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# Sick of traffic jams? Stop tailgating

The sudden backups on highways that appear even when there's no accident ahead have annoyed drivers for ages. Now, MIT researchers have found a simple solution to these "phantom traffic jams."

Almost everyone has sat through a traffic jam. It's awful in so many ways — the constant stopping, cars as far as the eye can see and worst of all, the lack of explanation for what caused it once you drive up to the front.

Turns out there's a term to describe these traffic bottlenecks that appear even when there's no accident ahead: phantom traffic jams.

These unexplained backups happen when a car suddenly decides to brake, causing the car behind it to slow down. This causes a ripple effect down the lane and builds up until it creates a full-blown traffic jam.

If everyone stopped tailgating, that would already dramatically improve the situation.- Berthold Horn, professor of computer science and engineering at Massachusetts Institute of Technology

Berthold Horn is a professor of computer science and engineering at the Massachusetts Institute of Technology. He drives along U.S. Interstate 93 to work every day, and one day decided he was fed up with the congestion. He got to work researching phantom traffic jams and came up with a simple solution to fix it by simulating the scenario using math models.

What he discovered was that if every car on the road keeps an equal distance between the car immediately ahead and behind, it'll cut driving time by almost half.

"There will still be disturbances travelling down the line of traffic [when a car suddenly brakes]," Berthold explains, "but they get attenuated down the line, and eventually die away."

In traffic situations today, the opposite happens: "The disturbances get amplified until you reach a full stop."

Phantom traffic jams were first studied in the 1930s and since then more than 1,000 papers have been published to explain the phenomenon. However, little has been done to solve it.

Past solutions tried to limit the number of cars on the road at a given time by using traffic lights and speed limit signs.

"Keeping the density down does reduce the incidence of traffic jams," Berthold says. "But the problem is you're not making full use of the road."

Berthold believes his solution is more effective and it's easy to implement. There's no need to build new roads or develop new technologies. A simple update to the current adaptive cruise control system available in certain brands of cars will do the trick.

Adaptive cruise control works by using sensors at the front of the car to detect and keep a safe distance from the car ahead. To implement Berthold's solution, "all you need to do is to add additional sensors to the rear end of the car and then replace the current adaptive cruise control algorithm with our bilateral control algorithm."

Berthold says Toyota funded his research and might be implementing this new two-way model of adaptive cruise control in the future.

However, to see significant changes in traffic times, there needs to be wide adoption and that won't happen instantaneously, Berthold says.

"It's going to require some impetus such as a mandate."

So, until a new kind of cruise control system becomes standard, what drivers can do now is stop tailgating the vehicle ahead if there's a large gap behind their own vehicle, Berthold says. Constantly checking the rearview mirror is not a good idea since it distracts drivers from what's ahead and increases the chance of an accident.

"But if everyone stopped tailgating, that would already dramatically improve the situation."

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