(USA TODAY) – Americans have been driving fewer miles every month since March, a decline fueled by factors ranging from the weak economy to high gas prices to aging boomers and teens driving less.

It’s the first time the nation has seen six consecutive monthly decreases since October of 2008.

A USA TODAY analysis of data from the Federal Highway Administration shows the miles driven during the year that ended in September were down 1% from a similar measure from February.

“With the number of Americans unemployed or underemployed, you have a reduction in disposable income, fewer commutes, fewer shopping trips and leisure trips,” says Troy Green of auto club AAA. “And we are on pace to set a new record for the average annual price of gasoline.”

In 2008, the price for a gallon of self-serve, regular unleaded gasoline hit a record $4.11. “Everybody remembers that,” Green says. “We had some tremendous peaks and some pretty low valleys that year, and by Dec. 31, 2008, it was down to $1.62 a gallon. The annual average for 2008 was $3.25.

“We haven’t had the valleys this year. It’s been above $3 all year. The annual average this year is $3.53, and it’s going to end the year above $3.50, which is more expensive than any other year.”

The autumn of 2011 saw the poorest gasoline demand since 2000, says Tom Kloza, chief analyst at the Oil Price Information Service. “There’s a little bit of driving fatigue,” he says. “There was a hunker-down mentality, especially in the fall. People realized they had spent as much money on fuel by Columbus Day as they had for the whole year the year before.”

The economy and gas prices are factors in the driving decline, but there are larger trends at work, too, says Robert Puentes, senior fellow at the Brookings Institution’s Metropolitan Policy Program. .

“For years and years, people just drove more and more, and we got used to this increase in driving every single year,” he says. The rising numbers were related to societal shifts such as women joining the workforce, minorities moving to the suburbs and sprawling metropolitan growth. “But those macro trends have started to become less intense,” he says.

Among the other likely factors contributing to the driving drop:

•The 78 million aging baby boomers driving less. “The biggest factor is boomers are no longer raising children,” says Jana Lynott, AARP’s transportation expert. “Raising children in the suburbs, which is where the majority of boomers live, is one of the great generators of driving trips. Kids in the suburbs are very active and involved, and parents are generally taking them to and from places.”

•More people taking public transportation. Ridership on public transit increased 2% in July, August and September compared to the same period last year, according to the American Public Transportation Association.

•Teenagers driving less. A study in August by researchers at the University of Michigan Transportation Research Institute found that, over the past 25 years, there has been a significant decrease in the percentage of young people with a driver’s license. In 2008, 31% of 16-year-olds had a license, compared with 46% in 1983, according to Michael Sivak and Brandon Schoettle.

More states implementing phased-in driving licensing for novice drivers, which means they’re licensed later, and higher teen unemployment might also be factors.