After holding steady in June and July, the average fuel economy of all new passenger vehicles on U.S. roads dipped to its lowest level since April. The average sales-weighted fuel economy — calculated from the monthly sales of individual models of light-duty vehicles, including cars, SUVs, vans and pickup trucks — dipped 0.1 mpg to 24.3 as low gas prices continued to provide Americans with a disincentive to buy fuel sippers, according to the University of Michigan Transportation Research Institute’s monthly report.
As of last week, U.S. gas prices had plunged 12 cents from a week earlier to $2.53 a gallon for regular unleaded gasoline. A refinery outage had caused regional spikes in gas prices in the two weeks prior, but it wasn’t enough to keep the national average up by more than a couple of pennies for long. Once the Whiting, Ind., refinery returned to service, the national average resumed its downward trend amid continued low international oil prices.
Although low gas prices have had an adverse impact on national fuel-economy figures, August’s 25.3 mpg average still compares favorably to the 20.1 mpg of October 2007, when the Transportation Research Institute first began tracking the figures. Since then, the improvement has been steady, despite month-to-month fluctuations. So far in 2015, the best numbers posted have been in May, when the average was 25.5, while the low of 25.2 was first set in February and repeated in April. The best all-time fuel economy since tracking began was in August 2014, when it reached 25.8 mpg.
August 2014 was also the year the U.S. vehicle fleet reached its lowest and best greenhouse-gas emissions figures, with UMTRI reporting an Eco-Driving Index of 0.78; that’s compared with the most recent measurement, for June 2015, of 0.82. Still, this recent figure improves on the October 2007 measurement by 18 percent.