The Toronto subway uses a variety of signalling systems on its lines, consisting of a combination of fixed block signalling and moving block signalling technologies. The oldest signalling system is known as automatic block signalling and was designed for the system's heavy rail lines: Line 1 Yonge–University, Line 2 Bloor–Danforth and Line 4 Sheppard. Since 2022, Line 1 had been fully converted to automatic train control (ATC). The remaining lines use ATC: Line 3 Scarborough uses an early form of ATC known as transmission-based train control (TBTC), while Line 1 along with Line 5 Eglinton, a light-rail line under construction, use a modern form of ATC called communications-based train control (CBTC). Transmission-based train control (Line 3) Line 3 Scarborough uses SelTrac IS, a transmission-based train control system originally developed by Alcatel-Lucent (now part of Thales Group) as part of the Intermediate Capacity Transit System (ICTS) technology employed by Line 3, which is identical to that of Vancouver's SkyTrain and the Detroit People Mover. The system is designed to allow Line 3 trains to be driverless; however, due to safety concerns, an operator is stationed at the front of each train in a cab equipped with a display of signal indications; there are no track-side signals. To control train operation, each two-car married-pair has multiple on-board computers communicating with a central computer at Kennedy station. Transit Control at the Hillcrest Complex has a terminal connected to the Kennedy station computer. Communications-based train control (Lines 1 and 5) The TTC used "Urbalis 400", a communications-based train control system made by Alstom, on Line 1 Yonge–University. It is engaged in a phased implementation of CBTC to replace the fixed-block signal system on the entire line. CBTC first went live on Line 1 in December 2017 on the newly inaugurated extension between Vaughan Metropolitan Centre station and Sheppard West station. Since then, CBTC has been extended as far as Eglinton station. Effective September 24, 2022, Line 1 had been fully converted to automatic train control (ATC). CBTC requires a set of equipment on trains and at trackside to gather and transmit data to central computers, and to receive instructions back for train operation. ATC beacons and axle counters sit at track level to detect the passage of a train with the axle counters backing up the beacons. The track-level beacons transmit signals to onboard controllers installed on each train. Onboard roof antennas (Data Communications