A Cambridge University study using miniature robotic cars has found that by "talking to each other" they could improve traffic flow by some 35 per cent.

The researchers programmed a small fleet of miniature robotic cars to drive on a multi-lane track and observed how the traffic flow changed when one of the cars stopped. The results illustrate the problem of car manufacturers designing their own self-driving systems rather than agreeing on common platforms. When there was communication between the cars, the difference to traffic flow was dramatic.

The study showed that when the cars were not driving cooperatively, any cars behind the stopped car had to stop or slow down and wait for a gap in the traffic, as would typically happen on a real road.

A queue quickly formed behind the stopped car and overall traffic flow was slowed.

"However, when the cars were communicating with each other and driving cooperatively, as soon as one car stopped in the inner lane, it sent a signal to all the other cars. Cars in the outer lane that were in immediate proximity of the stopped car slowed down slightly so that cars in the inner lane were able to quickly pass the stopped car without having to stop or slow down significantly", say the researchers.

They also found that when a human-controlled driver was put on the ‘road’ with the autonomous cars and moved around the track in an aggressive manner, the other cars were able to give way to avoid the aggressive driver, improving safety.

The results, presented, at the International Conference on Robotics and Automation (ICRA) in Montréal, will be useful for studying how autonomous cars can communicate with each other, and with cars controlled by human drivers, on real roads in the future.

Autonomous cars will be much more useful if they can "talk to each other".

"Autonomous cars could fix a lot of different problems associated with driving in cities, but there needs to be a way for them to work together," said co-author Michael He, an undergraduate student at St John’s College, who designed the algorithms for the experiment.

"If different automotive manufacturers are all developing their own autonomous cars with their own software, those cars all need to communicate with each other effectively," said co-author Nicholas Hyldmar, an undergraduate student at Downing College, who designed much of the hardware for the experiment.

The two students completed the work as part of an undergraduate research project in summer 2018, in the lab of Dr Amanda Prorok from Cambridge’s Department of Computer Science and Technology.

Many existing tests for multiple autonomous driverless cars are done digitally, or with scale models that are either too large or too expensive to carry out indoor experiments with fleets of cars.

 "Our design allows for a wide range of practical, low-cost experiments to be carried out on autonomous cars," said Dr. Prorok. "For autonomous cars to be safely used on real roads, we need to know how they will interact with each other to improve safety and traffic flow."

In future work, the researchers plan to use the fleet to test multi-car systems in more complex scenarios including roads with more lanes, intersections and a wider range of vehicle types.