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What About a Fourth Traffic Light Colour?

Thursday, February 16, 2023

Recent research on how to ease the adaptation period of autonomous vehicles has revealed that a fourth traffic colour, the so-called white phase might help autonomous vehicles and human drivers to navigate in the same traffic environment.

Navigating in the complex traffic flow of human drivers might be the biggest challenge for self-driving vehicles. However, new research from the Institute of Electrical and Electronics Engineers tackles that problem by proposing a fourth light on the tri-coloured traffic lights that is specifically for autonomous vehicles. As the authors of the paper claim, a “white phase” on traffic lights would serve both to help direct self-driving cars and let human drivers know where those cars are going (this leaves out how drivers will identify the AVs, which is different but tricky problem). Traffic lights would enter a “white phase” when coordinating AVs through traffic. The lack of traffic colour would indicate to human drivers that autonomous vehicles are being controlled. The human driver would then just follow the actions of the AV in front of them.  Red lights will still mean stop and green lights will still mean go.

The white phase concept is based on the idea that it is possible for AVs to communicate wirelessly with both each other and the computer controlling the traffic signal. When enough AVs are approaching the intersection, this would activate the white light.  When too many vehicles are approaching the intersection are being controlled by drivers, then the traffic light would revert to the conventional green-yellow-red signal pattern.

“Granting some of the traffic flow control to the AVs is a relatively new idea, called the mobile control paradigm,” one of the authors says. “It can be used to coordinate traffic in any scenario involving AVs. But we think it is important to incorporate the white light concept at intersections because it tells human drivers what’s going on, so that they know what they are supposed to do as they approach the intersection.”

To test the performance of this concept the researchers made use of traffic simulators. These simulators are computational models designed to replicate real-world traffic. The researchers compared simulated traffic behaviour at intersection with and without the white phase, as well as whether the number of AVs involved have a marked influence on that behaviour or not.

“The simulations tell us several things,” Hajbabaie says. “First, AVs improve traffic flow, regardless of the presence of the white phase. Second, if there are AVs present, the white phase further improves traffic flow. This also reduces fuel consumption because there is less stop-and-go traffic. Third, the higher the percentage of traffic at a white phase intersection that is made up of AVs, the faster the traffic moves through the intersection and the better the fuel consumption numbers.”

Personal Comment:

This idea of using a dedicated traffic light colour for AVs sounds reasonable. It isn’t an entirely novel idea, however. For example, this research proposed the so-called “blue phase” during which only CAVs can access the intersection through dedicated lanes and their movements are controlled to prevent collisions with conflicting vehicles.  A similar approach has been proposed in this research, where they introduced the “white phase” that is activated once there are enough CAVs near the intersection.  During this phase, groups of connected but human operated vehicles are led by CAVs, which are coordinated to reduce accidents and improve flow.

This area of finding new ways to ease the adaption of AVs is developing quickly. However, traffic agencies, road operators and municipalities are not likely ready to install brand-new traffic light systems at every intersection. Further, AVs are not yet at the stage where they can adopt the new distributed computing approaches proposed. Even so, I think it is better to start thinking now about how the current infrastructure can be adapted for AVs than wait until everything is ready and we have a crisis.

The Written by Kateryna Melnyk,
RISE Mobility & Systems