Fuel Economy Falls Along With Gas Prices

Following months of steady gains, the average fuel economy for 2013 light-duty vehicles sold in the U.S. dipped in September. Researchers at the University of Michigan Transportation Research Institute — who calculate average sales-weighted fuel economy using monthly sales of individual models of cars, SUVs, vans and pickup trucks, as well as respective models' EPA fuel-economy ratings — attribute the decrease to recent reductions in the price of gasoline.

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The "window-sticker" fuel-economy value of new vehicles sold in September was 24.6 mpg, down 0.3 mpg since August; that follows 0.1 mpg gains in both July and August, after a slight dip in June. Despite the decrease, compared with the same period in 2012, the average fuel economy was up 0.8 mpg. Moreover, since the institute started tracking the numbers in October 2007, the average fuel economy has improved by 4.5 mpg.

Meanwhile, motorists' greenhouse-gas emissions continued to decline in September, according to the University of Michigan's Eco-Driving Index, which estimates the monthly amount of greenhouse gases produced by an individual U.S. driver who has purchased a new light-duty vehicle that month. September's EDI stands at 0.8, a 20 percent improvement since October 2007 and an incremental improvement since June. EDI takes into account both the fuel used per distance driven and the amount of driving.

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