What is Railway Signalling? 5 Important Points

Table of Contents

Types of Railway Signals

Automatic Block Signal System (Permissive)

Interlocking Signal System (Absolute)

What are the Reasons for Railway Signalling Failures?

What is Railway home signal?

Railway Signal Principles?

Railway Signalling Technologies:

European Train Control System (ETCS)

Traffic Data Management Software

Driver Advisory System

Railway Signalling Systems are one of the few sophisticated systems of Railways that operates and manages a large number of train movements safely and efficiently.

However, the top-notch signalling system of the railway that we see today doesn’t develop overnight, it has been evolved in decades by rigorous research and development of Railway Signalling experts. In this blog, we will cover some key points of Railway Signalling.

Types of Railway Signals

Signals are provided to control and guard the railway network against the risk of overcrowding of trains. There are two types of Railway Signalling commonly used. The Permissive Signals system guards the railway network while the Absolute Signal system guard and control the network.

Automatic Block Signal System (Permissive)

Automatic Block Signal System applies the short circuits of the front and rear train wheels and axles and disconnects the relay.  So, when the replay is opened, the traffic signal is converted to Red Signal.

Interlocking Signal System (Absolute)

Interlocking signal System controls the signals for each rail network so when clearance is required from one network, it stops the other overlapping network with a controlled signal system. Initially Interlocking systems worked with the help of pushbuttons to control the signal system, but now electric relay-based interlocking is used to control the signal system.

What are the Reasons for Railway Signalling Failures?

Railway Signals normally fail when a short circuit takes place due to some unavoidable circumstances like heavy rainfall or ponding, etc. In an open environment, exposed cables or wear/tear of cable cover may crate short circuits and turn the signal to Red.

Regular maintenance of signal cabling, drainage kerbs, replacement of broken drainage gullies or kerbs, insulation of joints, replacement of old tracks, etc is some of the key mitigation measures that need to consider minimising abrupt signal failures.

What is Railway home signal?

In a railway network system, the primary “STOP” signal is known as “Home Signal” and the last signal is known as “Starter”. The first ‘STOP’ signal at each signal box is called the ‘Home Signal’. The last ‘STOP’ signal at each signal box is called the ‘Starting Signal’ (or ‘Starter’).

Home Signal provides early warning to the train driver and if it is needed to slow the train or stop the train, the rear signal (known as Distant Signal) inform the driver to completely stop the train at the Home Signals.

Railway Signal Principles?

The basic principles of Railway Signalling cover the following objectives to prevent railway traffic from:

1. The collision of one train bogies with others.
2. The derailment of train bogies
3. The collision of LRT or tram with road vehicles or pedestrians.
4. The collision of a train with railway assets (such as platform, footbridges, etc) and railway staff.

To meet the above objectives, signal enforcement systems are applied, and It comes with two key mechanisms. The trackside mechanism interfaces with the signalling system. Train borne mechanism that connects with the emergency braking system.

They both work collectively to enforce signal systems and meet those objectives.  

It keeps two running trains a safe distance away from each other and minimises the possibility of any collision of trains running on the same track. It also helps the controller unit regarding any obstruction along the train route by regular monitoring of the track route.

It also raises a warning when trains approach the signal so that a go-ahead or Stop message can be transmitted to the train driver at the appropriate time. It allows the train operator unit to maintain train running frequency and timetable as per the defined schedule.

Blog: Railway Track Design

Railway Signalling Technologies:

European Train Control System (ETCS)

European Train Control System (ETCS) work with the concept of interoperability of trains within the European train network. ETCS is significantly different from traditional fixed block signal systems. ETCS provides continuous or intermittent or on-demand data transmission from the tram/train unit to the train control centre and uses advanced data management software.

Traffic Data Management Software

Radio Block Unit uses advanced traffic data management software to efficiently operate the train network. It can significantly reduce headway and enhance network capacity.

Driver Advisory System

Driver Advisory System (DAS) inform train driver regarding the train operating speed that needs to be applied or maintained to efficiently utilise the network and resources. The operating speed is pre-recorded by using historical data and route network information are loaded before the journey begins.

I hope the above blog helps you to understand the railway signalling system briefly.

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