Fuel Economy Dipping As Motorists Return To Larger Vehicles

American motorists got a pleasant surprise for the Independence Day holiday: fuel prices falling below year-earlier levels despite some forecasts that gas might nudge $5 a gallon by this summer. But as gas prices have fallen so has the mileage of the new cars, trucks, and crossover U.S. motorists are buying, according to a new report.

The average fuel economy for new vehicles sold in June came in at 23.6 mpg, according to the University of Michigan’s Transportation Research Institute (UMTRI). That’s a full 0.5 miles per gallon less than the peak in March of this year, as it appeared fuel prices would spike to new record levels.  And it’s off by 0.1 mpg from May.

The decline is "likely reflecting the continuing reduction in the price of gasoline," writes Dr. Michael Sivak, UMTRI’s Director of Sustainable Transportation.

Sales data also suggest that as the U.S. economy slowly recovers Americans are migrating back to higher-price — typically meaning larger — vehicles.  And as the economy improves there is more demand for large pickups, vans and other work vehicles that will drive the mileage numbers downward.

On the positive side, the June mileage average was still up 3.5 mpg, or seventeen percent, compared to October 2007, when the school began tracking fuel economy trends. Those figures reflect the adjusted numbers the U.S. Environmental Protection Agency uses for the window stickers placed on all new cars.  A separate, unadjusted calculation shows fuel economy at 29.0 mpg, also a seventeen percent improvement since October 2007.

Meanwhile UMTRI’s Eco-Driving Index, which tracks the average monthly emissions of the typical American motorist stood at 0.81 for April, the latest month for which data are available. That’s a nineteen percent decline from October 2007. The Index is based on both fuel economy and the number of miles motorists clock each month.

March 2012 saw fuel economy hit an all-time high, the average vehicle sold in the U.S. getting 24.1 mpg, according to federal data. The spike was initially blamed on advancing tensions between the U.S. and Iran with threatened shutdown of the Straits of Hormuz, a key oil traffic passageway. In recent weeks the sabre-rattling has resumed and, consequently, oil and gas prices have been back on the rise.