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

TLDR

Claims of induced travel demand have hindered rational road development planning in the United States. The article examines methodological challenges in analyzing, measuring, specifying, and assessing the normative significance of induced travel demand. It reviews five empirical study types—facility‑specific, model forecasts, area studies with proxy or partial elasticities, and disaggregate analyses—and evaluates attempts to jointly model road supply and demand and identify interaction effects. A meta‑analysis indicates a substantial induced demand effect, yet methodological shortcomings continue to undermine confidence in the phenomenon.

Abstract

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.