More than development. Norwalk redevelopment.

Research: Doctor Congestion

Or, How I Learned to Stop Worrying and Love The Density

There’s a piece of fascinating transportation research published in this month’s Journal of the American Planning Association (JAPA).  It’s kind of dense, no pun intended (ok, a little intended), but worth a read if you like the occasional peek at the more scientific side of urban planning and transportation issues.  JAPA has chosen to make it a free download this month, so you can access it for a limited time here, or I’ve also uploaded it here.  It’s called “Does Accessibility Require Density or Speed: A Comparison of Fast Versus Close in Getting Where You Want to Go In U.S. Metropolitan Regions.” The authors are Jonathan Levine, Joe Grengs, Qingyun Shen, and Qing Shen.

For those that don’t want to wade through the journal abstract, the methodology, and all the charts and graphs, I will attempt a plain-English summary here.  The gist is this: when defined as “ease of reaching places,” transportation is best improved not by the types of improvements designed to increase vehicle operating speed (or, as its called in the literature, “mobility”), but rather by planning for higher densities and closer proximity among destinations, and this is true even when it results in road congestion and lower speeds.

Let’s break this down.

When we drive (and yes, this density argument is not about the virtues walking, biking, and transit — at least not directly — but an argument with the car foremost in mind), both the perception of our own progress, as well as the metrics within most conventional transportation literature, are based upon our ease of movement on the road, or put another way, our speed.  If we are able to move along, unfettered by other traffic, at a reasonable clip, we say that traffic was “good” and count it as a positive transportation experience.  If, on the other hand, the road was congested, and our speed was restricted by lights or slow traffic, those conditions are said to reflect transportation “problems” within the community or region.  And, to a large extent, this view of transportation has been the dominant paradigm for…well, pretty much forever.

But, in case you didn’t notice, there’s a key factor that’s missing in the approach above: destination.

It’s all very well to plop yourself down on a random road and evaluate its transportation quality based on how quickly the cars are moving.  But it would be a pretty decontextualized exercise.  The authors of this paper remind us that demand for transportation is derived; “that is, people rarely consume transportation for the pleasure of movement per se, but rather travel in order to reach opportunities available at destinations.”  In other words, it ultimately matters less how fast you go than how fast you get where you’re going.

Aren’t those things highly likely to be one and the same, you say?

No, and here’s where it gets interesting.  In a series of comparisons across 38 metropolitan areas in the US, the research showed that, by and large,  “mobility”-based transportation, while increasing speed of movement, can decrease access, because it erodes proximity.  Moreover, the net effect of this negative is worse than the corresponding negative of density-derived congestion.  Denser settlement does increase traffic congestion and decrease “mobility” (speed), but that effect is generally offset by gains in the proximity that density provides.  Put more simply, you end up moving slower, but you also have less far to travel.  With a bigger highway, you might move quicker, but chances are that you also have farther to go.