The average fuel efficiency of new vehicles has hit a two-decade low of 20.4 miles per gallon, according to a report released yesterday by the U.S. EPA. The report attributed the decline in fuel economy largely to the popularity of sports utility vehicles, which get notoriously poor fuel economy and are regulated by laxer rules than other passenger vehicles. The report will add fuel to the debate over whether the government should impose stricter fuel-economy standards on automakers. This summer, the National Academy of Sciences issued a report that found that higher standards could be implemented at a relatively low cost, but automakers are disputing that finding at a hearing today. Academy officials say any factual errors corrected as a result of the hearing would be unlikely to alter the report’s conclusions.