THE INTERACTION BETWEEN DISTANCE TO WORK AND VEHICLE MILES TRAVELED

Abstract

Economists have long been concerned with the externalities generated by automobiles, such as traffic congestion and air pollution. Since many of these externalities are closely bound up with the number of miles being driven, economists have been much interested in the behavior of what is known as vehicle miles traveled (VMT). Planners believe that land use can be manipulated to serve congestion management, air quality or related transport planning goals. The underlying idea is that household location may have a big impact on its transportation demand, including car ownership. In this context, I focus on distance to work (DTW) as the measure of household location. I chose a continuous measure of household location instead of a discrete one because, besides being easily measured, it matches better the data available for this study and it has a very straightforward interpretation--it allows me to calculate the contribution of commuting miles to total miles driven.

Despite the clear conceptual connection between DTW and VMT, and the constraining nature of household location, little is known about their joint behavior. City and household level attributes that may lead households to live close or far from their work may also lead them to drive few or many miles for non-commuting purposes. This effect must be accounted for when measuring the behavior of VMT conditional on DTW. I develop two models to analyze: (i) the role of city characteristics in explaining households' distance to work, (ii) the effect of distance to work on VMT and car ownership, (iii) the effect of city level attributes on VMT, conditional on DTW, (iv) the unobserved taste for driving, (v) differences between workers and non-workers. I find that: (i) City characteristics expected to affect commutes have a small effect on households' DTW, (ii) DTW provides an important effect on car ownership levels and VMT, (iii) City characteristics expected to influence non-commute miles have a small impact on VMT, (iv) taste for driving has a small but significant effect on VMT, and (v) non-workers are much less responsive to gas prices than workers.