Jan. 5 (UPI) -- More U.S. consumers seem to be buying light trucks rather than passenger vehicles, and that's skewed the average fuel economy lower, a study found.
The University of Michigan's Transportation Research Institute reported the average fuel economy of new vehicles sold in December was 25 miles per gallon, down about 0.8 percent from November.
"This drop likely reflects the increased proportion of light trucks versus passenger cars in the sales mix," the report read.
According to Kelly Blue Book, light trucks took the top three spots in best sellers, with the Ford F-series taking the No. 1 spot and a window-rating of 19 mpg in the city. The Toyota Camry was the top-selling sedan, in at No. 7 on the list and boasting 24 mpg in the city.
In total, for all of last year, the University of Michigan said average fuel economy for vehicles was 25.2 mpg, unchanged from the previous year.
President Donald Trump vowed last year to review, or possibly revoke, guidelines submitted by his predecessor that were aimed at putting more clean vehicles on the road. Former President Barack Obama during his second term in office issued a mandate that called for an increase in fuel economy to 54.5 miles per gallon by 2025.
In a February letter to the Environmental Protection Agency, the U.S. Alliance of Automobile Manufacturers said no conventional vehicle yet meets the target set by Obama in 2012 and, to get up to speed, the automotive industry would need to spend about $200 billion to comply with the rules.
A policy statement issued last year by the World Resources Institute notes most other leading economic powers, like China and Canada, the top oil exporter to the United States, have fuel efficiency standards comparable to the benchmark outlined by the Obama administration.
The University of Michigan said the average U.S. fuel economy is up 4.9 mpg since its first month of monitoring in October 2007, but 0.5 mpg lower than the peak from August 2014.
In terms of emissions, an index used by the university found the average driver produced 5 percent more than the low point from November 2013.