Analysis of Induced Travel in the 1995 Npts

In this paper we estimate the relationship between road capacity and vehicle miles of travel (VMT) from a sample of 12,000 respondents from 48 urban areas in the 1995 Nationwide Personal Transportation Survey (NPTS). Our approach seeks to account for the effects of residential location, employment location, and commute mode choice in estimating the effect of capacity on VMT. VMT is found to be directly related to road capacity, as well as indirectly related through the influence of road capacity on residential and work place densities. Introduction Induced travel responses to changes in road capacity have been recognized by transportation planners and economists since the first applications of cost-benefit analysis to road projects in the 1930s (Prest and Turvey, 1965). However, interest in determining the magnitude of induced travel responses has grown in recent years in response to policy concerns about the links between highway construction, air quality and urban development patterns, and the desire to ensure efficient resource allocation through more detailed evaluation of highway projects. It has also been suggested that induced travel responses have become more substantial as a result of worsening traffic congestion (Hansen, 1998). Efforts to estimate induced travel effects of road capacity expansions are complicated by the need to distinguish capacity-related effects from a variety of other determinants (Dunphy, 1998). In addition to capacity-related changes, the growth in vehicle miles of travel (VMT) over time can be attributed to changes in household demographics and economic status as well as