Induced Travel Demand: Research Design,Empirical Evidence,and Normative Policies

Claims of induced travel demand have seemingly paralyzed the ability to rationalize road development in the United States. Methodological issues related to resolution of analysis, measurement, specification, and normative significance are raised in this article. Five types of empirical studies— facility specific, model forecasts, area studies using proxy elasticities, area studies using partial elasticities, and disaggregate analyses—are reviewed and critiqued. Efforts to simultaneously model road supply and demand relationships and identify interaction effects are also reviewed. Based on a meta-analysis, the preponderance of research points to an appreciable induced demand effect; however, problems related to research design continue to cast doubts about our understanding of this phenomenon.