| Abstract
| - We examine the economic and environmental implicationsof the fuels and propulsion technologies that will beavailable over the next two decades for powering a largeproportion of the light duty fleet (cars and light trucks).Since R&D change is rapid, we treat the uncertainty aboutfuture technologies using bounding calculations. A life-cycle perspective is used to analyze fossil fuels [conventionalunleaded and reformulated gasolines, low sulfur reformulateddiesel, and compressed natural gas (CNG)], ethanolfrom biomass, and electricity together with current andadvanced internal combustion engines (ICE, indirect (port)and direct injection, spark, and compression ignited)and electric vehicles (battery-powered, hybrid electric,and fuel cell). Technological advances continue to improvethe efficiency and environmental performance of ICEautomobiles powered by low sulfur fossil fuels. Absent adoubling of petroleum prices or stringent regulation [due, forexample, to intense concerns about greenhouse gas(GHG) emissions], ICE using fossil fuels will dominate themarket for the next two decades. CNG cars have lowemissions, including GHG, but must be redesigned to storeenough CNG to achieve the current range. Battery-powered cars have limited range and are expensive, andthe life-cycle of battery components leads to dischargesof toxic materials. Although both hybrid and fuel cell vehiclespromise better fuel economy and lower emissions, in thenear term these do not justify their higher costs. If globalwarming becomes a major concern, CNG offers carbondioxide emission reductions of up to 30%, and bioethanolcould provide a fuel with no net carbon dioxide emissions,although the bioethanol price would be more than twicecurrent petroleum prices.
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