Walkability

| Thu Sep. 11, 2008 10:49 PM EDT

WALKABILITY....Responding to my post yesterday about walkability in Irvine (actually, just the Woodbridge area of Irvine, but whatever), Matt Yglesias brings up a key point: at low densities you can have a nice suburb and at high densities you can have a walkable neighborhood, but there's no happy medium where you have both.

This gives me the opportunity, just for the hell of it, to post an excerpt from Joel Garreau's Edge City, a book that's dated but still one of my all-time favorites. An edge city is basically just a suburb that also has lots of office space (like Irvine, for example, or Tyson's Corner), and its density is measured in FAR, or Floor-to-Area-Ratio. For example, 10,000 square feet of office space on 100,000 square feet of land gives you a FAR of 0.1. Developers think of FAR like this: "The fundamental unit of density, from which all calculations spring — parking, hence profitability, hence human behavior, hence civilization." Here are the basic, inviolate laws of FAR:
  • The level of density at which automobile congestion starts becoming noticeable in edge city: 0.25 FAR.

  • The level of density at which it is necessary to construct parking garages instead of parking lots because you have run out of land: 0.4 FAR.

  • The level of density at which traffic jams become a major political issue in edge city: 1.0 FAR.

  • The level of density beyond which few edge cities ever get: 1.5 FAR.

  • The level of density at which light rail transit starts making economic sense: 2.0 FAR.

  • The level of density of a typical old downtown: 5.0 FAR.

  • The density-gap corollary to the laws of density: Edge cities always develop to the point where they become dense enough to make people crazy with the traffic, but rarely, if ever, do they get dense enough to support the rail alternative to automobile traffic.

This comes from "The Laws," which is the appendix to Edge City and its most entertaining part. Highly recommended, even though it's now nearly two decades old.

Other worthwhile responses to my walkability post are here, here, and here. I also think the "tipping point" concept is probably useful here. One of the points I didn't make clearly yesterday but should have is that I don't think walkability is one of those things where you can hope to make incremental changes in order to get incremental improvements. (Outside of dense urban cores, that is.) Woodbridge, as suburbs go, is pretty walkable: probably about 70% as good as you're likely to realistically get. But this has not produced a neighborhood that's gone from 100% car-centric to 90% car-centric. At best, it's produced a neighborhood that's gone from 100% car-centric to 99.9% car centric.

The problem, I think, is that walkability comprises a lot of things and you have to have all of them in full measure. You need high density and street level retail and scarce and expensive parking and good transit and a wide variety of easily accessible shops and restaurants. And a few other things as well. If you have four out of five it's not good enough. If you have medium density but not high density it's not good enough. If shops are 20 minutes away instead of 5 minutes away, it's not good enough. Improving any one of these things has virtually no impact until all of them are good enough. And that's why genuine walkability is really, really hard to get outside of urban cores.

Plus Americans are lazy. Here's another one of The Laws: "In either a downtown or an Edge City, if you do everything you can to make casual use of the automobile inconvenient at the same time you make walking pleasant and attractive, you maybe, just maybe, can up the distance an American will willingly walk to fifteen-hundred feet. A quarter of a mile. And this at the substantial risk of everybody saying forget it and choosing not to patronize your highly contrived environment at all." And if you don't do this? Then the maximum distance an American will willingly walk is 600 feet.

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