Britain’s railways wouldn’t be complete without signalling. Signals are there to ensure that trains travel from A to B safely, without colliding with any other trains. Here is the YREA’s quick guide demonstrating the main principles with signalling.

Semaphores

There are many different types of signals found on the railways. Back in the 1920s, ‘Semaphore’ signals were introduced. Operated using rods linked to the nearest signal boxes (and in the 1900s, there were thousands of signal boxes) where the signal man would use a leaver frame to change the signals from one position to another. There were two main types of semaphore signals. The one shown on the left is an Upper Quadrant signal, and the one on the right is a Lower Quadrant signal.

Different types varied around the country, but both do the same job. The classic red/white semaphores like displayed above are stop/start signals. This is where the arm rests horizontal, and the red light is lit up. When the arm is lifted/dropped to an angle of 45°, the green light is lit up and allows trains to proceed. Distant signals, which support a yellow/black arm with a V-shaped notch at the end are used. These signals are useful to drivers, displaying whether the next signal is showing a red (stop) or a green (proceed) aspect. Like the stop/start signals, the distant signals are available as both types.

Subsidiary signals are found where the driver may need to shunt his train around. For example, if the driver needs to access a yard, change points onto the other track etc. These are smaller versions of the main semaphore signals and look like the diagram on the left. Round disk-like signals, mounted on the ground, also act as a subsidiary signal, used in yards and shunting about in stations. These are shown on the right.

Colour Light Signals

Colour light signals are what we find on most of the railways today. Like traffic lights we see on the road, signals use the classic red/yellow/green formation (upside down traffic lights if you like). There are 4 types of colour light signal in use on the railway today:

From left to right these signals are: 2 aspect stop / start, 2 aspect distant, 3 aspect and 4 aspect. Red tells the driver to stop. Yellow means ‘proceed with caution’, which tells the driver that the next signal will be red. Green means ‘proceed’, which tells the driver that the next signal will be either a yellow or another green. Now with 4 aspect signals (used on line such as the WCML or ECML), this allows the driver, who may be driving very fast, to know a bit more detail. Another yellow aspect is placed in at the top of the signal. When the driver gets a double yellow, this tells him that the next signal will be a single yellow. This top yellow aspect is only lit up when the other yellow is. Here is a diagram showing the aspects that would be used:

At a junction, a ‘feather’ is added to the top of the signal. All a feather is, is just a row of 5 lights pointing up at an angle showing the driver which route he is going. In low-speed areas such as stations (most major stations use these), the feather is replaced with a ‘theatre box’. This is a little box sat on top of the signal which, when lit up, displays a certain letter that tells the driver which route he is to take. Different letters apply for different routes, so a key to each letter would take a long time. Most of the time though, ‘M’ is use for mainline and sometimes directions are used such as ‘S’ for South.

Article Author: Jack Bowley.