Autonomous vehicles and the need for a fourth traffic light

The world of research into autonomous vehicles has thrown up a fascinating new approach to traffic management with a “white light” being proposed to reduce congestion.

A modelling study conducted by the North Carolina State University (NCSU) was based on how autonomous vehicles (AVs) could communicate with each other. The researchers believe  that adding a fourth light to traffic signals would shorten wait times for road-users.

Now a new study has “expanded [their] computational modelling to account for foot traffic”, says Ali Hajbabaie, a corresponding author of the paper and an associate professor of civil, construction and environmental engineering at NCSU.

The fourth traffic light has been titled the ‘white phase’. It works by making use of AVs’ ability to communicate with other AVs and the systems that control traffic lights. When enough AVs accumulate at an intersection, the white phase is activated. This then signals the AVs to coordinate their movement more efficiently.

Ali Hajbabaie

The authors say current literature on joint optimization of intersection signal timing and connected automated vehicle (CAV) trajectory pays little attention to pedestrians.

“This paper presents a methodology to safely incorporate pedestrians into signalized intersections with CAVs and connected human-driven vehicles (CHVs). The movements of vehicles are controlled using both traffic lights and mobile CAV controllers during our newly introduced “white phase.” CAVs navigate platoons of CHVs through the intersection when the white phases are active,” it says.

Autonomous vehicles favor cooperation

Remarkable the authors write that drivers of non-autonomous vehicles might need simply to trust AVs at intersections.

The white phase might take some counter-intuitive responses from non-AV drivers: The CAV “..informs human drivers that the safety of the fleet is preserved by CAVs, and they should follow their preceding vehicles.”

Hajbabaie says that their previous research has found “that the more AVs are on the road, the more efficiently the traffic moves”.  

The current study presents a methodology to safely incorporate pedestrians into intersections with AVs as well as normal human-driven vehicles. The researchers have done this by including a new set of parameters into the model.

“We found that, when pedestrians are added into the mix, the white phase concept still improves traffic efficiency for everyone,” Hajbabaie added. If “almost universal” adoption of AVs is implemented, the model suggests that “delays at intersections would decrease by more than 25%.”

Hajbabaie says the team is “currently setting up a physical testbed that will allow [them] to experiment with this concept in the physical world—not just in a computer model.” In addition they are “open to working with industry and research partners to explore ways to move forward with these technologies.”

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