The documentary gives the history of the two tunnels under the Hudson that Amtrak and commuter railroads depend on, and the controversy over reconstruction projects, especially since the Hurricane Sandy damage in 2012. The north tunnel (southbound) seems particularly vulnerable. The two tunnels are called the "North River Tunnels". In the past, the passenger would see an open area coming out of the tunnel in NYC before going into Penn Station (which has been completely remodeled). Now you don't see that. (You can't go right now because of the quarantines, but that is another matter.)
You can see the NJ/NY stateline inside the tunnels (as with the Lincoln Tunnel).
A permanent closure of one tunnel could cost NYC $16 billion a year.
Picture: embed from Wikipedia, north Bergen entrance, click for attribution