ANN ARBOR—Gas mileage of new vehicles sold in the U.S. slipped 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 December was 25.1 mpg, down from 25.3 mpg in each of the previous three months and down from an all-time high 25.8 mpg last August. Overall, vehicle fuel economy is up 5.0 mpg from October 2007, the first full month of monitoring by UMTRI researchers Michael Sivak and Brandon Schoettle.

“The recent reductions in gas mileage likely reflect the large and continuing decreases in the price of gasoline,” Sivak said.

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.

After setting a record-low 0.76 in August (the lower the value, the better), the EDI regressed for a second straight month to 0.79 in October. The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are now down 21 percent, overall, since October 2007.

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.