We May Be Getting A Fourth, White Traffic Light Just For Self-Driving Cars

Traffic lights may no longer control intersections as autonomous vehicles take over.


Jack Dunhill


Jack Dunhill

Social Media Coordinator and Staff Writer

Jack is a Social Media Coordinator and Staff Writer for IFLScience, with a degree in Medical Genetics specializing in Immunology.

Social Media Coordinator and Staff Writer

traffic lights

Let's get another color in there... Image credit: Alexey_Erofejchev/

With the addition of autonomous cars to our roads, it could soon come with a strange new idea – a fourth traffic light. New simulations suggest that a fourth light, which would be white, would help human drivers get a better idea of what’s happening on the road while helping autonomous vehicles control the flow of traffic, saving time and fuel. 

“This concept we’re proposing for traffic intersections, which we call a ‘white phase,’ taps into the computing power of autonomous vehicles (AVs) themselves,” says Ali Hajbabaie, corresponding author of the paper, in a statement.  


“The white phase concept also incorporates a new traffic signal, so that human drivers know what they are supposed to do. Red lights will still mean stop. Green lights will still mean go. And white lights will tell human drivers to simply follow the car in front of them.” 

In essence, the autonomous vehicles would take over the intersection whenever the white light shows. Autonomous vehicles could be able to communicate with each other in the future, precisely determining their location and next move in relation to themselves, and this is the basis of the white light. If enough autonomous vehicles approach an intersection, they would coordinate the best flow of traffic and the white light would tell us mere humans to follow their higher plan by just following the car in front. 

If there are no autonomous vehicles around, good ol’ fashioned red-amber-green lights will control traffic. The researchers also stress that it doesn’t need to be a white light, just a recognizable color that is universally agreed. 

When tested on a small simulation using computer models, the white light sped up traffic by a small but significant amount when autonomous vehicles composed between 10 and 30 percent of the total cars. At 30 percent, delays were reduced by 10.7 percent, but as the number of autonomous cars increased, so did the traffic speed. 


It would allow traffic lights to be sped up dramatically, as self-driving cars will be able to assess the best course of action as compared to a simple timed stop-start system, which anyone who has been stuck at a red light at a bad time would definitely welcome. However, while the simulations suggest the white light would be well-adopted, actual drivers may not enjoy added complexity to such a ubiquitous system. The researchers recognize that a new system would be difficult to implement any time soon, but they do see an opportunity for pilot trials. 

“However, there are various elements of the white phase concept that could be adopted with only minor modifications to both intersections and existing AVs. We also think there are opportunities to test drive this approach at specific locations,” Hajbabaie says. 

“For example, ports see high volumes of commercial vehicle traffic, for which traffic flow is particularly important. Commercial vehicles seem to have higher rates of autonomous vehicle adoption, so there could be an opportunity to implement a pilot project in that setting that could benefit port traffic and commercial transportation.” 

The study was published in IEEE Transactions on Intelligent Transportation Systems.


  • tag
  • cars,

  • traffic,

  • road safety,

  • driverless cars,

  • transport,

  • driving,

  • traffic lights,

  • autonomous cars