Kevin Drum has numbers suggesting that consumers are responding to gas prices a little more than had been thought. On a per capita basis, he notes, vehicle miles traveled are down about 6 percent this year–still disappointing given the 50 percent increase in gas prices, but impressive considering limited consumer options.

He also cites an Los Angeles Times story on trends locally. They’re positive:

After declining at the end of 2007, L.A. rail and bus ridership started rising in January. From January to March, average weekday boardings were up 16% on the Red Line rail system, 13% on the Blue Line and 17% on the Gold Line, which set a record for highest average weekday boardings in March with 22,231. Bus ridership grew 8% from January to March.

But, the MTA is concerned that the changes won’t stick:

The MTA usually sees a temporary increase in riders when gas prices reach certain thresholds, like $3, $3.50 and $4 a gallon, he said. Then ridership goes down once people become accustomed to the higher cost.

“What we hope every time,” he said, “is that as more people become introduced to using rail as an alternative, we can retain more of those discretionary riders over time.”

What is more likely, said Brian Taylor, director of the UCLA Institute of Transportation Studies, is that people will begin buying more fuel-efficient vehicles. In April, in fact, sales of passenger cars were up 5.2% nationally while light-truck and sport utility vehicle sales were down 17.4%.

I think that the kind of adjustment we can expect to see from commuters will depend upon expectations. If consumers expect gas costs to plateau, then they will become used to them, and the math may work out in favor of shelling out for a new car. If expectations become such that gas price increases will continue–will continue, actually, to increase by more than incomes or the rate of inflation–then this could change. Those willing to make a large upfront expense to save on gas will begin to think about a home convenient to transit rather than a new automobile.

But a big factor in this calculation is the very limited supply of homes convenient to transit, based on the very limited supply of transit stations. Those limits push the cost of transit-accessible homes up rapidly, forcing most commuters to seek other options. And unfortunately, those least able to afford a shiny new hybrid will also be those who are the first to be priced out of transit-oriented housing, rental or owner-occupied.

Perhaps instead of encouraging folks to pay for more efficient automobiles, which may themselves become too costly if gas doubles again, we should be focusing on investing our resources in other alternatives.