[ BEST ] Way to Learn Indian Railway Signalling System in 2020

It is the basic requirement of the railway to movements of the train from one station to another station and if you are not known what is railway signalling and how Indian railway signalling system works stick till the end of this post.

Indian railway signalling system
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Trust me, after reading this article you can’t stop yourself from growing interest in railway signalling and reading more articles from our blogs.

Having a railway signalling system on railways increases the number of trains of a running line or section without increasing railway tracks. This system usually differs for each country, here, we discuss Indian Railway Signalling System.

In fact, in this detailed guide, I will teach you how you can learn Indian Railway Signalling System and can get a good job in the railway signalling field.

Railway signalling can come out as a great alternative for those, who are not interested to work in an IT field.

We are focused here to get an idea of railway signalling and the importance of signalling in the Indian Railway Signalling System.

Before starting to learn all about of Indian railway signalling system it is must understand first what actually Railway Signalling System is.

What is Railway Signalling System?

Railway signalling is concerned about the safety movements of trains and increasing train capacity in line with keeping constant the railway tracks.

The signal is playing a vital role to communicate between the train driver and station master in the Indian railway signalling system.

This communication technology invented for the safe working of trains from one station to another station with ensuring proper safety.

Importance of Railway Signalling

  • Routes are correctly set for a particular movement of trains and avoid the prevention of collision in the same or opposite direction.
  • We are ensuring safety to receive and dispatch trains from the station.
  • Train control movements from one station to the adjacent station is acceptable only after ensuring the track on which the train moves on to reach the next station is free. Another train is not present in the same or opposite station also needs to ensure. This train control method is called Block System Working.
  • To achieve maximum line capacity.
  • The train doesn’t contain steering. It’s guided on a fixed track. So, the driver cannot stop his train within the distance he can see – he must need a prior warning to slow down and stay ahead when he was approaching a Stop signal.

Principles of Railway Signalling System

  • Fail-Safe Feature – Even the signalling system fails, safety should be achieved.
  • One aspect can show only One indication – One led showing only one light.
  • RAMS (Reliability, Availability, Maintainability, and Serviceability)
  • Continuous visibility of signal to the driver – The driver must have to see any signal from at least 400m distance of any approaching signal. A Repeater signal needs to place if this condition can’t be achieved.
  • Overlaps – Block Overlap (BOL) and Signal Overlap (SOL)
  • Keeping less number of Fixed Signal in a route.
  • Regular danger aspect should show in the signal, one operation and one clearance of the signal – Normally Red led should glow, yellow and green led should glow only after clearing signal
  • Signalling system uniformity should maintain
  • Signal clearance operation should be flexible for Station Master (SM)
  • Block Signalling to be independent of Yard Signalling

Why Railway Signalling differ from Road traffic Signalling?

All over the World Railway Transportation widely used, as this mode of transport is more cost-effective, environment-friendly and efficient transportation than road traffic.

Its moves on specific tracks (made of steel rail tracks) call rails and wheel in a guided line, and there is no provision of steering as road traffic.

Since load carried by train more and attained the speed also high, it must need more braking distance before coming to the stop position at the station from full speed.

Clear of obstruction is available in road transportation, so that same need to provide control over the movement of trains in the form of Railway signals, which convey the information to the drivers to stop or move and also the speed regulation at which they can pass a message.

The Concept of Indian Railway Signalling System

Trains vehicles are constrained to move on a fixed railway track. Trains are required to follow each one in the same direction on the length of the road; otherwise, for every train, separate parallel paths need to provide. It is not practicable.

The trains coming from the opposite direction need a diversion track; otherwise, both trains can go in now on the same path. So, to avoid this kind of activity, “Control over the movement of trains” required.

Two types of control could be taken:

1. Time Interval Method

The name “Time” defines that the trains run on the track one after another by maintaining an equal time difference between two trains.

Suppose a train is a dispatch from a station. Another train can dispatch from that station in the same direction after some time. This difference in time between two trains is called Time Interval.

If all trains run at the same speed and need to stop at the same station for equal time, a perfect time lag must be there. In this time lag, the next should be able to reach the next station.

But in Indian Railway Signalling System this system cannot be adopted because:

  1. All trains speed is not the same – Superfast, Mail & Express, Passenger or local
  2. Goods and passenger speed & weight also not same and both trains are often running on the same track
  3. The land of all over India are not the same – filled with mountain territory
  4. The braking power of all trains not the same.
  5. Most Important all trains are not stop Everywhere.
Time Interval Method
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Time Interval Method

Suppose no. 1 train dispatched from a station at 10:20:00 am towards another station. Time interval method explained a fixed interval of time present between two trains.

We take 10 sec as a example of time interval between two train.

