New York City officials have carved out plazas for pedestrians in the middle of Broadway, a storied street where cars have ferried V.I.P.s in ticker-tape parades. They have taken away more and more traffic lanes and parking spots to make room for bikes and buses.

Now, officials are taking their biggest step yet in making cars unwelcome on streets that they have ruled since they started rolling off Henry Ford’s assembly line. They are moving to all but ban from one of Manhattan’s main thoroughfares.

The busiest stretch of 14th Street — a major crosstown route for 21,000 vehicles a day that links the East and West Sides — will mostly be off limits to cars. Drivers will be allowed onto the street for just a block or two to make deliveries and pick up and drop off passengers. Then they will have to turn off.

The sweeping restrictions come as New York and other cities fundamentally rethink the role of cars in the face of unrelenting traffic that is choking their streets, poisoning the environment and crippling public transit systems by trapping buses and light rail systems in gridlock.