For decades, the American dream has been a suburban one: The detached, single-family home; the car (or two) in the driveway; the stereotypical white picket fence.
Now, reversing this pattern might be an important step toward averting climate change, according to a new Congressionally commissioned study by the National Research Council.
"Compact, mixed-use development—individuals living in denser environments with jobs and shopping close by—could reduce the number of vehicle miles traveled by shortening trip lengths ... and by making walking, biking, and public transit more viable alternatives to driving," the NRC explains.
The key point: less driving means lower carbon emissions.
In fact, the report's best-case scenario indicates that doubling residential density in 75% of new and replacement housing units in a metropolitan area—coupled with public transit improvements and higher employment concentration—would result in a 25% decrease in household driving. That, in turn, would cut emissions by 7-8% by 2030 and 8-11% by 2050, relative to a base emissions case.
In Europe, urbanization is already the name of the game, with 76% of Europeans living in cities with dense, livable cores and highly developed mass transit systems.
Though a full 80% of Americans today live in metropolitan areas, a decentralized pattern of population and employment continues to cause decreasing density at city fringes. As a result, the opportunities for higher-density development are huge.
"Changing demographics—an aging population, continued immigration—and the possibility of sustained higher energy prices could lead to more opportunities for the kinds of development patterns that could reduce vehicular travel, thereby saving energy and reducing CO2 emissions," the NRC writes.
The United States will require 57 million new and replacement housing units to accommodate an ever-expanding population by 2030, according to the study. That number jumps to between 62 million and 105 million new units by 2050, potentially doubling the 105.2 million housing units the U.S. had in 2000.
Tom Wright, executive director of the New York-New Jersey-Connecticut Regional Plan Association, says this surge in building stock will coincide with an already increasing need for more high-density development.
"There's an incredible demand for the new compact development forms, both from younger constituencies and from older ones," he said. "I don't think that as boomers retire they're going to agree to go to those same retirement homes they sent their parents to. They're going to want full-service communities. And so I think we're going to see a fairly dramatic shift in the market forces around real estate," he said.
Authors of the NRC report suggest that more compact urban development to meet this demand could be driven largely by public infrastructure investments and development incentive policies, targeted especially toward areas where density increases are already taking place—in the inner suburbs, near transit stops, and along major highways.
It might not be that simple, though. Significant hurdles still stand in the way of realizing the ambitious upper-bound scenario that would cut carbon emissions by as much as 11%.
Local zoning laws, for instance, often set tight restrictions on land use, and are likely to be strongly backed by politicians and homeowners with concerns about the impact of high-density development on their communities. And as some authors of the report point out, it's a long and difficult task to engineer a departure from the low-density development pattern that has characterized America for over half a century.
These NRC committee members point out that in many cities, curbing large-lot development at the urban fringe and building up the urban core would require "such a significant departure from current housing trends, land use policies of jurisdictions on the urban fringe, and public preferences that those measures are unrealistic absent a strong state or regional role in growth management."
For those reasons, emissions reductions from increased compact and mixed-use development in metropolitan areas will likely start out as modest and short-term.
In a more moderate scenario described by the study, just 25% of new and replacement housing would be built at twice the density of current new development levels, leading to a 12% drop in driving and an emissions reduction of 1% by 2030 (1.3%-1.7% by 2050).
Still, the NRC committee concludes that government policies to support compact, mixed-use development should be encouraged in the long term.
Wright says more federal involvement might be the key ingredient to kickstart a turnaround after years of low-density American development.
"We had eight years of absolutely no federal role in any part of the metropolitan context. And trying to do this without the federal government has proved just impossible. But now maybe there's an opportunity with the Obama administration—if the federal government can start to play a role in the metropolitan planning arena, we could start to turn things around in a big way," he said.
Federal measures to accelerate compact urban development could include coordinated investments in rail transit and other infrastructure—like the $13 billion in stimulus funding already allocated to improving the nation's high-speed rail system—as well as financial and tax incentives for developers of mixed-use building projects. According to NRC's report, these policies would work in concert with local government actions such as parking limitations and congestion pricing.
Despite numerous obstacles, Wright is optimistic about the potential for reaching the NRC study's upper-bound scenario within a few decades.
"I do think the 75% should be on table as a goal, and it's worth knowing what it does and that it's achievable, but it's not going to happen based on the kinds of policies and investments we've been doing so far," he said. "We're going to have to get creative at the local level to combat those classic externalities, to make sure the benefits of these compact development projects get fed back into the projects themselves."