Autonomous vehicles are steadily reshaping conversations about road safety, infrastructure, and liability across North Carolina. Now, transportation engineers at North Carolina State University are adding to the discussion with the idea of a fourth traffic signal color designed specifically for a future that includes self-driving cars.
In a recent study published in IEEE Transactions on Intelligent Transportation Systems, NC State researchers propose introducing a “white phase” at traffic lights. Unlike red, yellow, or green, a white light would signal that autonomous vehicles (AVs) approaching an intersection are coordinating traffic flow and that human drivers should simply follow the vehicle in front of them.
The concept is gaining national attention as states like North Carolina evaluate how prepared their roadways and laws are for increased AV deployment.
How the White Light System Would Work
Under the proposed system, the white light activates when enough autonomous vehicles are approaching an intersection. Those vehicles communicate wirelessly with each other and with the traffic signal, allowing them to collectively manage right-of-way and reduce stop-and-go congestion.
For human drivers, the instructions would be simple:
- If the car ahead moves through the intersection, you proceed.
- If it stops, you stop.
Traditional red-yellow-green signals would remain in place when autonomous vehicle numbers are too low to safely manage traffic flow.
According to study author Ali Hajbabaie, an associate professor of civil, construction, and environmental engineering at NC State, the goal is transparency. The white light tells human drivers that autonomous systems are actively coordinating traffic, reducing confusion at mixed-use intersections.
What the White Phase Study Found
Using advanced microscopic traffic simulators, which are models that replicate real-world driving behavior down to individual vehicles, the researchers compared intersections with and without the white phase.
Their findings suggest specific benefits, particularly as the use of autonomous vehicles grows:
- Reduced delays: Even with just 10% autonomous vehicles, traffic delays dropped by about 3%. At 30% AV adoption, delays were reduced by more than 10%.
- Improved efficiency: Higher percentages of AVs led to smoother traffic flow and faster travel times through intersections.
- Lower fuel consumption: Less stop-and-go driving translates into reduced fuel use and emissions.
The study also found that a newer, distributed computing approach, where autonomous vehicles share the workload instead of relying on a single centralized traffic controller, was more efficient and resilient to communication failures.
Why This Matters for North Carolina Drivers
While the white light concept is still theoretical, it arrives at a time when autonomous vehicle safety is already under scrutiny nationwide. Recent incidents involving Waymo vehicles improperly passing stopped school buses have raised concerns about how automated systems interpret traffic signals and roadway rules.
North Carolina law already allows fully autonomous vehicles to operate on public roads if they meet specific safety and insurance requirements. As discussed previously on the Raleigh Legal Examiner, when an automated driving system is engaged, the technology itself is treated as the legal “driver,” and responsibility may shift to the vehicle owner, manufacturer, or software developer.
However, a new traffic signal phase, even one intended to improve safety, adds another layer of complexity. Questions quickly arise:
- How will human drivers be educated about a white light signal?
- What happens if an autonomous system misinterprets or fails to respond correctly?
- Who is liable if a crash occurs during a white-light phase?
The NC State researchers acknowledge that the white phase will not appear at intersections overnight. Implementing it would require updates to infrastructure, vehicle software, and driver education. Pilot programs, such as in ports or commercial traffic hubs where autonomous vehicles are more common, may be the first testing grounds.
Still, the proposal highlights a broader reality: as autonomous technology evolves, traffic laws, roadway design, and liability frameworks must evolve with it. Even innovations intended to improve efficiency can introduce new risks if systems fail or drivers are confused about their responsibilities.
How North Carolina Drivers Can Stay Informed and Protected
Autonomous vehicles may eventually reduce crashes, but the transition period will involve experimentation, new technologies, and legal uncertainty. For North Carolina drivers, pedestrians, and cyclists, understanding how these systems work and how liability is determined when something goes wrong is increasingly important.
If you or a loved one is injured in a crash involving an autonomous or other type of vehicle, a North Carolina car accident lawyer can help those injured understand their rights and legal options. As technology changes the way we drive, accountability and safety must remain priorities. For more information or a free case review, contact the Whitley Law Firm online or call 919-785-5000.
