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Induced Traffic Confirmed The jury is in! Recent studies show that building or widening highways induces more traffic, called induced travel. Shortly after the lanes or road is opened traffic will increase to 10 to 50% of the new roadway capacity as public transit or carpool riders switch to driving, or motorists decide to take more or longer trips or switch routes. This is short-term induced travel. In the longer term (three years or more), as the new roadway capacity stimulates more sprawl and motorists move farther from work and shopping, the total induced travel rises to 50 to 100% of the roadwayıs new capacity. This extra traffic clogs local streets at both ends of the highway travel. The following table summarizes these studies. Elasticity -- % new capacity filled with induced traffic   Short-term Long-term (3+ years) SACTRA   50 - 100% Goodwin 28% 57% Johnson and Ceerla   60 - 90% Hansen and Huang   90% Fulton, et al. 10 - 40% 50 - 80% Marshall   76 - 85% Noland 20 - 50% 70 - 100% Fulton, Lewis, Daniel Meszler, Robert Noland and John Thomas. "A Statistical Analysis of Induced Travel Effects in the U.S. Mid-Atlantic Region," forthcoming in the Journal of Transportation and Statistics. Goodwin, Phil. "Empirical Evidence on Induced Traffic," Transportation, Vol. 23, No. 1, Feb. 1996, 35-54. Hansen, Mark and Yranling Huang. "Road Supply and Traffic in California Urban Areas," Transportation Research A, 31. 205-218. 1997. Johnston, Robert and Raju Ceerla. "The Effects of New High-Occupancy Vehicle Lanes on Travel and Emissions," Transportation Research, Vol. 30A, No. 1, 35-50. 1996. Marshall, Norman. "Evidence of Induced Demand in the Texas Transportation Instituteıs Urban Roadway Congestion Study Data Set," presented at Transportation Research Board, Washington, DC. Jan. 2000. Standing Advisory Committee on Trunk Road Assessment, Department of Transport (UK). Trunk Roads and Generation of Traffic. HMSO, London. 1994. Noland, Robert. "Relationships Between Highway Capacity and Induced Vehicle Travel," forthcoming in Transportation Research A. Noland, Robert, and William Cowart. "Analysis of Metropolitan Highway Capacity and the Growth in Vehicle Miles of Travel," presented to the annual Meeting of the Transportation Research Board, 2000. Up to Top | Printer-friendly version of this page