for such benefits to be significant. Lower-cost biofuel production methods and conversion processes will have to be developed for large-scale commercialization, but the initial high costs of biofuels, together with other barriers, may limit their market potential, absent policy interventions or significant oil price increases or supply disruptions. See Chapter 4.

Impacts of Alternative Technologies on Oil Use and CO2Emissions

To evaluate whether alternative technologies might be implemented more quickly than HFCVs to achieve significant reductions in oil use and CO2 emissions, the committee extended the modeling framework described above for HFCVs to include two alternatives—evolutionary vehicles and biofuel technologies. As with hydrogen, such modeling estimates are uncertain because of the complexities and unknowns inherent in any analysis of future transportation systems and fuel options. Insights from modeling were nonetheless of significant value in informing the committee’s judgment about the potential impacts of alternatives to hydrogen.

Toward this end, the committee developed and analyzed additional scenarios for the two selected alternative technologies with technological optimism and aggressive implementation similar to those for the Hydrogen Success case (the maximum practicable case). Case 2 (ICEV Efficiency) focused on improvements to conventional vehicles. This case shows (based on the analysis in Chapter 4) that aggressive implementation of evolutionary technology improvements for gasoline vehicles raised the average on-road fuel economy (which is typically 20 percent lower than the Environmental Protection Agency’s “sticker” miles per gallon [mpg]) of the light-duty fleet to about 30 mpg by 2020 and to nearly 40 mpg by 2035, with a small additional improvement by 2050. Conventional hybrid vehicles were estimated to improve to about 45 mpg by 2020, and then to about 55 mpg by 2035 and about 60 mpg by 2050. In Case 2, the growing penetration of hybrids gained them an 80 percent share of the total vehicle market by 2050 (see Chapter 6). These estimates assume that the evolutionary technologies result in efficiency improvements and that consumers buy them.

Case 3 (Biofuels) assumed aggressive development and use of biofuels to power the conventional vehicles of the baseline scenario. Most of this biofuel was in the form of cellulosic ethanol, which was to reach commercialization by 2010 (based on DOE’s biofuels roadmap), followed by rapid expansion to 16 billion gallons per year in 2020, 32 billion gallons per year in 2035, and 63 billion gallons per year in 2050. Grain-based ethanol production was assumed to reach a maximum of 12 billion gallons per year by 2015 and to remain at that level through 2050.

Full details of the assumptions used to analyze alternative vehicles and biofuels appear in Chapters 4 and 6 of this report. Here, the major results and implications of that analysis are highlighted.

The results from Case 2 (ICEV Efficiency) (Figure S.5) indicate that aggressive fuel economy improvements in conventional light-duty and hybrid vehicles follow the reference case, which includes the 2007 CAFE standards through 2020, but then could potentially deliver greater reductions in U.S. oil demand and CO2 emissions compared to the Hydrogen Success scenario, through about 2040. Subsequently, under the assumptions of this scenario, the rates of growth in the benefits of potential efficiency improvements begin to slow at a time when benefits from the Hydrogen Success case are still increasing. Breakthroughs and rapid market penetration in other developing vehicle technologies, such as plug-in hybrids and diesel hybrids, potentially could increase the benefits of reduced oil consumption and CO2 emissions above those shown in Case 2 (ICEV Efficiency), particularly in the 2030-2050 time frame.

The results of Case 3 (Biofuels) (also shown in Figure S.5) suggest that biofuels alone also could potentially reduce oil

FIGURE S.5 Comparison of (left) annual gasoline use and (right) annual greenhouse gas emissions (as equivalent CO2) for Cases 1-3 compared with the reference case.



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