Michael Schreckenberg, professor at the University of Duisburg-Essen, is one of Germany’s most highly respected traffic researchers. His area of expertise is the modeling, simulation and optimization of transport systems in large networks, especially in road transport. The Nagel-Schreckenberg model, which he formulated in 1992 with his colleague Kai Nagel, explained for the first time the “traffic jam out of nowhere.”
Prof. Schreckenberg, in 2016 the German automobile club ADAC counted1.3 million kilometers (807,783 mi) of traffic jams. How much economic damage resulted from this and what does the international situation look like?
Michael Schreckenberg: If we consider only the sum of the earnings that drivers missed out on due to traffic jams, it adds up to at least EUR 14 billion in Germany. A four kilometer (2.5 mi) traffic jam over three hours on a two-lane highway causes an estimated EUR 100,000 in economic damage. In an international context, the costs for lost time are lower in many countries, but this is then correlated with the cost of living.
What were the most common causes of traffic jams?
Michael Schreckenberg: In Germany, obstructions caused by road construction increased significantly in 2016, particularly due to bridge rehabilitation measures that had been put off for a long time. Construction sites caused traffic congestion in 20 percent of the cases; accidents were the cause in 15 percent. About 13 percent of the jams were caused by human error and 2 percent were caused by weather events like storms, heavy rain and fog. The biggest share, however, – about 50 percent – can be traced to exceeding the capacity of the road. The causes are also interlinked, of course. The data in the United States are comparable, whereas traffic jams occur much more frequently due to overloading road capacities in China. The same applies to Brazil. In the capital city of Sao Paulo, the biggest traffic jam of all time – 344 kilometers (213.8 mi) long – occurred a few days before the opening match of the FIFA World Cup on May 23, 2014.
How does the “traffic jam out of nowhere” form?
Michael Schreckenberg: In our model we showed that chance plays a part in every traffic jam. There are numerous disrupting factors, most of which result from human error. Time and again, individual persons trigger the jams. This is often the case when drivers in heavy traffic brake more sharply than the car in front of them because they didn’t maintain enough distance.
Another factor is lane changes in a jam that has already formed. This also triggers new waves of congestion that the drivers who cause them do not even notice. Drivers are much more likely to notice cars that are passing them than they are to notice the cars they themselves have passed. After all, they constantly see the former in front of them in a jam. And for this reason, many people think they are in the wrong lane. In reality, changing lanes does not save any time. The average speed in a traffic jam is 10 km/h (6.2 mph), regardless of the lane.
What does the anatomy of a jam due to network overload look like?
Michael Schreckenberg: Jams due to network overload consistently form at the same points – at interchanges, at connection points and at inclines. Traffic congests and slows down here. When a car stops, a backup wave forms. The fatal thing is that these areas act like pumps and create one wave after another.
And then when you finally drive out of a wave like that ...
Michael Schreckenberg: ... then it can get really dangerous since many drivers feel like they’ve been released and lose concentration. And then they often drive directly into the end of the next backup wave.
Do you differentiate between different types of drivers in a jam?
Michael Schreckenberg: The decisive difference lies between commuters and holiday traffic. Commuters know their route well, they want to get to work and they tend to behave cooperatively. In holiday traffic, on the other hand, people are stressed out and are driving through areas they are unfamiliar with, and the tendency for frustration and aggression is greater. A special feeling of togetherness often emerges in a traffic jam, however – if nobody is able to move forward, we’re all equal. As soon as someone gets in a car, they change. They behave differently than they do in their usual private lives. 15 to 20 percent of all traffic jams are avoidable. They are the direct result of the human ego.
This is precisely where the traffic jam pilot from Audi comes in. Can it ease the situation?
Michael Schreckenberg: I am convinced it can. Automated systems like the traffic jam pilot help minimize the human factor. It is important that customers gain trust in the system.
We Germans are generally quite skeptical of new technologies and it is therefore important to proceed incrementally and continue developing trust in each stage. In the United States and especially in China, people are much more open to new technologies. A Chinese customer would get into a conditional automated car without hesitation.
How will traffic on German autobahns change in the next few years?
Michael Schreckenberg: Transport by truck has grown by more than 2 percent annually for the past 15 years. And that will continue as long as the economy is doing well. Germany is a transit country in which most goods are transported by road. One truck wears down a road as much as 60,000 cars. Because of this, and because of the high need for repair, the construction site situation will become more complicated. This makes it all the more important for cars to use the remaining space efficiently and to move intelligently – with systems like the traffic jam pilot as well as in a tight network with each other and with
other people using the roads.
What can drivers already do today? What are five tips you have for proper conduct on the highway?
Michael Schreckenberg: Be cooperative and let others pass by. Create proper merging formations and emergency lanes. Always keep an eye on traffic behind you as well. Leave enough space behind you when you cut back into the right lane after passing. Also, take frequent breaks because stressed-out drivers are inefficient and aggressive.
And the five mistakes you should avoid?
Michael Schreckenberg: Avoid constant lane changes. When you hectically steer into gaps, you often cause the next backup wave. Do not drive onto the highway too slowly. Do not constantly accelerate and then brake. Drive at a consistent pace and stay relaxed. Do not try to make up time lost in a traffic jam – this will make your driving risky and reckless.