North of 57th Street provisions were built to extend the four tracks northwest through Central Park and under Eighth Avenue through the Upper West Side to Inwood, along the route later built as the IND Eighth Avenue Line. The provision existed for many years and would have allowed for a grade-separated junction, allowing Broadway service via 59th Street and Eighth Avenue to coexist. The provisions from two express tracks were connected to the BMT 63rd Street Line in 1989. The provisions from the two local tracks remain unused.