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A signal failure can refer to a number of situations... It can be down to a track circuit failure which means that the signaller cannot guarantee the safety of the train as he is unable to see on their screen or panel that the section of line is clear of any other trains. It could be down to one of the Train Protection Warning System failing which can cause trains to stop when it is not required, these are in place to stop drivers passing signals at danger and risking collisions, it is also in place on certain bends of tracks where there is a speed limit, this is to stop tragic accidents like the one recently in Spain. it can be the set of points which switch you from one line to another have failed in their position, there are thousands of different failures, it can be level crossings have failed.
Much as traffic lights regulate and control the flow of traffic on the roads, railway signals perform an analogous function on the railway network - not to permit crossing (which is illegal), but to prevent railway trains running into each other's rear. As a safety measure, the default position of any railway signal is "danger", that is, indicating a hazard ahead. Any signal giving an ambiguous display (one where the meaning is unclear) is, in the instructions of train drivers, to be regarded as "danger" until proved otherwise. In the days when signals were given using a cable-operated baton, once the baton froze solid in the "all-clear" position, causing a terrible train crash. Signals were afterwards directed always to stand in the "danger" position when at rest, a system known as a fail-safe
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Para as outras partes da sua pergunta, elas parecem acontecer com frequência porque o sistema é grande, complexo e antigo. Além disso, não queremos pagar por isso. No geral, o registro é impressionante. No ano passado, por exemplo, o DLR alcançou a maior taxa de pontualidade em 26 anos.
Para sua última pergunta, eles nunca serão totalmente eliminados, mas as reduções de ano a ano estão em média em torno de 10%.
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