Household vehicle ownership and fleet composition are choice dimensions that have important implications for policy making, particularly in the energy and environmental sustainability arena. In the context of household vehicle ownership and type choice, it is conceivable that there are substantial spatial interaction effects due to both observed and unobserved factors. This paper presents a multinomial probit model formulation that incorporates spatial spillover effects arising from both observed and unobserved factors. The model is estimated on the California add-on data set of the 2009 National Household Travel Survey. Model estimation results show that spatial dependency effects are statistically significant. The findings have important implications for model development and application in the policy forecasting arena.Paleti, Bhat, Pendyala, and Goulias
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INTRODUCTIONThe contribution of transportation to energy consumption and greenhouse gas emissions is undoubtedly dependent on the nature of vehicular travel undertaken by households. The number of vehicles owned, the types of vehicles owned (in terms of size, weight, fuel type, and age), and the extent to which different vehicles are used (miles of travel) are all key determinants of energy consumption and greenhouse gas emissions. Over the past 25 years, the split between cars and light duty trucks in the nation's vehicle fleet has changed dramatically; whereas light duty trucks (including pick-up trucks, minivans, and sport utility vehicles) accounted for just about 20 percent of the fleet 25 years ago, they now account for about one-half of all vehicles on the nation's roadways (1). This dramatic shift in the vehicular fleet composition and utilization has had far reaching energy and environmental consequences.The impact of the composition and utilization of the household vehicular fleet on energy consumption and greenhouse gas emissions calls for the incorporation of behavioral models of vehicle type choice and utilization in transportation demand forecasting models. Such models would provide the ability to forecast energy and environmental impacts of shifting vehicle ownership and utilization patterns arising from alternative policy decisions, the advent of new alternative fuel vehicle technologies, and changes in household and personal vehicular preferences. In this context, while there have been several earlier efforts in the literature on vehicle ownership analysis, much remains to be done in developing behavioral models of household vehicle fleet composition and utilization choices -and connecting such choices to energy and emissions estimates.In particular, an important issue that has not been adequately addressed in the vehicle ownership and utilization literature is that there may be spatial interaction effects in household vehicle ownership and type choice that are both observed and unobserved. Vehicle choices that households make are likely to be influenced by their interactions with neighboring households and the choices that neighbori...