And this article from the Examiner.com says part of that drop is due to alternative-fueled vehicles, including those running on biodiesel and ethanol:
“A combination of demographic change and policy change means the heady days of gasoline growing in the U.S. are over,” said David Vergin, chairman of IHS Cambridge Energy Research Associates, winner of the Pulitzer Prize for his history of the oil industry. Exxon-Mobil’s CEO Rex W. Tillerson acknowledged that U.S. gasoline demand peaked in 2006, anticipating future declines. While the country’s “Great Recession” and high gas prices have kept Americans off the roads, more fuel efficiency and alternative-fuel vehicles promise to keep demand down. Current and past administrations continue to press for alternatives to fossil fuels.
Now, while the article’s author makes a good point about the alternatives helping bring down overall gasoline demand, I think he makes some wrong assumptions that ethanol hurts the environment, especially the water supply. He does make some good points that more alternatives in public transportation, such as natural gas buses, electric subways and light-rail, will contribute greatly to the overall drop in petroleum-based gasoline demand.