Under New York City is Another City
It is under New York City, a subterranean mass-transit mother of all transit systems that originally began in the 1920s. The Depression, the War, stalled it as funds were lacking. In the 1970's , some of the subway expansion tunnels were lengthened but not completed. Now, thousands work in a drippy, damp and humid underground world eight stories beneath NYC. These workers do it day and night, there are three shifts. Enough dirt has been hauled out from under Grand Central Station to cover Central Park in a foot of dirt. Some of the subway tunnels are 70 feet wide and 1800 ft. long. There will be six miles of new tunnels and a new underground terminal of 350,000 sq. ft.
The current subways carry 1.6 billion passengers a year and it is used by 5 million every day. Think incredible. The cost of the mammoth project to expand the NYC subway system is at $15 billion and scheduled for completion by 2019. It will bring riders into East and West Manhatten.
Carving a tunnel below existing sky scrapers requires new technology. To do so, they freeze the ground to -20F so not to destabilize the buildings above it. To do this, they inserted aluminum tubes inserted from the street and then a chemical was poured into the ground and cooled by a refrigeration plant. When the massive boring machine created the tunnel, the buildings above were not impacted.