The Fourth Color: How a New “White Light” Could Revolutionize Traffic

The Fourth Color: How a New “White Light” Could Revolutionize Traffic

The familiar red, yellow, and green of traffic lights may soon be joined by a fourth color, white, and experts say it could completely change the way we drive. Researchers are developing a new traffic light system designed to work hand-in-hand with autonomous vehicles, and it could make intersections faster, safer, and more efficient.

The Science Behind the New Light

The concept of a “fourth traffic signal” was proposed by transportation engineers at North Carolina State Universityand other research institutions. The idea is simple but transformative: when enough self-driving cars are on the road, they can communicate wirelessly with each other and the traffic infrastructure to manage intersections automatically.

In this system, the white light acts as a signal not just for cars, but for humans. When it’s illuminated, it means that autonomous vehicles are coordinating traffic flow, and human drivers should follow the movement of the cars around them, instead of traditional light sequencing.

“This white phase would basically tell human drivers to do what the self-driving cars are doing,” said Dr. Ali Hajbabaie, lead researcher at NC State’s Department of Civil, Construction, and Environmental Engineering. “If the autonomous vehicles are moving, you move; if they stop, you stop.”

Why Add a Fourth Color?

Today’s red-yellow-green model was designed in the early 20th century, long before digital networks or self-driving technology existed. But as vehicles become smarter and more connected, the old system may no longer be the most efficient way to manage traffic.

Researchers found that in simulations where connected vehicles made up at least 40% of traffic, the white-light system improved traffic efficiency by 20–30% and cut idle time dramatically. That means shorter commutes, less fuel burned, and fewer emissions.

“The new white signal doesn’t replace red, yellow, or green, it adds flexibility,” Hajbabaie explained. “It’s a bridge between today’s manual driving and tomorrow’s autonomous systems.”

How It Works in Practice

Here’s what a “four-light” intersection might look like:

• Red, Yellow, and Green still serve the same functions for standard vehicles.

• White Light activates when enough connected autonomous vehicles are present to coordinate the intersection themselves.

• During the white phase, human drivers follow the flow of nearby self-driving cars, which communicate with the light system and each other to optimize movement.

When autonomous vehicles are no longer in the majority, the system automatically reverts to the standard three-color cycle.

In essence, the white phase acts as a handover of control, allowing AI-coordinated cars to manage the crossing when they can do it better than humans.

The Benefits

1. Reduced Congestion – Smart coordination means fewer stops, smoother flow, and less time waiting at red lights.

2. Lower Emissions – Cars spend less time idling, which means a measurable reduction in CO₂ emissions.

3. Improved Safety – Connected vehicles can react faster than humans and anticipate movement from other autonomous cars.

4. Energy Savings – Shorter commute times and optimized routes mean less wasted fuel and energy use.

A Transition for the Future

Of course, the shift won’t happen overnight. The new system depends on widespread adoption of vehicle-to-infrastructure (V2I) communication, the technology that lets cars talk to traffic systems, as well as a significant share of vehicles being semi- or fully autonomous.

Transportation agencies are already testing prototypes of these “white phase” intersections in controlled environments. If successful, they could appear first in smart cities and areas with high concentrations of connected vehicles.

“Think of it as evolution, not revolution,” said Hajbabaie. “As more autonomous cars join the fleet, intersections will naturally become smarter. The white light is just a visible symbol of that shift.”

Changing the Way We Drive

For over a century, the red-yellow-green trio has governed how humans move through cities. The addition of a fourth, white light doesn’t just change the rules of the road, it represents a fundamental shift in who (or what) is doing the driving.

In the coming decades, when drivers approach an intersection and see that glowing white signal, it might mean the future of traffic management has finally arrived, a world where cars cooperate, congestion fades, and the road ahead is smarter than ever.