NHTSA proposed on Friday to amend FMVSS 108 and create a new, optional category of vehicle light: cyan "ADS marker lamps" that signal a vehicle is being driven by an automated driving system. It is the first US federal rule to define a distinct colour for autonomous operation — even though it obliges nobody to use it.

What the draft specifies

The agency wants to standardise colour (cyan), mounting locations, activation and visibility. As reported from the draft, the lamps would stay steadily lit rather than flash, be visible from the front, rear and both sides, sit at least 15 inches off the ground, come on only while the system is driving — never while a human is — and switch on and off together.

The rest of the package clears out requirements that make no sense on a car with no steering wheel. Manual turn signal, hazard warning and beam-switching control requirements are modernised for ADS-only vehicles; the rigid 12.8-volt test for integral beam headlamps is replaced with certification at design voltage, which suits long-life LEDs; and the rule dictating the vertical ordering of low and high beams is deleted.

The comment period runs 30 days, Docket No. NHTSA-2026-1519 at regulations.gov. The proposal travels separately from the negotiated rulemaking the agency announced earlier this month.

Why a marker lamp at all

The rationale is first-responder practice, not aesthetics. When a police officer or an ambulance crew approaches a stopped car, they need to know within a second whether the empty driver's seat means "driverless" or "driver missing". No standardised signal for that has existed. Manufacturers have improvised their own; in China, the government has now explicitly asked them to stop.

Where the idea came from

The proposal is not invented from scratch. Mercedes put cyan exterior lighting forward alongside DRIVE PILOT, its Level 3 system trialled for two years in California and the first genuinely hands-off system in the US — unlike Tesla's Full Self-Driving, which remains Level 2 because the driver stays responsible. SAE backed the colour choice. China published an essentially identical draft standard the same week: optional, turquoise, taking effect in 2028.

The catch: optional

A colour nobody is required to show only partly solves the first-responder problem. Automakers can skip the lamps and save a few dollars — though LEDs cost so little that many will likely fit them anyway to prepare for a possible mandate. That is precisely what an optional standard is for: it establishes the reference before the requirement arrives.

The second tension is regulatory sequence. FMVSS was never written for vehicles like Tesla's Cybercab or Zoox's robotaxi, and the agency is rebuilding the rulebook around them in parallel: the first exemption granted for commercial robotaxi deployment, a first FMVSS for ADS safety in development with the SAE Industry Technologies Consortia, and an overhaul of federal AV guidance, the first since 2017. Writing rules after the vehicles are already on the road is where the sequencing argument starts.

What happens next

Thirty days of comments, then a final text. If the lamps arrive, they will appear first on robotaxis and on Level 3 cars like DRIVE PILOT — precisely where a human is no longer sitting at the wheel. Whether this becomes a mandate will depend on whether first responders and insurers describe an optional colour as insufficient.

Sources