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Railway signalling is a system used to direct railway traffic and keep trains clear of each other at all times. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormous weight and inertia of a train, which make it difficult to quickly stop when encountering an obstacle. In the UK, the Regulation of Railways Act 1889 introduced a series of requirements on matters such as the implementation of interlocked block signalling and other safety measures as a direct result of the Armagh rail disaster in that year. Most forms of train control involve movement authority being passed from those responsible for each section of a rail network (e.g., a signalman or stationmaster) to the train crew. The set of rules and the physical equipment used to accomplish this determine what is known as the ''method of working'' (UK), ''method of operation'' (US) or ''safeworking'' (Aus.). Not all these methods require the use of physical signals, and some systems are specific to single track railways. The earliest rail cars were first hauled by horses or mules. A mounted flagman on a horse preceded some early trains. Hand and arm signals were used to direct the “train drivers”. Foggy and poor-visibility conditions gave rise to flags and lanterns. Wayside signalling dates back as far as 1832, and used elevated flags or balls that could be seen from afar. == Timetable operation == The simplest form of operation, at least in terms of equipment, is to run the system according to a timetable. A fixed schedule is drawn up with which every train crew must be familiar. Trains may only run on each section of track at their scheduled time, during which they have 'possession' and no other train is permitted to use the same section. When trains are running in opposite directions on a single-track railroad, meeting points ("meets") are scheduled, at which each train must wait for the other at a passing place. Neither train is permitted to move before the other has arrived. In the US the display of two green flags (green lights at night) is an indication that another train is following the first and the waiting train must wait for the next train to pass. In addition, the train carrying the flags gives eight blasts on the whistle as it approaches. The waiting train must return eight blasts before the flag carrying train may proceed. The timetable system has several disadvantages. First, there is no positive confirmation that the track ahead is clear, only that it is scheduled to be clear. The system does not allow for engine failures and other such problems, but the timetable is set up so that there should be sufficient time between trains for the crew of a failed or delayed train to walk far enough to set warning flags, flares, and ''detonators'' or ''torpedoes'' (UK and US terminology, respectively) to alert any other train crew. A second problem is the system's inflexibility. Trains cannot be added, delayed, or rescheduled without advance notice. A third problem is a corollary of the second: the system is inefficient. To provide flexibility, the timetable must give trains a broad allocation of time to allow for delays, so the line is not in the possession of each train for longer than is otherwise necessary. Nonetheless, this system permits operation on a vast scale, with no requirements for any kind of communication that travels faster than a train. Timetable operation was the normal mode of operation in North America in the early days of the railroad. 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「railway signalling」の詳細全文を読む スポンサード リンク
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