Next up is a realignment of Vanderbilt Avenue and the pedestrian corridors beneath it, leading into and out of Grand Central Terminal. The idea behind the Vanderbilt Avenue project is, Mr. Washburn said, to “create a new gateway to Midtown.” The complication? “Vanderbilt is not on terra firma,” he said. “So Vanderbilt leaks. Every walking surface is below or above infrastructure, train sheds, subways, underground passageways. It’s an age-old problem, and the new public space offers us the opportunity to fix it.”

A number of city projects now pushing forward have, at some stage, been a series of enlightened doodles in his sketchbook. They include the reconfigured Coney Island plaza; rezoned West Chelsea with its High Line park; the planned interior improvements at Moynihan Station, across from Pennsylvania Station; and the brainstorming behind Mayor Michael R. Bloomberg’s much publicized micro-unit housing prototype. “We put a thesis worth of housing law into that tiny space,” he said. Recently, Mr. Washburn’s two-wheeled ride, the brawniest in the bicycle lineup, was parked on the ground floor of 22 Reade Street. The building is headquarters for the Department of City Planning and its commissioner, Amanda Burden. The driving force behind the design squad, Ms. Burden decided in 2007 that the city had gone for too long — since the 1970s — without the contributions of an urban design division. She felt new public projects and their attendant zoning changes could be best approached if drawn in three-dimensional scale from the perspective of a pedestrian navigating the city.

So she enticed Mr. Washburn away from W Architecture, his six-year collaboration with Barbara Wilks, whom he met when both shared studio space in Williamsburg. There, he said, “we used to sneak past the chain-link fence and the warehouses to get down to the East River and marvel at the views of Manhattan. It’s kind of ironic that we wound up designing what was probably the first public park in Williamsburg.” He was referring to the public plazas adjacent to the Edge.

Ms. Burden said the urban designers are making a difference in the way residents interact with the monolith they inhabit.

“Alex and his team have integrated design into city-making,” she said. “On the streets, design detail means everything. The team studies what makes great places: the width of the sidewalk, the spacing of street trees, the diversity of retail — and they integrate these details into our plans, turning projects into places that people want to be.”

Mr. Washburn, who worked for Hartman-Cox Architects in Washington, his hometown, after receiving a graduate degree from Harvard, has previous government experience. He left Hartman-Cox to become Senator Daniel P. Moynihan’s public works adviser and, later, the president of the Pennsylvania Station Redevelopment Corporation, a post accompanied by a perk: office space on the 62nd floor of his favorite skyscraper, the Chrysler Building. “It has noble bones,” he explained.