Personal transportation is a major component of greenhouse gas emissions as well as household expenses in the United States, accounting for about 18% of each. Both vehicle miles traveled and car ownership, the major determinants of both emissions and household costs, have risen continuously since the 1940s and at far higher rates than general population growth. Yet, it is only relatively recently that the effects of land use and transportation infrastructure investments, on the one hand, and pricing policies for roads, parking, auto insurance, fuel, and vehicles, on the other hand, have begun to attract significant researcher attention.