Complex sentence: In 2009, there were disputes about the locations of the station entrances, which were all south of 96th Street, which divided the neighborhoods of the Upper East Side and East Harlem.
Split into simpler sentences: In 2009, there were disputes about the locations of the station entrances, which are all south of 96th Street. This was particularly of debate because 96th Street divides the neighborhoods of the Upper East Side and East Harlem.