Road Expansion is a Fundamental Cause of Growth in Vehicle Travel

California is unlikely to meet its climate goals if it doesn’t reduce vehicle travel. So far, however, state and local efforts to reduce vehicle miles traveled (VMT) have fallen short of expectations, even as cities grow more compact and public transit funding has increased. To better understand the role of highway expansion in meeting California’s climate goals, we analyzed whether a simple model that only considers road capacity and population growth can predict VMT as well as traditional transportation models. We also looked at the share of recent VMT growth that has been caused by expanded road capacity, and the reductions in VMT from transit and other projects funded by California’s climate investments.