Block Signals
Block signals are the most commonly used signals on the Toronto subway and RT. 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.
| 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) |
GT (grade timing) 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.
Read more about this topic: Toronto Subway And RT Signals
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