The average fuel economy of new vehicles sold in the U.S. in December fell 0.2 mpg to 24.9 mpg from the revised value for November, according to the University of Michigan's Transportation Research Institute.

This decline is likely due to continuing falling prices for gasoline in December and increased sales of pickup trucks, SUVs, and crossovers.  Fuel economy is down 0.9 mpg from the peak reached in August 2014, but still up 4.8 mpg since October 2007.

The average fuel economy of vehicles sold in calendar year 2015 was 25.3 mpg, down 0.1 mpg from the value for the vehicles sold in 2014.

The University of Michigan Eco-Driving Index (EDI) — an index that estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver — was 0.84 in October, up 0.01 from September (the lower the value, the better).  This value indicates that the average new-vehicle driver produced 16% lower emissions in September 2015 than in October 2007, but 6% higher emissions than the record low reached in August 2014.

The EDI takes into account both vehicle fuel economy and distance driven, the latter relying on data that are published with a two-month lag.