Americans are simply not driving as much as they used to; most experts agree we hit “peak car.” But that’s not the story according to the Department of Transportation’s forecasts, which year after year show skyrocketing demand for more roads—and year after year are proven wrong. Still, states use this data to fund lots of new construction. Wait—what?

Over at Vox, Brad Plumer explores what’s sadly become standard practice in transportation infrastructure: State agencies use outdated traffic projections to prove that so many more cars will be traveling along these routes in the future that they must get more funding for highway projects. This same data helps to fuel rampant—and often unnecessary—road construction across the country.

How much is the DOT inflating its projections? This one chart says it all. The various blue and red lines shown here represent aggregated state DOT forecasts for vehicle-miles traveled as far back as 1999. The shows Federal Highway Administration reports on how many miles were actually traveled. Each year the forecasted curve is just about the same—explosive, steep growth—but the reality never delivers.

All is not lost: As Plumer reports, states are starting to fight back, questioning the forecasts and pushing cities to at least provide more documentation for why new roads are needed. He looks at one expressway in Illinois, a proposed $1.5 billion, 47-mile toll road that was swatted down by citizens who begged the state to re-examine the data:

That project took a hit when Chicago’s Metropolitan Agency for Planning pointed out that only 20,000 vehicles were likely to use the expressway each day — about one-third of planned capacity and well below initial projections. That meant tolls wouldn’t be able to cover the expressway’s costs, and because of the way the project was financed, taxpayers would be on the hook for the shortfall, potentially diverting public money away from useful projects elsewhere.

This past May, environmental groups filed suit against the expressway, citing the harm the project could do to prairies as well as those inflated population and traffic forecasts. They didn’t have to wait long. On June 2, Illinois Gov. Bruce Rauner announced that he was removing the expressway from his list of approved projects, and it’s frozen for now.



AP Photo/Reed Saxon