Average U.S. fuel economy dives 0.4 mpg in Oct., study says

The average fuel economy for new cars and light trucks sold in October dropped 0.4 mpg from September to 24.8 mpg -- the biggest drop since July of 2013, the University of Michigan Transportation Research Institute said today.

The decline can be attributed to the increasing amount of light trucks sold in the U.S. compared to cars, researchers Michael Sivak and Brandon Schoettle said in a statement.

The researchers also noted that the small reductions in window-sticker fuel economy ratings in many 2017 model-year vehicles were from recent EPA calculation adjustments.

Despite the 5.9 percent drop in year-over-year total vehicle sales in October, light-truck sales managed a slight increase of 1.1 percent, while car sales dropped 16 percent, according to the Automotive News Data Center. Premium crossovers led truck sales with a 7.5 percent gain, followed by a 6.6 percent increase for SUVs and 4.3 percent increase for pickups.

The average window-sticker fuel economy rating for vehicles is still up 4.7 mpg from October 2007, when the study began. However, the value is down 1 mpg from its peak of 25.8 mpg in August 2014.

The national average for regular gasoline was $2.196 per gallon on Thursday, which AAA reported is down from the previous year, when a gallon was $2.210.

In a separate study, the institute said its greenhouse gas emissions index for U.S. drivers was 0.81 in August, down 0.01 from July. The value shows the average new-vehicle driver released 19 percent fewer emission in August than in October 2007. Though the study also said the August 2016 emissions value is 3 percent higher than the record lows in August 2014 and 2015.