If You Want Heavy Rail, You Need Density

A Greater Greater Washington reader named thisisbossi dreamed up an impossibly ambitious scheme for expanding WMATA’s heavy rail network:

Dave Alpert responded by saying the map brings to mind the actual heavy rail network of Paris, which “has more lines than even thisisbossi’s map, and in a smaller space, too.” To Alpert this shows that “the political will exists to build some of the best transit in the world in a nation’s capital city, while here, at least a significant part of one major political party would spend absolutely nothing on transit or the capital city.”

There’s something to this, but I once again need to return the fact that in terms of population density Washington is closer to Fargo than it is to Paris. People notice that central Paris doesn’t have skyscrapers and want to start analogizing it to America’s skyscraper-less capital. But Paris has over 54,000 people per square mile. If that many people lived in DC, we’d have well over 3.2 million people living in the city instead of about 600,000. And clearly if that were the case we’d have the tax base to support a much more expensive mass transit system.

The issue is that even leaving aside the issue of restricted building heights in the central business district, DC’s zoning code mandates densities in the bulk of residential neighborhoods that are low by Paris standards. I think big-time heavy rail investment is a smart idea that’s paid off for Paris, London, New York, Tokyo, Berlin and many other cities around the world. But the thing that makes heavy rail pay off is that it facilitates high densities, and high density facilitates high productivity. But it doesn’t make sense unless you’re willing to pair the construction with substantial relaxation of low-density zoning mandates. Otherwise it largely just functions as a subsidy to people who happen to live near the new train station.