Suburban Nation - Andres Duany [39]
WHY ADDING LANES MAKES TRAFFIC WORSE
There is, however, a much deeper problem than the way highways are placed and managed. It raises the question of why we are still building highways at all. The simple truth is that building more highways and widening existing roads, almost always motivated by concern over traffic, does nothing to reduce traffic. In the long run, it actually increases traffic. This revelation is so counterintuitive that it bears repeating: adding lanes makes traffic worse. This paradox was suspected as early as 1942 by Robert Moses, who noticed that the highways he had built around New York City in 1939 were somehow generating greater traffic problems than had existed previously. Since then, the phenomenon has been well documented, most notably in 1989, when the Southern California Association of Governments concluded that traffic-assistance measures, be they adding lanes, or even double-decking the roadways, would have no more than a cosmetic effect on Los Angeles’ traffic problems. The best it could offer was to tell people to work closer to home, which is precisely what highway building mitigates against.
Across the Atlantic, the British government reached a similar conclusion. Its studies showed that increased traffic capacity causes people to drive more—a lot more—such that half of any drivingtime savings generated by new roadways are lost in the short run. In the long run, potentially all savings are expected to be lost. In the words of the Transport Minister, “The fact of the matter is that we cannot tackle our traffic problems by building more roads.”2 While the British have responded to this discovery by drastically cutting their road-building budgets, no such thing can be said about Americans.
There is no shortage of hard data. A recent University of California at Berkeley study covering thirty California counties between 1973 and 1990 found that, for every 10 percent increase in roadway capacity, traffic increased 9 percent within four years’ time.3 For anecdotal evidence, one need only look at commuting patterns in those cities with expensive new highway systems. USA Today published the following report on Atlanta: “For years, Atlanta tried to ward off traffic problems by building more miles of highways per capita than any other urban area except Kansas City … As a result of the area’s sprawl, Atlantans now drive an average of 35 miles a day, more than residents of any other city.”az This phenomenon, which is now well known to those members of the transportation industry who wish to acknowledge it, has come to be called induced traffic.
The mechanism at work behind induced traffic is elegantly explained by an aphorism gaining popularity among traffic engineers: “Trying to cure traffic congestion by adding more capacity is like trying to cure obesity by loosening your belt.” Increased traffic capacity makes longer commutes less burdensome, and as a result, people are willing to live farther and farther from their workplace. As increasing numbers of people make similar decisions, the long-distance commute grows as crowded as the inner city, commuters clamor for additional lanes, and the cycle repeats itself. This problem is compounded by the hierarchical organization of the new roadways, which concentrate through traffic on as few streets as possible.
The phenomenon of induced traffic works in reverse as well. When New York’s West Side Highway collapsed in 1973, an NYDOT study showed that 93 percent of the car trips lost did not reappear elsewhere; people simply stopped driving. A similar result accompanied the destruction of San Francisco’s Embarcadero Freeway in the 1989 earthquake. Citizens voted to remove the freeway entirely despite the apocalyptic warnings of traffic engineers. Surprisingly, a recent British study found that downtown road removals tend to boost local economies, while new roads lead to higher urban unemployment. So much for road-building as a way to