Is Mobility More Important than Density?

Urban planners, land-use scholars, and other experts often advocate for greater density. But economist Tyler Cowen has an interesting blog post suggesting the US would do better to promote mobility, instead. His argument for mobility has considerable merit. But much depends on what kind of mobility we are talking about. Currently, increasing mobility in the sense of speed of transportation is less significant than increasing mobility in the sense of making it easier for people to “move to opportunity” by migrating from one place to another. Increasing the latter type of mobility often requires allowing greater population density (though, as discussed below, that may be compatible with increasing per-person living space).

Here’s Tyler’s argument:

American history is much more about rapid and cheap transport than about extremes of population density.  Even New York, our densest major city by far, became dense relatively late in American history.  To this day, the United States is not extremely dense, not say by European or East Asian standards.

But in American history, themes of horses, faster ships, safer ships, turnpikes, canals, our incredible river network, railroads, cars, and planes have been absolutely central to our development.  America has put in a very strong performance in all those areas.  When it comes to density, we have a smaller number of victories….

These days I see an urbanist movement that is more obsessed with density than with mobility.  I favor relaxing or eliminating many restrictions on urban density, and American cities would be better as a result.  Upward economic mobility would rise, and Oakland would blossom.  But still I am more interested in mobility, which I see as having a greater upside.

One issue is simply that urban density seems to lower fertility.  It is not obvious the same can be said for mobility.

And do you really want to spread and replicate the politics of our most dense areas?….

The density crowd is very interested in high-speed rail, which I (strongly) favor for the Northeast corridor, but otherwise am not excited about, at least not for America.  Otherwise, the density crowd works to raise the status of a lot of low-speed means of transport, for instance bicycles…..

I prefer to look to a better future where higher-speed transport is both affordable and green.  Ultimately, low-speed transport is a poor country thing….

I do not want to see the United States moving in poor country directions.

If you are obsessed with mobility, you will attach great importance to Uber, Waymo, self-driving vehicles more generally, and better aviation.  To me these are major advances, and they all can get much, much better yet….

These points were obvious to many people in the 1960s.  The Jetsons had their (safe) flying cars.  The ultimate innovation in Star Trek was the transporter.

I share Tyler’s enthusiasm for high-speed transport. It would be great to have flying cars like the Jetsons! The Star Trek transporter would be even better. I also love the Uber, Lyft, and other similar enterprises that have made transportation faster and cheaper. I even share some of Tyler’s relative distaste for bicycles, and dislike how they  tend to slow down traffic.

Still, I think Tyler is emphasizing the wrong type of mobility. What really built America is not so much fast transportation (though that surely helped), but the ability of people to “vote with their feet” by moving to places where there is greater freedom and opportunity. Foot voting opportunities, not mere speed of transportation, is the more important secret of America’s success. Most obviously, America developed as a result of large-scale foot voting through international migration. But, in addition, we have a long history of internal foot voting, through such things as westward expansion, and migration of groups to places where there was greater economic opportunity and freedom from various types of oppression. I provide an overview of that history and its significance in “Foot-Voting Nation.”

Today, the US suffers far more from constraints on foot-voting mobility, than limitations on transportation speed. Exclusionary zoning prevents millions of people from moving to opportunity, thereby denying them better work and educational options, and slowing down growth and innovation. Immigration restrictions have a similar damaging impact on international migrants, and also greatly impede growth and innovation.

Cutting back on these barriers would lead to greater population density, especially in major metro areas that have many job and educational opportunities. That’s often good! Density often creates useful “agglomeration” effects that increase productivity.

We usually think of density as causing crowding. But it can be increased in ways that simultaneously increase per person living space. Breaking down barriers to housing construction would make it cheaper and easier for people seeking more living space to purchase or rent larger homes. Reducing immigration restrictions would increase the construction work force (recent immigrants are disproportionate contributors), thereby also expanding the amount of housing and making it cheaper. In this way, contrary to Tyler’s fears that density leads to lower birthrates, the extra density created by breaking down barriers to foot voting, can actually be pro-natalist, by making housing cheaper and more plentiful.

Tyler and I agree more than we differ. I too am a fan of increasing transportation speed. By all means, bring on the flying cars! But real-world Jetsons and others like them could benefit even more from increasing the kind of mobility that enables foot voting.

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