CityLab has an article about the continuing funding for road widening despite ample evidence that it only induces demand and worsens the problem. This is a teachable example on the limits to evidence-based policy making when faced with an issue defined by an entrenched popular narrative.
Critics of road widening argue that it creates "induced demand", or it invites more trips until the gridlock returns or even worsens. As economist Anthony Downs famously wrote, "On urban commuter expressways, peak-hour traffic congestion rises to meet maximum capacity." The CityLab article writes,
In 1955, urban observer Lewis Mumford wrote a series of essays in the New Yorker titled “The Roaring Traffic’s Boom,” in which he memorably compared a highway planner widening a congested highway to “the tailor’s remedy for obesity — letting out the seams of trousers and loosening the belt. [T]his does nothing to curb the greedy appetites that have caused the fat to accumulate... Downs’ iron law applies not only to U.S. cities, which have grown more traffic-jammed despite billions of dollars in fresh pavement, but also to those around the world. Highway expansions in Norway and Britain haven’t reduced congestion there, either. The principle now meets little opposition among economists and urban planners. “It’s widely accepted,” says John Caskey, who teaches induced demand as part of his urban economics course at Swarthmore College. “For economists interested in urban transportation, there isn’t really any debate.”... Caskey... explains the process, using Philadelphia’s Schuylkill Expressway as an example. “Think about what happens if you widen the Schuylkill,” he says. “Before, I was driving at 5 a.m. to avoid the traffic, but now that you widened it, I’ll start driving at peak time. Maybe I used to take transit on SEPTA, but now I’ll drive. By increasing the supply of expressway space, you’re going to lower the price in time, and you’re going to increase the volume of travel.” The hypothetically expanded Schuylkill might offer faster travel for a year or two, but any time savings will prove fleeting.
Critics point to a coalescing of vested interests consisting of vehicle owners and users, automobile manufacturers, construction contractors, officials of Transportation and other related departments, and politicians jumping on the gravy train. Instead, they advocate investments in mass transit, again pointing to evidence about its positive impacts in reducing congestion.
This is a teachable example. Despite the apparently overwhelming evidence, near consensus of the issue, on both evidence against road widening and in favour of investments in mass transit, road widenings are the norm even among US transportation authorities. So what gives?
The article contains the answer. The powerful coalition of interests aligned in favour of road widenings is aided by an even more powerfully entrenched popular perception.
The idea that a big highway will end up more congested than a smaller one still strikes many people as strange. “The whole notion of induced demand is a little counterintuitive,” says Sundquist. “Highway building seems like a straightforward thing to do. And it does make cars go faster — for a little while.” Caskey agrees. “I understand that if someone who drives everywhere sees traffic congestion, their immediate solution is to keep paving things. It’s sort of a natural reaction.” That makes the topic of induced demand a challenging one for policymakers. “Everyone with a driver’s license thinks they understand transportation,” says Rosenberg. Meanwhile, politically potent contractors, unions and automakers have an incentive to keep the public confused.
No evidence, howsoever rigorous, can shake-off this entrenched narrative. Dismantling it requires a counter narrative. This is illustrative of problems elsewhere in development, where evidence can do little on the face of entrenched narratives. Development, and many public policy responses, are, what Lant Pritchett calls, faith-based activities.
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