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More Highways, Less Congestion

The theory of ‘induced-demand’ fails the road test.

Mar 7, 2011, Vol. 16, No. 24 • By JONATHAN V. LAST
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One of the reasons the unenlightened masses tend to be so pro-highway is that there’s some opposing research that suggests, heretically, that the induced-demand effect is modest. The most intriguing of these counterarguments came from a group of engineers and statisticians at the University of California, Davis, in 2002. The team reexamined the results of the original study by Hansen and Huang, using the same data, but a different mathematical model. They concluded, “the size of the induced-traffic effect that can be attributed to capacity enhancements may be sufficiently small that its detection .  .  . would be difficult, if not impossible.”

And in the real world, adding highway capacity can prove quite helpful. The Texas Transportation Institute’s annual Mobility Report, for instance, demonstrates an uncanny correlation between capacity and traffic congestion: Areas that add capacity tend to have lower levels of congestion. And induced demand doesn’t always -materialize. Take, for example, the city of Phoenix, a town built with almost no freeway system.

As a result, the Phoenix metro area historically had some of the worst congestion in the nation. Between 1982 and 2007, Phoenix decided to build the highways it should have had in the first place. They added so much asphalt that, according to the research firm Demographia, the city’s highway-lane-miles per capita grew by 205 percent. During that period, highway-vehicle-miles-traveled per capita increased by only 12 percent. And, like magic, traffic congestion plummeted.

Now what is true for Phoenix may not be true for Philadelphia. And building highways almost certainly induces some demand. The real issue, lost in all the statistical analysis and wonky planning, is, Why do we get in our cars in the first place?

That’s a question that drives Wendell Cox a little nuts. The principal at Demographia, Cox has spent a lot of time pushing back against the induced-demanders. He maintains that the entire framing of the issue is faulty: “Latent demand” for a highway, he notes, isn’t actually a desire to drive on that stretch of road. People only want the road as a means to an end. “Transportation is not a primary activity,” Cox explains. “There is no ‘love affair’ with the automobile. Driving is not something we would choose to do.” What we choose to do, for the most part, is go to our jobs.

A metropolitan area typically has about half as many jobs as people. But, because of geographical constraints, not every job is accessible to every person. Highways are, far and away, the most efficient way of delivering people to a job. When we add capacity to a highway, we’re actually expanding the universe of available jobs to everyone in the area. If that means that more people take advantage of the road space in order to find a job, get to work, or take a better job, that’s not a bug. It’s a feature.

In other words, a metric like “vehicle-miles traveled” is only superficially important. What we really care about is maximizing the number of potential jobs that people can reach, which increases affluence. Traffic, then, is a symptom of an economy with a mobile workforce, where workers can seek out better jobs with ease. Modern, multi-lane highways, even when they are sometimes congested, are the road away from serfdom.

Jonathan V. Last is a senior writer at The Weekly Standard.

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