Accounting for the “iron law of congestion”

Why is building more lanes to address traffic issues not the best way to go? See the iron law of congestion:

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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 turning down a new highway lane remains politically challenging. “The highway construction system has vast momentum,” says Rose, the historian. “It has the authority of highway contractors, builders and labor unions. Here is something that labor and management really can agree on: a highway contract.” The auto industry, too, continues to benefit from ongoing investments that expand the “floor space” allotted to its products. In 2019, Tesla CEO Elon Musk tweeted that induced demand “is one of the most irrational theories I’ve ever heard.”

Build it and they will come.

As I read through the longer narrative in this article, it seems that the needs of the automobile were prioritized by drivers, businesses, those in the road industry, and politicians. This has been going on for roughly a century; would academic theories with evidence behind them be able to overcome these interests?

Perhaps at some point in the future, we will able to look back at “peak road” or “peak highway.” Is there a point where new roads and highways or lanes are no longer pursued in the United States? Even if population growth stagnated or slowed, would the United States continue to build roadways? Maybe the costs of maintaining all those roadways will help lead to this moment. It is hard to imagine other scenarios; even as fewer people drive to work compared to earlier years, traffic continues.

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