Red light, green light, white light: new traffic signal could ease congestion

RALEIGH: For over a year, researchers at North Carolina State University have been working on a project that consists of using a new type of traffic light on signals at busy intersections in order to improve traffic flow.

Initial simulations indicate that the new approach could prove beneficial for all kinds of road users.

Adding a fourth colour to traditional traffic lights could significantly reduce waiting times and thus make traffic flow better, benefiting all road users, whether they're riding in self-driving vehicles or not, according to a study by civil engineering researchers at the University of North Carolina in the USA.

And the more self-driving vehicles there are in the traffic network, the shorter waiting times will be for everyone. Average delays at intersections could be reduced by up to 27%, according to the researchers.

A fourth traffic light colour, which the researchers refer to also known as "white phase," would make use of the ability of autonomous vehicles to communicate with one another, as well as the system controlling the light signals, to optimise traffic flow.

If the system becomes aware that a large number of autonomous vehicles are approaching an intersection, the white light is activated.

In practice, this means that human drivers simply have to follow the car in front of them.

In this way it's the autonomous vehicles that would be dictating traffic flows by coordinating with one another, to facilitate the movement of traffic through the intersection and surrounding area. When a majority of the cars approaching are being driven by humans, the system would revert to a conventional green-yellow-red system.

The study showed that the use of a white light - or another designated colour distinct from the traditional red, green and yellow - could reduce waiting times at intersections and cut the number of unnecessary stop-and-go episodes, with fluidity being most optimised in the case of a fleet made up exclusively of autonomous vehicles.

However, in all scenarios, such a system appears promising for improving traffic flow, and consequently reducing fuel consumption and hence greenhouse gas emissions.

The researchers' modelling also found that even when pedestrians are in the mix, all users, including those on foot, benefit from more efficient traffic flow.

This research was published in Computer-Aided Civil and Infrastructure Engineering.