Signalling of the Toronto subway

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. The remaining lines use automatic train control (ATC): Line 3 Scarborough uses an early form of ATC known as transmission-based train control (TBTC), while part of Line 1 as well as Line 5 Eglinton, a light-rail line under construction, uses or will 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 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.[1]

Communications-based train control (Lines 1 and 5)

The TTC uses "Urbalis 400", a communications-based train control system made by Alstom, on a portion of 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.[2] Since then, CBTC has been extended as far as Queen station.[3] Implementation on Line 1 was to be fully completed by 2019, but as of February 2018, completion is expected to be one or two years later.[4]

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 System antennas) transmit information such as speed and location from the controllers to Trackside Radio Equipment which relays the data to central computers and to the TTC's Transit Control Centre. The central computers send speed and braking instructions back to the train, whereby the central computers are effectively directing each train. With computers operating the train, trains can operate safely on closer headways than with the fixed block system. CBTC allows more frequent service and increased line capacity.[4]

With the old fixed block signal system, the TTC can schedule 25.5 trains per hour on Line 1, occasionally operating up to 29 per hour. With CBTC, the TTC can operate 30 to 32 trains per hour with a more consistent frequency. However, this goal depends on how well the TTC can manage dwell time in stations, crew changeovers and turnaround at terminals.[4][5]

The grade-separated section of Line 5 Eglinton, between Mount Dennis station and Science Centre station, will also use CBTC. Unlike on Line 1, the system on Line 5 will be supplied by Bombardier Transportation using its Cityflo 650 technology.[6]

Fixed block signalling (Lines 1, 2, and 4)

As of 2018, fixed block signalling is used on the section of Line 1 Yonge–University where CBTC is not active, and all of Line 2 Bloor–Danforth and Line 4 Sheppard. It uses a combination of wayside block signals and interlocking signals as light-based indicators to give instructions to train operators. This system, also called the NX/UR system of signalling, is also used on the New York City Subway, the Chicago "L", and the MBTA subway in Boston.

With fixed block signalling, the line is subdivided into blocks, each protected by a signal that train operators must obey. At the beginning of each block, there is a train stop mechanism to trip the train's emergency brakes if its operator disobeys the signals. For safety, the system requires that there be a gap of two full blocks between trains. This requirement reduces the number of trains that can operate on the line compared to using automatic train control.[4]

Overview

The system works on fixed signal blocks (a section of track that can be occupied by a train), with lit aspects indicating whether it is safe for a train to proceed into the next fixed block. Interlocking signals or protected signals are used where track features such as crossovers and pocket tracks exist where it is possible to route trains in either direction. The signals are directly connected to a trip arm that has the ability to stop a train if it violates a signal (runs a red light). This safety method is identical to that of the New York City Subway system.

If a train is occupying a block, the next two to four signals behind the train will be red with the trip arms in the danger position so that a train cannot proceed into the area. This allows for a safe stopping distance, even if a train behind violates a signal (the trip arm would trip the train's emergency brakes).

Grade timing is a method of speed control that is worked into the signalling system. In a grade timed section the signal preceding the timed block has a lunar white aspect below the coloured signal. The following signal is red (only because the section is timed) and the signal will blink the red aspect (or the top red aspect in a home or interlocking signal) for a predetermined time before the signal clears. In addition to lunar white signals, grade timed sections are sometimes indicated by a sign with the letters "GT", or simply "T", in white.

Station timing, a method of evening out trains, has been imposed on certain stations with interlocking (or home) signals. These signals turn to a red aspect as a train passes it, and is forced red for a variable amount of time. This time depends on the distance between the last train that passed the signal, and the train that comes after the next train. This system is computerized, and can accurately calculate the relative distances. If the next train is closer to the train before than the train after, then the signal will hold the train at the station. If the next train is closer to the train after it than the train before it, then the signal will clear.

There are several limitations to this signalling system that can result in "signal problems" and "signal delays". One of the most common problems is track down. A track down occurs when a block gets a false reading and places signals into the danger position even when there is no train occupying the block. This can occur if debris interrupts the block by grounding out the track circuit mimicking the electric circuit caused by an actual train in the area.

When a signal fails to clear, depending on the area, there are three different ways to rectify the situation. On home signals, and station timed signals transit control can perform a "call-on" where an orange aspect blinks and the trip arm is released even when the aspect displayed is red. The second option is a "key-by". Some signals have a plunger that the operator can stop, reach out the window, operate the plunger dropping the trip arm and then operate the train to a less restrictive signal. Where neither of these options exist, the only way to get past a defective signal is to "trip through". The operator at slow speed must trip the signal (which in turn trips the train and places it into emergency). The crew must then reset the emergency valve (by going out the front door of the train) before proceeding.

