As anyone who has taken an economics course knows, the laws of supply and demand are simple: When demand increases while supply decreases, the price goes up, and demand will eventually go down. Economists, for all our eagerness to forecast and predict people's behavior, recognize there is a lag time between the increased prices and decrease demand, but they'll be darned if they can tell you what that is.

Well, it looks like Americans may have finally reached their threshold for what they are willing to shell out for gas. The Federal Highway Administration said this week that Americans drove 0.4 percent less in 2007 than 2006, from 3.01 trillion miles to a mere 3 trillion miles. 0.01 trillion miles doesn't sound statistically significant, until you realize that's actually 10 billion miles.

Using the combined CAFE for cars and light trucks produced in 2007 of 22.2mpg, that's about 450 million gallons of oil not turned into greenhouse gases and other pollutants by vehicles last year. Not bad.

Will this translate into reduced CO2 emissions? Well, mass transit ridership is increasing, and this year's New York Car Show is exhibiting lots of fuel efficient rides. Considering the U.S. was recently admonished by the International Energy Agency for having some of the sorriest CAFE standards in the world, we'd like to think that larger changed are imminent.

Of course, this week's news could be due to the economic downturn and the fact Americans are too busy trying to keep their homes from foreclosure to be able to joyride around the mall. But beggars can't always be choosers when it comes to reducing emissions.