I keep looking for signs that the collapse in gas prices has started to have an impact on how much people drive. In a normal economy, you’d expect that as gas got cheaper, people would drive a bit more — the reverse of the trend we saw last summer, when gas prices were reaching record highs and people were cutting way back on car travel.

But this simply isn’t a "normal" economy. Just as gas prices fell, family incomes started taking a beating too. So, sure, it costs a lot less to fill a tank now than it did last summer, but people also had less money to spend on gas. And the two contradictory trends leave me scratching my head: will gas consumption continue to dip, stay flat, or start to trend upwards again?

The latest federal numbers on vehicle travel may offer some hints. As the Contra Costa Times notes, gasoline consumption fell in December 2008, compared with the previous December. But looking at the numbers, the year-over-year decline was actually the smallest since the previous February — suggesting, perhaps, that low prices are beginning to subtly boost driving.

Driving, year over year, 2008

Nationally, driving fell by about 1.6 percent in December 2008, compared with December 2007 — a decline of 3.7 billion miles. But the steepest declines by far were in Oregon, where vehicle travel fell an estimated 15 percent, and Washington, where it fell 11 percent. Those are simply astonishing numbers — in the “hard to believe” range, except when you consider the long and unusual stretch of snowy December weather that brought travel in western Washington and Oregon to a virtual standstill for several days.

But if you exclude the massive declines in December driving in Washington and Oregon, the nationwide decrease in year-over-year travel registered at only about 1.2 percent — a significant cut, but nothing like what we saw earlier in the year, when year-over-year declines reached as high as 5.6 percent.

We’ll keep our eyes on the numbers. I’m betting that, if gas prices stay low, we may see a pause in the decline in vehicle travel. But I suppose we’ll have to wait until the next month’s figures come out to be sure.

Anyone want to take a guess what’ll happen next? Comments welcome!

Update: Looks like the Wall Street Journal is reading the same tea leaves I am. Gas consumption is still down compared with a year ago, but it’s edging up a bit.

This post originally appeared at Sightline’s Daily Score blog.