ANN ARBOR—Gas mileage of new vehicles sold in the U.S. declined for the second straight month in September, say researchers at the University of Michigan Transportation Research Institute.

The average fuel economy (window-sticker value) of new vehicles sold last month was 25.2 mpg—down 0.1 from August.

“This decline likely reflects the increased proportion of light trucks among the vehicles sold,” said UMTRI research professor Michael Sivak.

Overall, fuel economy is down 0.6 mpg from the peak reached in August 2014, but still up 5.1 mpg from October 2007—the first full month of monitoring by Sivak and colleague Brandon Schoettle. The model year 2016 average was 25.3 mpg—the same as model years 2015 and 2014.

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 July, the EDI improved to 0.82 (the lower the value, the better) from a mark of 0.83 in June. The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are down 18 percent, overall, since October 2007—but 4 percentage points higher than the record low reached in both August 2014 and August 2015.

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

U-M Sustainability fosters a more sustainable world through collaborations across campus and beyond aimed at educating students, generating new knowledge, and minimizing our environmental footprint. Learn more at sustainability.umich.edu.