With another year of soaring gasoline prices — the nationwide average is now $3.81 per gallon — Americans are altering their driving habits. But for a country that’s still heavily dependent on the automobile, that’s a slow, painstaking process.

Time to take the Metro? (Andrea Bruce/Staff)

The shift appears to be real, but it’s also gradual. According to a dataset maintained by the University of Michigan’s Michael Sivak, the average fuel economy of new vehicles sold in the United States has nudged up from 20.7 miles per gallon in October 2007 to 23.7 miles per gallon in February 2012.

Likewise, according to the American Public Transportation Association, mass transit use increased 2.31 percent in 2011 over the previous year. The shift wasn’t confined to big, subway-heavy metropolises like New York City. In fact, the largest percentage increase, at 5.4 percent, occurred in smaller towns with fewer than 100,000 people.

Even so, Americans say that gasoline prices would have to get much, much higher to induce drastic lifestyle changes. A Gallup poll from early March found that the price of gas would have to hit around $5.30 per gallon for most Americans to “cut back on spending in other areas or make significant changes in the way they live their lives.” By contrast, just 14 percent of Americans said they’d make significant changes in their lives with gas prices at current levels. For many people, there’s just no substitute for the automobile.

One reason why costly gasoline my have had a limited impact on behavior is that many Americans could well believe gas prices will eventually sink again. A recent NBER paper (pdf) by economists Shanjun Li, Joshua Linn and Erich Muehlegger found that a 5-cent gas tax has more effect on curbing gasoline consumption than a similar 5-cent increase in gas prices. As Ryan Avent comments, “consumers may be more likely to read tax changes as permanent.”

Either way, this underscores a trend we’ve noted before. The United States has gotten better and better at squeezing more and more economic activity out of a given barrel of crude. But our oil efficiency hasn’t gone up fast enough to totally offset the pain of rising prices. According to a recent Washington Post-ABC poll, 63 percent of Americans say that gas prices are causing financial hardship (and 36 percent say they’re causing “serious hardship”). Those are actually the lowest hardship numbers since May of 2008 — which suggests that Americans are slowly adapting to our era of pricey oil. But 63 percent is still quite high.