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Catch points and trap points are types of turnout which act as railway safety devices. Both work by guiding railway carriages and trucks from a dangerous route onto a separate, safer track. Catch points are used to derail vehicles which are out of control on steep slopes (known as ''runaways''). Trap points are used to protect main railway lines from unauthorised vehicles moving onto them from sidings or branch lines. Either of these track arrangements may lead the vehicles into a sand drag or safety siding, track arrangements which are used to safely stop them after they have left the main tracks. A derail is another device used for the same purposes as catch and trap points. == Trap points == ''Trap points'' are found at the exit from a siding or where a secondary track joins a main line. A facing turnout is used to prevent any unauthorised movement that may otherwise obstruct the main line.〔 〕 The trap points also prevent any damage that may be done by a vehicle passing over points not set for traffic joining the main line. In the United Kingdom, the use of trap points at siding exits is required by government legislation.〔 An unauthorised movement may be due to a runaway wagon, or may be a train passing a signal at danger. When a signal controlling passage onto a main line is set to "danger", the trap points are set to derail any vehicle passing that signal. Interlocking is used to make sure that the signal cannot be set to allow passage onto the main line until the trap points have been aligned to ensure this movement can take place. Trap points should preferably be positioned to ensure that any unauthorised vehicle is stopped a safe distance from the main line. However, due to space limitations, it is not always possible to guarantee this. If the lines are track circuited and a wagon or train using the catchpoint could foul an adjacent line, then a track circuit interrupter will be fitted to one of the run-off rails. When a train runs off it will break the track circuit and set main line signals to 'danger'. 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「catch points」の詳細全文を読む スポンサード リンク
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