The Impact of Residential Density on Vehicle Usage and Energy Consumption
The debate concerning the impacts of urban land use density on travel in general, and on residential vehicle use and fuel consumption in particular, lacks reliable quantitative evidence. The 2001 U.S. National Household Transportation Survey (NHTS) provides information on vehicle miles of travel (VMT) based on odometer data, as well as annual fuel usage computations based on information about the make, model and vintage of all household vehicles. In addition, the 2001 NHTS has been augmented with land use variables in the form of densities of population and residences at the census tract and block level for each of the more than 69,000 households in the dataset. In order to obtain unbiased estimates of the effects of any of these land use variables on annual VMT and fuel consumption the authors present a model system that accounts for both self selection effects and missing data that are related to the endogenous variables. Results for the State of California show that the residential density effects are substantial and precisely estimated. Comparing two households that are similar in all respects except residential density, a lower density of 1,000 housing units per square mile implies a positive difference of almost 1,200 miles per year and about 65 more gallons of fuel per household. This total effect of residential density on fuel usage is decomposed into to two paths of influence. Increased mileage leads to a difference of 45 gallons, but there is an additional direct effect of density through lower fleet fuel economy of 20 gallons per year, a result of vehicle type choice.