ANN ARBOR—Gas mileage of new vehicles sold in the U.S. dipped last month, according to researchers at the University of Michigan Transportation Research Institute.

Average fuel economy (window-sticker values) of cars, light trucks, vans and SUVs purchased in August was 25.3 mpg, down 0.1 mpg from July.

“This decline likely reflects the decreased price of gasoline in August and the consequent increased sales of light trucks and SUVs,” said Michael Sivak, a research professor at UMTRI.

Overall, fuel economy is down 0.5 mpg from the peak reached in August 2014, but up 5.2 mpg from October 2007—the first full month of monitoring by Sivak and colleague Brandon Schoettle.

In addition to average fuel economy, Sivak and Schoettle issued a monthly update of their national Eco-Driving Index, which estimates the average monthly emissions generated by an individual U.S. driver. The EDI takes into account both the fuel used per distance driven and the amount of driving—the latter relying on data that are published with a two-month lag.

During June, the EDI remained at 0.82 (the lower the value, the better) for the second straight month. The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are down 18 percent, overall, since October 2007. EDI reached its best level (0.78) in August 2014.

More information:

• Fuel economy (with graph and table of current/recent mpg)
• Eco-Driving Index (with graph and table of current/recent values)
• Michael Sivak
• Brandon Schoettle