We hear it all the time: The road lobby insists that the only way to reduce mind-numbing traffic congestion on the roads they built is to build new roads. Federal funding gives huge blank checks to state DOTs, which tend to prioritize road building over transit, bridge maintenance or anything else. But mounting evidence suggests that building new roads won’t do anything to alleviate congestion.
In a paper to be published soon in the American Economic Review, two University of Toronto professors have added to the body of evidence showing that highway and road expansion increases traffic by increasing demand. On the flip side, they show that transit expansion doesn’t help cure congestion either.
We’ll spare you the calculus in the report. 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.
Duranton and Turner say building more roads results in more driving for a number of reasons: People drive more when there are more roads to drive on, commercial driving and trucking increases with the number of roads, and, to a lesser extent, people migrate to areas with lots of roads. Given that new capacity just increases driving, they find that “a new lane kilometer of roadway diverts little traffic from other roads.”
Given the huge amount of time consumed by driving (the average American household spent nearly three hours per day in a car in 2001), the authors note that “the costs of congestion are large.” Considering the economic value of time spent doing anything but sitting in bumper-to-bumper traffic, that becomes an economic problem of the first order.
“Transportation accounts for about one dollar in five that Americans spend,” Turner said in an interview with Streetsblog. “The interstate highway system eats up on the order of two dollars of every $100 of every market transaction in the United States. That’s a huge part of the economy and a huge part of people’s lives. Understanding how that works is really important; you don’t want to make mistakes on something that important. You don’t want to build roads and have them not deliver the effects that you expect them to.”
The implications for this research are significant, especially as Congress considers whether to integrate performance measures into federal transportation spending decisions. These findings make a strong case that Congress should not allocate too many scarce resources to road expansion when that’s not a real solution for congestion.