With gasoline prices falling in much of he counry, the average fuel economy or window-sticker value of new vehicles sold in the U.S. in May was 23.7 miles per gallon or  down 0.2 miles per gallon from April, according to statistics compiled by the University Of Michigan.
The drop in the figure reflected a shift towards more fuel-efficient vehicles that had prevailed over the previous six months. Nonetheless, interest in small cars remains strong, according to  J.D.Power & Associates.
The 23.7 miles per gallon figure up 3.6 miles per gallon or or 18 percent from the value in October 2007, which is baseline for the U-M Index and the first month for the university’s monitoring.  
The drop in May Index likely reflectedg the slight reduction in the price of gasoline, U-M officials said.
The Eco-Driving Index or EDI --an index that estimates the average monthly emissions generated by an individual U.S. driver--stood at 0.83 in March 2012, an improvement of 17 percent since October 2007.  The EDI takes into account both vehicle fuel economy and distance driven, which rlelies on data that are published with a two-month lag. 
The unadjusted CAFE performance in May was 29.1 miles per gallon, an improvement of 4.4 miles per gallon or 18 percent since October 2007.  (This index is based on a different set of EPA ratings than the window-sticker values. By Joseph Szczesny