An important aspect of railway design, construction and safety is the signals deployed along the track. Signalling is a crucial part of the railway infrastructure and over the past decade, upgrades to signalling systems on railway networks around the world have helped to improve the overall safety of those rail networks, enabling trains to move safely around the network.
What is railway signalling?
Railway signalling is essentially a sophisticated traffic light system for the railway network. Here in New Zealand, we don’t have a huge rail network, however, we do have a busy network in and around a couple of our major cities, especially in Auckland.
In other countries, such as the UK or the USA, there are huge complexities with moving a huge number of passenger and freight trains around a huge network. A large network means lots of stations and it is around these stations that signalling becomes so important, especially from a safety perspective.
A signalling system has to ensure trains are kept safely apart as well as allowing for large stopping distances. That means you can’t simply turn a light to red and expect a train to stop like you would with a motor car.
The signalling system on rail networks are far more complicated than the traffic lights we are all familiar with on the roads to account for things like stopping distances and the system comprises of many parts.
When we talk about railway signalling, we are not simply talking about the light system you see on the side or railway tracks. These are simply the signals that form part of the signalling system. They tell drivers when to stop and go as well as informing them about the route they will take, however, the wider signalling system takes into account a lot of different variables including:
- Positioning of trains
- Controlling of the timetable
- Direction the trains will take
Within the signalling system, other systems are also at work to determine what movements are safe and a train protection system protects against driver errors.
How do railway signals work?
Many railway networks around the world are moving to a digital signalling system that will eventually see trackside signals replaced by in-cab signalling. This is already happening in countries like the UK and the USA, however, it is a slow roll-out process due to the size of their networks. Trackside signals will still be an integral part of railways networks for the considerable future, however, the move to a digital system will help to improve the overall safety of railway networks.
Currently, most signalling systems use trackside signals to control the safe movement of trains on a network as well as telling them where to go.
Most people think that the signals on a railway network are the same as the traffic light signals we see on the roads, however, despite some similarities, they are more complex and display more information to train drivers.
As well as telling them when to stop, go and slow down, the signals also indicate which route has been set up for the train and which way it must go. With the modern day signalling systems that are rolling out, this information is also displayed in the train cab.
The modern-day signalling systems are a far cry from the original signalling systems deployed on railway networks throughout the world. In the earliest days of the railway, policemen would stand on the road with flags to tell train drivers if the track ahead was clear. With no way of communicating to the next policeman along the track, this system relied on timings and ensuring they left enough time before letting the next one pass – not quite fool proof but effective.
This system was not a feasible option as network began to grow and so a mechanical semaphore signalling system was introduced. These signals were controlled by signalmen who could communicate with each other using lamps and bells. Signalmen were an important aspect of developing safer railway networks and whilst the need for signalmen has diminished, you will still find some of the mechanical semaphore signals on tracks around the world including the UK and USA.
Today’s modern signals typically use LED technology that help to reduce faults as well as extending the life of the signals.
How are railway signals powered?
Usually, signals and other equipment (such as track circuits and level crossing equipment), are powered from a low voltage supply.
The specific voltage varies with the country and equipment used.