In 2008, the city started the Summer Streets program, in which certain roadways were closed to car traffic during parts of weekends. In August, the city tried out its first Shared Streets day in Lower Manhattan, during which cars could drive into the historic zone but were advised by the police upon entering that they should travel no more than five miles per hour.

In Paris, Mayor Hidalgo described her effort to pedestrianize major arteries as an “almost philosophical project, which consists of seeing the city in another way than through the use of cars.”

Imparting that kind of vision should be fairly simple in New York, a city where auto ownership is expensive and difficult.

But New Yorkers are a stubborn lot, fiercely protective of the familiar. When, in 2009, the Bloomberg administration first proposed putting bike lanes along Prospect Park West, progressive residents of Park Slope were up in arms in protest. (“Don’t get me wrong, I love bike riding, but …”

There is often initial resistance to pedestrianization, said Michael Replogle, former director of the Institute for Transportation and Development Policy and currently the deputy commissioner for policy at the city Department of of Transportation. In many cities, restaurants and stores have argued that such efforts reduce customer flow and make deliveries difficult. (A number of European cities allow deliveries during off hours.) But Mr. Replogle said there were various solutions to address those concerns, and that studies of pedestrianization generally showed positive economic benefits for restaurants and retail stores.

“There’s no city that has tried it that said, ‘No we want to go back to cars,’ ” he said.

Ms. Trottenberg acknowledged that she didn’t know of any “full-throated program to close Broadway” to car traffic at the moment. But she added that the city was continuing to experiment.

In fact, Broadway meets many criteria that typically render pedestrianization a success: The 1, 2 and 3 subway lines offer ample public transportation from top to bottom to serve as an alternative to auto use. And the other north-south avenues, with their synchronized lights, are better for getting up and down Manhattan anyway. Who in their right mind wants to drive on Broadway?