By Larry Copeland and Paul Overberg

Americans drove 30 billion fewer miles from November through April than during the same period in 2006-07, the biggest such drop since the Iranian revolution led to gasoline supply shortages in 1979-80.

The numbers released Wednesday may reflect more than a temporary attitude change in consumers toward high gas prices, Transportation Secretary Mary Peters said. Previously, she said, "people might change their pattern for a short period of time, but it almost always bounced back very quickly. We're not seeing that now."

The decline in total miles traveled, though only 1%, means that many drivers are cutting back far more because the number of drivers and vehicles grows by 1% to 2% a year. Americans are driving about the same number of miles as in 2005, when the USA had 8 million fewer people, according to a USA TODAY analysis of Federal Highway Administration data. The declines are sharpest on rural roads, indicating that people are cutting back on long-distance and vacation trips.

"It's not a blip," said Marilyn Brown, professor of energy policy at Georgia Tech, citing data showing surging transit ridership, dropping sales of sport-utility vehicles and sharply increased demand for gas-efficient vehicles. "I think the difference between now and 1979, when prices were comparable when you adjust for inflation, is there's a sense of sustained pain. There's a sense that the era of cheap energy is a thing of the past."

Among potential impacts of Americans driving less:

•Drivers might notice "some reduction" in traffic congestion, said Tim Lomax of the Texas Transportation Institute. "But over several months, the typical commuter will adjust their driving patterns," he said. "If they normally leave at 6 a.m., they might find they're getting to work without congestion, so they'll say, 'I'm going to spend an extra 15 minutes sleeping or reading the paper and leave at 6:15.' You get enough people doing that and you're back to congestion."

•Housing patterns could change as more people buy houses closer to work or find jobs closer to home, Lomax said. "We might not be seeing so much of that right now since so many people are upside down on home loans because of the mortgage crisis," he said.

•A shift in the way the nation pays for roads, bridges and transit. As people drive less, the federal Highway Trust Fund — derived from gasoline and diesel taxes — is receiving billions less, Peters said. She's promoting tolling and making drivers pay more during peak hours.

David Snyder, 40, an engineer in Internet operations at Turner Broadcasting in Atlanta, is moving from suburban Alpharetta to a new project near downtown. "It costs more than $60 a week in gas, and that's not including parking," Snyder says of his current costs. "That's this week. It might be $75 by next week."