Mr. de Blasio, who announced the plan last week, said the crowd size would determine when exactly vehicular traffic would be restricted. In a radio interview, the mayor said, “When there isn’t much pedestrian activity, the N.Y.P.D. will have the option of if they want to open up some more lanes to let more traffic flow.”

Advocates and bus officials complained that the street closings would slow buses, frustrating the commuters who depend on them.

14th Street busway

Also in Manhattan, passenger cars are all but banned in the heart of 14th Street, which was long known for its crawling traffic. Now, from 6 a.m. to 10 p.m. daily, only buses, trucks and emergency vehicles are allowed to drive on the street between Third and Ninth Avenues.

The result: A speedier bus ride than many can remember. And the view of the street is “startling,” my colleague James Barron recently wrote. “I could see all the way from First Avenue to Third Avenue.”

250 miles of bike lanes

On the heels of a surge in cyclist fatalities, city lawmakers in October passed a $1.7 billion plan that would lead to 250 miles of protected bike lanes. Corey Johnson, the City Council speaker, called it an effort to “break the car culture.”

There are now 1,250 miles of bike lanes, of which 126 miles are protected. Under the new plan, 30 miles of protected bike lanes must be built in the first year , and 50 miles each subsequent year.

Parking spaces

By some estimates, New York has about three million on-street parking spaces — almost one for every three people. Nearly all of those spaces are free of charge.