Induced Demand isn’t an argument against highways.

Watching the Coogs pwn Pedo State here, it’s a good feeling.

Anyway, Induced Demand (which I’ve also heard referred to as “Triple Convergence”) is the phenomenon whereby traffic rapidly expands to fill newly-created highway lanes.

From where I sit the arguments look a lot like those on global warming. There’s broad consensus across disciplines that it exists, though some claim otherwise. And it often gets used to justify really, really crappy policies. Like not building highways, or even tearing them down.

So here’s a few problems I see with the arguments.

1: You’re still carrying more people.

One of the more common arguments against widening goes like “such and such a highway averaged just 28mph at rush hour in [year]. Five years after they finished widening it, it was still clogged, averaging just 31mph in [later year]. Clearly, building more highways won’t fix congestion.”

The problem here lies in defining congestion as speed irrespective of capacity. If you have a four-lane highway moving at 30mph, you’re maybe carrying 80,000 cars a day. Going to a ten-lane highway while retaining the 30mph jam-up means you’re carrying north of 200,000 cars a day. That’s, at a minimum, 120,000 people who get to benefit from that capacity, even if it’s not moving super-fast. 120,000 people who got to move closer to where they want to live, got to take a different, better job, or just eat dinner somewhere on the far side of town.

2: You can narrow the rush hour

There’s a post over on Greater Greater Washington about “Myths about highways”, and under one of them the writer says “Neither Atlanta nor Houston’s multiple Beltways have erased congestion.” Right. Beltway 8 doesn’t have magical powers. But what Houston’s capacity increases have done is narrow the rush hour. Think about it.

Everywhere in the US (except, perhaps, Toledo) is jammed at 4:45 in the afternoon. But what’s it like at 6? 7? 8? In Portland you can leave downtown at 7:30, head north, and still hit a slowdown when you get to the Interstate Bridge. The Schuylkill Expressway in Philadelphia has one of the widest rush hours I’ve ever seen; that road jams up on Sundays. Everywhere, always. But in a city with massive capacity like Houston, the rush hour starts and ends quickly. I’m accustomed to doing 70+ on IH 10 into the mid-afternoon, and I’m likewise accustomed to free-flow on US 59 as early as 6:00, 6:30pm. Congestion shows up, and then it leaves. It doesn’t linger.

Looking at “rush hour” conditions creates a blinkered view. It’s almost impossible to build a non-toll highway system which will operate at LOS A at 4:30pm. But it’s quite possible to build one that will clear up within the hour. And it’s the difference between that highway and the one that stays clogged until 9pm that controls whether people eat dinner across town, how much they socialize with people in other places, whether a given metro area or region is truly connected.

3: You enabled the decisions which led to the induced demand

On that same “myths about highways” post, the author argues that, rather than take traffic off Lee Highway or Arlington Boulevard, a wider I-66 would have lead to “More people … living west of Manassas and working in downtown DC.” And what, exactly, is wrong with that? Given that some people want to live in the ‘burbs regardless, would you rather have a completely fragmented economy, where ‘burbians work in the ‘burbs and city people work in the city?

I recall reading in a book somewhere that San Jose’s West Valley Freeway, originally intended to provide a smooth bypass around downtown, instead attracted so much new housing development around it that it was congested within a year or two. But I don’t really see that as a negative.

Transportation networks enable long-term land use decisions. That’s why cities like Portland are so gung-ho on Streetcars, the permanance of the rails leads developers to build big mixed-use condoblocks. Freeways work the same way with lower-density uses, like single-family detached homes. 85 opened up the southwest flank of San Jose to development. Certainly if I was one of the developers building those neighborhoods, I’d be very happy that they filled up so fast that the freeway was jammed within a year.

Now, let’s say you don’t like the very idea of single-family housing, you think we should live in high-density apartment blocks, preserve open space, etc. OK, I’m receptive to that. I’ve read a bunch of stuff that says Dutch kids are happier than American kids, score lower on measures of dysfunction (teenage pregnancy, drug use, whathaveyou) and they certainly live denser than we do. But that’s not an argument against the freeway’s effectiveness. You’re not saying “The freeway doesn’t work,” you’re saying “the freeway isn’t conducive to the kind of development I prefer.”

Rhetorical Gimmicks

That list bit is, let’s be honest, a rhetorical gimmick. At the urban-suburban level, freeways promote low-density housing development. Most of the people arguing against freeways don’t really like low-density housing development. But if you make a facial argument that “low density development is bad,” you’ll get a lot of responses like “I like my backyard” or “what do you have against being able to find a parking space,” maybe even a backlash group or two.

On the other hand, if you can argue “freeways don’t work, they’re always jammed up,” you might very well get that same person who likes her yard, her two car garage, to say “well, I get stuck in traffic a lot, you might be right.” Might even get them to sign on to the idea that we shouldn’t build any more freeways, because traffic.

But it’s still a gimmick.

2 thoughts on “Induced Demand isn’t an argument against highways.”

  1. Highways are ugly. They divide cities, they divide hoods, they divide people. Highways are disgrace.

  2. What if the highway was there first? Uptown Houston, Bellevue Washington, Research Triangle Park. Their highways originally divided cows from cows… now they’re vital areas of business and commerce.

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