Block signals

Block signals are the most commonly used signals on the Toronto subway. They are used to keep trains properly spaced, and are controlled by the trains themselves, based on their distance relative to other trains. The following block signals are used by the TTC.

A series of block signals south of Yorkdale station
  • Proceed
  • Proceed with caution, next signal is currently red
  • Stop. Passing this signal trips the train stop.
  • Entering timed block, next signal is red only due to grade timing
  • Timed block, timer has not yet run out (red light flashes when timer is about to run out); next block is timed as well as lunar aspect is indicated (in this example this signal would only clear to yellow)

Grade timing (GT) is used in sections where a sharp turn requires a speed limit or where a downhill section would cause a train to accelerate to an unsafe speed if the driver were unwary. When entering a block which is subject to GT, one of two things controls the signal: the distance to the train ahead, or grade timing. If the current state of the signal is due to proximity to the train ahead, the white light below the signal (termed "lunar aspect" by the TTC) will not be illuminated. The lunar aspect is used only to indicate that the signal is being controlled by GT.

As well, despite the images shown above, a flashing red light may be shown without the lunar aspect. The flashing red indicates the end of a GT block whose timer has not expired, while the lunar aspect indicates the start of a GT block whose signal is currently being controlled by GT. Therefore, the signal at the end of the last block of a GT section may be flashing red to indicate that the timer has not yet run out, but that location will never have a lunar aspect since the next block is not subject to GT.

Interlocking signals
A TTC interlocking signal

Interlocking signals are used in interlockings, which are any areas where train movements may conflict with each other. They are controlled by either human operators or a computer, not by the trains. Interlocking signals also tell operators which way points are set. The following interlocking signals are used on the TTC.

  • Proceed, points set to straight
  • Proceed with caution, points set to straight, next signal is currently red
  • Proceed with caution, points set to diverge.
  • Stop and stay
  • Call on (train has been given permission to pass red signal)
  • Entering timed block, points set to straight, next signal is red only due to grade timing
  • Entering timed block, points set to diverge
  • Timed block, timer has not yet run out (top red light flashes when timer is about to run out); next block is timed as well as lunar aspect is indicated (in this example this signal would only clear to yellow over green)

Signal numbers

All signals have an alpha-numeric number that relates to their location within the subway system. The number is assigned using the Chain system of measurement, whereby a signal's number is assigned based on the nearest chain measure.

Each line or portion of a line has an assigned letter, and that precedes the number ascertained by the Chain measure. Signals that are on a northbound portion of track use the nearest even valued chain measure, where signals on a southbound portion of track use the nearest odd valued chain measure.

Line Signal prefix Even Odd Chain 0 mark
Yonge N (northbound only)
S (southbound only)		 northbound southbound Does not exist (continues from the University numbers)
University U northbound southbound South of St George station (counts up towards Museum)
Spadina

(no longer uses block signalling)

 SP (former) northbound southbound North of St George station (counts up towards Spadina station (YUS))
Bloor-Danforth B westbound eastbound West of Kipling station (counts up towards Islington)
Sheppard SH westbound eastbound West of Sheppard station (counts up towards Bayview)

Temporary signals

In work zones, staff place yellow beacons on the track bed between the rails to inform train operators that a "slow order" is in effect; the first beacon is usually accompanied with a speed restriction sign indicating the speed limit for the affected area. A green beacon indicates the end of a work zone and allows operators to resume normal operation. In outdoor sections, yellow and green flags are also used for the same purpose. A flashing blue light at track level indicates workers may be present, subway operators are required to sound their horn, and follow the signals of track workers when approaching and passing them.

See also

Videos

References
  1. Bow, James (December 28, 2016). "The Scarborough Rapid Transit Line". Transit Toronto. Retrieved 2017-01-13.
  2. "Alstoms signalling system equips Toronto subway extension". Alstom. December 18, 2017. Retrieved 9 January 2019.
  3. "TTC extends signal system to Queen Station". Progressive Railroading. 25 February 2020. Retrieved 9 March 2020.
  4. Moore, Oliver (December 22, 2018). "TTC will not complete subway signal-system upgrade by 2019 deadline". The Globe and Mail. Retrieved December 30, 2018.
  5. Moore, Oliver (June 2, 2017). "Signals from the future: How the TTC's subway auto-pilot will streamline your commute". The Globe and Mail. Retrieved June 2, 2017.
  6. "Bombardier's Rail Control Division Further Expands North American Presence". Bombardier Transportation. October 8, 2015. Retrieved 9 January 2019.
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