The average fuel economy of new cars sold in the US is going back up after dropping for a couple of months. The University of Michigan Transportation Research Institute (UMTRI) calculated a 24.8 mpg average for new light-duty vehicles sold in the US during November 2013. That's not as high as the 24.9 reported in August, but the numbers have been coming back up. The November rating was up 0.1 mpg from October.

Corporate average fuel economy is up 4.7 mpg since UMTRI researchers began documenting the data in October 2007. The figure is calculated by monthly sales figures of individual vehicle models and their combined city-highway fuel economy ratings published in the US Environmental Protection Agency's EPA Fuel Economy Guide.

The Institute's Eco-Driving Index also has seen improvements since the reporting began in 2007. The index tracks greenhouse gas emissions from a US driver who bought a new vehicle during the month. For September, the index was 0.80 for the fifth month in a row. That indicates a 20-percent improvement from the base score of 1 set in October 2007, said researcher Michael Sivak in a statement. The Eco-Driving Index figures in both the fuel used per distance driven and the amount of driving, Sivak said.

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