Complex sentence: There was once an out-of-system passageway to Pennsylvania Station one block west, but this was closed in the 1990s and passengers now must walk at street level to connect to the commuter railroads.
Split into simpler sentences: There was once an out-of-system passageway to Pennsylvania Station one block west. This passageway was closed in the 1990s and passengers now must walk at street level to connect to the commuter railroads.