Traffic congestion driven by sprawl

Analysis finds new roads aren't making things better as promised; in fact, they may just make things worse.

provided by the Surface Transportation Policy Project

nalysis is finding that traffic congestion is getting worse in major American metropolitan areas because of sprawl and its impact on driving habits. Using new data from the Texas Transportation Institute, the companion analysis by the Surface Transportation Policy Project finds that neither population growth nor too few roads are to blame for the rise in traffic jams.

While the population in all 68 metro areas studied grew by 22 million since 1982, the increase in driving has crowded the roads with the equivalent of 70 million more drivers. For example, in Washington DC, a population increase of 765,000 feels like an increase of more than 2 million on the roadways, because residents are driving 77 percent more.

"This analysis shows just why drivers have felt so besieged by ever-increasing traffic. Sprawl is making just about everyone drive farther and more often, and that fills up the roads." said Roy Kienitz, Executive Director of STPP. The paper, Why Are the Roads So Congested? A Companion Analysis of the Texas Transportation Institute's Data on Metropolitan Congestion, was provided by the Surface Transportation Policy Project.

Sixty-nine percent of the increase in driving from 1983 to 1990 was due to factors influenced by sprawl, such as longer car trips and a switch to driving from walking or transit. Population growth itself was only responsible for 13 percent of the growth in driving.

STPP found that every 10 percent increase in the highway network results in a 5.3 percent increase in the amount of driving, over and above any increases caused by population growth or other factors. This confirms other research on induced travel, the phenomenon in which increased road capacity generates additional traffic. In addition, road-building has not been an effective congestion-fighting measure: the metro areas that added the most highway space per person have seen congestion levels rise at a slightly higher rate than areas that added few roads per resident.

"It turns out that the most common response to congestion, road building, is just making things worse," said Kienitz. "We don't need more of the same: we need new solutions that give people a way to avoid traffic jams."

STPP's full analysis is available at The Texas Transportation Institute provided STPP with early access to its data. To view the Texas Transportation Institute's report, please go to

The Surface Transportation Policy Project is a nationwide network of more than 250 organizations, including planners, community development organizations, and advocacy groups, devoted to improving the nation's transportation system. STPP, 1100 Seventeenth Street, NW, 10th floor, Washington, DC 20036; (202) 466-2636; Fax: (202) 466-2247; email: