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Railway Signaling

Railway signaling is a safety system used on railways to prevent trains from colliding.Trains are very susceptible to collision because of running on fixed rails.They are not capable of avoiding a collision by steering away as the vehicles on the road.

In the very early days of railways，men were employed to stand next to the line at certain intervals to watch.These men used hand signals to inform train drivers that a preceding train had passed a certain number of minutes ago.This was called“time interval working”.If a train had passed the man only a short while ago，the following train was expected to slow down or stop to allow sufficient space between the trains，to prevent a collision.

This system was flawed，as the watchman had no way of knowing whether the preceding train had cleared the tracks ahead.If the preceding train broke down or stopped for some reason，the following train would collide with its rear-end.Accidents of this type were common in the early days of railways.However，with the invention of the electrical telegraph，it became possible for the station or signal box ahead to send message back to confirm that a train had passed and that the line ahead was clear.This was called the“block system”.

The block system came into use gradually during the 1850s and 1860s，and became mandatory in the United Kingdom after parliament passed legislation in 1889 as a response to numerous railway accidents.