Brian Latouf, Executive Director
Global Safety & Field Investigations, Regulations
General Motors LLC, Mail Code: 480 210 2V
30001 Van Dyke
Warren, MI 48093-2350
Dear Mr. Latouf,
This responds to your letter dated March 18, 2016 requesting an interpretation with respect to the meaning of “vehicle hazard warning signal operating unit” in Federal Motor Vehicle Safety Standard (“FMVSS”) No. 108; Lamps, reflective devices, and associated equipment, as applied to a new cruise control system General Motors (“GM”) is developing.
You state that GM is developing a new adaptive cruise control system with lane following (which GM has referred to as “Super Cruise”) that controls steering, braking, and acceleration in certain freeway environments. When Super Cruise is in use, the driver must always remain attentive to the road, supervise Super Cruise’s performance, and be ready to steer and brake at all times. In some situations, Super Cruise will alert the driver to resume steering—for example, when the system detects a limit or fault. If the driver is unable or unwilling to take control of the wheel (if, for example, the driver is incapacitated or unresponsive), Super Cruise may determine that the safest thing to do is to bring the vehicle slowly to a stop in or near the roadway, and the vehicle’s brakes will hold the vehicle until overridden by the driver.
You indicate that GM plans to develop Super Cruise so that, in this situation, once Super Cruise has brought the vehicle to a stop, the vehicle’s automated system will activate the vehicle’s hazard lights. You state that you believe that this automatic activation of the hazard lights complies with the requirements of FMVSS No. 108 for several reasons. You state that the system’s activation of the hazard lights in this situation alerts other drivers that the vehicle is stopped and ensures overall traffic safety. Your letter cites and discusses several past agency interpretations, and asserts that automatic activation of the hazard lights in the situation GM describes is similar to at least one situation in which NHTSA has previously interpreted the standard to permit automatic activation of the hazard lights—immediately following a crash event. You state that you believe that there would be no ambiguity about the meaning of the hazard lights in this situation, and it would be the safe thing to do. You ask NHTSA to confirm that activation of the hazard lights by the vehicle’s automated system in the unresponsive/incapacitated driver situation described above complies with FMVSS No. 108. As we explain below, we interpret FMVSS No. 108 to allow the type of automatic hazard activation described in GM’s letter.
FMVSS No. 108 requires that all vehicles to which the standard applies, except trailers and motorcycles, be equipped with, among other things, a vehicular hazard warning operating unit and a vehicular hazard warning signal flasher. As defined in the standard, a vehicular hazard warning signal operating unit is “a driver controlled device which causes all required turn signal lamps to flash simultaneously to indicate to approaching drivers the presence of a vehicular hazard.” As also defined in the standard, a vehicular hazard warning signal flasher is “a device which, as long as it is turned on, causes all the required turn signal lamps to flash.” These requirements for hazard lights have been in the standard, largely unchanged, since it was first adopted in 1967. The purpose of the hazard warning is to indicate to approaching drivers that the vehicle is stopped or is proceeding at a slower rate than surrounding traffic.
As an initial matter, although not explicitly stated in GM’s letter, we assume for purposes of this interpretation that the vehicle GM describes has a manually-activated hazard warning control that satisfies the requirements in S6.6.2 and S4 for a “driver controlled” hazard warning operating unit, and also satisfies the requirements in FMVSS No. 101 for a hazard warning signal control and telltale. Nothing in GM’s letter indicates otherwise. Moreover, this is consistent with the vehicle having, as GM describes, a Level 2 automated system.
Past agency interpretations of automatic activation of hazard lights have reached different conclusions about their permissibility. Some past agency interpretations of FMVSS No. 108’s definition of “hazard warning signal operating unit” have construed it to preclude automatic operation of the hazard warning lights, on the basis that automatic activation would not be “driver controlled.”
However, since those interpretations were issued, NHTSA has clarified that automatic activation is permissible in certain circumstances. In a 2002 interpretation letter issued to Bartlett Industries, Inc., NHTSA explained that the hazard lights may be automatically actuated following a vehicle crash:
[A] series of . . . letters reflect our opinion that hazard warning system lamps must be activated and deactivated by the driver. This conclusion was based upon the definition of hazard warning systems by the Society of Automotive Engineers (SAE) as “driver actuated.”
