U.S. Faces First Decline in Annual Mileage Since 2007

It may be by only fractions of a percent, but 2015 is on track to be the first year in nearly a decade in which U.S. fuel economy was worse than the year before. According to the latest monthly fuel-economy report from the University of Michigan's Transportation Research Institute, the average gas mileage of new cars sold in October, known as the "window sticker rating," dipped 0.2 mpg to 25 mpg, the fifth straight month the figure either declined or stayed the same.

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While month-to-month decreases have not been uncommon since institute researchers Michael Sivak and Brandon Schoettle began tracking U.S. fuel economy in October 2007, the average year-over-year improvement has been just less than 0.9 mpg. The biggest annual gains came in 2010 and 2012, when fuel economy increased by 1.2 mpg compared with the previous year, while the lowest annual bumps came in 2011 and 2014, both improving about 0.6 mpg from the preceding year — but always improving.

This year, however, the fuel economy of new cars sold in the U.S. has taken a beating. Through the first 10 months of this year, fuel economy averages 25.3 mpg. That's compared with the average for January through October 2014, which was just a tick less than 25.4 mpg. Given that the last two months' mileage in any given year generally dips slightly or remains flat, the trend points to the U.S. closing out a year with poorer gas mileage than the year that preceded it for the first time since tracking began.

"If the current trend continues, the average fuel economy of vehicles sold in calendar 2015 may turn out to be lower than those sold in calendar 2014," Sivak told Cars.com in an email, noting that October 2013 through September 2014 mileage was the same as October 2014 through September 2015, at 25.3 mpg. "That has not happened since we started our monitoring in 2007."

While this regression may seem surprising, it doesn't exactly come as a surprise. In the first 10 months of 2015, fuel economy was worse than the same month the year before a record eight times. For context, mileage for a given month decreased from the same month the preceding year only six other times total from 2007 to 2014.

"The main culprit is the decreasing price of gas," Sivak said.

Indeed, despite week-to-week fluctuations, gas prices have been on a steady decline for months, with some industry analysts predicting prices of less than $2 a gallon by 2016. The resulting relief consumers are feeling at the pump correlates to an ongoing increase in the sales of lower-mileage pickup trucks and SUVs. October new-car sales were up nearly 14 percent over October 2014, while midsize pickup trucks and compact SUVs surged 31 percent and 26 percent, respectively; full-size pickup sales were up more than 4 percent.

Despite the current situation, new-car fuel economy remains up by nearly 5 mpg since October 2007.

Editor's note: This story was updated on Nov. 6 to correct the range of dates during which fuel economy was unchaged at 25.3 mpg.