The Energy Independence and Security Act of 2007 requires that the fleet of new automobiles sold in the United States by 2020 average at least 35 miles per gallon, a 40 percent increase from today's 25 mpg average. To achieve climate and energy security goals, it is widely expected that even greater improvements in fuel economy, along with reductions in travel demand and substitution of alternative fuels, will be needed in the longer term.
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