Friday, February 14, 2014

My Curmudgeonly Take on Sneckdowns

Sneckdowns are a thing. First coined by Streetfilms’ Clarence Eckerson all the way back in 2006, now everybody is on the lookout. Some have called it the winter of the transportation nerd. The gist is that vehicle paths through the snow in streets show that vehicles don’t use the whole street for mobility most of the time. This is a clever idea presented as a collection of suggestive anecdotes. The popularity and fervor that people seem to be embracing the concept worries me that sneckdowns will lead to bad policy.

First off, however, this post is not meant to troll or anything of the sort.  I think roads are overbuilt and we damage our neighborhoods by designing for cars and trucks over people. That said, I have two main complaints about sneckdowns.
1)     To be unnecessarily jargon-y about it, sneckdowns are observational data for partial equilibrium models. Partial equilibrium is where your observed effect holds if all else is held constant. PE isn’t stable. Neither are sneckdowns because they reflect driver activity under unusual conditions, namely snow and ice. When it snows drivers behave differently than they do when conditions are ideal (hence not everything is equal). Drivers follow the tire tracks left before, for instance, and they drive slower and more cautiously. Such behavior is also true for pedestrians and cyclists! Everybody moves differently in slipperly conditions, then once desire paths are established they get followed. Here is a picture of a Harlem sidewalk after a snow but before it was cleared. You can clearly see that people follow previous footsteps. No one would argue this is evidence that the sidewalk is too wide:

Below is a picture of the Columbia campus, and most of the time people are walking all over the place, but since paths are established people use them. This does not mean that Columbia should get rid of all the space not currently used by people walking around, unless of course any new construction was for new Urban Planning faculty offices. Local roads are bigger than they need be, but sneckdown behaviors are caused by and reinforced by the weather and residual snow conditions.

2)     So my first point was really curmudgeonly, but my second point is my larger concern in that we shouldn’t argue about allocating space for modes by how much specific parts of infrastructure are used. That is an argument that bikes and pedestrians will lose. Arguing over perceived underutilized road space is what led to awful policies such as allowances for hybrids in carpool lanes, for instance.  If you observe a bus stop you might conclude that they are underused, too, as most of the time the stop is empty.  But that’s not an argument for getting rid of bus stops. Most sidewalks are underused, but that doesn’t mean we should get rid of sidewalks or make them narrower.

Sneckdowns are a clever way for looking at street space usage, but let’s not get carried away. While I think we should make pedestrians the primary focus of street and sidewalk design, arguing such a normative view from pseudo-empirical sneckdown claims will be a losing effort and may lead to even more stupid policy. There is a fine line between stupid and clever

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