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. There are three fare control areas – two at the northern end of the station, and one at the southern end. All lead directly to the Eighth Avenue Line on the upper level platforms; access to the Sixth Avenue Line on the lower level is via stairs and elevators from the upper level and/or the full-length mezzanine between the two levels. Several escalators are present, which go directly between one of the lower level platforms to its corresponding upper level platform. The elevators, added in April 2005 to make the station ADA-accessible, provide access to both levels and to the mezzanine. The track walls on both levels have a green trim line with a forest green border, though in many places the green tiles have been replaced with hunter green ones. Small tile captions reading "WEST 4" run below the trim lines at regular intervals. Hunter green I-beam columns run along all the platforms, alternating ones having the standard black station name plate; The signs read "West 4 Street", replacing the older signs which simply read "W4". Exits The station does not have an exit to Fourth Street itself anymore, though an exit formerly existed there. The northern exits are on the northern side of 6th Avenue and Waverly Place. Two staircases go up to the northeast corner, both built into alcoves of stores, and one to the northwest corner. The southern exits are at West Third Street, on the east and west sides of 6th Avenue. Two to the northwest corner (within building), one to the northeast corner (within building) of Sixth Avenue and Waverly Place One to the east side of Sixth Avenue north of Waverly Place One elevator and staircase on the northeast corner of Sixth Avenue and West Third Street One on the west side of Sixth Avenue at West Third