Ever wondered what causes those inexplicable traffic jams on open stretches of highway, the ones without any accidents, construction, or other obvious bottlenecks? A Japanese group has an answer: It's pure physics. A simple experiment shows that when the density of vehicles on a road passes a certain threshold, traffic jams emerge because of fundamental instabilities inherent in multiparticle interactions. In other words, just a few mildly inconsistent drivers on the road will eventually cause a wave of backups.
The cause of so-called phantom traffic jams has been quite controversial, says Dirk Helbing, who studies the physics of social interactions at the Swiss Federal Institute of Technology in Zürich, Switzerland. One camp of traffic researchers believes that even phantom jams have external causes, be they merging traffic, curves, hills, or even a few bozos abruptly changing lanes. But other researchers contend that jams will spontaneously appear simply if the vehicle density exceeds a certain critical value. Yuki Sugiyama, a physicist at Nagoya University in Japan, says the predictions of these models have matched observations of highway traffic.
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