Does smart growth reduce carbon emissions? Bet the house on it.

There’s a compelling graph in researcher Todd Litman’s article in the Spring 2011 Center for Real Estate Quarterly, a publication of Portland State University in Portland, Oregon.

Attached at top right, the graph shows vehicle miles traveled (VMT) in three types of neighborhoods in Portland. Neighborhoods with good transit and mixed use average 9.8 VMT/household/day. Neighborhoods with good transit but no mix of uses average 13.3 VMT/household/day. The rest of the region, with no mix of uses or good transit — mostly characterized by suburban sprawl — averages 21.8 VMT/household/day.

This difference — 55 percent less automobile use in mixed-use, transit-served neighborhoods compared to sprawl — is dramatic.

In his article, “Can Smart Growth policies conserve energy and reduce emissions,” Litman explains why people drive so much less in compact urban places. “In multi-modal, smart growth locations residents tend to own fewer vehicles, drive fewer annual miles, and rely more on alternative modes. Even larger vehicle travel reductions occur where smart growth is implemented with efficient road, parking and fuel pricing; such pricing reforms tend to be more effective (price elasticities increase) at reducing vehicle travel if travelers have viable alternatives.”

Is this just a quirk of the Portland area, the planners' utopia with an urban growth boundary and an extensive light rail system? Thankfully, The Center for Neighborhood Technology (CNT) has VMT and greenhouse gas emissions from automobile use across the US. The map for Portland is shown at upper right. Below that, you can see the map for Pittsburgh. Notice any similarity? It’s the same pattern.

Drill down a little more on this interactive site, and the differences become even clearer. In Pittsburgh, for example, the close-in city neighborhoods range from 7,000 to 11,000 VMT/household/year, while the distant suburbs range from 21,000 to 25,000 VMT/household/year. The same general pattern holds for literally every metro region. Without exception. You can see it with your own eyes; just go to the site, click on a region, and select the variables "CO2 per household" and "VMT per household."

The National Association of Home Builders (NAHB) would have us believe that this is all a coincidence. “The existing body of research demonstrates no clear link between residential land use and greenhouse gas emissions and leaves tremendous uncertainty as to the interplay of those factors,” NAHB writes in published early in 2011.

NAHB relies on papers that it has funded by consultants like Eric Fruits of Economics International. In a recent article for The Center for Real Estate Quarterly, Fruits concedes: “On its face, the linkage between compact development and greenhouse gas emissions seems obvious: (1) if individuals drive less, then vehicle emissions will decline, and (2) if families live in more compact developments, then they would likely drive less and use less energy, and therefore (3) compact development would reduce greenhouse gas emissions.”

Well, yeah, when this pattern holds for every Metro area in the US, that would seem obvious. But notice, also, that Fruits reduces smart growth to one characteristic: “compact,” or density.

Having isolated one variable, Fruits performs his own analysis of the research, and comes to the conclusion that the “available data indicate that the connections are weak, bordering on non-existent,” between density and greenhouse gas emissions.

Litman cites studies that show density alone does in fact have “modest impacts” on VMT and greenhouse gases. But the big impacts from smart growth are from a series of related characteristics — street connectivity, mixed-use, availability of transit, thoroughfare design, and effective parking management among them — that are also correlated with reductions in VMT.

In other words, if all you do is bring people closer together, you get modest reductions in gasoline consumption. But if you do all of the other things associated with smart growth — that is to say, create a walkable environment with multiple destinations and alternative modes of transportation — the impacts on VMT, energy use, and greenhouse gas emissions are huge. It’s worth glancing at Litman’s table, “Land use impacts on travel,” attached here, which is a summary of research on how various smart growth strategies affect automobile use.

The overwhelming evidence from the research, therefore, confirms what we see with our own eyes in, once again, every metro area in the US.

Why is NAHB denying this? Calvert Asset Management Company, an investment fund based in Bethesda, Maryland, in December, 2010, on how the 10 largest publicly held homebuilding firms in the US are doing on sustainability.

The verdict: Most of them fare poorly. While their record on home energy use is merely poor, their performance on land-use practices is dismal, Calvert notes. Six of the 10 builders got a score of zero out of a 100 in this category, and the other four all scored under 20.

To sum it up: the 10 largest homebuilders have a dismal record on sustainable land-use policies, and the national organization, NAHB, is in denial about how land use affects global warming.

Now, it’s time to ask the home builders: How’s that working out for you?

The industry is in deep depression, with new home sales at their lowest level since records have been kept in a half century. Many of the leading homebuilders are losing money hand over foot. And indicates that the market for large-lot single-family housing, the homebuilders bread-and-butter for 60 years, is not coming back for at least another decade.

It also happens to be that large-lot single-family housing is the type that generates the worst greenhouse gas emissions.

Furthermore, also indicates that the same housing that produces fewer greenhouse gases — transit-oriented, compact development — is also the kind that is likely to be more successful for decades to come.

I know that the summer beach season is almost upon us, but even so, it’s time for the NAHB, and the major builders, to pull their heads out of the sand.

Download Litman's and Fruits's papers at the