Signals are there to protect something. It might be a train or something in a siding. Home signals protect a station yard. Starting signals protect track sections ie. the track between stations. In life everything has a purpose therefore a signal must have a purpose. Weather it is on a real railway or a model it must be protecting some asset or it has no purpose.

This is why placement of signals is important. Another factor that effects signal positions is the ability of the train driver to sight the signal. Some times there are additional signals like outer home signals and advance starter signals. Distant signals are used to warn the driver of the trains approach to a stop signal on track sections between stations. They also tell the driver on approach to a station weather the train is required to stop at the station or not. This is only true with semaphore signals. Colour light signals used as approach signals are really just repeaters giving advanced warning of the state of the home signal.

The interlocking is designed to make sure the track is properly set before the relevant signal can be pulled. It also prevents points from being changed while the route is set. Interlocking bars and leavers are used to accomplish this as well as locking the points against movement. In the signal cabin beneath the floor there are cams which move with the leavers. These cams lock leavers that control opposing train movements.

The mechanism for operating the signals is by a leaver pulling a wire. A weight on the signal post sets the signal back to danger once the wire is released by the leaver. The points have metal rods and leavers connecting them to the leaver in the signal cabin. These rod are usually one inch pipe painted black. The leavers are cut from steal plate and allow the motion to turn corners.

These days everything is electric. Points have electric motors. Most signals use LED lights. There are relay rooms to allow every thing to be operated remotely. These relay rooms also house the interlocking which is electric of course. Electronics is used extensively. How else will the computers operate everything. Because of the interlocking computers can not set an opposing or dangerous movement. Logic to operate the signalling system correctly is also built into the computer’s programmes.

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.

In the early seventies I was in the Gladstone Model Railway Club. We built a donut shaped layout. It was basically a flat table without scenery. It had a single track with two crossing loops. One might think how could this possibly draw a Crowd?

Well it did because of one thing, automation. You see one could have three trains continually running on it and crossing each other in the loops. It worked like the normal railway worked on single line sections. Trains would take their turns on the two single line sections. They would wait in the loops for their turn.

This setup could run for hours unattended. The speeds of the trains could be said to be normal track speed.  That is usually much slower than a lot of models are operated but it is realistic.

One of the problems with operating it was the fact that members would want to run their trains too fast. When this happened, the inevitable run through would occur. Then the train in the opposite direction would be hit as it was entering the loop. Maybe this was what the observers were looking for. However the patrons would clear out until the trains were running again.

All this magic was done by the humble surplus telephone relay. There were two banks of them in one of the end sections of the donut. The plugs and sockets for the wiring were octal type as used in thermionic valve equipment. Another problem occurred during moving the layout. The relays did not handle the traveling too well. The clappers would often become dislodged requiring realignment.

In 1975 I got classed to Cloncurry as driver. When I returned this layout had been changed. They had made it three tracks, no more automation. It was just three trains racing each other around and around. The interest in it was never the same after that at Exhibitions. It simply lost its appeal.

I thought it would look good with Moura Short Line CTC of the era. It was already setup for right hand running. It just needed trailable facing point’s indicators and colour light signals. Once that was done, a backdrop could have been added. Then a little scenery wouldn’t have gone astray. Alas! That wasn’t to be. Ah well, maybe someone who reads this might be inspired to do something similar.