of vehicles on the road and the miles traveled. These vehicles will be mainly ICEVs, with an increasing share of HEVs. In addition, biofuels mandated by the Renewable Fuel Standard (RFS) could displace a significant amount of petroleum fuels by 2030, especially if coupled with advances in processes for producing “drop-in” cellulosic biofuels (direct substitutes for gasoline or diesel fuel).

Additional policy support may be required to promote increased sales of CNGVs, BEVs, and FCEVs. Even then the nation is unlikely to reach a 50 percent reduction in petroleum use by 2030 because very little time remains for achieving the required massive changes in the on-road LDV fleet and/or its fuel supply. Many of the vehicles on the road in 2030 will have been built by 2015, and these will lower the fuel economy of the on-road fleet.

Finding: The goal of an 80 percent reduction in LDV petroleum use by 2050 potentially could be met by several combinations of technologies that achieve at least the midrange level of estimated success. Continued improvement in vehicle efficiency, beyond that required by the 2025 CAFE standards, is an important part of each successful combination. In addition, biofuels would have to be expanded greatly or the LDV fleet would have to be composed largely of CNGVs, BEVs and/or FCEVs.

The committee considers that large reductions in LDV use of petroleum-based fuels are plausible by 2050, possibly even slightly more than the 80 percent target, but achieving reductions of this size will be difficult. A successful transition path to large reductions in petroleum use will require not only long-term rapid progress in vehicle technologies for ICEVs and HEVs, but also increased production and use of biofuels, and/or the successful introduction and large-scale deployment of CNGVs, BEVs with greatly improved batteries, or FCEVs.

Extensive new fuel infrastructure would be needed for FCEVs. CNGVs would require new supply lines in areas where natural gas is unavailable or in limited supply, and many filling stations. The infrastructure needed for BEVs would mostly be charging facilities, since electricity supply is already ubiquitous. The technology advances required do not appear to require unexpected breakthroughs and can produce dramatic advances over time, but they would have to be focused on reducing fuel use rather than allowing increases in performance such as acceleration. Thus, a rigorous policy framework would be needed, more stringent than the 2025 CAFE/GHG or RFS standards. Large capital investments would be required for both the fuel and vehicle manufacturing infrastructure. Further, alternative vehicles and some fuels will be more expensive than the current technology during the transition, so incentives to both manufacturers and consumers may be required for more than a decade to spur purchases of the new technology. Figure S.1 shows potential petroleum use for technology-specific scenarios.

Finding: Large reductions are potentially achievable in annual LDV GHG emissions by 2050, on the order of 60 to 70 percent relative to 2005. An 80 percent reduction in LDV GHG emissions by 2050 may be technically achievable, but will be very difficult. Vehicles and fuels in the 2050 time frame would have to include at least two of the four pathways: much higher efficiency than current vehicles, and operation on biofuels, electricity, or hydrogen (all produced with low GHG emissions). All four pathways entail great uncertainties over costs and performance. If BEVs or FCEVs are to be a majority of the 2050 LDV fleet, they would have to be a substantial fraction of new car sales by 2035.

Achieving large reductions in net GHG emissions from LDVs is more difficult than achieving large reductions in petroleum use. In addition to making all LDVs highly efficient so that their fuel use per mile is greatly reduced, it will be necessary to displace almost all the remaining petroleum-based gasoline and diesel fuel with fuels with low net GHG emissions. This is a massive and expensive transition that, because LDVs emit only about 17 percent of U.S. GHGs, would have to be part of an economy-wide transition to provide major GHG reduction benefits.

The benefits of biofuels depend on how they are produced and on any direct or indirect land-use changes that could lead to GHG emissions. Several studies indicate that sufficient biomass should be available to make a large contribution to meeting the goals of this study, but the long-term costs and resource base for biofuels produced with low GHG emissions need to be demonstrated. Hydrogen and electricity must be produced with low-net-GHG emissions, and the costs of large-scale production are uncertain. Achieving the goals does not require fundamental breakthroughs in batteries, fuel cell systems, or lightweight materials, but significant continuing R&D yielding sustained progress in cost reduction and performance improvement (e.g., durability) is essential.

Overall, the committee concluded that LDV GHG emissions could be reduced by some 60 percent to somewhat more than 80 percent by 2050 as shown in Figure S.2. The cost will be greater than that for meeting the 80 percent petroleum reduction goal because options such as CNGVs, or BEVs operating on electricity produced without constraints on GHG emissions, cannot play a large role.

Finding: None of the four pathways by itself is projected to be able to achieve sufficiently high reductions in LDV GHG emissions to meet the 2050 goal. Further, the cost, potential rate of implementation of each technology, and response of consumers and

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