Can We Build Our Way out of Congestion?

The 2007 Urban Mobility Report contends that, in theory, it is possible for regions to build their way out of congestion. In regions where traffic growth exceeded the growth in road capacity by a wide margin, congestion got worse faster than in communities with a smaller gap. In the short run, it appears, you can mitigate congestion by adding capacity, as shown in the chart above. (I’ll defer discussion of the problem of “induced demand” and what happens over the long run when that new capacity enables dysfunctional land use patterns.)

Here’s the problem: Adding new transportation capacity is really expensive! Here’s how the Urban Mobility puts it:

It would be almost impossible to attempt to maintain a constant congestion level with road construction only. Over the past 2 decades, only about 50 percent of the needed mileage was actually added. This means that it would require at least twice the level of current-day road expansion funding to attempt this road construction strategy. An even larger problem would be to find suitable roads that can be widened, or areas where roads can be added, year after year.

As regions urbanize, acquiring the rights of way to expand roadway capacity increases exponentially. And here’s a factor that the study does not mention: As large developing countries like China and India become major consumers of construction materials, they drive the global cost of those materials. The real, inflation-adjusted cost of road building is more expensive than it used to be. As the cost rises, the Return on Investment declines.

What worked in the 1950s — building Interstate highways with inexpensive construction materials and acquiring cheap right of way by running roughshod over the property rights of poor communities — won’t work today. Transportation strategy must adapt to the reality that adding capacity is more expensive than it used to be. Unless we want to tax ourselves into oblivion, we have no choice but to pursue other strategies.