Photo via Wikimedia.

Photo via Wikimedia.

The University of Michigan’s Transportation Research Institute (UMTRI) has shown a drop in average sales-weighted miles per gallon for the month of November.

The average mpg for Sept. 2015 was 25.2, followed by 25.1 in October. In November, that number dropped to 25.

"This decline likely reflects the continuing drop in the price of gasoline in November, as well as the increased sales of pickup trucks, SUVs, and crossovers," according to the report produced by the institute's Michael Sivak and Brandon Schoettle. Fuel economy is down 0.8 mpg from the peak reached in August 2014, but still up 4.9 mpg since October 2007.

The University of Michigan Eco-Driving Index (EDI) — which estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver — was 0.83 in September, up 0.02 from August (the lower the value, the better). This value indicates that the average new-vehicle driver produced 17% lower emissions in September than in October 2007, but 5% higher emissions than the record low reached in August 2014.

The average sales-weighted fuel economy was calculated from the monthly sales of individual models of light-duty vehicles such as cars, SUVs, vans, and pickup trucks, and the combined city/highway fuel-economy ratings published in the Environmental Protection Agency (EPA)'s Fuel Economy Guide (window sticker ratings) for the respective models. For both monthly and model year averages, sales-weighted arithmetic means were calculated.

For cases in which the EPA Fuel Economy Guide contained multiple fuel-economy ratings for a vehicle model, the average of these ratings was used. When a vehicle model was sold during a particular model year but it is not listed in that year’s EPA Fuel Economy Guide, the fuel-economy ratings from the most recently available year were used.