So 2nd train will dispatch at 10:20:10 from that particular, and 3rd train dispatch at 10:20:30 am, and next all train follows this 10 sec time interval.

So, hence Indian Railway signalling system adopted Space Interval Method. It is quite simple and more effective in all regions.

2. Space Interval Method

  1. The name “Space” defines that the train runs on the track one after another by maintaining proper distance between two trains.

In this method, the total length of tracks is divided into sections called “Blocks.” The entry of a train into a block is allowed in such a manner only when it is free. That means between two consecutive trains, and there is a fixed space interval.

  • The space interval method is controlled at the entry point of any station.

The relevant train position can know from the controlling point, and this position decides the entry of the next train if the previous train reached the next station.

Since the total station massive in length, another controlling point also set at the end of the station.

With these two controlling points statuses, we can know the exact position of the train.

  • Information about the status of the block shared by exit point to the entry point and the entry point transmit this data to the train driver. Hence the driver can know that the next block is clear or not by this information. If it’s not, the clear driver should stop and wait.
Space Interval Method
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Space Interval Method

Ideally, this information is shared by a color light or signal and maybe Semaphore.

The driver gets information from the color of Signals that he should stop or proceed.

Space Interval method introduced Block Signalling Concept. A block section is present between two stations.

At a time, only one train can present in a single block.

If the next block is free, i.e. no train is present in the advance block, then the only signal will clear (glowing green led).

In the above picture, where a train is present in block section previous signal of that block is showing ON aspect (glowing red led).

A Quick Overview on the Evaluation of Railway Signalling

  • The evaluation of railway signalling started with a red flag in Hartlepool, England.
  • Hand flag signals consist of red and green start to use in 1829 by the USA and lighted lantern in the night in Balti- more Ohio Rail Road followed by block signalling.
  • British Railway invented the middle of the 18th Century metal disk, and the Quadrant Signalling system devised for a semaphore signal made of the mechanical arm.
  • Then mechanical interlocking installation started in the UK by C.H. Georgy.
  • James Annet invented the siding in 1876.
  • Colour light signal came into a role in signalling from 1904 by the USA.
  • In 20th Century CAB signalling was introduced and ETCS level 1 to 3 added.

Quadrant Signalling System – Origin of the Indian Railway Signalling System

Quadrant system in Railway Signalling is started from the middle of the 18th Century, and after a great evolution of railway signalling system, colour light signals stands today. The semaphore signal is started to use by UK Railway. In later, it is adopted by the Indian railway signalling system.

Semaphore signals used a mechanical arm to indicate the different aspects of the signal. This arm can be shown on the left side or right side of the signal post of a quadrant, as shown below.

A circle is divided into four parts. Each part consider as a Quadrant.

Lower Quadrant Two Aspect
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The bottom two-quadrant is situated at the lower side of a circle and is called a lower quadrant. Two aspect signal works in the lower quadrant.

So, Two aspect railway signalling system is called as Lower Quadrant Signalling System.

The upper half of any circle contains two smaller half. Multiple aspect signal works on this upper half and hence it is called as Upper Quadrant Signalling System.

Upper Quadrant in Right hand Side Multiple Aspect
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The Upper Quadrant Signalling System can work in left and right both principles. It is also called Higher Quadrant Signalling System.

Upper Quadrant Multiple Aspect
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Indian Railway Signalling System including all other country follows upper quadrant signalling system in railway signalling. Left or right both are acceptable in railway signalling as it able to show multiple aspect.

A fixed signal can operate on any one of four quadrants of a circle. Since the Left side is preferable in Indian Railway Signalling System, the left-hand side upper quadrant utilized in Indian Railway Signalling System.

The Main Three Components Used in Indian Railway Signalling System


It is the essential component in railway signalling to convey information to the driver. We all see a fixed post on railway tracks having red, yellow, and green light called a colour light signal. In earlier days semaphore signal made of the mechanical arm is used instead of a colour light signal.

  • Semaphore or Mechanical Signal

A semaphore signal is made of a mechanical arm. It looks like square-ended, painted Red with a White bar parallel to the square end in front.

It is painted in white with a black bar in the rear in case of stop signal or warner signal; a fish-tailed is used to distinguish from a stop signal easily.

The different positions of the arm are indicating a different aspect. The arm follows lower quadrant signalling for 2-aspect signal and upper quadrant for multiple aspect signal. But at night time, the driver can’t recognize the position of the arm.

mechanical signal
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So, hence light is inbuild in the existing arm of the semaphore signal to indicate aspects to the driver at night time.

Disc type shunt signal is known as “Subsidiary Signal” made of circular disc painted white with a red horizontal bar in the front and white with a black bar in the rear.

Miniature arm type shunt signal, calling on the signal, and other miscellaneous signals like a co-acting signal, repeater signal also used by the mechanical arm in earlier days. Still, now all are changed into colour light signals made of led.

