Complex sentence: Line 3 Scarborough is currently the only subway line on the TTC network which is operated by one conductor allocated at the front of the train, on which he/she has the dual role of both operating the train and controlling the doors.
Split into simpler sentences: Line 3 Scarborough is the only line on the TTC network which is operated by one conductor allocated at the front of the train. He/she has the dual role of operating the train and controlling the doors.