Skidmore, Owings & Merrill (SOM) is designing the new space, which will feature a huge skylight over what had been the Farley’s mail-sorting facility. “Imagine a space about as big as Grand Central, lit from above,” explains Roger Duffy, the SOM partner in charge of the project. By reusing the building’s existing steel trusses, his design “creates a dialogue between the history of the building and the new construction,” he says.

The new hall will allow Amtrak and Long Island Rail Road passengers to access platforms from the west, bypassing the existing Pennsylvania Station. A new underground concourse linking street-level entrances with the platforms, also designed by Duffy, has already opened. “It’s essentially a found space that now looks like the 21st century,” he says.

Pennsylvania Station serves some 650,000 passengers a day—some three times its intended capacity. Critics say that the station’s problems won’t be solved without the construction of a long-delayed tunnel under the Hudson River, which would bring additional tracks to the station. (ReThink Studio, headed by Jim Venturi, has suggested a way ​to increase capacity by extending and widening existing platforms and using a reduced number of tracks efficiently.) But Duffy believes that the Moynihan Train Hall will have a “profound” impact east of Eighth Avenue, because every passenger who uses it means one less passenger crowding into the existing station. “The big statement is west, but the effects are also east,” he said.

Crews employed by Skanska USA have already removed 6,000 tons of concrete and 800 tons of steel in preparation for construction of the new room, according to a Skanska spokesman. Meanwhile, two large tower cranes to facilitate skylight construction are expected to be place by the end of September, per SOM.

The train hall will be ringed by some 700,000 square feet of restaurant and retail space. Two of the biggest commercial real estate firms in the city, Vornado Realty Trust and Related Companies, will together contribute $630 million to the project in exchange for a 99-year lease. The other $970 million will come from public sources.

Plans to use parts of the Farley Building as a station were first announced in 1993 but foundered when the Postal Service refused to​ relinquish the structure. Then mail volume plummeted, and the Service abandoned much of the facility anyway. In recent years, the former mail-sorting room has been used for fashion shows and parties. Meanwhile, there were at least four previous iterations of the train hall, including two by David Childs (now a consulting partner at SOM) and one by HOK. The ​hall is expected to open in 2020.