IT WAS JUST a year ago that Washington ran out of gasoline. The shortages and the lines at the filling stations had started on the West Coast and arrived here, gradually, in mid-May. A lot of people spent last Memorial Day looking for gas. Only one out of every four filling stations was open, most of them briefly. Only in July did the lines gradually vanish. This year prices are up but, even over the holiday weekend, there weren't lines. What made the difference?

There's a simple and instructive answer. People are driving less -- not much less, but enough to make a big difference. A year ago there wasn't enough gasoline to go around. This year the supply of gasoline is actually lower. But people are getting more careful about using their cars. Prices have moved up, and consumption has moved down.

A year ago, in the shortage months of May and June, the supply of gasoline was running around 300 million gallons a day -- about 2 gallons a day for every car, bus and truck on the road. A year earlier, those vehicles had been using an average of 2.15 gallons a day. The shortage that produced the lines worked out to about one-seventh of a gallon daily per vehicle. That's not a huge amount, but the idea that there wasn't enough set off a brief panic.

Currently the supply of gasoline is only about 280 million gallons a day, and the number of cars has risen. The statistics through early May indicate that Americans are now using about 1.8 gallons a day for each vehicle. The typical motorist now buys five gallons for every six he was buying two years ago.

Motorists who have bought more efficient cars may be driving just as far. But one thing is beyond argument: it's the higher prices that are enforcing this trend. Prices are going to keep rising, and supplies of gasoline are going to keep falling. The lesson of this spring, compared with last year, is that there's a simple way to avoid lines -- use less gas.