Why More Highway Lanes Means More Traffic

The following is an excerpt from City Limits: Infrastructure, Inequality, and the Future of America’s Highways by Megan Kimble.

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City Limits: Infrastructure, Inequality, and the Future of America's Highways

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American cities have been carved up by roads, places paved over to create the arteries that allowed us to get someplace else. In 1924, as the automobile became ascendant, Herbert Hoover, then the secretary of commerce, declared that “locality has been annihilated, distance … folded up into a pocket piece.” Our cities reflect that annihilation of locality, the dissolution of the neighborhood unit as an anchoring force. As we built highways through—and away from—cities, we could get anywhere we wanted to go, but we found ourselves increasingly farther away from one another. Across the country, cities are sprawling farther and farther into previously undeveloped areas, enabled by the longer and wider highways that carry people home.

Conquering distance has come at enormous cost. There’s the environmental cost: Transportation is the leading source of greenhouse gas emissions in the United States, accounting for a third of the country’s total emissions. The majority of transportation emissions come from passenger cars and trucks. Even as our cars have become more fuel efficient, even as electric vehicles have trickled onto the market, emissions from passenger vehicles continue to climb. In Austin, the average driver emitted 12 percent more greenhouse gases in 2017 than they did in 1990, according to Boston University’s Database of Road Transportation Emissions. In Dallas–Fort Worth, they emitted 27 percent more. Why? We are driving much more. “Suburban driving, including commuting, has been a major contributor to the expanding carbon footprint of urban areas,” the project’s lead researcher concluded. And Texas is the elephant in the room.

In 2018, the last time TxDOT did an analysis of the greenhouse gases generated on its roads, it found that on-road emissions in Texas account for nearly half a percent of total worldwide carbon dioxide emissions, more than some whole countries. Highway widenings in Texas alone have the potential to increase greenhouse gas emissions by more than thirty million metric tons by 2040.

There’s the financial cost: It is very expensive to get around in a car. Today, the average family in Houston spends nearly 20 percent of their household income on transportation, compared with only 9 percent in New York City, where most people use transit. That cost disproportionately burdens low-income people. In 2015, a Harvard study found that in counties across the United States, the longer average commutes were, the harder it was for families to escape poverty. Indeed, commute times were the “single strongest factor” in predicting upward mobility.

And then there’s the human cost, the roughly forty thousand people killed every year on our roads and the thousands more who get sick from breathing polluted air. Ten percent of the nation’s trafc fatalities occur in Texas. In 2010, a panel convened by the Health Effects Institute looked at seven hundred worldwide studies of trafcrelated air pollution. The panel found that within an exposure zone of roughly a quarter of a mile from a highway or major roadway, “the evidence is sufcient to support a causal relationship between exposure to trafc-related air pollution and exacerbation of asthma,” particularly among children. A 2013 study found that air pollution related to road transportation contributed to fifty-three thousand early deaths every year.

In 1974, Yacov Zahavi, an Israeli engineer working for the World Bank, introduced the idea of a travel-time budget, which is the amount of time every day we’re willing to devote to getting around. Whether in a rural village or a burgeoning metropolis, throughout human history the daily round-trip commute of any particular person has averaged out to just over an hour. Cities grew in concentric tree rings as we traveled farther but faster—on horseback, then in chariot and train, and, eventually, by car. In his book Traffic: Why We Drive the Way We Do (and What It Says About Us), the journalist Tom Vanderbilt writes, “Higher speeds enable life to be lived at a scale in which time is more important than distance … As societies, we have gradually accepted faster and faster speeds as a necessary part of a life of increasing distances.”

This is the bargain of Austin and Houston and Dallas, the bargain of most American cities—increased distance predicated on speedy access. Across the country, as we built bigger and faster roads, we increased the sheer volume of land available for settlement. So we sprawled, pushing the limits of our cities farther and farther into the distance, assuming that speed would always be available to us.

But there is a growing movement to resist this form of development, to recalibrate our bargain with speed. Of all the costs of a world built on speed, the most dangerous one might be the cost to community. Highways divided our cities and dispersed us to far flung suburbs, forcing us into cars to get anywhere worth going to. In the name of efficiency—of speed—we homogenized our cities, replicating placeless places across the varied wild landscapes of America. And as our communities fattened, we became increasingly anonymous and isolated within them, connected by wide rivers of concrete through which we hurtled at evolutionarily unthinkable speeds.

Once built, a highway can seem fixed, like a mountain—an unmoving feature of the urban landscape. But unlike a mountain, a highway breaks down. A highway is made of concrete, which degrades over time. Asphalt cracks. Steel rusts. Piers warp. Across the country, the urban highways we built so prolifically in the 1950s and 1960s are coming to the end of their physical life spans. Almost every city in the country has an aging highway coursing through its center that needs to be rebuilt. Mostly, state departments of transportation are dedicating billions of dollars to build those highways back wider and higher—despite decades of evidence that wider highways don’t fix traffic.

In 1962, an economist named Anthony Downs published a paper titled “The Law of Peak-Hour Expressway Congestion.” A native of Evanston, Illinois, Downs was a prolific researcher and spent his career as a consultant for think tanks, real estate developers, and the federal government. In the 1960s, he worked for the National Advisory Commission on Civil Disorders, which became known as the Kerner Commission after its final report, which Downs helped write, became a bestseller with its searing indictment of racism in America. The article he published in the journal Traffic Quarterly a few years before garnered significantly less attention.

Recent experience on expressways in large U.S. cities suggests that traffic congestion is here forever,” Downs began. It was only six years after President Dwight D. Eisenhower signed the Interstate Highway Act, catalyzing an unprecedented road-building boom. But no matter how many new roads were built, cars still slowed to a crawl at rush hour. This would seem to indicate, to frustrated commuters, “abysmally bad foresight by highway planners,” he wrote. But to an economist, these results were so predictable as to be axiomatic. Downs’s Law of Peak-Hour Traffic Congestion stated, “On urban commuter expressways, peak-hour traffic congestion rises to meet maximum capacity.” Just as demand for goods fluctuated, demand for travel was not static. When presented with a wide-open expressway, commuters would flock to that expressway, eschewing other forms of travel. Offered this new ease of access, they might decide to move farther from their job or school, extending their commute, or take trips that might previously have been too costly, in time or money. Demand increases, outstripping the newly created supply. “We thus arrive at the paradoxical conclusion that the opening of an expressway could conceivably cause traffic congestion to become worse instead of better, and automobile commuting times to rise instead of fall!”

Researcher after researcher would replicate these findings: More lanes meant more traffic. Between 1993 and 2017, the hundred largest urbanized areas in the United States spent more than $500 billion adding new freeways or expanding existing ones. In those same cities, congestion increased by 144 percent, significantly outpacing population growth. And yet, somehow, the truth behind this basic phenomenon—so basic that in 2011 two economists would call it the Fundamental Law of Road Congestion—eluded transportation engineers across the country, who insisted, year after year, project after project, that this time they would be able to solve traffic congestion.

Excerpted from City Limits: Infrastructure, Inequality, and the Future of America’s Highways, by Megan Kimble. Copyright 2024.