Traffic shockwave observed in lab

Have you ever been driving on the highway when you suddenly get stuck in traffic which when you get to the front has no apparent cause? Well, the New Scientist has an article about Japanese scientists who have managed to reproduce this in the lab.

The scientists had 22 cars going around a track all of which were told to drive at a steady 30 kilometers / hour. Eventually a wave caused by one driver briefly putting on his brakes travelled back through the stream of cars and caused several to come to a complete stop.

via slashdot

Follow up: Stu kindly sent a link to this little Java applet that simulates traffic flow. If you try the ring road simulation you will see how the traffic bunches up and eventually stops.