The one exception to driver actuation that our recent letters reflect is automatic activation of the hazard warning system in the aftermath of a vehicle crash. As we informed
Mr. Steele, “we would not view automatic activation of the hazard signals in the event of a crash as a noncompliance with Standard No. 108 since there can be no ambiguity about the signal's meaning at that point.”
GM states that in the event that a human driver fails to respond to Super Cruise’s request that the human retake control of the vehicle, and Super Cruise consequently determines that the safest thing to do is to bring the vehicle slowly to a stop in or near the roadway, Super Cruise-equipped vehicles will activate the vehicle’s hazard lights automatically once the vehicle is stopped. We agree with GM that the situation it describes is similar to the situation in which the Steele (and Bartlett) letters that interpreted FMVSS No. 108 to permit automatic actuation of the hazard lights. Although GM’s system does not activate a vehicle’s hazard warning signal after a the vehicle has been disabled or damaged in a crash and come to a stop, it does activate the hazard lights when the vehicle has already stopped, very possibly as a result of the driver’s having become disabled. In these circumstances, the vehicle is unlikely to begin moving again soon. This is the prototypical situation in which the hazard lights are intended to be used, and it is one of the situations that other motorists have come to expect when they see the hazard signal. There would appear to be no ambiguity about the signal’s meaning in this situation, and we believe that it is unlikely that the use of the hazard lights would confuse other motorists. Therefore, the automatic activation of the hazard lights in the circumstances described by GM would be permissible. Any other automatic activation of hazard warning lights would need to be evaluated on a case-by-case basis. NHTSA may also consider amending the relevant provisions of FMVSS No. 108 at some point in the future in order to clarify situations when hazard lights may activate automatically.
We note that GM indicates that when the driver is unable or unwilling to take control of the vehicle the system will bring the vehicle to a stop “in or near the roadway.” We urge GM to fully consider the likely operation of the system it is contemplating and ensure that this fallback solution does not present an unreasonable risk to safety.
If you have any further questions, please contact John Piazza of my staff at (202) 366-2992.
Ref: Standard No. 108
 See 32 FR 2408, 2411-2412 (Feb. 3, 1967). Before 2012, FMVSS No. 108 incorporated by reference the hazard warning provisions in standards promulgated by SAE (formerly the Society of Automotive Engineers), specifically, SAE J910, Jan. 1966 (hazard warning signal operating unit), and SAE J945, Feb. 1966 (hazard warning signal flasher). In a 2007 final rule, NHTSA reorganized FMVSS No. 108 by streamlining the regulatory text and clarifying the standard’s requirements. 72 FR 68234 (Dec. 4, 2007). The final rule, among other things, reduced reliance on third-party documents incorporated by reference by inserting the text of those documents directly into the regulatory text of FMVSS No. 108. This final rule, which incorporated the hazard warning requirements directly into the regulatory text, became effective on December 1, 2012. 76 FR 48009 (Aug. 8, 2011).
 61 FR at 2,865 (Jan. 29, 1996) (quoting Letter from Stephen Wood, Acting Chief Counsel, to Larry Egley (Aug. 8, 1989)) (stopped vehicle); Letter from Frank Seales, Jr., Chief Counsel, to Sen. Richard Lugar (May 9, 2000) (vehicle stopped or proceeding at slower rate), available at http://isearch.nhtsa.gov/files/21478.ztv.html (last accessed Apr. 6, 2016). See also SAE J910, Jan. 1966 (“A vehicular hazard warning signal operating unit is a driver controlled device which causes all turn signal lamps to flash simultaneously to indicate to the approaching drivers the presence of a vehicular hazard.”).
 NHTSA defines Level 2 automation consistent with the SAE J3016 levels of automation, as “the driving mode-specific execution by one or more driver assistance systems of both steering and acceleration/deceleration using information about the driving environment and with the expectation that the human driver perform all remaining aspects of the dynamic driving task.” See NHTSA’s September 2016 Federal Automated Vehicles Policy, available at http://www.nhtsa.gov/ (last accessed Sept. 28, 2016), and http://www.sae.org/misc/pdfs/automated_driving.pdf (last accessed Sept. 28, 2016).
