Traffic congestion closely resembles the physics of phase transitions, such as when ice melts or a metal becomes superconducting.
Shin-ichi Tadaki at Saga University in Japan and his colleagues used a high-resolution laser scanner to track cars travelling around an empty indoor baseball stadium, then analysed those data as if they were studying phase transitions in a material. They found that above a critical density of cars, traffic flow became unstable and changed from free-flowing to a jam.
Scaled up, that density value fits with those seen on real-world motorways, the authors say.
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Traffic jams follow the laws of physics. Nature 503, 168 (2013). https://doi.org/10.1038/503168a
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DOI: https://doi.org/10.1038/503168a
