This is something I became aware of a while ago. It is a project similar to the "High Line" project in which they created a park on the old elevated subway tracks, but underground. People seem to be reclaiming space and turning it into green space, but this takes the idea to a whole other level. Check out the link from WCBS880.com, complete with video of the space as it is now.
Peter Hine Of MTA Real Estate Stars In Video Walking Tour Of Essex Street Trolley Terminal Which Some Hope Gets Coverted Into Underground Park Dubbed 'Low Line' « CBS New York
UPDATE: Dan Barasch and James Ramsey have a Kickstarter Campaign going to fund their Low Line project. Get involved in this unique idea by donating a couple of dollars to the project. Even $5 helps. <sigh> 'Gotta love the ingenuity of New York and its people!