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How Do We Prioritize? | Nov 7th at 5:45pm

Posted by Ryan Avent | 1

I had an opportunity to check out the exhibition space, which was very well put together. I particularly enjoyed a series of tables presenting big questions in urbanism and allowing participants to weigh in on the answers by placing a marble in a jar corresponding to their preferred answer. It was a nice idea, and the results intrigued me.

Forgiving the author his regrettable photography, I’ll ask you to have a look at the first image, asking which policy a participant might support the most. As you can (hopefully) see from the picture, the use of urban brownfields for agriculture is far more popular than the elimination of car lanes for bike lanes, which is itself more popular than the use of congestion pricing in a downtown area. Keep in mind that most of these votes were cast by urban planning professionals, attending a conference dedicated in no small part to the use of urban policy to reduce dependence on oil and to reduce carbon emissions.

In fact, ordering the policies by their effectiveness on those measures would likely generate the exact reverse ranking. It is quite true that agriculture involves intense use of carbon. On the other hand, the supply of good urban space is very limited. Using valuable urban land to support agriculture would result in the displacement of potential urban residents, who would be pushed into residence elsewhere—potentially in places less dense, and more carbon intensive. Potentially, in fact, into the city’s suburbs, where existing farmland might well be plowed up to make way for new homes. This isn’t a good trade-off in nearly all circumstances.

Congestion pricing, on the other hand, has been shown (in places like London, Stockholm, and Singapore) to reduce driving and increase transit use. By reducing traffic volume, it becomes easier to allocate street space to other modes, like bikes and surface transit. Best of all, pricing raises revenue, which can be used to invest in new transit, or retrofit inefficient buildings, or invest in renewable power generation, and so on. So why is that policy the least popular? It is, I suppose, the least sexy. It’s playing with prices rather than turning old industrial land into crops. The latter, no doubt, is more visually gratifying to those concerned about environmental activities. But we must always remember that the most important thing is the results.

Or consider this question, concerning where we ought to build to accommodate the rising urban population. As you can see, dense urban infill is vastly preferred to suburban infill or suburban greenfield development. Few people, myself included, would think that greenfield building is the best way to go. As desirable as dense urban infill is, however, we must keep the size of the challenge in perspective. I live in Washington, DC, a district 66 miles square that’s home to 600,000 people. Were we to double its carrying capacity, an additional 600,000 people could be housed. I would welcome this (and we may get there, with good planning).

In Washington’s inner suburbs (inside the famous Capital Beltway but outside the District), a little over 1 million people live on approximately 240 square miles. Doubling the carrying capacity of that area would increase the metropolis potential population by another million. What’s more, that additional density would help to make many parts of the suburbs that aren’t currently walkable, walkable.

And in Washington’s outer suburbs something like 3 million people live on thousands of square miles of land. By doubling the density of the population living on that land, we could accommodate an additional 3 million people, boosting the metropolis’ total population by 50%. And again, the higher density level would shift many parts of the outer suburbs to densities more conducive to walking and transit.

In other words, most people live in places that aren’t that dense. It may be simpler, institutionally, to add density in places that are already dense, but the return to adding people in suburbs is potentially much larger, especially if we can, in the process, improve land use. In a world where billions of people must ultimately be housed in metropolitan areas, we must work where the work delivers the highest returns.

Ryan Avent is an economics writer living in Washington, DC. He authors The Economist's economics blog, Free Exchange, and covers environmental and urban policy issues for Grist.