Skip to Content
77 Mass Ave

Eliminating Unexplained Traffic Jams

A new algorithm could mitigate mysterious freeway backups.
February 18, 2014

Everybody’s experienced it: a miserable backup on the freeway, which you think must be caused by an accident or construction until it thins out at some point for no apparent reason.

Such “traffic flow instabilities” have been studied since the 1930s, but although there are a half-dozen ways to model them mathematically, little has been done to prevent them.

Berthold Horn, a professor of computer science and engineering, has developed a new algorithm for alleviating traffic flow instabilities. He believes that it could be implemented with a modified version of the adaptive cruise-control systems available in many high-end cars.

Traffic flow instabilities arise, Horn explains, 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,” he says. “That will propagate upstream and increase in amplitude as it goes away from you.”

A car with adaptive cruise control uses sensors to monitor the speed and distance of the car in front of it. When traffic gets backed up, the car automatically slows, returning to its programmed speed when possible.

A car equipped with Horn’s system would, counterintuitively, also monitor the car behind it. Staying roughly halfway between the cars in front and behind means a car won’t have to slow down as sharply if the one in front brakes—and makes the car less likely to pass disruptions “upstream.”

Horn found that this approach could be modeled using something called the damped-wave equation, which describes how oscillations, such as waves propagating through a heavy fluid, die out over distance. Once he had a mathematical description of his dynamic system, he used techniques standard in control theory to demonstrate that his algorithm could stabilize the string of moving vehicles.

traffic jam in Singapore
Traffic jam in Singapore

Of course, Horn’s algorithm works only if a large percentage of cars are using it. And the laser range finders and radar systems used in existing adaptive cruise-control systems are relatively expensive.

But digital cameras are cheap, and many cars already use them to monitor drivers’ blind spots. Horn’s chief area of research is computer vision, and his group has previously published work on extracting information about distance and velocity from a single camera.

“Strangely,” he says, “while it’s difficult for a monocular camera to get distance accurately without additional information, and it’s difficult to get velocity accurately without additional information, the ratio can be had.” Horn is investigating whether his algorithm could use only that ratio, rather than absolute information about speed and distance.

Keep Reading

Most Popular

Workers disinfect the street outside Shijiazhuang Railway Station
Workers disinfect the street outside Shijiazhuang Railway Station

Why China is still obsessed with disinfecting everything

Most public health bodies dealing with covid have long since moved on from the idea of surface transmission. China’s didn’t—and that helps it control the narrative about the disease’s origins and danger.

crypto winter concept
crypto winter concept

Crypto is weathering a bitter storm. Some still hold on for dear life.

When a cryptocurrency’s value is theoretical, what happens if people quit believing?

individual aging affects covid outcomes concept
individual aging affects covid outcomes concept

Anti-aging drugs are being tested as a way to treat covid

Drugs that rejuvenate our immune systems and make us biologically younger could help protect us from the disease’s worst effects.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.