How does a railway signal work?

Answer 1

Depends on type. Some are operated by manual lever and cables from the signal-box. Others use electric servo-motors, controlled by switches, especially where a few power-boxes have replaced many of the old lever-frame signal boxes.

The signals are heavily interlocked mechanically or electrically with each other and with any points that they guard, so they cannot be put to "off" (clear) if the road ahead has not been set correctly or if another train has been signalled to proceed along or across the second train's path.

The signalman has a large map-like diagram above the controls to indicate what signals and points are where, and how they are set. He also has some form of communication with his colleagues along the line, so in effect they are passing each train from the care of one to another as it proceeds.

The failure and default modes are "on", i.e. red lights, or red lamps plus horizontal arms on semaphore signals. This means stop at that signal.

In British practice there are two main types of signal. Red or Green Stop / Starter signal (stop at the signal or proceed past it if safe to do so); and Yellow or Green 'Distant' which warns of the next signal's aspect, red/green stop or proceed. On high-speed lines a further, Double Distant signal with two yellow/green lamps is used.

Answer 2

A person from the controll room sends the signal to the perticular signan

The current passes through the coil

From there through the iron nail

The thread passes the current to the signal

• Then the bulb glows