The Clarendon section of Arlington, Va., has rows of new town homes within walking distance of the subway.

Study: Denser development may cut pollution Would Americans drive less if they stopped living on big lots far from urban centers? If so, would that reduce pollution and dependence on energy? By how much? Meeting the growing demand for conveniently located homes in neighborhoods designed to encourage walking could significantly reduce the number of miles Americans drive while giving people more housing choices, a national research panel has concluded. How much it would shrink the nation's carbon footprint is not as clear. Such questions, which have dominated the debate over "smart growth" for two decades, are getting the attention of lawmakers. The Senate will debate a bill this fall that would cap greenhouse gas emissions, and Congress asked the National Academy of Sciences to quantify the effect of where Americans live on driving habits. A boost from science After reviewing almost 100 studies conducted over 20 years, the National Research Council — one of the academy's research bodies — released findings last week. The research is potentially significant because it comes from a non-partisan group of mostly academics, scientists and researchers rather than advocacy groups: • More compact development would cut driving by 5% to 12%. "Simply reducing family-lot sizes — say, from 1 acre to a quarter-acre — should reduce vehicle trip distances by bringing origins and destinations closer together," the report says. Denser development can concentrate enough people in one area to attract businesses, public transit, schools and jobs. That, in turn, can reduce the need to drive everywhere. • Denser development will cut fuel use and carbon dioxide emissions. By how much is murky. "It will take awhile for that new development to have a very perceptible effect" on the number of miles driven, says José Go´mez-Ibáñez, chairman of the committee that produced the report and a planning professor at Harvard University. "Even if we started (developing) more compact and densely today, given (that) new housing stock is only 1% or 2% of housing stock every year, it will be several decades before there is an impact." If 75% of new and replacement housing units were built in more compact development — a scenario the report considers unlikely — residents of these communities would drive 25% less. Such a decline would cut carbon dioxide emissions 7% to 8% by 2030 and 8% to 11% by 2050, the report concludes. A more realistic scenario envisioned by the researchers has 25% of future housing in denser communities. The benefits: A 12% reduction in driving but as little as a 1% drop in emissions by 2030. The research suggests that many variables make it difficult to quantify the effect of denser development: • Building more densely won't stop driving if jobs and services are not nearby or if a community is built without sidewalks. • If cars become "greener," driving's impact on emissions will change. • Access to public transportation, such as light rail, subways, trolleys and buses, reduces driving more. Research 'underwhelming' The research council's findings are "underwhelming," says Samuel Staley, director of Urban & Land Use Policy for the Reason Foundation, a libertarian think tank. Staley, who says Americans should have a choice to live in exurbia if they want to, says the research offers scant evidence that dense communities produce great benefits. "CO2 reduction between 1% and 11%? That's a huge variation," he says. "In order to achieve this, we're talking about essentially not giving people much choice" of where to live. Greater benefits will come from technological improvements, such as plug-in hybrid cars, he says. "What comes out loud and clear is that if the miles we drive continue to grow at the projected rate, you blow your climate goals out of the water," says David Goldberg, spokesman for Smart Growth America, a national coalition that advocates denser development. "The basic message I got from this is that you can't go wrong by pursuing this strategy." In a 2007 report, the Urban Land Institute reached similar findings. "The most important thing is to reduce the amount we drive," says Ed McMahon, senior resident fellow at the institute, a research group that studies land use. "By just building two houses per acre from one house per acre would reduce (driving)." The research stresses that "you could have substantially more compact development without giving up single-family housing," Go´mez-Ibáña says. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more