According to a monthly report by Michael Sivak and Brandon Schoettle from the University of Michigan, the average fuel economy of newly purchased vehicles in September fell from an August record high.

The average fuel-economy (window-sticker) value of new vehicles sold in the U.S. in September was 24.6 mpg. This value is down 0.3 mpg from August, likely reflecting the recent reduction in the price of gasoline. Despite this drop, vehicle fuel economy is up 4.5 mpg since October 2007 (the first month of our monitoring). For a description of the calculations and the recent mpg values, click here.

The average fuel economy of model year 2013 vehicles (vehicles sold October 2012 through September 2013) was 24.7 mpg. This is up 1.2 mpg from model year 2012 vehicles.

Emissions

The University of Michigan Eco-Driving Index (EDI)--an index that estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver--stood at 0.80 in July (the lower the value the better). This value indicates an improvement of 20% since October 2007. 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). Please click here for a brief description of what the EDI is, how it is calculated, and the current and recent values of the EDI.

According to GasBuddy, the national average in September was five cents per gallon lower than it was in August, which may contribute to the decrease in fuel economy of new vehicles. Americans tend to buy less fuel efficient vehicles when gasoline prices are falling. The average pump price in September according to GasBuddy was $3.54 per gallon, while prices in Augustaveraged $3.59 per gallon.