The average fuel economy of new vehicles sold in August, decreased by 0.1 mpg to 25.3 mpg compared to the previous month, according to a study by the University of Michigan's Transportation Research Institute (UMTRI). 

The decline comes with low fuel prices that have spurred increased sales of less fuel efficient light trucks and SUVs.

Fuel economy is down 0.5 mpg from the peak reached in August 2014, but up 5.2 mpg since October 2007 (the first month of our monitoring), according to data provided by UMTRI researchers Michael Sivak and Brandon Schoettle.  

The average sales-weighted fuel economy was calculated from the monthly sales of individual models of light-duty vehicles and the combined city/highway fuel-economy ratings published in the EPA Fuel Economy Guide for the respective models. For both monthly and model year averages, sales-weighted arithmetic means were calculated. 

The sales-weighted unadjusted Corporate Average Fuel Economy (CAFE) performance was calculated from the monthly sales of individual models of light-duty vehicles and the unadjusted combined city/highway fuel-economy ratings for the respective models. Unadjusted mpg remained consistent at 31.3 mpg from June to August 2015. 

Unadjusted fuel economy ratings didn't exactly match up to window sticker ratings published in the EPA Fuel Economy Guide, according to Sivak and Schoettle. 

Overall, from January to August 2015, the sales-weighted fuel economy averages at approximately 25.35 mpg.