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