Researchers from the Japanese "Mathematical Society of traffic flow" have shown how a traffic jam can develop for no apparent reason. They had 22 drivers circle a track and asked them all to keep a constant speed of 30 kph. Small fluctuations in people's speeds caused little disruptions that snowballed into full-fledged jams. The traffic jams propagate around the track like a wave through a spring.[youtube width="425" height="355"]http://www.youtube.com/watch?v=Suugn-p5C1M[/youtube]We wonder how many day-to-day traffic slowdowns are due to this phenomenon, as opposed to a real capacity problem on streets.