"Build it and they will come." "New roads just trigger more congestion." "There's no way to build your way out of highway gridlock."
Are the charges of the transportation skeptics right?
Fresh findings on the impact of a major expansion on Interstate 270, a 12-mile stretch outside of Washington, D.C. suggest so.
In the mid-'80s congestion became close to unbearable on the roadway, which runs northwesterly from the (in)famous Capital Beltway into prosperous suburban Montgomery County. So the county applied to the Maryland state government for $200 million to expand the road up to 12 lanes. The state -- tapping chiefly federal funds -- agreed.
Now, less than eight years after the expansion was completed, the highway is again reduced to what one official described to the Washington Post as "a rolling parking lot." The daily auto and truck usage is running as high as 210,000 vehicles a day, beyond the official capacity of 190,000, in fact more than state highway officials had projected for 2010.
Welcome to what many transportation experts are now calling "induced traffic." The math they use is complex, but the theory straightforward: widened roadways create excess capacity. Drivers anxious to cut their driving times switch from other roads. Where roads (like I-270) lead to less developed outer suburbs, homebuilders see opportunity, there's a rush of residents out of the city and older suburbs, and congestion mounts.
In the five years before I-270 got widened, 1,745 new homes were approved in the 12 miles north of Rockville, the major community on the route. In the following five years, 13,642 were approved.
Other studies bolster the induced traffic thesis. In California, University of California researchers checked 30 urban counties from 1973 to 1990 and found that every 10 percent increase in new lane-miles generates a 9 percent increase in traffic.
Says David Walters, transportation expert at the University of North Carolina-Charlotte: "The availability of the transportation acts as a catalyst for more movement, so that the more roads we build, the more places we can drive, the more we drive."
The added traffic generated may be relatively small in the short run. But it grows and grows over the long term as people travel further and further on the new or widened roads to take advantage of less expensive land.
So government actually pushes sprawling development, siphoning growth and vitality from existing cities and closer-in suburbs. City and established suburb residents pay most of the bill. Longer commutes and trips end up generating more congestion, more energy consumption, more pollution.
But highway departments, anxious to justify road expansions, are rarely willing to feed induced travel into their calculations. "Engineering driven, developer and road builder backed, these agencies use an elaborate set of outdated models and design standards to deliver preordained answers," charges Hank Dittmar, former director of the Washington-based Surface Transportation Policy Project.
Induced travel has its skeptics. Highways don't cause traffic, they claim; increased population growth and increased economic activity are the drivers.
But the evidence for the theory isn't just U.S.-generated. Great Britain has been busy reinventing its basic transportation policy in the wake of a study by an official expert panel concluding that "induced travel can and does occur."
The British team even found, based on analysis of 60 cases worldwide, that where roads have actually been closed, or their capacity severely reduced, an average of 20 percent and as much as 60 percent of the former traffic disappears entirely -- isn't even siphoned off onto other roads.
Americans might scoff, suggest abandonment of any roads here would be unthinkable. But after a portion of Manhattan's West Side Highway collapsed in 1973, forcing closure of most of the route, 53 percent of the prior trips simply disappeared. No one can argue New York was seriously damaged.
San Francisco's Embarcadero Freeway collapsed in the 1989 Loma Prieta earthquake. Citizens and local officials decided not to rebuild it. Horrific traffic jams were predicted; they never materialized. Ditto seven years later, when the upper deck of San Francisco's unstable Central Freeway was torn down.
The widely predicted Bay Area gridlock didn't happen. Nor has Portland ever regretted closing the six-lane Harbor Drive beside downtown in order to build its handsome Tom McCall Waterfront Park.
Some areas would have a tougher time with highway closures. But at least we need to ask, much more critically, about each piece of highway construction or expansion: What will it really achieve? Could we use the money better-- for transit, for example? Or for subsidizing housing so that moderate-income folks don't feel forced to move to less expensive, far-out suburbs?
The "induced traffic" research at least gets us closer to an honest debate about those issues.