by Clark Williams-Derry
A study adds to the evidence that compact neighborhoods reduce driving.
Sometimes I feel a little like Captain Ahab, forever in search of an elusive white whale. In my case, though, the whale is profoundly geeky: I'm in search of a definitive study, or set of studies, showing the relationship between urban design and transportation habits -- particularly, how neighborhood design affects fuel use.
So far, that particular white whale remains elusive -- but searching for it turns up all sorts of interesting tidbits. Like this one: University of California researchers David Brownstone and Thomas Golob have looked at the relationship between residential density and driving habits, and concluded that:
Comparing two California households that are similar in all respects except residential density, a lower density of 1,000 housing units per square mile...implies an increase of 1,200 miles driven per year...and 65 more gallons of fuel used per household.
Thar she blows!!
Let's look at those numbers a bit.
A thousands households per square mile translates into about one and a half households per acre. So going from a neighborhood designed on the post-war, upper middle class ideal -- your own home on 2 private acres -- to the reality in many of the Northwest's more compact urban areas -- a mixture of single family homes with small yards, together with some multifamily housing, with an average of around 10 housing units per acre -- you increase density by just over 6,000 housing units per acre.
And, according to the numbers that these authors have crunched, living in a compact neighborhood rather than a sprawling exurb would lead to a decline in gasoline consumption of...wait for it...395 gallons of gasoline per household per year!
That's a lot of gas. By comparison, the average resident of the Northwest states consumes about 390 gallons per year; so living in a denser neighborhood does as much to reduce your driving as having one fewer person in your household.
So if Brownstone and Golob are even close to being correct, the kind of neighborhood you choose has a tremendous influence on your total gas consumption, and the overall impact of your daily driving on the climate. And their findings argue that one way to reduce fuel consumption is to encourage new development in compact neighborhoods.
This, of course, is just one study among many. There are some researchers who find that the relationship between density and driving is far more tenuous. Still, these sorts of results are what keep me searching for that white whale. (It's there...I know it...)
Clark, you might find some of the lectures from the University of Melbourne's 2009 Festival of Ideas of interest.
Here, Kvan talks of the effects that land ownership has had on the way in which land is developed into suburbs (particularly reference to a plan for a centre of 800,000 people in Hong Kong territories, all within 800m of the new station)
In another talk, the point was made that urban density and reducing transport needs are more environmentally effective than any number of green buildings. (Although there's no reason you can't have both, of course)
Greenhouse Gas Emissions from Urban Travel: Tool for Evaluating Neighbourhood Sustainability
Thanks for the tips!!! The problem, I find, is that there are still quite a few studies that look carefully at the relationship between neighborhood design and transportation -- often in the US -- and don't find much. I tend to think that those studies are inconclusive -- perhaps they're looking at the wrong things, or perhaps US cities are just so uniform and sprawling that it's hard to tease out a relationship in a way that satisfies the statisticians. Regardless, those sorts of studies certainly muddy the waters -- which makes white whales harder to spot.
If you read closely, the study cited here actually concluded that the effect of density was not sufficiently large to be effective as a policy tool (and used some very dated data to make the point). That is probably true with respect to density alone (imagine a pod of high-rises in an outlying greenfield).
But density works best in concert with other neighborhood characteristics. And I would add that regional accessibility is perhaps the most important factor that has been studied. Regional accessibility (which measures the distance or travel time between a given location and other important locations/destinations within a metro region) is often associated with neighborhood density, mixed use, transit access, and walkability, so many studies do not segregate the various factors. But those that do (Ewing, Cervero, Walters, etc.) find all five to be individually significant. Neighborhood density coupled with transit, mixed uses, walkability and, especially, a good relatively central location, can be quite powerful in reducing driving and associated emissions. (I have a longer discussion with some links on my own blog from earlier this year for those who are interested.
I did read that, but I simply thought that that particular statement was NOT justified by the rest of their study. As I saw it, they were saying "it's hard to change the average density of existing neighborhoods, so policymakers should pay attention to other things to reduce fuel consumption."
But as zoning boards and regional planning organizations are considering NEW development, this sort of study is still massively important to keep in mind. The *marginal* climate impact of new development will be enormously affected by the form and location it takes place -- whether as compact developments or infill in existing neighborhoods, or as new sparse development on the outskirts of town.
And besides, neighborhood form doesn't change much year to year. But over the long haul -- over the course of decades -- it's among the most important things to get right.