 Letter from Frank Seales, Jr., Chief Counsel, to Mark Steele, Steele Enterprises (Dec. 6, 1999) (“This means that the hazard warning signal unit must be activated by the driver and not automatically.”), available at http://isearch.nhtsa.gov/files/20856.ztv.html (last accessed Apr. 6, 2016); Letter from Frank Seales, Jr., Chief Counsel, to Eric Reed (Feb. 29, 2000) (“An automatic activation of the hazard warning unit would not be ‘driver controlled’ and is therefore not permitted.”), available at http://isearch.nhtsa.gov/files/reed.ztv.html (last accessed Apr. 6, 2016); Letter from Jacqueline Glassman, Chief Counsel, to Ted Gaston, Muncie Indiana Transit System (Apr. 25, 2005) (“We have previously interpreted ‘driver controlled’ to mean that the hazard warning signal system must be activated and deactivated by the driver and not by automatic means . . . .”), available at http://isearch.nhtsa.gov/files/GF002470.html (last accessed Apr. 6, 2016).
 Letter from John Womack, Acting Chief Counsel, to Timothy Bartlett, Bartlett Industries, Inc. (Jan. 28, 2002) (“Bartlett letter”) (citations omitted), available at http://isearch.nhtsa.gov/files/23695.ztv.html (last accessed Apr. 6, 2016) (quoting Letter from Frank Seales, Jr., Chief Counsel, to Steele Enterprises (Feb. 25, 2000) (“Steele letter”), available at http://isearch.nhtsa.gov/files/21171.ztv.html (last accessed Apr. 6, 2016)). As noted above, see supra n.4, the referenced SAE document is now incorporated into the text of FMVSS No. 108.
 Automatic activation of hazard lights may also be permissible under the theory that the automatic-activation function represents “supplemental lighting” in addition to the driver- (manually-) controlled hazard lights. Supplemental lighting is not permitted to impair the effectiveness of required lighting; see S6.2.1. In recent years, NHTSA has generally concluded that the use of required lighting equipment for other than its original purpose would impair the effectiveness of the required lighting because it would compromise and reduce its safety and effectiveness. See, e.g., Letter from Frank Seales, Jr., Chief Counsel, to the Honorable Orrin G. Hatch (Aug. 5, 1999), available at http://isearch.nhtsa.gov/files/20180.ztv.html (last accessed Sept. 28, 2016). Regardless of whether automatic activation of hazard lights was construed as supplemental lighting, NHTSA would still look to whether the automatic activation of the hazard lights was consistent with the purpose of hazards and whether it would create ambiguity or risk confusing other motorists.
 Since the mid-1990s, several interpretations have addressed situations in which automatic activation of hazard lights would not be permissible because the message that the hazard lights would convey in those instances would not be consistent with the purpose of hazards, i.e., to indicate to approaching drivers that the vehicle is stopped or is proceeding at a slower rate than surrounding traffic. See, e.g., Letter from Frank Seales, Jr., Chief Counsel, to David Coburn, Steptoe & Johnson LLP (Aug. 6, 1999) (“We believe that a hazard warning system should not be used for the auxiliary purpose of indicating sudden accelerator release, a signal that bears no relationship to a hazard warning signal and one which could create confusion were the hazard warning signal used for an unrelated purpose.”), available at http://isearch.nhtsa.gov/files/19886.ztv.html (last accessed Apr. 6, 2016); Letter from Frank Seales, Jr., Chief Counsel, to Mark Steele, Steele Enterprises (Oct. 7, 1999) (FMVSS No. 108 does not permit the hazard lights to signal the activation of the anti-lock brake system because that could result in confusing signals), available at http://isearch.nhtsa.gov/files/20662.ztv.htm (last accessed Apr. 6, 2016). NHTSA would continue to consider automatic activation of hazard lights in such situations to be inconsistent with FMVSS No. 108.
 Federal law requires the recall of a vehicle that contains a safety-related defect (i.e., that may present an unreasonable risk of an accident occurring or of death and injury in an accident). 49 U.S.C. §§ 30102, 30118.