The cars and trucks plying Ameri ca's roads and highways generate roughly 20 percent of the nation's total emissions of carbon dioxide, a pollutant that is, of course, of increasing concern because of its influence on climate. Motor vehicles also account for most of our country's dependence on imported petroleum, the price of which has recently skyrocketed to near-record levels. So policymakers would welcome the many benefits that would accrue from lessening the amount of fuel consumed in this way.
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