Mysterious source of traffic jams discovered

After more than a decade of research team led by Prof Yuki Sugiyama of Nagoya University has solved the mysterious underlying cause of traffic jams when there is no obvious reason for the delay. In the New Journal of Physics a study by his group explains why we’re occasionally caught in jams for no obvious reason.

The real origin of the snarl up often has nothing to do with obvious obstructions such as accidents or construction work but is simply the result of there being too many cars.

The team discovered the importance of traffic density by applying techniques to model the movements of lots of particles to real-life moving traffic. The research shows that even tiny fluctuations in car-road density cause a chain reaction which can lead to a jam.

Mathematicians led by Dr Gábor Orosz of the University of Exeter have done similar work and he comments: “Many researchers believe that the effect of spontaneous jam formation (caused by tiny fluctuations above a critical traffic density) is the main reason for traffic jams and this view is supported by Prof Sugiyama.”

The Exeter work is different because the reaction time delay of drivers is included, revealing that the late reaction of drivers even one second can have big knock on effects when driving at much higher speeds than in the Japanese study.

“In a typical situation a vehicle dropping its speed from 80 mph to 65 mph may cause a ripple that later vanishes while dropping its speed from 80 mph to 62 mph may cause a ripple that is amplified and leads to traffic jams.”

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