A Fast Road to Nowhere | Germany| News and in-depth reporting from Berlin and beyond | DW | 09.03.2005
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A Fast Road to Nowhere

Plagued by chronic traffic jams, Germany's autobahn is often more of a long parking lot than a high-speed automotive paradise. Some scientists are hoping to explain the hassle of stop-and-go with physics and game theory.


Next time, take the train

Traffic jams don't discriminate. Regardless whether you're a CEO or a plumber, if you're stuck on the highway at one of Germany's classic chokepoints like Lotte-Osnabrück or Swisttal-Heimertsheim, you're stuck no matter what your station in life. And if you're sitting still on a stretch of the supposedly mighty autobahn instead of whizzing along at 200 kph, you may wonder why.

It's certainly not by chance as some may think.

"Around 80 percent of traffic jams occur because there are simply too many people on the same part of the road at the same time," said Michael Schreckenberg, a professor of traffic physics at the University of Duisburg-Essen.

As happens every year at the start of the summer holidays when thousands of German drivers head south, all it takes is for one of them to slam on the brakes just a bit too zealously for smooth-flowing traffic to implode.

"Those behind brake even harder and it just continues on down the line," said Peter Wagner, head of the traffic IT department of the German Institute for Aerospace. "The people way in the rear will end up completely stopped."

The masses effectively end up not only stopped, but moving slower overall, said Schreckenberg. Speeds of 15 kph are all it takes to cause jams on Germany's autobahn. A good case of road rage comes on a lot faster, since the traffic backup grows quickly with new victims in the rear approaching faster than those up front can get clear.

On-ramp horror

Verkehr Autobahn A8

Bad enough are the bottlenecks near construction sites or accidents. But worst of all are the highway on-ramps, where a gaggle of cars wants to join the flow of traffic. Schreckenberg said the whole process is like breathing: "It's a periodical phenomenon. The system breathes in cars and breathes out traffic jams."

There are already plenty of scientists who want to understand traffic jams in order to be able to predict where there might be trouble. Some researchers have even compared autos to physical particles. "As long as there's enough space, they move more or less freely like a gas," explained Wagner. "If I increase the pressure they begin to flow like a liquid. Only with even higher pressure will they, so to say, freeze."

And apparently gas particles hate bumping into each other as much as autobahn drivers. But the comparison only goes so far. "There are people sitting in cars, not particles," said Schreckenberg. "They react differently, such as braking sooner or later."

They also, unfortunately, think. If automatic traffic signs call for a speed limit of 60 to keep things flowing, the crafty drivers will often go 80, said Wagner. "That doesn't get rid of the slowdown but at least they're out in front."

Get off the road

To ease pressure on the autobahn, drivers actually need to head to an off-ramp and move on to surface streets, said Martin Treiber, who works on traffic modelling at the Dresden's Technical University. "Of course, that wouldn't do much for them, but it would help the autobahn speed up. It's a game theory problem."

Urlaub auf der Autobahn

Of course, nobody is altruistic enough to actually get off the highway for others, but potential detours are often quickly overloaded anyway. That's why Wagner likes a "Cellular-Automation-Approach" when looking at traffic jams. It essentially cuts the road into a grid and allots one cell to each car. If a cell is full, another car cannot move ahead until it is empty. It calculates that if 1,800 cars roll through a cell in one lane in an hour, things will grind to a halt.

Apparently Germans spend on average 58 hours a year sitting in traffic. A BMW study said such gridlock costs the economy €100 million each year, not including the cost to your nerves.

But Schreckenberg said Germans are traffic wimps compared to other countries. "We complain all the time, but if you look at Seoul, Istanbul or Tokyo -- with things routinely backed up over 10 kilometers -- now that's a traffic jam!"

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