WASHINGTON -- So now we know: The price point is $4.

At $3 a gallon, Americans just grin and bear it, suck it up, and, while complaining profusely, keep driving like crazy. At $4, it is a world transformed. Americans become rational creatures. Mass transit ridership is at a 50-year high. Driving is down 4 percent. (Any U.S. decline is something close to a miracle.) Hybrids and compacts are flying off the lots. SUV sales are in free fall.

The wholesale flight from gas guzzlers is stunning in its swiftness, but utterly predictable. Everything has a price point. Remember that "love affair" with SUVs? Love, it seems, has its price too.

America's sudden change in car-buying habits makes suitable mockery of that absurd debate Congress put on last December on fuel efficiency standards. At stake was precisely what miles-per-gallon average would every car company's fleet have to meet by precisely what date.

It was one out-of-a-hat number (35 mpg) compounded by another (by 2020). It involved, as always, dozens of regulations, loopholes and throws at a dartboard. And we already knew from past history what the fleet average number does. When oil is cheap and everybody wants a gas guzzler, fuel efficiency standards force manufacturers to make cars that nobody wants to buy. When gas prices go through the roof, this agent of inefficiency becomes an utter redundancy.

At $4 a gallon, the fleet composition is changing spontaneously and overnight, not over the 13 years mandated by Congress. (Even Stalin had the modesty to restrict himself to five-year plans.) Just Tuesday, GM announced that it would shutter four SUV and truck plants, add a third shift to its compact and midsize sedan plants in Ohio and Michigan, and green light for 2010 the Chevy Volt, an electric hybrid.

Some things, like renal physiology, are difficult. Some things, like Arab-Israeli peace, are impossible. And some things are preternaturally simple. You want more fuel-efficient cars? Don't regulate. Don't mandate. Don't scold. Don't appeal to the better angels of our nature. Do one thing: Hike the cost of gas until you find the price point.

Unfortunately, instead of hiking the price ourselves by means of a gasoline tax that could be instantly refunded to the American people in the form of lower payroll taxes, we let the Saudis, Venezuelans, Russians and Iranians do the taxing for us -- and pocket the money that the tax would have recycled back to the American worker. Continued...