Why Widening Highways Doesn’t Fix Traffic—But Congestion Pricing Can

Interstate 45 is getting a $13-billion makeover in Houston. The project aims to reduce congestion by adding new lanes—a common story for the many highway expansions that are constantly happening across the U.S. In nearby Austin, Tex., I-35 is being widened as part of a $4.5-billion project, for example, and near Sacramento, Calif., an expansion of I-80 for close to $500 million is underway. A planned project that involves a major expansion of the New Jersey Turnpike will cost $10.7 billion.

Despite the massive price tags, these projects likely won’t reduce congestion for long. That’s because of a phenomenon that transportation researchers call induced demand: in areas with a lot of pent-up demand for driving, any new capacity from added lanes gets filled up quickly.

After a widening project, “congestion gets better for a little bit…, and then we’re back to where we were. And then somebody says, ‘Oh, we’ve got to widen again,’” says Susan Handy, a transportation engineer at the University of California, Davis. “So how far is it going to go?”

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It has already gone quite far—12-lane freeways bisect many major cities across the U.S. But there is another, less expensive type of traffic release valve: congestion pricing. Implementing it can be a win-win for cities and drivers, and it can free up cash to invest in a future where everyone can spend less time stuck in traffic.

Widening roads has been the go-to strategy for reducing congestion for at least a century, Handy says. It sounds logical and intuitive: if you have a limited supply of something in high demand, such as the ability to drive on a particular stretch of road, increasing the supply by adding new lanes should make that experience available to more people.

But increasing the supply of something also drops its cost—which can encourage more people to take advantage of it. More supply sometimes induces demand, or at least it allows more of any pent-up demand to be expressed. “Adding capacity makes driving cheaper from the standpoint of travel time and inconvenience and annoyance,” Handy says. More people might opt to drive on the road involved, which can eventually cause congestion to rebound.

Whether congestion returns to its previous levels depends on how much pent-up demand already existed—that is, the extent to which people had been choosing not to drive on that stretch of road because of the traffic. In highly congested areas, “everyone has some version of adjusting to traffic congestion,” says Kelcie Ralph, a transportation planning researcher at Rutgers University.

For Ralph, it’s her gym habits that are affected. Rather than driving to the gym that has a pool but is all the way across campus, she usually walks to the one that is closest to her office to avoid rush-hour traffic. Meanwhile someone else may choose to go to the grocery store near their house instead of driving to the Whole Foods in the next town over. Another might choose to stay home rather than driving to a nearby city to see a show.

The specter of stop-and-go traffic can prevent people from making trips altogether, says Mark Burris, a civil engineer at Texas A&M University. But more commonly, people simply adjust their travel time, route or mode of transport to avoid the traffic. People that commute to work might get up at the crack of dawn to beat rush hour, use a park-and-ride train or take a more roundabout path to the office. In the same way, when a highway is expanded, and congestion decreases, those commuters might opt to drive at rush hour and thus cause congestion to go back up.

But even if congestion returns, a widened highway can still accommodate more cars. Additional lanes increase the volume of traffic that passes through the congested area each hour, which means that more drivers are taking their preferred route, Burris says. “Over time, the congestion usually does come back—but it’s back with a whole bunch of benefits for the people that are traveling there,” he says. “They’ve got lifestyle differences that they really benefit from, and you can’t ignore those benefits.”

The question then becomes: Are those benefits worth the costs? That cost can be monetary, such as the sticker price of the expansion and the money required for ongoing maintenance. Then there’s the cost to human health and the environment. A gain in a highway’s capacity leads to a larger number of idling cars, which increases pollution from carbon dioxide, particulate matter and noise. This disproportionately affects people of color, whose communities are often bisected by urban highways because of discriminatory housing and development policies. Exposure to these pollutants can increase rates of lung disease, especially childhood asthma, heart disease and learning delays.

For urban planners like Ralph and Handy, widening is a means of doubling down on an unsustainable way of organizing our cities and towns (where most people have no choice but to be stuck in traffic) rather than diversifying the available modes of transport to suit many different needs. Major widening projects “lock us into decades of infrastructure that doesn’t build the future we want—or doesn’t build the future I want,” Ralph says. Often, she says, that money would be better spent investing in reliable and expansive train networks, better mass transit or safe walking and biking paths.

Fortunately for people stuck in traffic today, congestion pricing programs are short-term solutions that work like “escape valves” on congestion, and they’re being implemented across the country. Unlike widening, which decreases the cost of driving and thus causes demand to rebound, congestion pricing regulates the cost of driving in a particular area or lane to tamp down on traffic, Burris explains. Some, such as the program recently rolled out in New York City, include tolls for entering a certain high-volume area. London, Stockholm and Oslo also have similar programs.

Another popular approach to congestion pricing is the use of high-occupancy toll (HOT) lanes, faster-flowing lanes that drivers can pay to use. Highways near dozens of major cities have HOT lanes, including Houston, Seattle, Los Angeles, Salt Lake City, Utah, and Charlotte, N.C. Some HOT lanes have fixed toll prices that vary throughout the time of day; others have dynamic pricing models that update as often as every few minutes to keep traffic moving in the lane. Either way, drivers can choose whether to use them, and even those who don’t pay can still benefit; the presence of at least one lane of free-flowing traffic often speeds things up for everyone.

Congestion pricing programs cost far less to implement than highway widening projects, and they generate revenue that can be invested in other types of transportation, including mass transit. Because drivers experience these pricing programs’ costs directly, they can sometimes be a hard sell. But once people observe congestion pricing programs start to work, “you almost always see the approval rating head upward,” Burris says.

“When people see it, they like it—time and time again,” Ralph says.

And while widening a highway isn’t always a bad option, Ralph stresses the importance of considering what opportunities we forgo with this approach. Widening projects are sold to the public by touting benefits that won’t last, but their unadvertised costs will remain for decades. “I just want us to make conscious choices that consider the sort of pros and cons” based on what we realistically know will happen, she says—and to stop assuming that adding more lanes will break us out of the gridlock.