Engineers, Traffic and Social

'Induced demand' as a conservative insight

A fellow on Twitter who enjoys disagreeing with urbanists wrote this last month:

The Suburbanist @The_Suburbanist

Why does the silly "Induced Demand" narrative persist, despite its conflicting with common sense? 1) Makes people feel smart; "I know something the masses don't know" 2) "More = less" is counterintuitive, making it especially appealing 3) It signals urbanist tribal affiliation

“Induced demand” refers to the insight and widely observed phenomenon that widening highways/increasing highway capacity often leads to more traffic, such that travel times and congestion do not improve. In his latest book, Charles Marohn writes that the only way to “fix” or “solve” congestion is to get people out of their cars. In the same vein, it’s often argued that you can’t build your way out of congestion. (I suppose you could, but where would 40 or 50 lanes of highway actually go?)

In just one of the iconic examples of induced demand, Houston famously widened its traffic-choked Katy Freeway in the mid-2000s, to more than 20 lanes. Travel times improved in the short term. But by the time several years had gone by, peak traffic was worse than before the widening.

This kind of thing can sound unbelievable. For certain conservatives who think of urbanists as car-hating ideologically driven busybodies, it sounds too perfect. But it’s basically true.

Now there’s a lot going on here, and much of it has to do with land use rather than any magic property of road capacity to generate traffic. Obviously, if induced demand were some kind of universal phenomenon, no road anywhere would ever have any free capacity. What people are mostly talking about is commuting routes and freeways, where the widening project often encourages peripheral development, which in turn generates more commuting trips.

Daniel Herriges at Strong Towns wrote an excellent piece about all of this last August, distilling it very clearly in layman’s terms.

He starts like this, which is helpful when you’re addressing people who aren’t already convinced or have simply never heard of this stuff before:

This lack of clarity, in turn, has actually sometimes hurt the arguments of those calling for sanity in transportation budgets and expansion plans. We risk opening ourselves up to attack for being imprecise or intellectually lazy or peddling pseudoscience.

Induced demand is not pseudoscience. It’s very real, and it’s backed up by research. But the term is a bit of a convenient fiction. It conflates multiple different things actually happening to driver behavior. So let’s break that down.

As far as the land-use angle, he writes:

Over time, development in the places that are now better served by road becomes more profitable and attractive. A lot more people are interested in buying a house that’s 30 minutes from a major downtown than are interested in buying one that's 50 minutes away. So when you shorten the trip, newly-marketable development follows the new roads.

And you can imagine what happens to traffic as these changes in the development pattern play out.

Here’s another good piece about this in Governing, by Jake Blumgart. If this interests you, read both pieces in full as well as the one I linked above about Houston’s big freeway.

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But in this post, I’m less interested in proving induced demand to you than in thinking about the kind of insight that it is. The fellow on Twitter who I showed you at the beginning here is a libertarian or conservative. But in fact, contra his opinion, I think induced demand is a profoundly conservative insight about how human behavior works.

At heart, it’s an argument that human behavior is dynamic, not static. People are always evaluating and responding to incentives and making calculations. You can’t fix congestion by building more lanes, because people respond to the reduced time-cost of driving by doing more of it. You can’t hold driving habits or development constant in the real world, because these things interact with each other in ways that we can’t always predict or plan for. What we call “traffic” is much more complex than inputs and outputs—it’s a human, social phenomenon.

In other words, induced demand is a sort of argument against social engineering and a warning about unintended consequences.

Conservatives are quite familiar with this kind of argument. They often make it in regard to social programs, arguing that welfare weakens families or work ethic or what have you. They warn that it’s not as simple as providing social assistance to people in need, because (they argue) there’s something about those programs being available that can change human behavior in a way that makes those programs more necessary. Or, as the British conservative writer Theodore Dalrymple puts it, in more rarefied language, “misery increases to meet the means available for its alleviation.”

I’m not saying this true; just that it’s familiar logic for conservatives. It’s even a more complex question than the observable relationship between freeway widening and congestion. (It also matters, a lot, how exactly social programs work; you can’t simply talk about “welfare” if you’re trying to actually understand how to do social programs well. My understanding is the simpler, the better.)

But other than welfare—in fact, almost everywhere—genuine conservatives are cautious, aware of how fragile our current order can be, and humble, even skeptical, in terms of the ability of policy to fix human problems without unintended consequences.

Everything we’ve done to cities in the last century, and the way in which we’ve totally oriented our land use around the car, is the sort of massive experiment that conservatives should look askance at. And here, the notion that you could ram 20-lane freeways through cities and out into the countryside without altering many other variables is the kind of technocratic, top-down hubris conservatives warn about. They should be as skeptical of traffic engineers as social engineers.

Induced demand—which can sound like some sort of lefty anti-car theory—fundamentally embodies a very conservative way of thinking about the dynamic and unpredictable nature of human behavior.

The fact that urbanists do tend to lean left is mostly an accident of American politics and culture war, and it has very little to do with most of what’s being advocated at heart. I’m not sure how many people who write about induced demand think about it the way I just outlined—but the phenomenon speaks for itself.

These are not left or right concerns. They’re just human concerns—having a good place to live, having lots of ways to get around, and not wasting hours in traffic.

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Related Reading:

The Path of Most Desire

The Housing Crisis is a Policy Problem

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