Ms. Trottenberg said she was aware of Barcelona’s superblocks plan and would consider applying the concept in New York — if not the name. In urban planning circles, the term “superblock” has been used to refer to sprawling public housing projects in American cities. “We’re certainly formalizing things that are close to that concept,” she said. “There are a lot of different models, and there’s not a one-size-fits-all.”

The city tried a one-day “Shared Streets” test in August that promoted recreational use of a 60-block area of Lower Manhattan. The speed limit was reduced to 5 miles per hour, and people were encouraged to take to the streets alongside cars. The program was intended to expand on another initiative, “Summer Streets,” in which a section of Park Avenue south of 72nd Street and all of Lafayette Street were closed to vehicles on three August Saturdays.

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New York City tried a one-day “Shared Streets” experiment in August that promoted recreational use of a 60-block swath of Lower Manhattan. Credit George Etheredge/The New York Times

Hundreds of people participated, though not everyone got along. Pedestrians said the slower speed was not strictly enforced, while drivers complained about not being given enough warning and kept honking at people in their way.

Still, Paul Steely White, the executive director of the nonprofit Transportation Alternatives, said, “It helps give people a taste of what their life could be like if that space was reapportioned for people rather just for automobiles.”

In recent weeks, the organization has called on the city to reconfigure 14th Street in Manhattan as a “PeopleWay” to accommodate more pedestrians and cyclists when a section of the L train shuts down for repairs. The proposal would limit car traffic, add bus and bike lanes and widen sidewalks.

Ms. Trottenberg called it “an interesting idea,” noting that the city is working with the Metropolitan Transportation Authority, which operates the city’s subways and buses, to look at options.

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Pedestrians stroll through the neighborhood of El Born. Credit Daniel Etter for The New York Times

In Barcelona, the superblock is not a new idea. The first one was introduced in 1993 near a historic church, the Basílica de Santa Maria del Mar, in the El Born neighborhood in the center of the city. Two more superblocks followed in 2005 in Gràcia, a northern neighborhood known for its plazas and narrow streets.

But superblocks did not become a priority until Ada Colau, a housing activist, was elected mayor last year. Ms. Sanz Cid, the deputy mayor, said that instead of focusing on the big commercial developments favored under previous city-planning policies, the current administration was interested in “concrete, precise interventions” to directly benefit local residents. “We want to look back at the neighborhoods and rethink urban planning,” she said.

The superblocks are part of a comprehensive program to improve the city’s transportation networks and reduce their environmental impact, Ms. Sanz Cid said. The effort, called the Urban Mobility Plan, includes increasing bus service, extending train lines to the suburbs and tripling the number of bike lanes.

Josep Mateu, president of the Royal Automobile Club of Catalonia, which has about one million members, has called for more discussion of the superblocks plan. He described it as well intentioned and said he welcomed the city’s decision to test it in El Poblenou, a less trafficked area in Barcelona. But he added, “We cannot forget that the project does also have other, less positive effects.”

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Iñaki Baquero and Jaime Batlle teach architecture at the International University of Catalonia. Credit Daniel Etter for The New York Times

Mr. Mateu said that superblocks, if applied across the city, would significantly limit road capacity for vehicles without reducing the actual number of vehicles to the same extent. “There would be a considerable increase of congestion, which is the situation that produces more pollution,” he said. “It is true that there are areas that will lose vehicular traffic, but it is also true that this traffic would eventually move to other roads and other districts, leading to a strong division between winning roads and losing roads.”

He also noted difficulties some residents could have in gaining access to public transportation, a loss of parking spaces the program could create and negative effects it could have on businesses. “We should also take into account that the superblock project does not seem to be a priority” for Barcelona residents, he said, suggesting that issues like unemployment were more pressing.

Salvador Rueda, the director of the Urban Ecology Agency, the agency that designed the superblock model, said a lesson learned from earlier superblocks was that initial opposition gave way to acceptance, in part because of a growing consensus about the benefits. No one has sued the city to remove a superblock, Mr. Rueda said. “Now we know that the main problem is the resistance to change that occurs at the beginning of the implementation of the superblocks.”

In Gràcia, where more than two-thirds of the streets were turned into public spaces, car traffic has dropped to 81,514 trips annually from 95,889 before the superblocks were established. Street life is thriving: Pedestrians now make 201,843 trips annually through Gràcia, up 10 percent from before the superblocks. Cyclists make 10,143 trips annually, a 30 percent increase.

The transformation has been even more significant in El Born, which by the 1990s had become so run-down that many people avoided it. “It was very tough to walk because they used to park cars on top of the sidewalk,” recalled Isabel Ruiz, 53, a longtime resident of the neighborhood.

On a recent afternoon, Jaime Batlle and Iñaki Baquero, who teach architecture at the International University of Catalonia, walked along El Born’s cobblestone streets pointing out changes the superblock had produced. Palm trees and benches were in the middle of streets. Trash was collected by an underground pneumatic system rather than trucks.

There were no curbs or sidewalks, only a single lane that Mr. Batlle called a “common platform” for drivers and pedestrians so that no one felt more ownership. The lane also forced drivers, when allowed in the street, to drive cautiously. Where storefronts once stood empty, customers now flowed in and out of restaurants, wine shops, hair salons and boutiques.

“It used to be full of cars, and now it’s not,” Mr. Batlle said. “Imagine that for the rest of the city. This is the kind of city we want everywhere.”

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