CARS.COM — The average fuel economy for all new cars sold in the U.S. in November brought the nation closer to posting its first decline in annual gas mileage since 2007. The average sales-weighted fuel economy, calculated monthly by researchers at the University of Michigan’s Transportation Research Institute, was 25.0 mpg last month — bringing the U.S. to a full half-year of worsening month-to-month gas mileage.
Related: U.S. Faces First Decline in Annual Mileage Since 2007
The ongoing glut of cheap gasoline has fueled this backslide, as American motorists lack a financial disincentive to buy bigger, less-efficient vehicles.
“The decline likely reflects the continuing drop in the price of gasoline in November, and the consequent increased sales of pickup trucks, SUVs, and crossovers,” institute researchers Michael Sivak and Brandon Schoettle stated in their monthly report.
While the average fuel economy for all new cars sold in the U.S. is still up 4.9 mpg since researchers began tracking the figure in October 2007, it’s down 0.8 mpg from the peak reached in August 2014. Moreover, while the figure fluctuates month to month, there has never been a year since tracking began in which the annual figure didn’t improve over the year that preceded it. This year is on pace to almost certainly break that trend of improved efficiency, as December gas mileage historically has either dipped or remained stagnant compared with the month before.
On the positive side — or at least the slightly less negative side — researchers have revised their initial October fuel-economy figure to 25.1 mpg from 25.0. The institute earlier reported that gas mileage had dipped 0.2 mpg from September to October, but later determined the monthly dip to be half that. Another 0.1 decline in the December figure would bring fuel economy below 25.0 mpg for the first time since January 2014.
With declining fuel economy, it makes sense that greenhouse-gas emissions would also get worse. According to the university’s Eco-Driving Index, which measures the monthly emissions of greenhouse gases generated by an individual U.S. driver, the figure for the most recent month recorded, September, was 0.83, up 0.02 from August.
“This value indicates that the average new-vehicle driver produced 17 percent lower emissions in September 2015 than in October 2007, but 5 percent higher emissions than the record low reached in August 2014,” researchers stated.