Railway Signalling CTC/RCT Modeling

If you can find a book at your local library called “Red for Danger”, read it. Not only is it a good read, it will give you a good insight into how signalling came to be and improve your understanding on the subject.

Basically, signalling became necessary to prevent trains from running into each other. In the early days, semaphore signals became the norm on many railways. Both upper and lower quadrant versions were used. To prevent the wrong signal from being pulled interlocking was invented. Pulling is the action needed to set the signal to proceed. Signalmen are responsible for making sure the track is clear before admitting a train.

CTC/RCS are acronyms for Centralised Traffic Control and Remote Controlled Signals. Basically it’s the same system evolved. These times the network controllers have computer screens in front of them with diagrams showing where all the trains are. These diagrams are a miniature representation of the railway network with all the stations, signals, points etc. All traffic is also shown, along with its direction and state of motion. To set a route for a train the network controller need only click the mouse on the train and then click the station/siding where the train is to travel. The system does the rest, setting points, setting signals and organising crossings with other trains.

In the past, there were many different signal versions. Today perhaps the most common form is the colour light signals. Very similar to traffic signals on our roads but the red light is on the bottom. Junction signals are used when trains are required to diverge from the main line. Some areas have automated signalling. This allows trains to run closer together in peak times in suburban areas. It also allows for closing the gap between trains and queuing in some areas.

Track sensing is used to sense the presence of trains. Previously in the old days this was not available or widely used. The first detection systems were just a short length of track electrically isolated from the rest of the track. They were usually placed on the approaches to signals that the signalmen couldn’t see. This allowed the signalman to become aware of a train standing at the signal. A train standing on the detection track acts like a switch, its wheels completing a circuit. Magnetic systems are also common.

In modern times there are axle counters to count trains into and out of different sections of track. Electrical detection is also used. On model railways these systems are replicated. There are other systems used with models as well. Ones like LDRs (Light Dependent Resistors) and field effect transistors and so on. Basically on a model what ever works is ok.