In addition to connecting the BMT Nassau Street and IND Sixth Avenue Lines, as well as the Sixth Avenue Line to the Manhattan Bridge, the Chrystie Street Connection is one of the few completed sections of the SAS. The Grand Street station was built to serve as a transfer point between the Sixth Avenue and Second Avenue lines. The connection was built this way because the original 1960s plans for the SAS had Second Avenue and Sixth Avenue Line trains sharing two island platforms in a four-track layout, with connections from the Second Avenue Line to the Sixth Avenue Line and the Manhattan Bridge. Because Second Avenue Subway construction was halted in 1975, this station has only served Sixth Avenue Line trains since its opening. As part of the contemporary Second Avenue Subway construction, a new station is planned for construction below the current station during the fourth and final phase of the project; Phase 1 of the project on the Upper East Side opened on January 1, 2017, with Phase 2 in planning and two other phases with no funding commitments.