Jamey Volker – PhD candidate, Transportation Technology and Policy, University of California Davis
Dr. Susan Handy – Professor, Department of Environmental Science and Policy, University of California Davis, NCST Director
Chris Ganson – Senior Advisor for Transportation, Governor’s Office of Planning and Research
Gordon Garry – Former Senior Staff Member, Sacramento Area Council of Governments
Attempts to address traffic congestion commonly rely on increasing roadway capacity, e.g., by building new roadways or adding lanes to existing facilities. But studies continue to show that adding capacity is at best a temporary fix: adding roadway capacity in congested areas actually increases network-wide vehicle miles traveled (VMT) by a nearly equivalent proportion within a few years, which reduces or negates any initial congestion relief. That increase in VMT is called “induced travel.” The induced travel effect is explained by bedrock economic principles of supply and demand: adding roadway capacity reduces travel time; and as that effective “price” of driving goes down, the quantity of driving increases. The magnitude of that increase is commonly measured as the elasticity of VMT with respect to lane miles. Studies generally show that a 10% increase in roadway capacity is likely to increase network-wide VMT by 6 to 10 percent (an elasticity of 0.6 to 1.0). Yet methods of calculating project-level induced travel frequently vary and are often opaquely explained in transportation impact studies. NCST researchers developed a web-based induced VMT calculator to help with that.
- Gives an overview of the induced travel concept;
- Summarizes the academic research on induced travel elasticities;
- Introduces the new induced VMT calculator developed by NCST researchers; and
- Provides discussion on the calculator from two California transportation planning and policy experts.
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