Enraged at the spill in the Gulf and the American appetite for oil that ultimately caused it? Stop land development on farmland, forests and other fringe locations and direct future development to close-in opportunities. A massive new study, years in the making, makes it crystal-clear that it can make a big difference.
In particular, transportation uber-researchers Reid Ewing (University of Utah) and Robert Cervero (UC-Berkeley) have published a painstaking ‘meta-analysis’ of nearly 50 published studies on the subject of land use and travel behavior. Writing in the Journal of the American Planning Association, the two return to a subject to which they have dedicated most of their careers, in this case updating their previous meta-analysis from 2001.
What they found: location matters most when it comes to land use, driving and the environment.
In the US, two-thirds of oil use goes for transportation, and most of that for driving. The study's key conclusion is that destination accessibility is by far the most important land use factor in determining a household or person’s amount of driving. To explain, 'destination accessibility' is a technical term that describes a given location’s distance from common trip destinations (and origins). Within a region, relatively central locations are almost always the most accessible; the closer a house, neighborhood or office is to downtown (or a strong suburban center), the better its accessibility and the lower its rate of driving. The authors found that such locations can be almost as significant in reducing driving rates as other significant factors (e.g., neighborhood density, mixed land use, street design) combined.
The clear implication is that, to enable lifestyles with reduced driving, oil consumption and associated emissions, environmentalists and others concerned with oil overconsumption should continue to stress opportunities for revitalization and redevelopment in centrally located neighborhoods. As Ewing and Cervero put it: 'Almost any development in a central location is likely to generate less automobile travel than the best-designed, compact, mixed-use development in a remote location.'
The authors carefully examined each study, applying statistical analysis to tease out which land use factors had the biggest impacts on travel behavior when extraneous factors such as income were controlled. After discussing destination accessibility, the authors continue:
‘Equally strongly related to [vehicle miles traveled] is the inverse of the distance to downtown. This variable is a proxy for many [other factors], as living in the city core typically means higher densities in mixed-use settings with good regional accessibility. Next most strongly associated with VMT are the design metrics intersection density and street connectivity. This is surprising, given the emphasis in the qualitative literature on density and diversity, and the relatively limited attention paid to design. The weighted average elasticities of these two street network variables are identical. Both short blocks and many interconnections apparently shorten travel distances to about the same extent.’
My designer friends have educated me considerably over the past few years on the potential effects of a good street network, and they are thrilled that the study has confirmed their expectations. In addition to their effect on driving, Ewing and Cervero found that street networks have a huge influence on how much walking is generated from a given location:
‘Among design variables, intersection density more strongly sways the decision to walk than does street connectivity. And, among diversity variables, jobs-housing balance is a stronger predictor of walk mode choice than land use mix measures. Linking where people live and work allows more to commute by foot, and this appears to shape mode choice more than sprinkling multiple land uses around a neighborhood.’
Distance to a store was the second most influential factor in influencing walking, with location and the accessibility of transit next.
Since those of us who worked on the LEED for Neighborhood Development rating system tried hard to reward good, accessible locations (while keeping the most remote ones out) as well as intersection density, I think this research validates our approach. It does make me wonder, though, if we are giving enough emphasis to revitalization and street networks when we advocate in the arena of transportation policy. It also makes me wonder why more environmental groups, clearly incensed at BP and the Gulf oil spill, aren't paying more attention to land use.
For more about the new research findings and their implications, go here.
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Kaid Benfield writes occasional Village Green commentary on Huffington Post and (almost) daily about community, development, and the environment on NRDC's Switchboard. For daily posts, see his Switchboard blog's home page.