Robin Quinn's driving instructor would be proud.

Nearly four decades after Quinn started driving, she has abandoned some bad habits - the lead foot, for example.

Instead, she has joined a growing number of enthusiasts who practice something called "hypermiling." They strive to maximize the number of miles they get per gallon of gasoline by, say, driving at or below the speed limit and braking as little as possible.

Many trade tips and boast about their high gas mileage on online forums that are growing more popular as gas prices rise.

The average price for self-serve gas in Maryland topped $4 per gallon yesterday, according to AAA Mid-Atlantic.

Thanks to hypermiling, Quinn, a Randallstown resident, calculates that she is getting nearly 27 mpg in her 2003 Nissan Altima, compared with 24 mpg previously. That can save her more than $100 a year.

"I was just surprised at how effective this little change of driving habits was," she said. "I've only done it two weeks and I'm thrilled."

Estimates of potential savings vary, but one expert says the driver of a nonhybrid vehicle could improve his fuel economy 50 percent by applying basic tips.

Wayne Gerdes, who operates the Web site cleanmpg.com and teaches hypermiling clinics at his home in the Chicago suburbs, said he began developing his techniques after the World Trade Center attacks - he was concerned about the nation's dependence on foreign oil - and true hypermilers are always striving to improve their gas mileage.

Other hypermilers stress the environmental benefits.

But some auto experts question the safety of advanced hypermiling techniques such as "drafting" - closely following tractor-trailers to cut down on the flow of air against a vehicle.

Leon James, a University of Hawaii professor who has written about the psychology of driving, said hypermiling can become a form of aggressive driving if, for example, drivers practice it in the fast lane, forcing others to drive around them, or if they coast through stop signs.

"If you were behind someone who's practicing certain features of hypermiling, you get very annoyed," James said. "Hypermiling can be a selfish thing to do."

Ed Kriston of AAA said that the automobile group encourages gentle driving to save gas but discourages aggressive types of hypermiling.

"Some of the things they do are very dangerous," he said. He pointed to drivers going below the speed limit on highways such as Interstate 795, where the limit is typically higher than those posted on most highways.

Critics have also said that drafting is unsafe, and in fact cleanmpg.com's Web site includes a disclaimer stating that it does not endorse the practice.

Gerdes said critics don't understand hypermiling. He urges motorists to stay to the right both to yield to faster drivers - or "rabbits" - that dart ahead, and to take advantage of the low-pressure systems created by larger vehicles passing them.

He said that he also has been on the receiving end of rude gestures from other motorists.

"I can tell you that the dangerous people are going 10 miles over the speed limit," he said. "I'd much rather be with a hypermiler than one of those."