ANN ARBOR—Fuel economy of all new vehicles sold in the United States has dropped for the third month in a row—likely reflecting the continuing reduction in gas prices, say researchers at the University of Michigan Transportation Research Institute.

Average fuel economy (window-sticker values) of cars, light trucks, minivans and SUVs purchased in June was 23.6 mpg—down from 23.7 in May, 23.9 in April and 24.1 in March—but still a 17 percent increase (3.5 mpg) from October 2007, the first month of monitoring by UMTRI researchers Michael Sivak and Brandon Schoettle.

In addition to average fuel economy, Sivak and Schoettle issued their 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 vehicle fuel economy and distance driven—the latter relying on data that are published with a two-month lag.

During April, the EDI stood at 0.81, down from 0.83 in March and tying the best mark ever set in February (the lower the value, the better). The index currently shows that emissions of greenhouse gases per driver of newly purchased vehicles are down 19 percent, overall, since October 2007.

Finally, Sivak and Schoettle report the unadjusted Corporate Average Fuel Economy performance. This index is based on a different set of EPA ratings than window-sticker values.

For June, unadjusted CAFE performance was 29 mpg, down from 29.1 in May, 29.3 in April and 29.6 mpg in March, but an increase of 17 percent (4.3 mpg) since October 2007.

Related Links:

• Fuel economy calculations, along with a graph and table of current and recent mpg: www.umich.edu/~umtriswt/EDI_sales-weighted-mpg.html
• Eco-Driving Index calculations, along with a graph and table of current and recent values: www.umich.edu/~umtriswt/EDI_values.html
• Unadjusted CAFE performance, along with a graph and table of current and recent mpg:
• http://www.umich.edu/~umtriswt/EDI_sales-weighted-CAFE.html