WASHINGTON -- The government says new cars and trucks averaged a record 24.3 miles per gallon last year.

But falling gas prices and consumers' rekindled love of SUVs could endanger future fuel economy gains.

The Environmental Protection Agency says fuel economy rose last year by two-fifths of a mile per gallon, thanks to technical improvements that helped offset resurgent demand for larger vehicles.

It's the second straight year of modest gains after efficiency improved a more robust 1.2 miles per gallon between 2011 and 2012.

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The EPA's calculations are based on cars and trucks produced for sale in the U.S. each model year.

Officials predict slow growth for 2015. Automakers still expect to meet federal standards requiring a fleet-wide average of 54.5 miles per gallon by 2025.