Congestion can be alleviated throughout a metropolitan area by altering the trips of drivers in specific neighborhoods

December 20, 2012

By Denise Brehm
Civil & Environmental Engineering 

In most cities, traffic growth has outpaced road capacity, leading to increased congestion, particularly during the morning and evening commutes. In 2007, congestion on U.S. roads was responsible for 4.2 billion hours of additional travel time, as well as 2.8 billion gallons of fuel consumption and an accompanying increase in air pollution.

One way to prevent traffic tie-ups is to have fewer cars on the road by encouraging alternatives such as public transportation, carpooling, flex time and working from home. But a new study — by Professor Marta González and researchers at Central South University in China, the University of California at Berkeley and the Austrian Institute of Technology — incorporates data from drivers’ cellphones to show that the adoption of these alternatives by a small percentage of people across a metropolitan area might not be very effective. However, if the same number of people, but from a carefully selected segment of the driving population, chooses not to drive at rush hour, this could reduce congestion significantly.

The study, published in the Dec. 20 issue of the journal Scientific Reports, demonstrates that canceling or delaying the trips of 1 percent of all drivers across a road network would reduce delays caused by congestion by only about 3 percent. But canceling the trips of 1 percent of drivers from carefully selected neighborhoods would reduce the extra travel time for all other drivers in a metropolitan area by as much as 18 percent.

“This has an analogy in many other flows in networks,” says lead research Marta González, the Gilbert W. Winslow Career Development Assistant Professor in MIT’s Department of Civil and Environmental Engineering. “Being able to detect and then rel