By John Kemp LONDON - U.S. motorists are opting for larger, more powerful cars with worse fuel economy in response to the sharp drop in gasoline prices. The average fuel economy for vehicles sold in the United States in September was 25.2 miles per gallon, down by 0.6 mpg since August 2014, according to the University of Michigan Transportation Research Institute. “The decline likely reflects the decreased price of gasoline in September and the consequent increased sales of pickup trucks, sport-utility vehicles and crossovers,” the institute said. Fuel economy, using window-sticker values, has increased by 5.1 mpg, about 25 percent, since October 2007, when the institute began monitoring, thanks to higher fuel prices and tougher government standards. But the improvement has stalled as the reduction in fuel prices has encouraged buyers to trade efficiency for increased size and power (http://www.umich.edu/~umtriswt/img/EDI_mpg_September-2015.png). In the first nine months of 2015, sales of light trucks, a category that includes SUVs and pickups, surged more than 11 percent compared with the same period in 2014. Car sales dropped nearly 2 percent, according to WardsAuto. According to OPEC, the same trend is evident in China: lower prices are encouraging consumers to purchase larger and more fuel-hungry vehicles (“Monthly Oil Market Report” Sept 2015). Citing data from the China Association of Automobile Manufacturers, OPEC noted car sales were up 3 percent in January-July compared with the same period in 2014, but sales of SUVs surged 44 percent. Sales of larger vehicles, coupled with a big increase in the traffic in the United States and a number of other economies, have produced an increase in gasoline consumption compared with the previous trend. The boost to fuel consumption relative to trend from increased driving will probably fade as gasoline prices stabilise and consumers become more accustomed to them. In some sense, the boost from driving is likely to be a one-time gain, most of which will come in the first 12-24 months after prices fall, as driving behaviour adjusts. But if prices remain at current low levels the boost from larger vehicles will grow over time as the light vehicle fleet slowly turns over and trucks increase their share at the expense of cars. The longer fuel prices stay (relatively) low the bigger the impact on fuel consumption from changes in buying habits and the fleet mix.