ANN ARBOR (WWJ) – Emissions from new vehicles are down a record 20 percent in the last five years, according to researchers at the University of Michigan Transportation Research Institute.

U-M’s national Eco-Driving Index (EDI), which estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver, stood at 0.80 in July — down from 0.82 in both May and June (the lower the value, the better).

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It’s the lowest value on record since UMTRI researchers Michael Sivak and Brandon Schoettle began monitoring emissions in October 2007. 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.

“Emissions are down because we’re driving more fuel-efficient vehicles and we’re driving less,” Sivak said in a release.

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In addition to the EDI, Sivak and Schoettle issued their monthly update of fuel economy of all new vehicles.

They found that average fuel economy (window-sticker values) of cars, light trucks, minivans and SUVs purchased in September was 23.8 mpg, the same as in August, but tied for the fourth-best month on record. It marks an 18 percent increase (3.7 mpg) from October 2007.

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For more information on the EDI calculations, click here. For more information on fuel economy calculations, click here.