What the companies came up with was a series of neighborhoods, each with its own cove. They also persuaded the city to use materials from the Twin Towers excavations to build the southwest tip of Manhattan, instead of dumping them at sea.

Battery Park City, which was built on this new landmass beginning in 1980, had its own designers and city planners, but it feels like much of this earlier plan. And, Mr. Willen wrote on his website, it got better. There is a creek, a large green space and what Mr Willen described as a “softer progressive housing system based on the city grid”, instead of the rather imposing buildings his report had called for (which were part of the modernist aesthetic of his day).

In 1980, Mr. Willen collaborated with urban reformer John Belle, director of the architecture and planning firm Beyer Blinder Belle, to design an alternative to Westway, the failed proposal to bury the West Side Highway south of the 40th street. Mr. Willen and Mr. Belle’s plan, which they called River Road, was an at-grade highway bounded by parks and recreational areas. Officials dismissed it as too expensive and too disruptive.

While the entire effort to improve the West Side Highway has been mired in civic gridlock for decades (other designers have also submitted plans, none of which have been realized), it is worth noting that this which was eventually built, at least below the 30s of the West, is reminiscent of The River Road proposed by Mr. Willen and Mr. Belle.

Mr. Willen’s final project was an alternative to the 500-foot ramp planned by the Central Park Conservancy to render the newly restored Belvedere Castle, the 19th-century Romanesque Revival structure that rises from a steep rock outcrop above from the Turtle Pond in Central Park, accessible to all. Conservationists had felt that the long ramp would destroy the character of the park. Mr. Willen, who late in life had mobility issues and used a wheelchair, collaborated with Mr. Gutman and Theodore Grunewald, a historic preservation advocate, on a design involving an elevator.

“Paul had an inventive itch,” said Kent L. Barwick, former president of the Municipal Art Society, “and he couldn’t leave a bad situation alone.”