  • Colour light Signal

The representation of this Colour light signal is come from right hand upper quadrant signalling system.

  • Red is indicating 0° i.e., horizontal side (ON Aspect).
  • Yellow is indicating 45° i.e., middle position of horizontal and vertical (ON Aspect).
  • Green is indicating 90° i.e., vertical side (ON Aspect).

Colour light signals are provided for improved visibility, easier working, and maintenance.

In India railway signalling system practice, colour light signals are used as the above picture. But, red, yellow, and green are not written above every aspect.

colour light signal
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Aspect is nothing but a circle with an indication ( / ) in proper angle inside a circle to indicate different aspects.

I write all aspects to give you a better idea of the signal. Only this sign is used to represent a colour light signal in railway signalling drawing.

We all know as a default aspect Red light is glow in signal to indicate “Danger”. This default aspect is showing in the Indian railway signalling system by a double slash ( // ) at 0° angle like this ( || ) inside a circle.


Trains are guided on a fixed track, but when a diversion is needed, Points are used to take a diversion from one line to another line (Mainline to loop line) or vice-versa.

It has two Position Normal (N) and Reverse (R). The normal position indicated trains go on straight line and reverse indicate trains take a diversion into another line or loop line. This switching is achieved by Point Machine, which worked at 110V DC, and the control to operate the point is came from Interlocking System.

Signal indication is connected with points in such a way that signal indication and point operation are depended on each other otherwise, and safety can hamper. This arrangement is called Interlocking.


Trains move on a specified railroad, also called a permanent way as it doesn’t have any facility of steering like other road transport. This permanent railroad is known as track.

 It’s made of a set of parallel rows of steel. These tracks are used to transport people and freight from one place to another.

The crushed stones in tracks are used to hold the wooden cross ties in place, which in turn hold the rails or tracks in the proper place.

he first pictures showing a physical view of railway track in railroad structure. But in Indian railway signalling system practice, it’s not used.

The bottom one is the method to represent a track in the Indian railway signalling system. The total track is divided into smaller parts.

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A circuit is connected with each track in the station section to detects the presence of trains within the station. This circuit is called Track Circuit.

Here, 1 TPR, 2 TPR, 3 TPR, 4 TPR each is a track circuit relay called Track Proving Relay (TPR) and the number indicates track number.

Block System

The distance traveled by the train from the last signal (known as Advance Starter) of any station to the first signal (known as home) of the next station is called block section. The station section is the distance between the first signal to the last signal of any particular station.

The signalling system is working on that block section is known as Block Signalling System. Different methods are applied to control the train movements on this block section.

This system mainly ensures that not more than one train is permitted into the block section at a time which concept is first introduced in the space interval system.

Interlocking Principle – The Heart of Indian Railway Signalling System

Trains are to be crossed or overtaken at stations, points, and signals need to be worked in a proper arrangement to make passage of trains safe. This arrangement is known as Interlocking.

It allows safe simultaneous movements in the station. As an interlocking concern, the safety of train movements and not allow the un-safe movements of trains, it is the most essential element in the indian railway signalling system.

Interlocking between point levers and signal levers can be either mechanically or locking electrically with Route relay interlocking (RRI) system.

With RRI, a complete route can be set by one operation and restricted the conflicting movements.

In Indian Railway Signalling System RRI is widely used but nowadays, Electronic Interlocking (EI) is starting to use as an Interlocking system.

This interlocking system is based on microprocessors while RRI is made of Relay interlocking.

Standards of Interlocking

Trains speed are depending on the railroad structure and Indian railway signalling system component also. Based on speed four types of the interlocking standard are followed –

Standard of InterlockingThe maximum permitted Speed (Kmph)

Essentials of Interlocking

  • The condition needs to prove before clearing a signal in railway signalling system –
  1. All points are correctly set in route, overlap, and isolation.
  2. All facing points should be locked.
  3. All interlocked level crossing gate should be closed and locked against road traffic.
  • After clearance of the signal, it must not be possible to
  1. Changing the position of relevant points in route, overlap, and isolation
  2. Unlocking the relevant facing point
  3. Unlock and open the level crossing gate
  • Should not taking off any two fixed signal which may lead to conflicting movements
  • If possible, the point should be interlocked to avoid conflicting movements otherwise it can hamper other instruments of railway signalling.


Okay let’s wrap with some important point of learning Indian Railway Signalling System

  • Railway Signalling System – Importance and Principle
  • The concept behind the Indian railway signalling system
  • History of Railway Signalling System
  • Concept of Quadrant Signalling System
  • Essential three components used in Railway Signalling – Signal, Track, Point
  • Block System
  • Interlocking Principle – Standard, Essential

Any Queries?
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Any Queries?

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