The old tips that commuters and experts have passed around for years are still hard to beat:

* Drive gently. Keep it under the speed limit and avoid sudden acceleration and braking.

* Keep your car running at its best. That means enough air in the tires, maintenance up to date, and heavy junk out of the trunk.

* And of course, drive less. Combine errands, and try carpooling, telecommuting or catching the bus when you can.

The Road Worrier was sharing this distilled wisdom back in 2005, when we were reeling from the pain of $2.50 gas. It's still sound.

But with prices approaching $3.80 a gallon for regular this week, everybody's looking for new advantages.

So it is tantalizing to come across a hot new fuel-economy tip on assorted Web sites and in e-mail.

To get more miles out of each gallon, buy your gas cold. That's the thrust of a tip attributed to an unnamed veteran of the oil pipeline industry:

"Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground.

"The colder the ground, the more dense the gasoline. When it gets warmer, gasoline expands. So buying in the afternoon or in the evening ... your gallon is not exactly a gallon."

The Road Worrier received this shrewd advice in e-mail from a local lawyer pal -- he'd sue me if I told you his name -- and from a scholar with the International Monetary Fund. It has been cited by "Car Talk" callers and applauded by readers of assorted blogs across the country.

It's exquisitely scientific. And maddeningly impractical.

True, congressional testimony last year confirmed that gasoline grows about 1 percent in volume as it gets 15 degrees warmer -- from 231 cubic inches at 60 degrees to 233 cubic inches at 75 degrees. So in every gallon and every tankful, colder gas is a bit denser and more packed with energy than warmer gas.

But how much colder? An underground tank -- or a wine cellar, or your basement -- doesn't get much warmer by day and colder by night.

One of the nation's fuel-economy authorities scoffs at the idea that motorists can expect to boost their gas mileage by shopping for fuel presumed to have chilled overnight.

"I'm just skeptical myself of this temperature thing," David L. Greene, a senior energy policy researcher at the federal Oak Ridge National Laboratory in Tennessee, tells the Road Worrier.

"The temperature underground is not anywhere near as sensitive to temperature fluctuations as above-ground tanks are. If you dig down a few feet into the ground, you pretty much get the average year-round temperature."

Greene and his Oak Ridge colleagues maintain a reliable Web site with helpful advice for getting the most miles out of your dollar. It's called fueleconomy.gov.

Trying the bus?

More than 9,000 Triangle residents have signed up to take the SmartCommute Challenge. By pledging to park the car one day and try a different way to get to work or campus, they qualify for self-satisfaction and prizes.

The three-county event continues through May 30. Join the crowd at smartcommutechallenge.org. Learn your options at gotriangle.org.

Plans are under way this summer to start a new express bus route from Wake Forest to North Raleigh, and a local loop-route bus in Wake Forest. The Raleigh Transit Authority will solicit public comment on the plans at 3:30 p.m. Thursday, City Council Chambers, Upchurch Government Complex, 222 W. Hargett St., Raleigh.

Meanwhile, I'm working on stories about plans for better public transit service.

If you're driving less and enjoying it more, please let me hear from you.