Broadly speaking, cities create housing either by expanding their geographic footprint or by "densifying"—that is, filling in vacant land, or changing rules governing the use of that land.
In the main, most U.S. cities have been better at expanding than densifying in the last few decades. Almost 90% of new homes built in American cities in the 2000s put down foundations on undeveloped or suburban land, according to BuildZoom, a real estate website.
Indeed, when cities have stopped sprawling—like San Francisco, which is bounded by ocean and mountains—they've produced decreasing housing supply, and thus higher and higher housing prices. By contrast, cities that have allowed expansion, like Atlanta, have managed to keep housing increases more modest, the site's analysis shows.
Cities have three options going forward, says Issi Romem, BuildZoom's chief economist. They can expand "with gusto": building out suburbs, laying long freeways, and lengthening commute times (and end up looking like, say, San Antonio, Texas). Or they can give up on affordability, crowding out the less affluent and altering their "social character" (like, say, San Francisco). Or they can take a new approach to urbanism: one that embraces not only infilling and high-rises, but also changes to land-use regulations that currently stifle development.
Romem calls for the third approach, including incentives for multifamily development, fewer single-family homes, and transportation infrastructure that encourages people to leave behind their cars. But he doesn't think it will happen: planning decisions are highly dispersed in this country and anti-development landowners have lots of political sway.
That just leaves sprawl, which is not a nice thing, but the inevitable tradeoff if cities are not prepared to stand up to landowners, yet want to continue being melting pots.
"Sprawl is not something to be welcomed," he writes. "But people must understand that with neither outward expansion nor meaningful densification, U.S. cities cannot provide enough housing to prevent equally unwelcome changes to their social character."
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