ANN ARBOR – Despite cheaper gas prices, fewer people bought gas guzzling SUVs and pickup trucks, driving gas mileage higher in January for new vehicles sold in the United States for the first time in eight months, say researchers at the University of Michigan Transportation Research Institute.

The average fuel economy (window-sticker value) of new vehicles sold last month increased to 25.1 mpg from 24.9 mpg in December – the first time it had fallen below 25.0 mpg in nearly two years.

“This increase likely reflects the month-to-month seasonal decrease in sales of pickup trucks and SUVs,” said Michael Sivak, a research professor at UMTRI.

Overall, fuel economy is down 0.7 mpg from the peak reached in August 2014, but still up 5.0 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 November, the EDI improved to 0.82 (the lower the value, the better) from a revised mark of 0.83 in October. The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are down 18 percent, overall, since October 2007—but 4 percent higher than the record low reached in August 2014.