Revisiting the effects of the built environment on VMT in California using quantile regression

Vehicle miles traveled is a key policy variable because it is strongly associated with greenhouse gas emissions and the spatial structure of urban environments, including density and land-use diversity. Policies that promote higher density and more diverse land use are often expected to reduce VMT by encouraging non-motorized travel. However, this relationship remains inconclusive and may generate unintended consequences, particularly for vulnerable populations who commute long distances due to imbalances between job locations and housing affordability. Using data from the 2010–2012 California Household Travel Survey, this study develops quantile regression models to examine the nonlinear effects of the built environment on daily personal-level VMT across different levels of automobile travel. Three key findings emerge. First, the effects of built environment characteristics vary across the VMT distribution rather than operating uniformly across travelers. Second, population density shows heterogeneous impacts: a one-unit increase (equivalent to 1000 persons per m 2 in 20-minute driving accessibility) is associated with a 10–12.5% reduction in total VMT at quantiles above 0.60, about four times larger than the 2.5% reduction observed at the 0.20 quantile. Third, built environment characteristics also exhibit heterogeneous effects across different forms of automobile travel. For VMT from driving someone else, a one-unit increase in population density is associated with up to an 18% reduction at the 0.80 quantile, while for VMT as passengers the reduction reaches up to 12.5% at the 0.85 quantile.