The IND mezzanine opened in various phases. Around August 2011, the William Street end of the Eastern mezzanine opened, coinciding with the opening of the 135 William Street entrance. In October 2011, due to a major realignment of the temporary transfer passageway between the Eighth Avenue Line station and the Lexington Avenue Line station, parts of the Western Mezzanine opened as well. The realignment sent passengers through the construction site of the Fulton Building. By January 2012, the Western Mezzanine had opened to the northbound Nassau Street Line platforms. In June 2012, an underpass under the Lexington Avenue Line platforms, traveling approximately under Fulton Street, re-opened and was connected to the Western Mezzanine. With the opening of the new passageway, the older underpass connecting to southbound Lexington Avenue Line platform was simultaneously closed. As a result, the Western Mezzanine was substantially completed. On August 2, 2012, the southbound Nassau Street Line platform was connected to the Eastern Mezzanine. An MTA press release regarded this as the substantial completion of the entire IND mezzanine.
