chave falsa

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Catch points and trap points are types of points 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 (known as runaways) on steep slopes. 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. Catch points are used where track follows a rising gradient. They are used to derail (or "catch") any unauthorised vehicles travelling down the gradient. This may simply be a vehicle that has accidentally been allowed to run away down the slope, or could be a wagon that has decoupled from its train. In either case, the runaway vehicle could collide with a train farther down the slope.