»Precedents for pedestrian zones
The Vision42 Project, a tightly-organised group of Midtown activists, have a great page about the precedents for their proposed pedestrian zone along 42nd Street (and its accompanying light rail).
In many ways, creating an auto-free street is largely a political, rather than a technical decision. A main stumbling block to the reintroduction of light rail in New York has been a reluctance to take any street space away from automobiles. In Manhattan, where only 23% of the households even own cars, perhaps a different set of priorities ought to obtain.