From a new report by the always-great Sightline Institute:

Tallying up all vehicle travel on state, county, and local roads, residents of Washington and Oregon are on track to burn less gasoline in their cars and trucks this year than at any time since 1996—less even than in 2008, when gas prices spiked and the economy cratered. At least for the moment, the plateau in gas consumption that began in the late 1990s has turned into a gentle downward slide.

Measured per person, though, northwesterners have aggressively reduced their use of motor fuel. Last year, per capita combustion of gasoline in Oregon fell to its lowest level since 1962—back when a gallon of gasoline cost 31 cents.2 Similarly, per person gas consumption in Washington fell to its lowest level since 1965. Early trends suggest that per capita consumption in the two states may be headed for a drop of as much as 2 percent in 2012.

Two concurrent trends have spurred the reductions in gasoline consumption: people are driving less, and vehicles have become more efficient. Of the two, declines in driving—particularly among northwesterners under the age of 35—have made the greater impact. Looking to the future, however, gains in vehicle efficiency, combined with high and volatile gas prices, demographic shifts, and a range of social and technological trends, all point towards continued declines in gasoline use in the Pacific Northwest.

Here's the full report.