Roundabouts improve traffic jams

Less traffic jams from self-driving cars

Small share - big effect: if only every twenty-second car on the road were self-driving, this could improve the flow of traffic enormously. This is now shown by an experiment on the influence of automated vehicles on stop-and-go situations. Because the few self-driving cars absorb the traffic jam, they could also reduce the risk of rear-end collisions and fuel consumption - for all road users.

Autonomous vehicles should revolutionize the traffic of the future. Prototypes can be called by the driver at the push of a button and are intended to ensure greater safety by recognizing pedestrians, wrong-way drivers and traffic jams. With fully automated vehicles, however, a moral dilemma quickly arises - namely when the car itself suddenly decides within milliseconds whether it will protect the life of the driver or avoid a careless pedestrian at all costs.

So far, however, supportive driver assistance systems such as brake assistants or spacers that, for example, independently regulate the speed, have been used. A study by a team led by Raphael Stern from the University of Illinois shows what positive effect it has on the flow of traffic when a few cars are already on the road with such auxiliary systems that are already available.

“Stop and Go” in the roundabout

For their investigation, the researchers let 22 cars drive in a circle. One of them was controlled by a specially trained driver and was equipped with an assistance system that took control of the cruise control at the push of a button. The instruction to all 22 human drivers was as follows: Follow the vehicle in front as you would during rush hour: close large gaps but do not open up to them.

When all drivers drove for a while on the 260-meter-long circular path, the researchers observed sudden waves of traffic jams, as expected: unfavorable braking by the driver resulted in the well-known stop-and-go phenomenon of congested roads and highways in the roundabout. In such situations, the vehicle was then switched to automated operation.

When 22 cars are driving in a circle, the typical “stop and go” occurs after a short time. © Jonathan Sprinkle

Five percent for free travel

The result: shortly after the assistance system had taken over the cruise control, the jam wave dissipated. The programmed control was designed to dampen the congestion waves through "anticipatory" driving and distance regulation. The automated drive also prevented traffic from stalling again.

"Our tests show that we can prevent man-made stop-and-go waves with automated vehicles - even if only five percent of the vehicles are equipped with the assistance system," reports Stern's colleague Daniel Work.

Fuel consumption almost halved

Maintaining the flow of traffic is not the only positive effect that the individual automated vehicle brought: Because the constant braking and acceleration was reduced, the gasoline consumption also fell significantly in the test. According to the researchers, the fuel savings were up to 40 percent - so the manually driven cars also benefit from the automated operation of one vehicle.

What makes the scientists particularly optimistic: The programming used for the automated vehicle is comparatively simple. “I figured we'd need more advanced cruise control techniques,” says Jonathan Sprinkle of the University of Arizona. "But as we have shown in the experiment, simple control loops that even first-year students could program serve their purpose."

Follow-up tests in heavy traffic

With the first test results, the researchers have already provided clear indications that even a few automated vehicles on the roads can have a noticeably positive effect on the flow of traffic. In follow-up studies, they now want to check whether their results can also be reproduced when the traffic is denser and human drivers are given more freedom - for example changing lanes. (University of Illinois, 2017; arXiv: 1705.01693v1)

(University of Illinois College of Engineering, May 10, 2017 - CLU)

May 10, 2017