Beginner's guide to semaphore signals

Over the years, signals have been at the mercy of numerous legislative introductions to improve safety on our railways, that together with regional variation means that you would have to pretty much be an actual signalman to get signalling completely accurate on a layout. Even real-life train drivers have got their hands full when route learning as railways can be too complex to offer a one suits all set of rules. Despite this signalling is a big part of a viable model railway, so here is a general beginners guide to the world of signalling.

British railway lines are divided up into blocks. These blocks can be different lengths depending on line speed and the complexity of railway within the block. Under normal circumstances, only one train is permitted on each track within a block at a time. The simplest way to control the movement of trains in/out and within a block is with the use of signals. The most familiar of signals is the stop/go (on/off) signal called a home signal which is red in colour and sports a white stripe vertically through the signal arm as seen in the pictures at the top of the page.

If the signal arm is horizontal, the train has to stop at the signal, if the signal is positioned at a 45-degree angle (which can be up or down depending on region and period of history and is known as an upper quadrant and lower quadrant) then the train is free to proceed.

But trains are not like road transport and require a substantial distance to come to a halt, due to this home signals are preceded by a distance signal, yellow in colour with a black chevron. These are placed before the home signal at a distance relevant to the line speed (the higher the speed the further away the signal will be). Their purpose is to warn the driver not only to the presence of an upcoming home signal but also to what aspect the signal will be showing. Therefore trains do not stop at distance signals, they are there purely to advise. 

The next signal is called a permissive signal. They are red with a horizontal white stripe and are about two-thirds of the size of a home signal. Where there is a requirement for a permissive signal they can be found on the same signal post as the home signal (usually just below it). Their purpose is to allow a train into a block that is already occupied by a train, the drivers will only be allowed to proceed at a speed at which they can stop well within the distance that they can see to be clear.

The most common scenarios where a train would require entry to an occupied block would be for two trains to share a platform at a station, for a light engine to back onto its rolling stock, for additional rolling stock to be added to a train or for a shunting movement that only requires a limited encroachment into the occupied section.

Disc shunting signals work in a similar way to permissive signals, when the disc is rotated so that the discs red band displays a 45-degree angle the driver may proceed at a limited speed as far as the next home signal or the occupied stretch of track.

There is also a yellow and black variation of the disc signal. These would usually be situated at the exit to a siding where the train has a choice between joining the mainline or continuing into a head-shunt, the signal can be passed at danger for movements into the head-shunt only.

Junction signals otherwise known as splitting signals are where you get more than one home signal side by side controlling one track, they indicate which way a train has been routed at a junction. The most simple way to describe how they work is to imagine two home signals side by side and a junction just beyond with a choice of left branch or right branch. If the left signal is activated it would indicate the left route had been set and vice versa for the right route. Of course, it is not always that clear cut and junction signals can have as many as five home signals attached to them, sometimes varying in height, there is no set standard for what each signal communicates. That is usually a consideration of what would make the most sense for the junction in question so this is another situation where drivers route learning is essential.

It is important to recognise when signalling your layout that there are many variations of the standard signals, different eras and regions produced a plethora of designs and operating practices, so if you are after an authentic prototypical layout than we would suggest doing a little bit of research first. However, if your layout is generic and more for fun, then a few distance signals and appropriate home and junction signals should start you off in the right direction.