University of California Transportation Center

Several recent studies have demonstrated an association between increases in highway capacity and increases in vehicle miles of travel (VMT). That phenomenon, called induced travel, has increasingly been cited as a basis for rethinking travel demand modeling, land-use/transportation interactions, and the environmental impacts of highway projects. Yet before the policy community can firmly conclude that induced travel is an important phenomenon, one lingering doubt must be addressed. Do new highways really induce additional travel, or are the associations between lane miles and VMT driven by a reverse causal link - namely that new highways are built in anticipation of expected increases in travel demand? The debate remains contentious, in part because the empirical evidence on induced travel is mostly from aggregate data that are aggregated over broad geographic areas, such as counties or states is difficult, and focusing on individual projects can help clarify matters. In this light, we examine three highways in a rapidly growing urban area to pose the following question: Do new highways influence urban development in ways that suggest that they induce new automobile traffic, or are urban growth patterns somewhat impervious to the completion of new highways?