A June 2002 study of urban congestion found that cities whose highway construction kept close pace with traffic growth were successful in limiting drive times for commuters.
The 2002 Urban Mobility Report, written by researchers at the Texas Transportation Institute and sponsored by 10 state departments of transportation, studied 75 U.S. urban areas from 1982 to 2000. The institute found that only six of the cities studied attempted to keep highway expansion a close pace, less than a 10 percent difference, with traffic growth. Twenty-nine areas built highway capacity to stay between 10 percent and 30 percent of traffic growth, and the remaining 40 cities allowed road growth to lag behind traffic by greater than 30 percent.
The institute used the data and measured congestion results based on a “travel time index,” which is a ratio that shows the additional time required to complete travel during congested times of the day.
The average TTI for all the urban areas studied was 1.39, compared to a standard of 1.0, which represents what length of time a normal trip would take. The 1.39 measure of congestion means an average 20-minute trip would increase to 28 minutes during peak travel periods.
According to the report, the institute found that “the more that travel growth outpaced roadway expansion, the more the overall mobility level declined.”
For example, since 1982 the urban areas that failed to keep highway construction close to traffic growth saw their TTI rise to an average of about 3.3, more than tripling the length of an average trip in the early 1980s. The few cities that attempted to keep pace with traffic growth stayed under a 1.5 TTI.
Robert Poole, director of Transportation Studies for the Reason Public Policy Institute in Los Angeles, attributes the traffic problems most cities have with their misplacement of priorities. He says too many of them think they can’t “build their way out of congestion,” and instead seek alternatives such as mass transit.
Los Angeles by far had the sharpest increase in congestion the last 20 years, followed by San Francisco; Minneapolis; and Portland, Ore., according to the Texas Transportation Institute study.
Meanwhile, cities such as Houston and Tampa that channeled more transportation funding to increase highway capacity had modest increases.
The institute’s conclusion was that “changes in roadway supply have an effect on the change in delay.”
The only North Carolina city studied by the institute was Charlotte, whose TTI rose from 1.08 in 1982 to 1.27 in 2000.
Chesser is associate editor of Carolina Journal.