"But the models show that even if all drivers drive by the exact same rules, and no one does anything wrong, these waves can still arise." "We're usually inclined to think that these must be caused by an individual driver," Seibold says. But if there are enough cars on the road, even if people anticipate approaching traffic to the best of their abilities, phantom traffic jams will form. On the other hand, this sort of behavioral change doesn't totally eliminate phantom traffic jams - it merely makes them less likely to form (specifically, it means that a higher density of cars on the road is required for traffic waves to develop). This will lead to you avoid sudden braking when possible. "If people anticipate higher traffic densities ahead, and take their feet off the gas earlier and leave more room in front of them - instead of waiting until they have to brake - that can prevent traffic jams from arising," Seibold says.Īnother way to think of it, says Berthold Horn - an MIT computer scientist who's worked on the same topic - is to try driving so that you stay halfway between the car in front of you and the one behind you. In one sense, it seems reasonable to blame these phantom traffic jams on individual drivers. The models indicate that these jams are more likely to form when people drive as fast as possible, then finally brake when necessary to avoid hitting the car in front of them, triggering a chain reaction. So who's to blame for these traffic jams? In one, they instructed 22 drivers to drive at the same speed (18.6 mph), and preserve the same amount of space between cars, on a small circular road. Japanese researchers have also conducted real-world experiments that come to the same conclusion. He and others developed the concept of these waves (which they call jamitons, because they're analogous to waves in physics called solitons) using computer algorithms that simulate driving behavior: "Then, after that, they slowly accelerate again." "It's typically 100 to 1000 meters long, and it usually begins with vehicles running into a sudden increase in density at the start, and a drop in velocity," Seibold says. One car brakes slightly, and the ones behind it brake just a bit moreĮven when cars leave this traffic wave, though, the wave itself doesn't disappear: it gradually drifts backward, against the direction of traffic. "These traffic waves arise from small perturbations in a uniform traffic flow, like a bump in the road, or a driver braking after a moment of inattention," says Benjamin Seibold, a mathematician at Temple University who's worked with colleagues on understanding the phenomenon. If there are enough cars on a highway, any minor disruptions to the flow of traffic can cause a self-reinforcing chain reaction: one car brakes slightly, and the ones behind it brake just a bit more to avoid hitting it, with the braking eventually amplifying until it produces a wave of stopped or slowed traffic. They also have suggestions on how to stop these jams. Why does this happen?Īs it turns out, a few different groups of researchers have been using mathematical calculations and real-world experiments to try answering this question. The weirdest part: there's no construction, accident, or other possible explanation for the traffic. Minutes later, it begins to move again, and then suddenly, you're moving at full speed. Traffic slows to a crawl, then stops entirely. If you've ever driven on a highway, you've probably seen it happen.
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