Suburban Nation - Andres Duany [40]
If traffic is to be discussed responsibly, it must first be made clear that the level of traffic which drivers experience daily, and which they bemoan so vehemently, is only as high as they are willing to countenance. If it were not, they would adjust their behavior and move, car-pool, take transit, or just stay at home, as some choose to do. How crowded a roadway is at any given moment represents a condition of equilibrium between people’s desire to drive and their reluctance to fight traffic. Because people are willing to suffer inordinately in traffic before seeking alternatives—other than clamoring for more highways—the state of equilibrium of all busy roads is to have stop-and-go traffic. The question is not how many lanes must be built to ease congestion but how many lanes of congestion you want. Do you favor four lanes of bumper-to-bumper traffic at rush hour, or sixteen?
This condition is best explained by what specialists call latent demand. Since the real constraint on driving is traffic, not cost, people are always ready to make more trips when the traffic goes away. The number of latent trips is huge—perhaps 30 percent of existing traffic. Because of latent demand, adding lanes is futile, since drivers are already poised to use them up.4
While the befuddling fact of induced traffic is well understood by sophisticated traffic engineers, it might as well be a secret, so poorly has it been disseminated. The computer models that transportation consultants use do not even consider it, and most local public works directors have never heard of it at all. As a result, from Maine to Hawaii, city, county, and even state engineering departments continue to build more roadways in anticipation of increased traffic, and, in so doing, create that traffic. The most irksome aspect of this situation is that these road-builders are never proved wrong; in fact, they are always proved right: “You see,” they say, “I told you that traffic was coming.”
Adding lanes adds traffic: although it is well proven, induced traffic has had little impact on transportation policy
The ramifications are quite unsettling. Almost all of the billions of dollars spent on road-building over the past decades have accomplished only one thing, which is to increase the amount of time that we must spend in our cars each day. Americans now drive twice as many miles per year as they did just twenty years ago. Since 1969, the number of miles cars travel has grown at four times the population rate. bbAnd we’re just getting started: federal highway officials predict that over the next twenty years congestion will quadruple. Still, every congressman, it seems, wants a new highway to his credit. bc
Thankfully, alternatives to road-building are being offered, but they are equally misguided. If, as is now clear beyond any reasonable doubt, people maintain an equilibrium of just-bearable traffic, then the traffic engineers are wasting their time—and our money—on a whole new set of stopgap measures that produce temporary results at best. These measures, which include HOV (high-occupancy vehicle) lanes, congestion pricing, timed traffic lights, and “smart streets,” serve only to increase highway capacity, which causes more people to drive until the equilibrium condition of crowding returns. While certainly less wasteful than new construction, these measures also do nothing to address the real cause of traffic congestion, which is that people choose to put up with it.
We must admit that, in an ideal world, we would be able to build our way out of traffic congestion. The new construction of 50 percent more highways nationwide would most likely overcome all of the latent demand. However, to provide more than temporary relief, this huge investment would have to be undertaken hand in hand with a moratorium on suburban growth. Otherwise, the new subdivisions, shopping malls, and office parks made possible by the new roadways would eventually choke them as well. In the real world, such moratoriums are rarely possible, which is why road-building