Traffic jams that seem to occur without a cause and then thin out again for no reason -- dubbed "traffic flow instabilities" -- have been studied at length, but little has been done to prevent them, researchers at the Massachusetts Institute of Technology said.
Traffic flow instabilities arise, they explained, because variations in velocity are magnified as they pass through a lane of traffic.
"Suppose that you introduce a perturbation by just braking really hard for a moment, then that will propagate upstream and increase in amplitude as it goes away from you," MIT computer scientist Berthold said. "It's kind of a chaotic system. It has positive feedback, and some little perturbation can get it going."
Horn said he has developed a new algorithm that could alleviate traffic flow instabilities by being implemented in a variation of the adaptive cruise-control systems found on many of today's high-end cars.
In such systems sensors monitor the speed and distance of the car in front so the driver doesn't have to turn the cruise control off when traffic gets backed up: The car will automatically slow when it needs to and return to its programmed speed when possible.
Horn's system would also use sensors to gather information about the distance and velocity of the car behind. A car that stays roughly halfway between those in front of it and behind it won't have to slow down as precipitously if the car in front of it brakes; but it will also be less likely to pass on any unavoidable disruptions to the car behind it, he said.
Since the system looks in both directions at once, Horn said it would offer "bilateral control."