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The Toronto rapid transit system signals are a system of light-based indicators to give instructions to the Toronto Transit Commission's (TTC) trains on the Toronto rapid transit system. It uses block signals and interlocking signals. The TTC uses the NX/UR system of signalling, which is also used in New York on the New York City Subway, in Chicago on the 'L', and in Boston on the MBTA. ==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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Toronto rapid transit signals」の詳細全文を読む スポンサード リンク
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