If You Build It, They Will Come

I have long thought, particularly when stuck in traffic, that the Federal Highway Act of 1956 AKA the Interstate Highway Defense Act might have been counter-productive. As it turns out, I may have been right:

As a kid, I used to ask my parents why they couldn’t just build more lanes on the freeway. Maybe transform them all into double-decker highways with cars zooming on the upper and lower levels. Except, as it turns out, that wouldn’t work. Because if there’s anything that traffic engineers have discovered in the last few decades it’s that you can’t build your way out of congestion. It’s the roads themselves that cause traffic.

The concept is called induced demand, which is economist-speak for when increasing the supply of something (like roads) makes people want that thing even more. Though some traffic engineers made note of this phenomenon at least as early as the 1960s, it is only in recent years that social scientists have collected enough data to show how this happens pretty much every time we build new roads. These findings imply that the ways we traditionally go about trying to mitigate jams are essentially fruitless, and that we’d all be spending a lot less time in traffic if we could just be a little more rational.

The point seems to be that marginal increases in the number and size of roads, slowly and over time, changes habits and preferences in such a way as to produce more traffic. The alternatives suggested include enormous over-capacity (a “100 lane highway”) or some sort of disincentive scheme like congestion pricing or raising parking fees.

10 comments… add one
  • CStanley

    The problem is poor planning and zoning. We don’t load the kids in the car in order to check out the new lanes of the highway, we do it to get to the new Super WalMarts and Best Buys.

    Instead of handling pent up demand, the building that accompanies new or expanded roads creates additional demand.

  • Super WalMarts and Best Buys are the creatures of the highway system. The highways make it possible to go where land and rents are cheap and where property and sales taxes are low.

  • Tim

    There’s also providing people with increasingly viable alternatives. In Chicago, our fractured system of regional governance and the Highway Act combined to make the corridor northwest of O’Hare a major employment center that is for all intents and purposes inaccessible via transit (unless you happen to live close to a Metra station and work at one of the few facilities close to one or have an employer that will bus you from same).

    The road opened the area up to jobs meaning there were people who needed to get there – and the only way is the highway.

  • Positive feedback loop. The roads make new areas available for development which induces lobbying for more roads which open up new areas for new new development.

    That’s the reasoning behind the title of this post.

  • TastyBits

    In a compact urban environment, there is little space for new businesses to open. This does have the benefit of keeping the riff-raff in their place.

  • You read between my lines so well.

  • jan

    There’s a counter movement out there mainly exercised in socially progressive communities. It’s referred to as “traffic calming,” calling for restrictive reconfiguration of existing byways and highways in order to discourage and ultimately eliminate traffic density.

    For instance, a 4-lane boulevard would be reduced to a 2-lane road by turning a large swathe of the center roadway into a landscaped or turn-out median strip with generous bicycle lanes provided in both directions. A 2-lane road is also altered by tightening up the width of its traffic lanes in order to provide a continuation of bike lanes on both sides. Oftentimes, corner turn lanes have evolved into shrub-filled bulges making right turns impossible, and forcing traffic into a straight forward flow.

    All of these roadway adjustments have been made to encourage the use of bicycles, walking, and mass transit over vehicular transportation. That, at least, is the hypothetical reasoning promoting these changes. However, the reality has been traffic gridlock all day long, versus what used to be only early morning and late afternoon rush hour slowing. As for those bike lanes — they remain scantily occupied. The buses are equally empty. And pedestrians are primarily seen in the promenades/enclosed shopping malls, where they have always been, as the traffic outside impatiently waits to gets nowhere.

  • TastyBits


    As reality keeps beating them about the head and shoulders, you can expect this petty nonsense to get worse. Rather than take off the clown attire, they will move-on to the next worthless theory to screw things up.

  • Jonathan Last makes a counterargument here, though it predates this particular study.

    Induced demand is a thing. I find the exactness of the reported results to be on the suspicious side, though that maybe the reporting. However, people take commute times into account when deciding how close or far from work to live and reducing congestion decreases time and increases desire. It’s also certainly the case that if we went in the Wayback Machine and didn’t build the Interstate system, everything would look different from how it does.

    From a city growth standpoint, though, I can’t help but think my home city has benefited from the concrete. At least in part because the explosive growth it has since obtained would not be possible otherwise. That can be considered zero-sum on a national level, maybe. I do think that throttling Interstates, or high cost-accrual of traveling, will backfire in the face of those that think that people will just leave the suburbs. I think it’s as likely as not that a lot of businesses will follow them out unless there are some really good public transportation options.

    On the other hand, where and how much it shows up often seems to depend on what you’re looking at. The Texas A&M Transportation Institute continues to show increasing capacity decreases congestion. Other studies, of course, come to different conclusions.

  • steve

    Induced demand? Then build no roads and you will have no congestion.


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