A few years ago, a block on Sancho de Ávila Street in Barcelona looked like a fairly typical city block—a couple of lanes of traffic, a row of parked cars on one side, and a bike lane on the other. Today, it’s almost unrecognizable. The cars are gone, there are picnic tables and planters in the middle of the street, and kids use the area as a playground.

It’s part of Barcelona’s “Superblocks” project, which transforms nine-block grids of the city into areas that prioritize pedestrians and cyclists instead of cars (on some streets, cars are still allowed, but they only have a single lane of traffic and lower speed limits). The city has created six superblocks to date but has talked about creating a total of 503. A new study looks at how that massive transformation would impact health—and calculated that it could prevent nearly 700 premature deaths each year, increase life expectancy by an average of almost 200 days, and save around 1.7 billion euros a year.

“When you build a [superblock], the idea is that you take away space from cars and put in space for people,” says Mark Nieuwenhuijsen, director of the Urban Planning, Environment and Health Initiative at ISGlobal, the Barcelona Institute for Global Health, and one of the authors of the study. “When you take the cars away, what is going to happen is that will reduce air pollution levels. Noise levels go down. There’s more space for green space that you can put there, and that also reduces heat island effects . . . and people do more physical activity, they don’t use the car as much.”

Reducing smog from cars has the biggest benefit for health, but reducing traffic noise also has a significant impact. Making the city cooler by adding green space also matters, since that mitigates the effect of heat waves, which can be deadly. Switching to electric cars would help cut pollution and noise somewhat, but it doesn’t have as much benefit as rethinking urban design. “You definitely still need to have the same infrastructure for electric cars as normal cars so you still would have this strong heat-island effect because you still need to have the asphalt there,” says Nieuwenhuijsen. He notes that some of the air pollution from cars comes from tires, not the exhaust—and electric cars still create that type of pollution. If it’s easy to drive electric cars, people will still be less likely to walk or bike or take public transit.

If Barcelona implements its planned changes for the entire city, the result will cover far more area than Oslo’s car-free city center or a car-free area in Madrid, both of which are around one square kilometer; Barcelona is about 80 square kilometers. “It would be a much bigger impact,” he says. Because traffic can still flow around the perimeter of the superblocks, it also might be somewhat easier to implement than a fully car-free city. “There’s so much invested interest in the car that it’s very hard to get the car completely out of the city.”

Something similar could happen in other cities. A city council member in Seattle, for example, is interested in bringing a six-block superblock to Seattle’s Capitol Hill neighborhood. The design would be less effective in typical sprawling American suburbs, says Nieuwenhuijsen, but “where you get a bit of density, I think that would work quite well.” Where it does work, it can have benefits beyond health—as people gather at playgrounds and parks that replace streets, meeting neighbors, for example, and as greenhouse gas emissions shrink and green spaces grow. “A lot of people live in cities or are going to be living in cities in the future,” he says. “So we need to make these cities also very livable, and healthy. We need innovative ideas like the superblocks to do this.”