Monday, October 11, 2010

Explain that!

Readers of this blog know that I worry about aggregate measures used to describe large metropolitan areas. Here is a discussion that highlight's "L.A.'s traffic" and cites the latest Texas Transportation Institute congestion rankings. There is also a link to this report that criticizes the TTI approach.

TTI relies on the ratio of the metro area's lane-miles to its vehicle miles traveled (with minor tweaks). But is way too simple; it says nothing about sub-metropolitan variations -- and opportunities.

How is it that metropolitan areas have grown and yet survived and even lived to grow further? The biggest metros, after all, have managed to stay on top. Why is this key fact overlooked in all of the hand-wringing?

I do not know the answer to the second question, but the answer to the first question is fairly simple. It has two parts: (i) these metro areas provide offsetting advantages ("agglomeration economies"); and (ii) these places manage to grow in ways that mitigate the associated growth in congestion. Subcentering and suburbanization are not random "sprawl", but rather facilitate survival and competitiveness by offering agglomeration benefits outside the traditional center while also taking congestion pressures off the traditional center. Land markets do this. Nothing else can.

If, on the other hand, growth were accompanied by random sprawl, the stability of metro area rankings at the top could not be explained.