Each New Highway Built Drains a City's Population by 18%


Photo via Rutgers
How Highways Kill Cities
A new study reveals that with the construction of each freeway in a major city, population declines by an estimated 18%. Which is a pretty serious figure. The reasons for this aren't revelatory--highways make commuting greater distances possible, and provide arteries to towns outside the city, where those who can afford to commute can build bigger homes for less money. Which is pretty much how suburbs were born in the first place. But it's fascinating to dissect how this happens, and to what extent, as the new study by Nathaniel Baum-Snow does. Here's Nathaniel Baum-Snow talking about his study in an interview with Planetizen:
if suburb A builds a highway to connect to suburb B, that's going to effect the distribution of commutes not only between those suburbs but also the commutes in the region as a whole. So there are going to be these externalities where someone in suburb C has a faster way to get to work, so they're going to start using it and filling up this new highway. And a business downtown might say, hey, there's this new infrastructure, let's go locate out there and I can have a lot more space to work with. So anytime one part of a region changes something, it's going to effect population and employment throughout the metropolitan area
So essentially, both employers and workers, once centralized, are now more apt to spread out, and find a location along the highway where there's more space, or it's less expensive to live or operate. The employers that skip town then inevitably bring their job openings along with them. As a result, the net effect is that 18% of a major city's population gets drained.

Highways Between Suburbs
Interestingly, after this has happened, the bulk of the commuting shifts to only minimally involve the metropolitan area, which was ostensibly what the highway was originally built to serve in the first place.

the nature of residential and employment locations have changed dramatically, but the nature of commuting patterns have also changed dramatically. Now, the vast majority of commutes do not involve the central city at all, even commutes made by people who live in metropolitan areas, whereas in 1960, the majority certainly involved central cities either as origins or destinations or both. And that's a major change. I think the next step is to try to understand all the things that generated that change.
So now, people are commuting on highways built to help people go to and from a central city without ever even going to that central city. They're going instead from say, a suburb outside the city to an office park in another suburb outside the city. And it seems to me that change may be simply that the central city has been made unnecessary to fulfillment of the immediate needs of an individual--employment, goods, and housing are all available outside of it, often for cheaper prices.

As a result of all this, we're left with smaller cities and suburbs that are much more difficult to connect via mass transit, and the dependence on cars is perpetuated.

More on Cities and Transportation
$27 Billion in Stimulus Package for Highways to Hell
Time To Build Highways Underground?

Related Content on Treehugger.com