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Urban Mobility Study

For more information:
Tim Lomax
979-845-9960
t-lomax@tamu.edu
or
David Schrank
979-845-7323
d-schrank@tamu.edu
Publication:

Urban Roadway Congestion: Annual Report 1998

Traffic jams: Not just big-city problem

The amount of time commuters spend stalled in traffic in small and medium-sized cities has more than quadrupled since 1982, growing at a far faster rate than it has in larger cities and illustrating what's fast becoming one of life's basic truths: traffic congestion isn't just a big-city problem.

Texas Transportation Institute (TTI) researchers Tim Lomax and David Schrank have studied roadway congestion in the country's 50 largest urban areas since 1987, but they added another 20 cities to the research effort this year to allow more comprehensive tracking and more meaningful comparisons of traffic conditions from city to city. The current study incorporates information collected through 1996, the most recent year for which all necessary data are available. The population of cities studied ranged from Boulder, Colo. (105,000), to New York (17.1 million).

The findings, researchers say, will give transportation professionals, policy makers and individual citizens important information related to a growing problem, and a common language to use in discussing the array of possible solutions. "The idea," Lomax says, "is to develop measures that respond to the needs of both technical and public audiences."

As one method of quantifying congestion, researchers use a roadway congestion index, a density measurement that considers traffic volume (demand) and the number of freeway and major street lanes (supply) in an area. An index value of greater than 1.0 indicates problematic congestion.

The five areas showing the highest congestion levels were: Los Angeles (1.57), Washington, D.C. (1.43), Miami-Hialeah (1.34), Chicago (1.34) and San Francisco-Oakland (1.33). Cities with the lowest congestion levels were: Bakersfield, Calif. (0.68), Laredo, Texas (0.73), Colorado Springs, Colo. (0.74), Beaumont, Texas (0.76), and Corpus Christi, Texas (0.78). While San Diego and Las Vegas saw their congestion levels increase by more than 50 percent since 1982, conditions worsened at the same rate in three smaller cities: Salt Lake City, Utah, Albany-Schenectady-Troy, N.Y., and Eugene-Springfield, Ore.

Conditions improved in only two areas — in Houston, where the congestion index dropped by 5 percent, and in Phoenix, where the index dropped by 1 percent.

The travel rate index presented by Lomax and Schrank provides another way of looking at peak travel periods, focusing on time.

The study showed that rush-hour travel took about 50 percent more time than non-rush hour trips in Los Angeles, San Francisco-Oakland, Seattle-Everett, Washington, D.C., and Las Vegas. Areas showing the least difference between rush hour and non-rush hour trips included: Eugene-Springfield, Ore., Boulder, Colo., Albany-Schenectady-Troy, N.Y., Corpus Christi, Texas, and Beaumont, Texas. Rush-hour trips in those cities required only 5 to 10 percent more time than non-rush hour trips.

Researchers also calculated the amount of fuel wasted as a result of congestion, noting that drivers stuck in traffic wasted more than six billion gallons of fuel in 1996 — enough to fill 670,000 gasoline tank trucks or 134 super tankers. In the nation's most congested cities, the waste amounts to more than 100 gallons per eligible driver per year. Drivers in the least congested cities waste about 20 gallons per year.

The total cost of traffic congestion in the cities studied amounts to almost $74 billion. Delay costs account for 88 percent of that total, with the remainder due to wasted fuel. The annual congestion cost per eligible driver ranged from $1,290 in Washington, D.C., to $125 in Boulder, Colo.

Researchers say that a full array of solutions and measures are essential in addressing the mobility problem.

"Urban areas are not solving the problem simply by building roads," Lomax says. "The future solutions won't be limited to roads, and therefore the measurement techniques cannot be limited to roadway-based measurements."

Other possible solutions include:

  • slowing the growth of vehicle volume on the road with bus and carpool lanes or transit service;
  • changing the time that vehicles use the road with flextime and telecommuting techniques;
  • more efficient traffic management with coordinated signals and incident management; and
  • providing more land use pattern alternatives that might reduce the need for vehicle travel.

"The combination of techniques used in an urban area is a product of public support along with financial and environmental concerns," Lomax says. "The solution may be different in every urban area."

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