Unite d'Habitation le Corbusier Marseille from esmuz via flickr
Robert Moses lives!!!
The zoning laws that currently guide city planning were created in 1961, and allowed for developers who agreed to build small and off the street to sell their air-rights to nearby building sites, allow them to build higher than the regulations permit.
Most of the city's public housing projects were built before then, from the 1930's-1960's, back when Modernist, Le Corbusier, "tower-in-the-park" ideas of one largish tower surrounded by green space were all the rage.
Thus, many of them are sitting on unused open space or below unused air rights that they could sell off to the highest bidder, and have already looked into doing so in Chelsea and Hell's Kitchen.
Area pols have figured out that there are major loophole possibilities here, since public housing projects are governed by the city zoning laws, but aren't by the rigorous land use process that other property owners are who want to auction off air rights.
For more, check out my story in Monday's amNY.
--David Freedlander