Clark Williams-Derry

More roads = more traffic

Research director for the Seattle-based Sightline Institute, Dec 20, 11.

Tagged with sprawl, roads, vehicle miles traveled

Tuesday’s news carries a story that I’ve been expecting for a while: Connecting Washington, a task force convened by Washington’s governor, has called for $21 billion in new transportation investments over the next 10 years. I haven’t seen the recommendations themselves, only the news report. But it looks like the money would get spread around a bit—with some for ferries and some for transit—but from what I can gather, most of the money would be slated for roads.

So in the upcoming months, I expect we’ll be hearing a lot about how investing in new roads will help clear up traffic problems, particularly in greater Seattle and the Washington side of greater Portland.

But a study that’s been sitting on my desktop for a while—which I count as the single most interesting transportation paper [PDF] I ran across all year—suggests otherwise. Co-authored by researchers Gilles Duranton and Matthew A. Turner from the University of Toronto, it’s a careful and remarkably thorough analysis of the relationship between urban highway space and traffic volumes in the U.S. And its key finding is straightforward:

For interstate highways in the densest parts of metropolitan areas, we find that vehicle kilometers traveled [vkt] increases in exact proportion to highways.
In short, the authors find that building new urban highways simply increases traffic volumes—not in some general, intuitive sense, but in the sense that a 1 percent increase in urban highway space increases urban road travel by precisely 1 percent.

Full Story: Highway to hell: More roads = more traffic
Source: Grist, December 15, 2011

More Commentary