Young people are getting driver's licenses later or not at all. They take the train or bus or bike to work, or telecommute. If they need a car, they can rent one by the hour.
"It's so much easier to get around the city without a car," said Jim Krider, 21, of Havertown. A junior at Temple, he didn't get his license until he was 20 and doesn't own a car.
"You don't have to pay for gas or insurance or the car," he said.
"I really never had a real need for it," said Marysia Pomorski, 24, a social worker from Haddonfield, who also waited until she was 20 to get a driver's license. When she attended Oberlin College in Ohio, she said, she "biked everywhere" and didn't miss having a car or a license.
Many of her classmates from urban areas were also without licenses, while students from the Midwest "were always very surprised that I didn't have it, because they wouldn't have had a choice," she said.
Although some decline in vehicle use and ownership may be a result of the recession that began in 2008, several important indicators began to decline earlier and may not be reversed by an improving economy.
The declines before 2008 "make me believe something else is going on," said Michael Sivak, a research professor at the University of Michigan Transportation Research Institute. "Some of the trends are likely to be permanent."
In a recent paper, "Has Motorization in the U.S. Peaked?," Sivak noted that vehicles per person, per driver, and per household all peaked in 2006, before the recession began.
Sivak suggested that "societal changes that influence the need for vehicles" may be prompting the decline.
The vehicle miles traveled per person have dropped eight years in a row. They are now about 7.5 percent below their 2004 peak.
And the drop-off in driver's licenses began even earlier.
In 2010, 69.5 percent of 19-year-olds had a driver's license. That was down from 75.5 percent in 2008 and 87.3 percent in 1983.
Smaller declines in licenses have also occurred in all other age groups, except those over 70 and those between 25 and 29, Federal Highway Administration data show.
Meanwhile, public transportation use has been rising - in the Philadelphia region and around the nation.
SEPTA last week reported its highest-ever commuter-rail ridership, at 36 million passengers per year, up 50 percent in 15 years.
To cross the Delaware, fewer commuters are driving and more are taking the train: PATCO rail ridership reached an 11-year high last year, while vehicle traffic fell to an 11-year low on the four toll bridges operated by the Delaware River Port Authority.
Amtrak is on track this year to set another annual ridership record, its 10th in 11 years.
Buses, trains, subways, and trolleys carried 10.56 billion riders in the United States in 2012, the second-highest total since 1957, according to the American Public Transportation Association.
"There's a generational trend going on that's very real," said Art Guzzetti, vice president of policy at APTA. "Baby boomers had a love affair with the car. Now times are different. Now young people find freedom in different ways, with the cellphone or texting. It's not all about a car."
High gas prices and traffic congestion have also helped boost public-transit use, Guzzetti said.
APTA calculates Philadelphia-area residents could save $12,120 per year by taking public transit, based on a two-person household using one fewer car.
Sivak suggested four key factors in the shift from cars:
Economics: It's more difficult to afford the costs of buying, insuring, and maintaining a car.
The Internet: People can interact, shop, and be entertained without driving somewhere.
Urbanization: Young people and empty nesters are moving to cities where they don't have to own a car.
The environment: Young people are more environmentally conscious than their elders, interested in burning less gasoline.
The American Automobile Association, which was founded in 1902 at the dawn of the auto age, doesn't believe the car is in its twilight years.
"There may be a trend here, but it is clearly being overstated," said Jenny Robinson, spokeswoman for AAA Mid-Atlantic in Philadelphia.
"Consumers have been balancing economic uncertainty with family and/or personal transportation needs," she said. "We don't believe this downward trend is the 'new normal,' rather an artifact of the poor economy over the last five to six years."
Vehicle sales have rebounded since the recession, she said. After peaking at 17.8 million in 2000, sales of light-duty vehicles (cars, pickups, SUVs, and minivans) fell to 10.6 million in 2009 before recovering to 14.8 million in 2012.
Robinson noted that the number of licensed drivers has been increasing in Pennsylvania (faster than the population) and that the number of vehicles registered in Philadelphia has grown over the last seven years (more slowly than the population).
She also said: "People have been forming families a bit later in life, but many eventually find their way to the suburbs, where they still need cars."
Any shift in vehicle ownership and driving habits may require a change in the way Americans pay for their transportation.
Currently, most road and bridge construction and public-transit projects are funded by gasoline taxes. But as people drive less, vehicles become more fuel efficient, and inflation reduces the purchasing power of the taxes, gas-tax revenues are falling short.
In 2008, for the first time, the federal Highway Trust Fund did not collect enough to meet highway costs, and Congress took $8 billion from the general fund to keep it solvent.
The raids on the general fund have continued: Last year, Congress authorized an $18.8 billion transfer to the Highway Trust Fund, and by the end of next year, $54 billion will have been taken from the general fund to make up for the shortfall in federal gas-tax revenue.
States also are struggling to meet their transportation costs without significant gas-tax increases.
In Pennsylvania, legislators left Harrisburg this month without approving a new transportation-funding law, prompting warnings of bridge closures and transit cuts.
Contact Paul Nussbaum at 215-854-4587 or firstname.lastname@example.org.