Complex sentence: Fixed block signalling has been used throughout the system since the inception of TTC subway in 1954 except for the Scarborough RT, which uses automatic train control (ATC), meaning it could be operated autonomously.
Split into simpler sentences: Fixed block signalling has been used throughout the subway system since the opening of Toronto's first subway in 1954. Line 3 Scarborough uses automatic train control (ATC), meaning it could be operated autonomously.