The new cars Americans bought in December had an average fuel economy of 25.1 miles per gallon, says the University of Michigan Transportation Research Institute (UMTRI). Not exactly shabby, but that's down from 25.3 mpg in November and an all-time high of 25.8 mpg in August and, naturally, indicates a slight uptick in emissions numbers. In fact, last month's new cars had the worst monthly fuel economy average since last February.
The lower mpg figure falls in line with green-car sales numbers from December. Last month, Americans bought about 46,000 hybrids, plug-in hybrids, battery-electric vehicles and diesels. That number was down 7.8 percent from a year earlier. And that decline is likely a result of lower gas prices, which average about $2.19 a gallon, according to AAA. That marks a decline from $2.68 a month ago and from $3.31 a year ago.