The West Fourth Street station was built by the IND as the major transfer point between its two Manhattan trunk lines. It can be considered the "heart" of the IND system as it is the location of the zero point on the IND chaining. It is a bi-level station with a connecting concourse between the two platform levels. The Eighth Avenue Line occupies the upper level, while the Sixth Avenue Line uses the lower level. Both levels use identical platform arrangements–two island platforms between four tracks, allowing for cross-platform interchanges between local and express trains in each direction.