Complex sentence: Just to the north, the Rockaway Line gains two extra non-revenue tracks straddling the two revenue tracks; the western track is a test track, installed in 2001 and called the Far Rockaway Test Track, while the eastern track is used to relay shuttle trains.
Split into simpler sentences: Just to the north, the Rockaway Line gains two extra non-revenue tracks straddling the two revenue tracks. The western track is a test track, installed in 2001 and called the Far Rockaway Test Track, while the eastern track is used to relay shuttle trains.