The unexplainable traffic jam

Researchers in Japan have managed to recreate the frustrating phenomenon of the ‘shockwave’ traffic jam. The ‘shockwave’ traffic jam occurs when a road is almost at maximum capacity and a single driver slows down. After the first vehicle slows down, so must the vehicle behind and then the one behind that causing a wave of traffic. This mathematical theory was discovered over 15 years ago to explain the sudden and random halts in traffic. The theory has frequently been modelled in computer simulations, and seems to fit with observations of real traffic, but this is the first time it has been recreated experimentally.

Drivers were asked to keep a constant speed of 30km/hr on a single lane circuit and started off well. However, soon clusters of several vehicles appeared forcing some to stop completely.

Pinpointing the causes of shockwave jams is an exercise in psychology more than anything else. “If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred. Human error is needed to cause the fluctuations in behaviour,” said Tim Rees of TRL, a UK transport research firm.

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