September 28, 2010

On Density and Pedestrian Planning

Over at Human Transit, a great post about density, its relationship to transit, and its statistical elusiveness.

the perils of average density

I especially want to highlight the post's deconstruction of the statement “the net density of Toronto is ###/hectare.”

  • “Density” in an urban planning context is always some kind of quantified human presence divided by some kind of land area, but it can be residential density (residents or homes per acre) or it can be total development density -- including homes, businesses, schools etc – or it can be an economic density such as the number of jobs in an area.
  • “Net,” as opposed to “gross,” means that the human presence is being divided by a smaller unit of area instead of a larger one. In calculating the area, for example, you might take out undevelopable land, and bodies of water, and the land taken up by streets and highways -- or you might not. There are arguments for or against excluding each of these things from “net density,” and an opinion about each of them is hiding inside the word “net.”
  • “Toronto,” of course, can be the City of Toronto, or the Toronto Transit Commission area, or the whole urban mass of greater Toronto. These obviously have utterly different average densities.
Lies, damn lies, and statistics. Having this much slipperiness built into the very vocabulary is frustrating, and in the absence of rigorous specificity, is a source of many fruitless headaches.

The post engages the topic of density in light of the measurement's prominence in Transport for Suburbia. Author Paul Mees makes the unconventional claim that density is not a necessity for effective transit. Or at least, not density in its sloppier iterations. For example, Mees demonstrates that Residential Density per Metropolitan area (red flag right there) yields unexpected results:

Metro Area Density (pop/ha) Transit mode share for work trips.

Los Angeles 27.3 4.7

New York 20.5 24.8

Las Vegas 17.7 4.1

Vancouver 17 16.5

Los Angeles, you know, the densest of the dense urban metropolises!

Since this post is entirely me piggy-backing and publicizing noteworthy insights of a planning professional, it is fitting to give him the final word:
To me, Mees’s table proves that average density over a whole urban area is the wrong kind of density for understanding transit. The impression you probably have of the densities of these cities is actually closer to the kind of density that matters.
Transit reacts mainly with the density right around its stations. It is in the nature of transit to serve an area very unevenly, providing a concentrated value around its stops and stations and less value elsewhere. So what matters for transit is the density right where the transit is, not the aggregate density of the whole urban area.
The granular details of where the transit is can be quite granular indeed: a footpath through the end of a cul-de-sac, a footpath over a creek. Human Transit gives a more detailed run-down here.

All in all, an excellent reminder that transit and urban planning projects can hinge on what might appear to be insignificant design details.

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