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  Overview This National Research Council report assesses the from engine and drivetrain efficiency improvements and potential for reducing petroleum consumption and green- load reduction (e.g., weight and rolling resistance). Load house gas (GHG) emissions by the U.S. light-duty vehicle reduction will improve the efficiency of all types of vehicles fleet by 80 percent by 2050. It examines the technologies regardless of the fuel used. that could contribute significantly to achieving these two If their costs can be reduced and refueling infrastructure goals and the barriers that might hinder their adoption. created, natural gas vehicles have great potential for reducing Four general pathways could contribute to attaining petroleum consumption, but their GHG emissions are too both goals—highly efficient internal combustion engine high for the 2050 GHG goal. vehicles and vehicles operating on biofuels, electricity, Drop-in biofuels (direct replacements for gasoline) or hydrogen. Natural gas vehicles could contribute to the produced from lignocellulosic biomass could lead to large additional goal of reducing petroleum consumption by 50 reductions in both petroleum use and GHG emissions. percent by 2030. While they can be introduced without major changes in fuel Scenarios identifying promising combinations of fuels delivery infrastructure or vehicles, the achievable production and vehicles illustrate what policies could be required to levels are uncertain. meet the goals. Several scenarios are promising, but strong Battery costs are projected to drop steeply, but limited and effective policies emphasizing research and develop- range and long recharge time are likely to limit the use of ment, subsidies, energy taxes, or regulations will be neces- all-electric vehicles mainly to local driving. Advanced bat- sary to overcome cost and consumer choice factors. tery technologies are under development, but all face serious All the vehicles considered will be several thousand technical challenges. dollars more expensive than today’s conventional vehicles, Battery and fuel cell vehicles could become less expensive even by 2050, and near-term costs for battery and fuel cell than the advanced internal combustion engine vehicles of vehicles will be considerably higher. Driving costs per mile 2050. Fuel cell vehicles are not subject to the limitations of will be lower, especially for vehicles powered by natural battery vehicles, but developing a hydrogen infrastructure in gas or electricity, but vehicle cost is likely to be a significant concert with a growing number of fuel cell vehicles will be issue for consumers for at least a decade. It is impossible to difficult and expensive. know which technologies will ultimately succeed, because The GHG benefits of all fuels will depend on their produc- all involve great uncertainty. It is thus essential that policies tion and use without large net emissions of carbon dioxide. be broad, robust, and adaptive. To the extent that fossil resources become a large source of All the successful scenarios combine highly efficient non-carbon transportation fuels (electricity or hydrogen), vehicles with at least one of the other three pathways. Large then the successful implementation of carbon capture and gains beyond the standards proposed for 2025 are feasible storage will be essential. 1