Train stop

Part of a railway signalling system, a train stop, trip stop or tripcock (sometimes called a tripper) is a train protection device that automatically stops a train if it attempts to pass a signal when the signal aspect and operating rules prohibit such movement, or (in some applications) if it attempts to pass at an excessive speed.

Part of a railway signalling system, a train stop, trip stop or tripcock (sometimes called a tripper) is a train protection device that automatically stops a train if it attempts to pass a signal when the signal aspect and operating rules prohibit such movement, or (in some applications) if it attempts to pass at an excessive speed. ==Types of train stops== There are three types of train stops: Trip stop - stops train trying to pass red signal Timed train stop - stops train moving too fast Fixed train stop - prevents any trains from passing a point ===Trip stops=== The trip arm is raised whenever the signal is not displaying a proceed aspect. If a train tries to pass the signal, the trip cock on the train strikes the raised trip arm and the train is brought to a halt. When the signal indicates it is safe to proceed (clear or caution), the trip arm is lowered, and a train is able to proceed without further hindrance. In some cases, the trip arm will not be lowered when the signal to which it applies is exhibiting a proceed indication, e.g. when subsidiary signals are cleared, forcing a train to trip before proceeding, thus ensuring that movements are conducted at safe speeds. ===Timed train stops=== With a timed train stop, the trip arm stays raised until the approaching train has occupied a track circuit on the approach for a period of time corresponding to a set speed. If the train approaches at a speed higher than the one that is set, the trip arm remains raised and trips the train to a stop. If the train approaches at a speed equal to or lower than the set speed, the trip arm lowers before the train arrives, and the train is able to proceed without further hindrance. Some timed train stops require the driver to acknowledge a stimulus before the trip arm is lowered on a yellow signal. For sections of track with lower speed limits ( ) a simpler construction is also used. The trip arm rotates freely on a horizontal axis with a counterbalance attached to its lower end. If a train's speed is low, the arm will be rotated by the trip cock with a force insufficient to initiate braking. But if its speed is too high, force will be large due to the counterbalance inertia, causing the brakes to be applied. ==Installations== In 1901, Union Switch and Signal Company developed the first automatic train stop system for the Boston Elevated Railway. This system was soon adopted by the New York City Subway and other transit systems in the United States. Similar systems were installed around this time on the London Underground system. Because of its mechanical nature, the train stop has certain limitations in application. Severe snow and ice conditions, for example, could interfere with operation of the wayside trip arm. Its widest application, therefore, is on underground rapid transit lines, where conditions that might interfere with proper operation are readily controlled. It is also not suitable for high-speed operation, as the maximum speeds permitted often do not exceed 115 km/h (71 mph), citing risk of high impact forces breaking the arms. Train stops on London Underground lines are gradually being phased out in favour of ATP and distance-to-go signalling. Train stops remain standard equipment on all Sydney Trains metropolitan passenger lines in New South Wales, and on the electrified suburban railway system in Melbourne, Australia. The train stops on the Berlin S-Bahn were first installed in the late 1920s. They are named (or ) because of their testing and first installation on the Stettin Railway to the suburban town of Bernau. This was the first heavy rail rapid transit system with third-rail electrification in Germany. They are being phased out in favour of the ZBS system based on Eurobalises until 2025. ==Further reading== General Railway Signal Co. (June 1979). Elements of Railway Signaling

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