Study shows capacity fails to ease congestion

by Gloria Ohland


n analysis of the respected Texas Transportation Institute's (TTI) annual report on metropolitan congestion shows that the most common congestion-fighting strategy road-building has had virtually no impact on the growth of traffic congestion in major urban areas in the last 15 years.

The analysis, by STPP, was prompted by a number of recent studies questioning whether building new roads reduces congestion. Using TTI data, STPP compared metro areas that added significant new capacity with those that did not and found that while the first group spent roughly $22 billion more on construction, the average of TTI's "roadway congestion index" for each of the two groups was almost identical."

Widening roads to ease traffic congestion is ineffective and expensive," says Roy Kienitz, executive director of STPP. "It's like trying to cure obesity by loosening your belt."

The TTI study also projects the increase in lane miles needed to keep up with traffic growth. STPP's analysis of the data estimates that most urban areas would have to spend thousands of dollars per family each year to build new roads, ranging up to $3,243 in Nashville, Tennessee.

The STPP report says the problem may be partially explained by the phenomenon of "induced traffic." Several recent studies have documented that new roads actually encourage more driving.

A University of California study of 30 urban counties in the state found that every 1 percent increase in lane miles generates a 0.9 percent increase in traffic within five years, negating any congestion-easing effect.

The report did not control for other factors that might influence congestion, such as economic activity or population growth. But the large size of the data set (70 metropolitan areas) and long duration of the study (15 years) make it likely that any relationships between road-building and congestion would emerge.

The study concludes that given the enormous costs of roadway construction, officials need to investigate a broader menu of measures that include other transportation modes, new technology, pricing, land use and other strategies.

View the report at; TTI's study is at

  The Surface Transportation Policy Project (STPP) is a nonprofit, public interest coalition of more than 200 groups devoted to ensuring that transportation policy and investments help conserve energy, protect environmental and aesthetic quality, strengthen the economy, promote social equity and make communities more livable. STPP 617 S. Olive St., suite 1110, L.A., CA 90014. 213-629-2043; fax is 213-629-2259.