How do train sensors work?

A combination of sensors and radio signals determine the precise location and speed of the trains. Then, it dictates the safest distance for trains to be from each other. This information is then fed to the trackside signals. The way that the system works is to always default to a red signal to be as safe as possible.



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A low-voltage electric current is sent between the two rails via a series of relays like the ones in this photo. When a train approaches, the current runs through the train's metal wheels and axles instead of the relays. This short circuit activates the crossing signal.

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The railways use a train detection systems which can tell signallers exactly where every train is and how fast they are going. There are also systems that can automatically stop trains if the driver doesn't take the correct course of action or passes through a red signal.

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It's illegal in EVERY state for you to go around a lowered crossing gate or to ignore signs or flashing lights posted at a railroad crossing. Trains have the right of way because they can't swerve, stop quickly or change directions.

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The parallel lines of the rails converge toward the horizon and fool our minds into thinking the train is farther away than it actually is. It is virtually impossible to accurately judge the speed of a train when these combinations of illusions are present.

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Defective or damaged track circuits and axle counters are leading causes of signal failures. Damage to these components can be caused by moisture penetration, cuts, exposure to high temperatures, or rusting. In some cases, the damage may be caused by cable thieves who have pilfered cables for their copper content.

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Absolute signals are sometimes also known as “interlocking plant signals,” or more commonly today, “control points.” They received the name because these signals are typically operated in a control center by members of the Centralized Train Control (CTC).

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Electrical locomotives are used on subways and many commuter rail systems. Operators control the train by using the throttle, reversing gear and brake. The throttle controls the speed of the locomotive.

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By the time a train operator sees you, it is too late to stop the train in time. An oncoming train is moving faster and is closer to you than it appears. Similar to an airplane traveling at 150 mph that appears to float onto the runway, it's hard to determine a train's speed and distance from you.

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Trains cannot collide with each other if they are not permitted to occupy the same section of track at the same time, so railway lines are divided into sections known as blocks. In normal circumstances, only one train is permitted in each block at a time. This principle forms the basis of most railway safety systems.

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Trains can't stop quickly or swerve. The average freight train is about 1 to 1¼ miles in length (90 to 120 rail cars). When it's moving at 55 miles an hour, it can take a mile or more to stop after the locomotive engineer fully applies the emergency brake.

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