Their arrangement puts two sensors at each intersection: One measures incoming flow and one measures outgoing flow. Lights are coordinated with every neighboring light, such that one light alerts the next, "Hey, heavy load coming through."
That short-term anticipation gives lights at the next intersection enough time to prepare for the incoming platoon of vehicles, says Helbing. The whole point is to avoid stopping an incoming platoon. "It works surprisingly well," he says. Gaps between platoons are opportunities to serve flows in other directions, and this local coordination naturally spreads throughout the system.
"It's a paradoxical effect that occurs in complex systems," says Helbing. "Surprisingly, delay processes can improve the system altogether. It is a slower-is-faster effect. You can increase the throughput -- speed up the whole system -- if you delay single processes within the system at the right time, for the right amount of time."
The researchers ran a simulation of their approach in the city center of Dresden. The area has 13 traffic light-controlled intersections, 68 pedestrian crossings, a train station that serves more than 13,000 passengers on an average day and seven bus and tram lines that cross the network every 10 minutes in opposite directions. The flexible self-control approach reduced time stuck waiting in traffic by 56 percent for trams and buses, 9 percent for cars and trucks, and 36 percent for pedestrians crossing intersections. Dresden is now close to implementing the new system, says Helbing, and Zurich is also considering the approach.