– What causes traffic jams?Posted: May 5, 2011
Traffic that grinds to a halt and then restarts for no apparent reason is one of the biggest causes of frustration for drivers. Now a team of Japanese researchers has recreated the phenomenon on a test-track for the first time. The mathematical theory behind these so-called “shockwave” jams was developed more than 15 years ago using models that show jams appear from nowhere on roads carrying their maximum capacity of free-flowing traffic – typically triggered by a single driver slowing down.
After that first vehicle brakes, the driver behind must also slow, and a shockwave jam of bunching cars appears, travelling backwards through the traffic. The theory has frequently been modelled in computer simulations, and seems to fit with observations of real traffic, but has never been recreated experimentally until now.
There’s more explanation at the New Scientist web site.
Temple University maths Professor Benjamin Seibold, quoted in this CBS report, says “phantom traffic jams” are no one’s fault:
At high traffic volumes, any small disturbance in traffic flow can trigger a ripple-effect of drivers hitting the brakes, creating what he calls a “phantom traffic jam”. There’s no outside reason for those traffic jams. There’s no obstacle on the road. There’s no car in the breakdown lane. They’re an instability in the traffic flow, so they can occur without any visible reasons.
He told CBS reporter Mike DeNardo that “the wave can travel backward for miles, and spawn successive waves…… individual drivers can mitigate the effects by driving less aggressively and leaving a little more distance from the car in front — assuming another driver doesn’t cut into that space you just created”.