Abstract:Despite significant reductions in tailpipe emissions over the past two decades, motor vehicles still account for 30 to 70% of all urban air pollution in the US and up to 30% of emissions of carbon dioxide related to energy use. In most countries of the world, ground transportation uses petroleum based fuels exclusively, and is hence vulnerable to supply and price volatility of the world oil market. Environmental and energy supply concerns are motivating a search for lower-polluting and more widely produced alternatives to petroleum transportation fuels and to internal combustion engines.

To address environmental and energy supply problems posed by our current transportation system, the most attractive strategies are those where fuels could be (1) produced economically on a large scale from domestic resources and (2) produced and used with minimal emissions of criteria air pollutants (NOx, CO, unburned hydrocarbons, particulates, SOx) and greenhouse gases.

If transportation fuels were derived from renewable sources (solar, wind, hydropower, biomass), emissions of greenhouse gases would be largely eliminated. In the United States, as in many areas of the world, potential renewable energy resources are vast and could ultimately meet foreseeable transportation energy demands, especially if coupled with high efficiency vehicles. If renewable fuels were used in zero or near-zero emission vehicles (e.g. battery powered electric vehicles or fuel cell electric vehicles), emissions of local pollutants would be eliminated or greatly reduced.