Researchers from North Carolina State University (NC State) have proposed adding a white traffic light to intersections as a way to improve how human drivers and autonomous vehicles (AVs) share the road.
This innovation, known as the “white phase”, would not replace the existing red, yellow, and green signals but would complement them to manage traffic more efficiently. The white light system relies on vehicle-to-infrastructure communication, which allows AVs to exchange information with traffic lights in real time.
Traffic Lights With Four Color
Traffic lights may soon gain a fourth color white to accommodate the growing presence of autonomous vehicles (AVs) on the road, according to recent proposals from researchers at North Carolina State University and international pilot programs.
The concept is already under evaluation in simulations and testbeds and is seen as a bridge between current human-driven environments and a future dominated by smart, self-driving vehicles. Adding a fourth, white color to traffic signals marks a pivotal step toward integrating advanced automotive technology with traditional road safety infrastructure.
The white light
A white traffic light will be added to intersections in the future, lighting up only when enough autonomous vehicles (AVs) are present. This signals to human drivers that cars are coordinating traffic themselves, so drivers should just follow the car ahead. When AVs are absent, traditional red, yellow, and green lights will still work as usual. The system promises faster, safer, and more efficient traffic flow for everyone.
What is the Concept
In a 2024 research, Ali Hajbabaie, associate professor of civil, construction, and environmental engineering at North Carolina State University, highlighted the benefits of a fourth traffic light for autonomous vehicles (AVs).
“We had not yet considered the implications of this concept for pedestrians when we first proposed the idea of a fourth traffic light, known as a “white phase,” which uses the computational capacity of autonomous vehicles (AVs) to speed traffic at crossings,” Hajbabaie said.
“Now that we have included foot traffic in our computational simulation, the results are really promising for both pedestrians and vehicles,” he said.
How the White Light Works
The white light in traffic signals is a new, fourth signal proposed for intersections to work specifically with autonomous vehicles (AVs). Here is how it works:
| Step | Detail |
|---|---|
| AVs approach intersection | Autonomous vehicles communicate wirelessly with each other and the traffic signal system. |
| AV presence detection | When enough AVs are detected approaching, the white light activates. |
| White light signal | White light indicates AVs are coordinating traffic, signaling humans to follow the AV ahead. |
| Human driver response | Human drivers follow the vehicle in front rather than traditional traffic signals. |
| Distributed computing | AVs use their computing power collectively to negotiate safe paths and traffic flow. |
| Reversion to standard | If too many human-driven vehicles are present, traffic light reverts to normal red/yellow/green. |
“Our earlier research revealed that traffic moves more effectively when there are more AVs on the road,” Hajbabaie stated. “To be clear, this improves travel time, fuel efficiency and safety for all of the cars on the road, not just AVs.”
Why adding a fourth color to traffic lights
| Reason | Details |
|---|---|
| Coordination of Autonomous Vehicles (AVs) | White light activates when enough AVs approach an intersection and communicate to manage traffic flow |
| Clear Signal for Human Drivers | Informs human drivers to follow the vehicle ahead without relying on traditional lights |
| Traffic Flow Improvement | Significantly reduces traffic delays and congestion, especially as AV percentage increases |
| Fuel Efficiency and Emissions | Reduces stop-and-go driving, lowering fuel consumption and pollution |
| Enhanced Safety | Improves coordination, reducing human error and potential accidents |
| Transitional Support | Facilitates smooth operation during mixed traffic with both human-driven and autonomous vehicles |
| Pedestrian Considerations | System designed to maintain safe pedestrian crossings while improving overall traffic efficiency |
Where Will the Implementation of the White Light Phase Occur First
The NC State team is preparing to test the new white light system in controlled areas where autonomous vehicles (AVs) already operate regularly. Ports are ideal test locations because they have high traffic flow but few pedestrians, and their traffic patterns are repetitive and predictable. While white is the chosen color to signal AV coordination, any easily recognizable light could be used. This new light marks the start of an era where human drivers and smart cars communicate directly for faster, safer, and more efficient intersection management.
Future Implementation
“According to our models, intersection delays would drop by more than 25% if AVs were to become nearly universally used in the future. Even though the percentage of wirelessly connected AVs on the road will eventually decline, traffic time will still significantly improve.”
FAQs
What is the white light?
A fourth traffic light color signaling that autonomous vehicles (AVs) are coordinating traffic at the intersection.
How does it work?
When enough AVs approach an intersection, the white light activates, telling human drivers to follow the vehicle in front of them.
Will the existing lights disappear?
No, red, yellow, and green remain; the white light only activates when many AVs are present.
Why add a white light?
To reduce delays and congestion by letting AVs coordinate traffic flow more efficiently.
Where will it be tested first?
In controlled areas like ports, where AVs are already operating and traffic patterns are predictable.
