Researchers at the University of Michigan Transportation Research Institute say fuel economy of new vehicles sold in the U.S. set another record high last month.

According to researchers Michael Sivak and Brandon Schoettle, the average fuel economy (window-sticker values) of cars, light trucks, vans and SUVs purchased in May was 25.6 mpg, up 0.4 mpg from April and 0.2 from March-the previous high.

Vehicle fuel economy is now up 5.5 mpg from October 2007, the first full month of monitoring.

Sivak says the increase likely reflects the continuing high price of gasoline.

On the other hand, vehicle emissions from new vehicles increased, according to Sivak's and Schoettle's update of their national Eco-Driving Index, which estimates the average monthly emissions generated by an individual U.S. driver.

The EDI stood at 0.78 during March, up slightly from the record-low 0.77 in February.

The index currently shows emissions of greenhouse gases per driver of newly purchased vehicles are now down 22 percent, overall, since October 2007.