Concerns about climate change, dependence on oil, and unstable gasoline prices have led to significant efforts by policymakers to cut greenhouse gas (GHG) emissions and oil consumption. Within the transportation sector, light-duty vehicles (LDVs) are responsible for more than 65 percent of oil consumption and more than 60 percent of total GHG emissions, so meaningful reductions in oil consumption and GHG emissions can be achieved if a significant fraction the LDV fleet is replaced by more fuel-efficient technologies. This dissertation, consisting of three essays, investigates the potential benefits and impacts of deploying more fuel-efficient vehicles in the LDV fleet. The first essay uses data on 2003- and 2006-model gasoline-powered passenger cars, light trucks, and sport utility vehicles to investigate the implicit private cost of improving vehicle fuel efficiencies by reducing other desired attributes, such as horsepower. The second essay estimates the private benefits and societal impacts of electric vehicles, which have implications for efforts to incentivize the purchase and production of these vehicles. The third essay explores the implications of a large-scale adoption of electric vehicles, explaining that, although such an adoption is desirable with respect to goals for achieving energy security and environmental improvement, the decline fuel tax revenues that would result has adverse implications for the current system of transportation finance.