A new study by an economist at Johns Hopkins University and other researchers found that Stockholm’s decision to implement congestion pricing to control traffic in the center of the city also had a significant health benefit. (Vittorio Zunino Celotto/Getty Images)

When Stockholm began taxing vehicles to reduce traffic in the city center, the number of vehicles jamming its streets fell by at least 20 percent.

So did the number of children’s asthma cases — and by an even bigger amount, a new study says.

Researchers at Johns Hopkins University and other institutions who studied Stockholm’s congestion-pricing scheme found that the policy cut air pollution in the city center and reduced childhood asthma cases by nearly 50 percent. The long-term health benefit of congestion-pricing also seemed to become more apparent the longer the policy was in effect.

What’s perhaps even more striking is the possibility that the beneficial health effect from such a tax could be more profound in the United States, the authors say. That’s because even before congestion pricing went into effect in Stockholm, the city’s pollution levels were substantially lower than those in the United States as a result of stricter European regulatory standards.

The study — which according to the authors is the first to investigate a possible link between congestion pricing and health — comes as more jurisdictions in the United States are exploring similar strategies to reduce traffic in city centers or on commuter highways.

A task force convened by New York Gov. Andrew M. Cuomo (D) has recommended that New York City adopt a congestion-pricing plan that would charge a daily fee of nearly $12 for vehicles entering Manhattan below 60th Street. The state task force, Fix NYC, also urged the city to impose a surcharge of $2 to $5 on for-hire vehicles including taxis and ride-hailing services such as Uber and Lyft, the New York Times reports.


More jurisdictions in the United States are using congestion pricing to limit traffic in city centers and commuter highways. (Jahi Chikwendiu/The Washington Post)

Northern Virginia, which has had HOT lanes for years, this year began charging some vehicles nearly $50 to ride on a segment of Interstate 66 inside the Beltway at rush hour — a policy that has stirred outrage but also made trips on the 10-mile stretch of interstate faster and more reliable, backers say.

Sweden’s plan to tax vehicles heading into the city center generated outrage — at first anyway, Streetsblog.org has reported. The city first conducted a seven-month experiment with congestion pricing from January to July 2006; in August 2007, the tax became permanent. The city began charging vehicles $2.60 to drive downtown during the regular workweek. The tolls were collected automatically using license-plate scanners to bill drivers.

As traffic declined, so did air pollution. The amount of nitrogen dioxide in the air declined by nearly 8 percent; the amount of  soot and other particulate matter declined by about 15 percent, the study says.

Emilia Simeonova, an assistant professor of economics at Johns Hopkins’ Carey School of Business, was working at Stockholm University when the tax went into effect. Her work focuses on the intersection of economics and health, particularly on children and families, so she wondered whether the traffic tax might have health benefits, too.

“I said, ‘Wouldn’t that be neat to see if there’s an effect of the congestive pricing system on the health of children?’ ” she said in an interview. “It was like a no-brainer.” 

So Simeonova — along with colleagues at Princeton University, the University of California at Berkeley and Stockholm University — focused on asthma attacks. In particular, they sought health records on children younger than 5. Children that age are more likely to receive emergency treatment for asthma attacks, as their families are generally less likely to know how to prevent and treat the condition, which is marked by chronic inflammation of the airways and exacerbated by air pollution.

Using data from Sweden’s municipal environmental agencies and its national health-care system, the researchers analyzed young children’s inpatient and outpatient hospital visits during the trial period for congestion pricing, the interim and after the tax became permanent. The data covered a period from 2004 to 2010.

They saw an immediate impact that became more significant as time went on. During the trial period for congestion pricing, the number of pediatric asthma cases fell from 18.7 visits per 10,000 children to 16.4 visits — a reduction of 2.3 visits, or about 12 percent. After congestion pricing became permanent and remained so for a few years, the number of acute asthma cases in young children dropped by 8.7 visits, or nearly 47 percent.

As the researchers point out, such a reduction could have a huge impact in places such as the Bronx, the New York City borough crisscrossed by some of the most congested highways in the United States, including almost daily bumper-to-bumper traffic from the George Washington Bridge crossing. The borough also has a high incidence of asthma among children, the study says.

But no one’s holding his breath. The idea of charging drivers more to enter the city at peak periods has been proposed and rejected many times, including an unsuccessful attempt in 2008 led by New York City Mayor Michael R. Bloomberg.  On Tuesday, the Associated Press reported that the outlook for congestion tolling in New York appears poor again.

The new study, a working paper for the National Bureau of Economic Research, can be found here.

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