Professor Schreckenberg, what actually causes traffic congestion?
On interstates, in 60 to 70 percent of cases, it is quite simply because there are too many vehicles on the road. There is too much traffic heading in the same direction. This rapidly gives rise to slow-moving traffic that is still flowing at between 10 and 30 km/h. It is not until individual road users brake sharply or, by changing lanes abruptly, force other drivers to apply their brakes that everything comes to a complete stop. A wave of congestion develops that extends in the opposite direction to the flow of traffic at a speed of 15 km/h. In some cases, waves of congestion of this kind can even switch interstates via the exit ramps.
So is human error at the heart of every traffic jam?
In the kind of overload congestion depicted above, that genuinely is the case. Between 30 and 40 percent of all traffic jams have a specific cause, such as an accident or a narrowing in lane due to roadwork. Here too, individual driving behavior can contribute to the formation of a traffic jam, but not to the same extent. One example of this is how well drivers apply the “zipper merge” – letting alternate vehicles merge into the open lane. The same applies to the two percent of traffic jams that are caused by weather conditions, such as poor visibility due to fog or heavy rain.