Ever since the housing bubble burst, Americans have been fleeing the distant suburbs and exurbs. That’s one way to read a recent Census Bureau report showing that those areas are being eclipsed by growth in cities and “high-density suburbs” in the past year. Here’s a chart from Brookings:

(Source: William Frey, Brookings Institution)

William Frey, a demographer at Brookings, offers plenty of analysis. First, note that Census estimates are only estimates — they’ve been wrong in the past. But with that in mind, the outer exurbs do appear to be dwindling. Much of the housing boom exploded in these areas — in 2006, these outer fringe countries grew at a 2 percent pace. But when the bubble popped and gasoline started getting pricey, these areas suddenly looked less attractive. Last year, according to Frey, these counties grew just 0.4 percent. In some cases, the collapse was extreme: Kendall, Ill., went from America’s fastest-growing county in the 2000s to number 236th on that list in 2011.

So, where are Americans moving instead? To some extent, they appear to be heading back to cities. Urban researcher and writer Yonah Freemark takes a closer look at 21 of the largest U.S. metropolitan areas, and finds that only five of them (Cleveland, Baltimore, Cincinnati, St. Louis and Detroit) lost population in their central cores between 2010 and 2011. For the remaining 16, including Chicago, the District of Columbia and Philadelphia, urban cores are growing at a faster rate.

Down for now, but poised for a comeback? (Paul Beaty/AP)

In theory, there are plenty of reasons why those house-seekers might prefer to stay in the city or high-density suburb instead. For one, gasoline prices are rising, which makes it a pain to live far from employment centers. And there are demographics to consider. As Christopher Leinberger of Brookings has explained, surveys show that some 30 to 50 percent of residents in U.S. metro areas would prefer to live in walkable urban environments — a trend fueled by the increasing numbers of single and childless couples, who will constitute 88 percent of household growth through 2040. Many of America’s growing number of retirees are likely to seek out dense urban areas, as well.

But here’s the dilemma: As Leinberger notes, there are only enough truly walkable neighborhoods in the country to satisfy about 5 to 10 percent of all residents. If more and more people decided to ditch their cars and live in high-density areas, there’s a housing supply problem.

That means, writes urban analyst Aaron Renn, the outer suburbs are likely to rebound. “Part of the logic is simple math. If you add up the population of the municipalities of New York City, Los Angeles, Chicago, Philadelphia, San Francisco, Boston, Seattle, Washington, Portland, and Miami you only get 20 million people. That’s only about 20% of what the Census Bureau is projecting for just population growth by 2050,” Renn says. “With the difficulties of building in urban areas, there’s no way to accommodate just the new growth even if everybody wanted into the city. In other words, there’s just no way there is going to be some massive back to the city movement. I hate to break it to you, but that’s reality.”

That’s a topic dissected at length by Matthew Yglesias in “The Rent Is Too Damn High” and Ryan Avent in “The Gated City.” As long as there are all sorts of restrictions — zoning and otherwise — on building new housing units in densely populated urban areas, some people will be pushed out to the suburbs and exurbs. Those sprawling areas may be running on empty for now, but that may not always be the case.