Twelve lanes of Interstate 35 slice through the heart of the city of Austin. But that doesn’t appear to be enough: The highway is often choked with truck and commuter traffic, which is only thickening as the regional population balloons. A recent study named Austin’s section of I-35 the worst bottleneck in Texas.
The Texas Department of Transportation, known as TxDOT, says it knows what to do: Widen the freeway. The agency proposes adding eight more lanes, at a projected cost of $7.9 billion.
Many Austinites are skeptical. The plan would require destroying an estimated 150 homes and businesses and further embed an infrastructural barrier that has served as a racial dividing line since the 1940s. It would also increase vehicle emissions at a time when Austin is struggling to reach its climate goals. But TxDOT maintains that environmentally friendly alternatives to road widening, like investing in transit, are off the table. “We are allowed, right now, to be furious, to break things, to do what is needed to demand to be heard,” Austin Chronicle columnist Mike Clark-Madison recently wrote.
Beyond the damage that a bigger I-35 would do to racial and environmental equity, many city officials doubt that TxDOT’s proposal would achieve its stated goal of reducing congestion. “We know from experience, in Texas city after city, that a simple addition of lanes will not fix our traffic woes,” wrote Austin city council member Gregorio Casar, in a letter to TxDOT.
There’s a name for the principle behind that apparent paradox: induced demand. Economist Anthony Downs is often credited with first articulating this “iron law of congestion” in 1962, as construction crews were hacking interstates through American cities. Downs published a seminal paper with a stark warning: “On urban commuter expressways, peak-hour traffic congestion rises to meet maximum capacity.” In other words, adding lanes won’t cure snarled traffic; the additional car space inevitably invites more trips, until gridlock is as bad as ever.
Downs was not the first to sound an alarm about the futility of expanding urban roadways — not by a long shot. In 1932, an association representing streetcars warned that “as fast as improvements are made in existing arteries of travel … they are saturated by an increasing volume of traffic.” 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.”
But a scan of current headlines reveals that a sizable chunk of the U.S. transportation sector still believes otherwise. South Carolina wants to spend $3 billion (and displace a minority neighborhood) to widen a freeway interchange “choked with traffic” near Charleston. In Los Angeles, Metro lists several highway expansion projects on its website under the heading “Less Traffic.” Maryland’s “Traffic Relief Plan” revolves around widening I-270 in suburban Montgomery County. The budget for Portland, Oregon’s Rose Quarter freeway expansion, which promises to both smooth the state’s biggest bottleneck and boost economic development in the predominantly Black neighborhood decimated by the original freeway’s construction, is now north of $1 billion.
If the definition of insanity is doing the same thing over and over and expecting a different result, then these transportation agencies seem certifiably nuts. Why is it taking so long — and why has it been so hard — for officials to recognize the futility of urban roadway expansion?
Highway planners aren’t crazy. But they are operating within a political and financial system that rewards new construction, despite its consistent failures to reduce congestion. A stroll through transportation history suggests that, unless those underlying incentives change, we’re likely doomed to continue repeating the same predictable, costly mistakes.
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