Self-Driving Cars May Make Traffic Slower

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A new study finds that driverless cars can actually slow down travel time through intersections if they are not connected to each other.

“There are two significant reasons that people are interested in automated vehicles—improving passenger safety and reducing travel time,” says Ali Hajbabaie, associate professor of civil, construction, and environmental engineering at North Carolina State University.

He claims that there is plenty of research proving that automated vehicles improve safety, but this research shows that in order to also improve travel time, an increase in automated vehicles isn’t enough. “We need vehicles that are capable of communicating with each other and with the traffic-control systems that manage traffic flow at intersections,” he adds.

According to Interesting Engineering, the researchers in the study used a computational model that simulates traffic conditions. The researchers accounted for four types of vehicles: human-driven vehicles (HVs), connected vehicles (CVs, driven by humans but share information with other connected vehicles and with the control system that manages traffic lights), automated vehicles (AVs), and connected automated vehicles (CAVs).

Hajbabaie explains that because of their programming, AVs are assumed to move more cautiously compared to human drivers, while CVs and CAVs are designed to receive information about the future state of traffic lights and adjust their speeds to avoid stopping at intersections. As a result, the movement of CVs and CAVs is expected to be smoother and have a lower number of stops than HVs and AVs.

The researchers ran 57 traffic simulations to assess the impact of different variables on travel time through an intersection, seeing how traffic would be affected by different combinations of HVs, AVs, CVs, and CAVs.

They clearly saw that the intersection capacity grew with the number of CVs and CAVs, meaning that when more vehicles on the road were connected, more vehicles could quickly pass through the intersection.

On the other hand, higher percentages of Avs, which are not connected, slow travel times. Hajbabaie explains that the cause is the AVs being programmed to drive cautiously to reduce the risk of collisions. “Our findings underscore the importance of incorporating connectivity into both vehicles and traffic-control systems,” he concludes.