Complex sentence: There is an active tower just past the head end of the eastbound (railroad southbound) platform, and south of the station are bellmouths for a proposed line along the BMT Jamaica Line, or for a line under Jamaica Avenue.
Split into simpler sentences: There is an active tower just past the head end of the eastbound (railroad southbound) platform. This bellmouth for a proposed line along the BMT Jamaica Line, or for a line under Jamaica Avenue.