Last updated on
04 December 2012

Ickenham & District Society of Model Engineers


Signal box at nightThe signalling on the Ickenham Miniature Railway consists of a mixture of traditional semaphore signals and colour light signals. There are two signal boxes controlling the points and connections on the main lines. Away from the signal boxes the signalling works automatically.

Train Detection

Train detection is achieved by means of track switches placed at intervals along the line. As the train's wheels pass over the switch, the wheel flange depresses an arm which operates a micro-switch. Generally switches are placed a train length apart, the maximum train length being limited by the length of the turntable in the station. As a train passes over a switch the relay for that section of line is de-energised, turning the signal red. When the train is clear of the section it passes over another switch which re-energises the relay allowing the signal to clear again. Most switches will actually carry out both functions i.e. de-energising the relay for this section and re-energising the relay for the previous section.


Semaphore Signalcolour light signalSignals are a mixture of air operated semaphore signals and three aspect colour light signals. The semaphore signals are located near the main signal box and are visible from the public viewing area. The colour light signals are used on the section of line that passes through the wooded area of our site. Generally the signals work automatically, controlled by the train detection system. Where there are points, then the signals will also only clear if the points are set for the correct direction. Points are under the control of the signalmen but if they leave the points set one particular way then the signals for that route will work automatically, depending on whether or not a train is in that section of line.

The signalling is generally three aspect. This means that each signal is capable of being in one of three states. These are

(1) Stop, indicated by a red light for a colour light signal or by both the red and yellow arms of a semaphore signal being horizontal.

(2) Proceed but be prepared to Stop at the next signal, indicated by a yellow light for a colour light signal or for a semaphore signal by the red arm being lowered to 45o and the yellow arm being horizontal.

(3) Proceed, indicated by a green light for a colour light signal or for a semaphore signal by both the red and yellow arms being lowered to 45o .

The picture above left shows the junction semaphore signal which is showing (3) Proceed for the left hand route and (1) Stop for the right hand route.

The picture above right shows a colour light signal which is indicating (2) Proceed but be prepared to Stop at the next signal,

Signal Boxes

SignalboxDiagramThere are two signal boxes from which the points on the main line are controlled. The larger of the two is called Marsh Junction and controls the points leading to and from the steaming bay loop as well as the junctions between the inner and outer main lines and also the junction where trains from the station join the main line. It can be a very busy place and is generally operated by more experienced signalmen. The signalmen here control the points by means a lever frame of six levers. Generally each lever controls one point and the appropriate signals will clear according to the position of the points unless there is a train in the section concerned. The train detection system described above ensures that points cannot be moved as a train is passing over them.

Khazi LeversKhazi JunctionThe second signal box is a smaller structure located out in the woods. It controls the junction where trains leave the main line and head back towards the station. Known as Khazi Junction it is named after a nearby building that provides and important facility for the majority of people working on the railway. The signal box had just two miniature levers to control the junction but they work in a similar way to those in Marsh Junction Signal Box. 


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