EDGE CITY….David Brooks writes today about the new suburbs:

The truly historic migration is from the inner suburbs to the outer suburbs, to the suburbs of suburbia….The geography of work has been turned upside down. Jobs used to be concentrated in downtowns. But the suburbs now account for more rental office space than the cities in most of the major metro areas of the country….

His article, adapted from a forthcoming book, isn’t actually very enlightening, but it gives me a chance to recommend a book on this subject that Brooks obviously read as part of his research: Edge City, by Joel Garreau. The difference between an edge city and a suburb is basically the one Brooks makes: edge cities don’t just have homes, they also have lots of office space. People live and work in edge cities, they don’t commute.

Here, stolen from my review of the book, is my favorite part of Edge City: the appendix, which lists “The Laws,” rules of human nature that developers have learned from hard experience despite the best efforts of academics and urban planners to tell them they’re wrong. In fact, Garreau says that one of the things that developers find most perplexing is government bureaucrats and planners: “These people, developers believe…have self-evidently preposterous ideas about how human nature works in the real world.”

Here are a few of the laws that Garreau offers up:

  • The farthest distance an American will willingly walk before getting into a car: Six hundred feet. For example, sightlines in shopping malls never exceed 600 feet because people won’t walk that far.

  • The function of glass elevators: To make women feel safe. Not to offer a view out. Rapes rarely occur in glass elevators.

  • Why elected officials feel they must encourage commercial development or die: For every $1 of tax revenue that comes in from a residential subdivision, as much as $1.22 goes out to provide services, especially schools. By contrast, for every $1 of tax revenue that comes in from commercial development, at most 32 cents is required in expenditures, usually for roads.

  • The maximum desirable commute, throughout human history, regardless of transportation technology: 45 minutes.

  • The prime location consideration when a company moves: The commute of the chief executive officer must always become shorter. [This is not a joke; Garreau cites a genuine study that strongly suggests it’s true.]

  • What people who hire commercial real estate salesmen look for in a resume: Background as a jet-fighter pilot. It is an article of faith that the best commercial salesmen are former sky jockeys, although it is the sheerest speculation exactly why that correlation may exist.

And finally, a series of laws that helps explain the lack of mass transit in edge cities and why this will never change. Note that “FAR” stands for “Floor-to-Area Ratio,” the ratio of the total floorspace of a building to the area of the land the building is on. It’s basically a measure of population density.

  • 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.

It’s a good book if you’re interested in this stuff. He even explains how it is that the whole edge city phenomenon has been driven by women, and probably not in the way you’re thinking….