There’s an interesting exchange going on between Kevin Drum and Matthew Yglesias regarding the reasons that some communities may or may not be walkable. It seems that the Woodbridge section of Irvine, where Kevin Drum lives, is quite walkable, but hardly anyone does it. Yglesias seems to feel that if an area is made fairly accessible to driving, then driving will takeover.

Since I grew up in southern California and my father and stepmother live in Irvine, I thought I would second that sentiment. For instance, my parents, both of whom grew up in New York City without a car, now consider it to be a perfectly natural appendage as do most Americans. When my wife has insisted on walking from my father’s area to the campus of U.C. Irvine and the town center, we hardly ever run into anybody.

In a further, more academic explanation for the phenomenon of people choosing driving over walking, even when walking is possible, Yglesias further delves into the “tipping point” of driving vs. walking in a community. He uses the term “floor area ratio,” which is defined in Wikipedia as:

The total building square footage (building area) divided by the site size square footage (site area) … Thus, an FSI of 2.0 would indicate that the total floor area of a building is two times the gross area of the plot on which it is constructed, as would be found in a multiple-story building.

Thus, Matt explains, referring to the work of my favorite academic urban planner, Christopher Leinberger:

A successful drivable suburb needs a floor area ratio [FAR] that’s in the .005 to 0.3 range. By contrast, to create an area where people walk around a lot and there’s street life you need a FAR of at least around 0.8 (and for actual car-free lifestyles to be viable maybe as much as 1.5). Fall in the middle and you get someplace that just sucks — it’s crowded, but there’s nowhere to go and nothing to do.

So now I have a great, if somewhat wonky sounding measure for density: Floor area ratio. How’s this for a banner: “Higher floor area ratio, now!”