These shifts are having a noticeable impact. Researchers at the University of Michigan and elsewhere cite statistics that driving (in terms of miles driven) has dropped 5 percent since it peaked in the US in 2006. Americans are taking fewer trips in their cars and driving shorter distances when they do get behind the wheel. Because the country is so big, it takes years for any social change to reflect itself in statistics. Just a plateau in driving would be a significant development, but an actual drop in driving by the owners of the country’s 240 million registered light-duty vehicles is potentially earthshaking for Detroit, for policymakers, and for urban planners.

Northwestern’s Kevin Boyle sees a bit of back-to-the-future in all this. “More and more people want to live in center cities,” he says. Toyota officials say they’ve noticed the suburbs-to-city trend in many cities across America. These reverse pioneers had enough of distant suburbs and surrendering their free time to long commutes. They also want to reconnect with people, rather than be alone in their cars. Boyle sees this as exactly the opposite of his parents’ generation, who escaped cities in droves after World War II. “In some ways, they want to return to the 19th-century model of cities like Chicago and New York,” he says.

The most noticeable aspect of this is 20- and 30-somethings who have transformed neighborhoods in Brooklyn and Detroit. But plenty of Baby Boomers also are moving back downtown, once they become empty nesters, where their new lofts might have just one parking space instead of the three spots in their garages. Boyle says the permanence and character of urban places have become attractive in an ephemeral world in which news headlines are outdated almost as soon as they are tweeted.

Another set of statistics has gotten even more attention than the overall driving decline: the significant drop in the number of teens on the road. In 2008, when I was covering the auto industry for the Times, I came across data showing that fewer than 30 percent of teenagers got their licenses when they turned 16. Like pretty much everyone else in the 1970s, I lined up with my high-school classmates to take driver’s-education classes the summer I was eligible. I passed my driving test a few months later. Not today’s students. According to the AAA Foundation for Traffic Safety, still only half of teens have a license by the time they graduate. Even a year later, just 73 percent have passed their driver’s test, compared with 85 percent in 1996.

Two big policy changes have caused these numbers to drop, along with a broader social development. First, half of states require students to take formal driver’s education, but many school districts, led by those in Ohio, which made it optional in 1992, have dropped the classes, citing the expense and insurance concerns. That means students have to pay for commercial driving classes, which can cost hundreds of dollars. Moreover, a large number of states have tightened restrictions on teen drivers in an effort to reduce accidents and drunk driving. Some limit the hours when a teen can drive a car or require them to be accompanied by an adult until they turn 18.

Beyond that, some teens simply aren’t interested in making the effort to learn to drive. They’re overloaded with homework and school activities, and would rather spend whatever free time they do have online, texting, and videochatting with their friends. Once, to escape their parents, they had to get behind the wheel. Now they can just turn on their devices.

Gas prices, which have hovered at or above $3 a gallon nationally for the past three years, also are playing a role in keeping kids off the roads, especially when it is so hard for teens to find jobs. Beyond that, driving aimlessly around town, as youngsters did in American Graffiti, isn’t as attractive if they can’t show their friends they did something cool. “It has to be Instagram-worthy,” a 20-something man in Modesto, CA, told NPR’s Sonari Glinton.

Micheline Maynard is the editor of Curbing Cars, and a contributor to She is the former Detroit Bureau Chief of The New York Times and was senior editor of the Midwest public media project, Changing Gears.