South of 42nd Street–Bryant Park is a large interlocking with six crossovers and switches. The original express tracks ended just to the south at 34th Street–Herald Square and some services switched to the local tracks at the interlocking. This was done because the PATH's Uptown Hudson Tubes already existed under Sixth Avenue south of 33rd Street, and so the Sixth Avenue Line local tracks were built on each side of PATH. The section between West Fourth Street–Washington Square and 34th Street–Herald Square, the only express section of this line, was originally built as a two-track subway with the provision to expand to four tracks later. The express tracks were added in the 1960s during the Chrystie Street Connection projects. As a result, they are placed under the local tracks and PATH using the deep-bore tunneling method. At West Fourth Street–Washington Square, the express tracks return to the same level as the local tracks, and the two pairs of tracks in each direction are connected with diamond crossovers. A flying junction just to the south connects the local tracks of the Sixth and Eighth Avenue Lines. The Sixth Avenue Line then turns east under Houston Street with an express station at Broadway–Lafayette Street.