DRAFT Technical Background Document on Highway Capacity and Induced Travel

Although research on this topic goes back several decades, a surge of studies in the late 1990s and early 2000s, many focused on California, produced relatively consistent results using somewhat different methods. Included in the DRAFT Policy Brief on Highway Capacity are studies from California and the U.S. that focus on effects on vehicle-miles traveled (VMT) and that control for factors other than capacity expansion that influence VMT. Six studies published between 1997 and 2011 were included (see Table 1). The brief excludes studies that focused on traffic counts or average daily traffic (ADT) (e.g. Mokhtarian et al. 2002) or on the relationship between VMT and changes in travel time (i.e. travel-time elasticities) (e.g. Barr, 2000), as they do not have a direct relationship with greenhouse gas emissions.