The key is the kinds of cars that buyers drive off new car lots. The well-used lots will only get the cars that were originally sold as new. Many relatively poor people are driving huge, gas guzzling SUVs because that's what sold well to middle-class surbubia about 5 years ago. Not many years before that they were driving the Geo's and Hyundais of a few years earliere.

If we have a couple of years of low pricing, there is an opportunity to wash out upside-down SUV values, rotate through a generation of gas-guzzlers, and get the system well-primed with smaller cars and hybrids. This would be a good time for a gas-guzzler tax on high-consumption vehicles and a rebate for efficient vehicles, but that won't happen.

The immediate problem is that you can't buy many hybrids, CNG vehicles, or high-mileage diesels simply because there aren't enough made, and they don't cover the vehicle size range. Where are the hybrid or diesel/CNG minivans?

Better still would be to use this lower prices to roll out a lot of public transport growth -- if fuel costs less and deflation makes labor and materials less, this is a great period for infrastructure growth.........except that few cities or states can afford it.