ON a balmy night last June, the city’s Congressional delegation gathered for dinner at Gracie Mansion. Representative Anthony D. Weiner, who aspires to live in the mansion someday, knew he would have only a few minutes with the host, Mayor Michael R. Bloomberg. So he brought up the hottest topic he could think of: bicycle lanes, and the transportation commissioner who had nearly doubled the number of them, Janette Sadik-Khan.

“When I become mayor, you know what I’m going to spend my first year doing?” Mr. Weiner said to Mr. Bloomberg, as tablemates listened. “I’m going to have a bunch of ribbon-cuttings tearing out your [expletive] bike lanes.”

Mr. Weiner, a brash Democrat from Queens, had expected a bit of banter with his longtime adversary. Instead, Mr. Bloomberg adopted an exasperated, welcome-to-my-world expression. “His answer was, ‘Tell me about it,’ ” said a person who was there, one of two who recounted the tale. The mayor, some guests said, made it clear that Ms. Sadik-Khan was off on her own.

In four years as commissioner, Ms. Sadik-Khan has earned international fame for transforming the car-clogged streets of New York. She has directed the installation of more than 250 miles of bicycle lanes, turned parts of Broadway into pedestrian plazas and eliminated hundreds of parking spots across the city. Even some of her critics concede they are impressed with the scope and the speed of her achievements.