For decades, U.S. youth culture revolved around cars. Iconic American hits, from the Beach Boys’ “Little Deuce Coupe” to Bruce Springsteen’s “Thunder Road,” sang of horsepower, speed and open highway. The seminal shift from childhood to adulthood occurred at age 16, when seemingly every red-blooded American kid (except the suspect ones who lived in Manhattan) scored a driver's license. Maturity, adventure and freedom came in the form of four wheels and a full tank of gas.

Not, perhaps, anymore. An emerging body of national statistics bears out what observers of the bike-rack gridlock in Millennial-heavy neighborhoods like Washington’s Petworth or San Francisco’s Tenderloin may have guessed at: Today’s American teenagers and twenty-somethings aren’t loving—or driving—cars nearly as much as their predecessors did. They’re getting their freedom from smartphones, which can travel distances and reach speeds that make cars seem quaint. They’re increasingly interested in commuting by bike or public transit. And growing numbers of them say they see cars more as nuisances and less as toys.

If this change proves broad and enduring—a postmodern, post-automotive generational shift — it will have profound implications: for how the federal government spends transportation dollars, for how auto and oil companies make money, for future patterns of U.S. real-estate development. But that’s a big “if.” The signs of this change are new and spotty, so the extent of the change remains wildly unclear. This may indeed be the end of an era: American car culture running out of gas. Or it may be something less revolutionary: a shift in the interests mainly of an elite, citified segment of the young—and an economically-driven, and thus ephemeral, shift at that.

That today’s youth are driving markedly less than their predecessors seems clear. Between 2001 and 2009, a period in which the recession emerged and gasoline prices shot up, Americans of all ages reduced their driving. The U.S. population grew by about 10 percent during those years, but the total distance Americans drove fell by about 1 percent—a reversal from prior decades, when total miles traveled kept climbing, according to the Federal Highway Administration. Driving fell most sharply during the first decade of this century among those aged 16 to 30. Per-person miles traveled fell 2 percent among those 56 and older; 11 percent among those 31 to 55, and a massive 25 percent—more than twice as much as for the middle-aged group—among those 16 to 30. Another indicator: The portion of Americans aged 16 to 24 who have driver’s licenses fell to 67 percent in 2011, its lowest level in roughly a half-century, according to federal statistics cited in a report last year by the U.S. PIRG Educational Fund and the Frontier Group, two environmentally oriented organizations.

What’s going on?