400 nanometers: The federal color for driverless cars

The color cyan is becoming the official visual language for autonomous vehicles on American roads.

Federal regulators have moved to resolve a long-standing debate regarding how driverless cars should communicate their status. For years, the industry has experimented with various methods, including flashing text displays, audio alerts, and custom lighting configurations. The National Highway Traffic Safety Administration (NHTSA) has now released proposed changes to Federal Motor Vehicle Safety Standard No. 108. This update specifically rewrites the rules to accommodate autonomous vehicles. The agency aims to cut red tape for human-free designs while standardizing how robotaxis interact with the surrounding environment. The centerpiece of this proposal is the adoption of a distinctive blue-green light.

The timeline of this regulatory shift reveals a move toward uniformity. The auto industry has historically reserved specific colors for standard functions. Red indicates braking, amber signals turning, white represents headlights, and flashing blue or red lights denote emergency vehicles. NHTSA proposes cyan marker lamps to fill the remaining visual gap without confusing road users. This choice offers a clear signal to law enforcement and other drivers that an automated driving system is in control. There is some precedent for this approach. Mercedes-Benz previously received state-level approval for turquoise lights on its Level 3 Drive Pilot cars. Although the automaker has since moved toward a Level 2++ system, the federal agency wants to establish a national standard. This would allow operators like Waymo, Nuro, and Zoox, as well as manufacturers like GM and Mercedes, to adopt a consistent setup.

Under the proposed rule, these cyan lights would be optional for manufacturers. However, the federal standards would dictate the specific color, brightness, and location of the lamps. This ensures that any automaker choosing to install them uses a legal and consistent configuration rather than a confusing mix of different colors. The proposal also seeks to eliminate lighting requirements that do not make sense for vehicles without human drivers. Current rules mandate physical hazard switches, manual beam shifters, and turn levers inside the cabin. NHTSA proposes removing these mandates. The agency also plans to update the 12.8-volt testing standard. This change will allow automakers to build around modern LED architectures without navigating unnecessary administrative hurdles. Additionally, NHTSA is considering dropping requirements that dictate whether high-beam lights must sit above or below low-beam lights.

This update is part of a broader administrative push by the Department of Transportation to streamline the deployment of autonomous vehicles. The government aims to make it easier for manufacturers to build cars without traditional controls like steering wheels and pedals. These components are designed for human drivers but can complicate the design of fully autonomous machines. The proposed changes represent a significant step toward recognizing that future vehicles may look and operate differently from today's cars. By standardizing the external lighting, the agency hopes to create a predictable environment for all road users. This standardization is crucial as the number of robotaxis on the road continues to grow in major urban centers across the country.

However, regulators are still enforcing existing rules as they are currently written. This creates a transitional period where new standards are proposed but not yet fully in effect. Last month, NHTSA opened an audit query into the Tesla Cybercab. The agency is examining the process and technical data Tesla used when certifying the vehicle. The specific issue involves the absence of certain design features such as sideview mirrors, pedals, and a steering wheel. All of these elements are currently required under FMVSS. This audit highlights the tension between innovators who want to remove human-centric features and regulators who must ensure safety through established standards. The proposed cyan light rule is one step in resolving this tension by providing a clear, standardized way for these new types of vehicles to exist in traffic.