Hudson Yards is a 17-million-square-foot mixed use development currently under construction on the west side of Manhattan. Part of the development—including some 7 million square feet of office and residential space—will be built on top of the MTA’s West Side Yard. A 35,000-ton steel and concrete structure, which will support the buildings above without interfering with the layout and operation of the yard below—is currently under construction. Hudson Yards is expected to be completed in 2018. Gizmodo has more on the project’s unique engineering challenges.