If you build more roads, more people will drive 

Writers, politicians, and especially real estate developers constantly argue that we need to widen more highways and build new ones in order to alleviate traffic. I've often suspected this was false.

I see traffic congestion as a price -- a price of living far from where you work, and a price for driving rather than taking other transit. If you build more roads, you briefly lower the price. People who otherwise wouldn't have driven now drive. People who otherwise would work at home now work at the office. People who otherwise would live closer to town now live further out.

DC Streets blog quotes a study in the American Economic Review that concurs with my view. Here's the heart of the blogpost:

Here’s the upshot: “Roads cause traffic.”

Professors Gilles Duranton and Matthew Turner analyzed travel data from hundreds of metro areas in the U.S., resulting in what they call the most comprehensive dataset  ever assembled on the traffic impacts of road construction. They write:

For interstate highways in metropolitan areas we find that VKT [vehicle kilometers traveled] increases one for one with interstate highways, confirming the “fundamental law of highway congestion” suggested by Anthony Downs (1962; 1992). We also uncover suggestive evidence that this law may extend beyond interstate highways to a broad class of major urban roads, a “fundamental law of road congestion”. These results suggest that increased provision of interstate highways and major urban roads is unlikely to relieve congestion of these roads.

I've been on this topic since Northern Virginia developers in 2002 tried to hike the sales tax in order to pave more roads. As then-State Sen. Ken Cuccinelli put it, "The developers are asking you to pay for their driveway."

Also, if we want to curb our gasoline use, this is one place a to start. An oil exec once told me that the biggest subsidy he gets is federal highway spending.

My solution: don't pave new lanes (on old or new roads) unless they can pay for themselves in tolls. Otherwise, as I've written about Gov. Bob McDonnell's transportation plan, you're susbidizing developers.

This is an issue where Left and Right can agree. After all, I found this study through liberal environmentalist website Grist.

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Timothy P. Carney

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