Complex sentence: Some of the former elevated system of the BRT, dating to 1885, remains in use today, the largest being the J line running above Fulton Street from the Alabama Avenue station to a small section turning north after the Crescent Street station.
Split into simpler sentences: Some of the former elevated system of the BRT, dating to 1885, remains in use today. The largest section is the part of today's J line running above Fulton Street from the Alabama Avenue station to a small section turning north after the Crescent Street station.