1. Introduction to signalling systems

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Time for a deep dive into signalling systems – first, let's see where you'll be working as a Network Controller!

Signal Operators are based in the network control centre, working on an interface that looks something like this:

Network control centres vary in size and operating capacity, depending on the region they're overseeing. You can watch this video from a Queensland Rail network controller, for a sneak peak into the operations of a real Network Control Room.

It kinda looks like something out of a NASA centre, hey? Can you imagine yourself at a desk with five screens in front of you, working in a high-tech, high-paced environment? 😲

A little history for context...

Of course, signalling systems and control centres weren’t always so technologically advanced. In the early days of rail, for example, signalling consisted of what is know as Time Interval Signalling, which involved officers with stopwatches lining the railway in blocks, and managing the movement of trains through simple green, yellow, or red flags. ✅🟡❌

So, how has signalling evolved over time? 

The video below gives a comprehensive overview of the history of signalling:

As you can see from this, digital technology is being used to improve the flow of trains along the network and reduce the ripple effects of disruptions.

Today's signalling systems are know as 'fail-safe' systems

Fail safe systems are all around us in our every day lives. They're a staple of safe engineering.

Think of elevators – they're designed with special brakes that engage if the cable snaps or loses tension. Likewise, many machines will completely shut down if they detect that something's wrong. 


Well, the same applies to signalling! When there’s a fault, all signals will default back to red 🔴 to indicate stop and all level crossings will drop ❌ In rare cases where the signal bulbs don’t work at all (for example, where the bulb filament itself is the issue) the principle “signal off is equal to signal red” applies. That way, even when the signal is switched off, a driver will always know to stop, just to be on the safe side.

But how do signals know when to display what?

Signalling engineers make careful calculations taking into account the length and speed of the train, as well as what is referred to as the headway – that is, the distance between two trains on the track.

Most train systems in Australia still operate using what’s called ‘track circuits’, which basically use electric currents to detect when a train enters, occupies, and leaves a ‘block’ or section of track. The train's passage over the track circuits triggers a lights system a lot like your everyday red, yellow, and green traffic light.


Study the diagram below. Do you see how the pattern changes depending on what blocks are occupied, but the signalling system always maintains a minimum distance between the trains?

Head on to the next page to explore an example of a modern train signalling operations system that's being used by Inland Rail…

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