiliary lamps must be steady burning when activated. 

NHTSA had no such intention. The removal of the referenced “steady burning” language in the FMVSS No. 108 administrative rewrite did not change the underlying substantive requirements that had applied to auxiliary lighting. Before it was modified in 2007, FMVSS No. 108 included an explicit requirement that, with the exception of certain types of required lamps (e.g., turn signal lamps), all lamps on a vehicle, including auxiliary lamps, must be steady burning. In 2007, NHTSA implemented an administrative reorganization of FMVSS No. 108 which, among other things, clarified the blanket “steady burning” requirement (and its exceptions) by converting it into specified individual activation requirements for each type of required lamp.5 Although the reorganized rule no longer includes a blanket “steady burning” requirement, NHTSA stated in the preamble to the reorganized rule that its “rewrite of FMVSS No. 108 is considered administrative in nature because the standard’s existing requirements and obligations are not being increased, decreased, or substantively modified.”6 Further, NHTSA continues to believe that flashing auxiliary lamps would impair the effectiveness of required lamps by distracting or confusing other road users and we have continued to restrict flashing or strobing auxiliary lamps since the rewrite except under a few limited circumstances not relevant here.7 Therefore, because the “emergency warning lights” are not steady burning, they would not comply with FMVSS No. 108 and would impair required lighting. 

Motorists are Used to “Emergency Warning Lights.” Second, you state that one of NHTSA’s reasons for disallowing flashing auxiliary lamps—their tendency to divert attention and cause confusion—is no longer valid for “emergency warning lights” because “the use of flashing-amber lighting has become widespread.” You provide no data or information to support this assertion, except to refer to past agency letters which discussed the make inoperative provision as applied to owners installing flashing or strobe lamps on their own vehicles, including a state installing the lamps on state-regulated emergency vehicles. 

We disagree with your assertion that the letters are indicative of the pervasiveness of “emergency warning lights.” The interpretation letters to which you refer do not endorse the installation of flashing or strobe lamps by individuals or declare that the lights do not impair the effectiveness of required lamps. Rather, those letters simply recognize the limits of NHTSA’s authority under the Safety Act to regulate aftermarket lighting equipment. The agency made, and continues to make, no determination as to whether the flashing amber lights are “widespread.”

5 72 FR 68234 (Dec. 4, 2007).
6 Id.
7 These exceptions include auxiliary lamps that supplement required flashing lamps like turn signals. See Letter to Jerry Koh (Feb. 6, 1986), available at https://www.nhtsa.gov/interpretations/86-250; see also Letter to Lt. Col. Steve Flaherty (May 2, 2003), available at https://www.nhtsa.gov/interpretations/flaherty (deference to states applies to “the installation and use of emergency lighting devices on [undercover state police] vehicles”). 

NHTSA has long believed that flashing amber lighting can unduly divert driver attention and cause confusion among drivers, even among those who have seen them before. As we have stated, “traffic safety is enhanced by the familiarity of drivers with established lighting schemes, which facilitates their ability to instantly and unhesitatingly recognize the meaning lamps convey and respond to them.”8 Flashing amber lighting, except for turn signal lamps, is not “an established lighting scheme” within the context of FMVSS No. 108. The meaning of flashing lights can vary depending on the nature of the vehicle on which they are installed, the context in which they are used, and state or local laws. Motorists might not know if the flashing amber lamps are meant to signal the presence of the vehicle for general driver awareness or the need for drivers to yield the right-of-way or perform some other driving task. The use of flashing amber lights is not sufficiently established and standardized to avoid unduly diverting driver attention or causing confusion. Thus, we continue to believe these lights impair required lighting equipment.9 

Other Federal Regulations and State Laws Recognizing “Emergency Warning Lights.”
Finally, you argue that permitting flashing amber auxiliary lamps as original equipment would “harmonize” NHTSA’s requirements with Federal Motor Carrier Safety Administration (FMCSA) regulations and state laws. You state that an FMCSA regulation (49 C.F.R. § 393.25(e)) permits the use of flashing lights on several vehicle types and that a change in NHTSA’s approach would better ensure such lighting is properly wired and installed. We are also aware of exemptions granted by FMCSA permitting certain entities to use pulsating brake-activated amber lights as well as the operation of commercial motor vehicles equipped with the Intellistop device.10 

Our longstanding interpretation of FMVSS No. 108 regarding flashing auxiliary lights is not impacted by these FMCSA regulations, exemptions, or state laws. The FMCSA regulation does not require the flashing lamps to be installed as original equipment or by an entity subject to the make inoperative provision. Additionally, although you allude to safety concerns about owners improperly wiring or installing emergency warning lights on their vehicles to comply with state laws, we are not aware of any state laws requiring installation of these lights specifically as original equipment or by an entity subject to the make inoperative requirement. Nor is allowing installation by such entities necessary to address improper owner installations of these lights. 

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

Sincerely,
ADAM RAVIV
Adam Raviv Chief Counsel
 

Dated:12/13/24
Ref: Standard No. 108

8 Letter to J. Adam Krugh IV (May 22, 2003), available at https://www.nhtsa.gov/interpretations/002769drn.
9 Nothing in this letter is intended to conflict with our interpretation, stated in our May 2, 2003, Letter to Lt. Col. Steve Flaherty, that deference to states applies to “the installation and use of emergency lighting devices on [the state’s] vehicles.” Letter available at https://www.nhtsa.gov/interpretations/flaherty.
10 List of FMCSA exemptions in effect available at https://www.fmcsa.dot.gov/exemptions.