The graph above, created by the U.S. Energy Information Administration, shows gasoline consumption in the U.S. in millions of barrels per day. The red line is 2011, the green line is 2012 (so far), and the gray area is the 5-year range (2007-2011), meaning that consumption for the past 5 years never was above or below that range.
As is obvious from the red line, last year was already at the bottom of that range on most months. And this year often goes even below that, with first quarter numbers averaging 8.5 million barrels/day, which is 124 thousand bbl/day lower than 2011. The dotted line also shows that preliminary numbers for the second quarter look mixed, with higher numbers in April and May but also some lows during the high-driving season of June and July.
U.S. gasoline consumption peaked in 2007 at 9.3 million bbl/d and fell by an average of 3.2% (300 thousand bbl/d) in 2008 due to the recession and high gasoline prices, which topped $4 per gallon in June and July 2008. Gasoline prices fell in late 2008 and remained below $3 per gallon through 2009 and 2010, but gasoline consumption remained flat, increasing by just 0.1% in 2009 and falling slightly in 2010. Regular-grade gasoline prices rose in early 2011, peaking at an average of $3.91 per gallon in May 2011, and for the year averaged $0.74 per gallon higher than the year before. In response to higher prices, households again cut back on highway travel, and gasoline consumption fell by 2.9% (260 thousand bbl/d) in 2011 from the year before. (source)
Various factors can affect gasoline consumption. Improving vehicle fuel efficiency certainly plays a role, but macro-economic factors also play a major part; when the economy slows down, people just drive less and businesses have fewer goods to ship.