Among the several major issues that Congress addressed in the process of reauthorizing the Clean Air Act was the future role of alternative highway transportation fuels in reducing urban smog. As vehicular emissions control efficiencies rose past 90 percent, attention turned to the idea that some alternatives to gasoline have combustion and/or other physical and chemical properties that might allow the achievement of ultra-low emissions levels. The fuels of interest include methanol (wood alcohol), ethanol (grain alcohol), natural gas, electricity, and hydrogen. In this report, which is part of Office of Technology Assessment's (OTA's) ongoing assessment of "Technological Risks and Opportunities in Future U.S. Energy Supply and Demand," OTA gives a broad overview of the qualities of the competing fuels and examines in depth some of the most contentious issues associated with the wisdom of active Federal support for introducing the fuels. Areas of uncertainty that affect the debate on Federal support include fuel cost (including costs of building new infrastructure and modifying vehicles); the air quality effects of the new fuels; effects on energy security; other environmental impacts of the fuels; and consumer acceptance of the changes in vehicle performance, refueling procedures, costs, and other facets of the transportation system that would follow a large-scale introduction of any of the fuels. The report singles out for special examination the arguments concerning the costs, energy security implications, and air quality impacts of introducing methanol fuels into the fleet. However, the other fuels have similar levels of uncertainty and contentiousness.

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