Traffic engineers are quietly working on a radical idea: adding a white signal to the familiar red, yellow, and green. Instead of signaling drivers directly, the extra light would tell humans when to follow the lead of nearby autonomous vehicles, turning intersections into ad hoc computer networks. Despite breathless social media claims that white traffic lights are already being rolled out worldwide, the concept remains in the realm of research, simulation, and policy debate, not real-world deployment.
What is real, and moving quickly, is the push from researchers and some industry voices to get regulators ready for a fourth color before self-driving cars become mainstream. I see a widening gap between viral hype and the slower, more technical work of proving that a white phase can move traffic faster and more safely without confusing the people still holding the steering wheel.
How the “white phase” would actually work
The core idea is deceptively simple: when enough autonomous vehicles are present at an intersection, control of the signal would shift from a fixed timing plan to the cars themselves, and a white indication would tell human drivers to fall in line. Traffic engineers who study this problem describe a fourth “white” light that activates only when a critical mass of connected vehicles is nearby, allowing those vehicles to coordinate movements and then instruct everyone else to follow the car in front. That vision is laid out in detail by transportation researchers who explain that traffic engineers want to add this extra phase specifically to leverage autonomous vehicles as rolling computers.
In practice, the white signal would not replace red, yellow, or green, it would sit alongside them as a special mode. When the white light is on, human drivers would no longer watch the usual sequence, they would simply mirror the behavior of nearby self-driving cars, accelerating, slowing, or stopping as those vehicles negotiate the safest and most efficient pattern through the junction. Researchers describe this as a form of autonomous vehicles controlling traffic flow, with the signal acting as a visible cue that the algorithm, not the old timing chart, is in charge.
The NC State research behind the proposal
The most detailed work on this concept so far comes from civil and environmental engineers at North Carolina State University, who have spent years refining what they call a white phase for intersections. Their modeling shows that when enough self-driving cars are present, they can share data about speed, position, and intent, then collectively decide how to move through the junction while a white indication tells everyone else to follow. One overview of the idea explains that self-driving cars know where to move because they are constantly communicating with each other and the signal controller.
Researchers involved in this work describe the white phase as a new way for signals to “talk” to drivers, shifting from direct commands to a kind of delegation to the vehicle fleet. One technical explainer frames it as understanding the fourth, where the system could revolutionize urban mobility by letting connected cars handle the micro-decisions that fixed-time lights struggle with. To test that claim, the research team has relied on extensive computer simulation, reporting that delays at intersections could plummet by up to 94 percent when the white phase is active, a figure that helps explain why the idea has captured so much attention in transport circles.
From theory to simulations, not yet to streets
For all the excitement, the white phase remains a theoretical and simulated system, not a feature of any real-world traffic network. Analysts who track future mobility concepts describe how the white phase concept is triggered only when a threshold of autonomous vehicles is present, at which point the signal would activate the white light and let those vehicles coordinate. Other explainers walk through the basics for general audiences, noting that in the normal system red means stop, green means go, and yellow means prepare to stop, while in the proposed system a white indication would appear only when enough autonomous cars are near the intersection to manage traffic themselves.
The North Carolina State University team has been explicit that their work is still in the research phase. In their own description, they explain that at a traffic light red means stop and green means go, but CCEE researchers are now proposing a “white light” that would enable self-driving cars to help move vehicles through the intersection more efficiently, a concept laid out in detail by But CCEE researchers. A companion technical summary notes that the team has formulated the problem as a distributed mixed-integer non-linear program and developed a methodology to reach agreement between vehicles and the signal controller on when to activate the white light. None of these documents describe live roadside trials, only models and lab work.
Hype, misinformation, and the regulatory wall
As the research has filtered into mainstream coverage, social media has filled in the gaps with its own narrative, often blurring the line between proposal and policy. One widely shared Facebook post claims that the U.S. approves testing of 4-color traffic lights and describes a white light that could change driving forever in the United States, presenting the idea as if federal regulators had already signed off on pilot programs. That framing has helped fuel headlines and YouTube explainers that talk about a new color being added to traffic lights worldwide, even though the underlying research is still confined to simulations and academic papers.
More cautious reporting has tried to correct the record, pointing out that despite viral headlines, no official transport authority has approved or implemented four-color traffic lights anywhere in the world, a point made explicitly in coverage that notes that despite viral headlines, the idea remains untested on real streets. In the United States, the current MUTCD only recognizes the standard red, yellow, and green indications for general traffic and does not authorize a white signal for this purpose, which means any actual deployment would require a formal rulemaking process and likely hardware upgrades to the equipment that powers today’s signals.
Why engineers still see promise in a fourth color
Even with those regulatory and perception hurdles, many engineers argue that a white phase is one of the few ideas that truly treats autonomous vehicles as networked devices rather than just smarter cars. Some analyses describe how the concept relies on distributed computing for traffic control, using the processing power of all autonomous vehicles approaching an intersection to decide the optimal pattern. Public-facing explainers have amplified that message, with one Instagram post noting that Researchers from North Carolina State University have proposed adding a fourth white light to better manage traffic when self-driving cars are present, and another technical article recalling that the researchers first introduced a white phase concept in 2020, but that initial version relied on a centralized controller rather than the behavior of individual vehicles.
Popular videos have helped translate the math into something closer to a story. One YouTube explainer walks viewers through a new proposal to add a fourth light to traffic signals and tries to “connect the dots” on how it would work, a narrative that is captured in a clip shared on Jan. Another short video asks whether traffic lights could be getting a new color as autonomous cars reshape intersections, a theme echoed in a Nov clip that compresses the concept into under a minute. A longer explainer imagines a future where you are counting delivery drones, hitting 35, 36, 37, when the traffic lights change to white and the cars around you glide through the junction in a choreographed pattern, a scenario dramatized in a Dec video that leans heavily on the NC State research.
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*This article was researched with the help of AI, with human editors creating the final content.
