Raksha Kavach

Konkan Railway Corporation Limited

Anti-Collision Device (ACD) System


The Necessity
Accidents involving trains as a well as a train with a road vehicle at level crossing gates are more gruesome in nature compared to others. This is because of the magnitude of loss involved - loss of not only the life and property, but also more significantly, the 'trauma' it leaves on the minds of people, left behind by those dead.

Train Accidents that are 'Technologically' Challenged

• Trains colliding with each other in the circumstances that occurred in the recent past, namely, in the case of 'Khanna' (side collision) and 'Gaisal' (head-on collision) tragedies

• Parting of a train (and even rolling back in some cases), causing loss of precious human life due to rear-end collision of the parted portion with the train in rear


• Collision between Trains and Road Vehicles at Manned as well as Un-manned Level Crossing Gates, may be due to the error of road users or railway staff or both


• Mishaps occurring due to train crew becoming inactive for some time, due to any reason

Such Train Accidents, which have a 'human error' at their root cause, are not 'fully' preventable with the help of technology and system of working, 'currently' adopted on Railways.

ACD System - To Provide 'Additional' Safety Shield for Safer Train Operations

ACD is a 'state-of-the-art', 'Non-Vital' safety device, developed 'indigenously' by Konkan Railway. When installed on Locomotives and Guards' SLRs/Brake Vans and networked with other 'stationary' ACDs provided at Stations and Level Crossing Gates (both Manned and Un-Manned), it provides an 'electronic' Additional Safety Shield to its users, namely, Drivers, Guards, Station Masters and Gatemen

Thereby serving the 'Public' that is either

• Travelling in Trains as 'Passengers' and / or


• 'Road users' who are 'crossing' the Level Crossing Gates

ACDs fitted on a Locomotive and Guard's SLR/Brake Van continuously monitor the 'emergency' situations that may lead to 'collision-like' situations, while the train is either stationary or on move. They also detect presence of other train/s, Level Crossing Gate/s, Station/s etc., en-route, in their vicinity, by exchanging information with ACDs fitted on them.

Based on the 'relevant' train working rules programmed in it, the 'Loco ACD' analyses the situation on 'real-time basis and applies brakes 'automatically', either to reduce train speed to a 'pre-determined' level or to a STOP, as the case may be. It releases the control on braking mechanism for the driver, as soon as the task is accomplished.

If brakes do not apply 'adequately' in time, automatically by the 'Loco ACD', it will immediately give Audio-Visual indication to the driver to take urgent necessary action, as deemed fit.

Salient Features of 'Networked' ACD System

ACD System does not -

• 'Replace' or 'dilute' any existing safety rules of train working or train passing

• Give any 'positive' indication to staff to take any action or steps, over-riding existing procedures or safety rules for train operations

• Unilaterally create any 'Un-safe' condition additionally, in the event of its failure

ACD System does -

• Act as 'watch-dog' to ensure safer train operations


• Monitor 'specific' events related to 'collision-like' situations and communicate the same to each other within their 'radio-zones' of influence

• 'Sense' conflicts and initiate 'protective' steps in case a 'potentially' dangerous situation arises


• 'Prevent' collisions - or 'minimize' its impact - between two or more entities, protected by their safety shield

ACD System Steps into Action in Situations where -

• A 'collision' is perceived when none should have arisen as per the 'existing' system of train working


• Efforts of the 'humans' alone become 'inadequate' to avert 'collision' due to 'practical' constraints like 'lack' of time, 'tempestuous' weather, 'difficult' terrain conditions, 'hostile' environment etc.

• Under existing rules of train working, 'more than two' errors/omissions/failures have already taken place

About 'Networked' ACD System -

• 'FIVE' Types of Networked ACDs are as under:


• Loco ACD - ('Fixed' & Moving) - It is permanently installed in the locomotive alongwith its Auto Braking Unit (ABU).


• Guard ACD - ('Portable' & Moving) - It is 'portable' so that it can be removed 'easily' from SLRs/Brake Vans alongwith its antennae, when they are abandoned by Guards after completing the train journey.


• Station ACD - ('Fixed' & Non-Moving) - It is permanently installed in Station Master's office.

• Level Crossing Gate ACD - ('Fixed' & Non-Moving) - It is permanently installed in Gate Man's cubicle.

At Un-Manned LC Gate, a stand-alone 'anti-theft' arrangement is made for fixing of ACD system alongwith provision of 'solar powered' secondary battery charging.

• Repeater ACD - ('Fixed' & Non-Moving) - It is used only when MINIMUM 'radio-range' of THREE Kms between TWO Loco ACDs not available in the section.

• ACDs exchange 'data' and 'commands' with each other when they are within their 'radio-range' of influence and also accept 'specific' manual inputs, in 'emergencies' or for 'initialization' purposes

• Based on the 'relevant' train working rules programmed inside, the ACDs take decisions 'automatically', act 'independently' and appraise the same to the user whenever necessary, through appropriate 'audio / video / text' interfaces

Composition of Locomotive ACD
As shown in the block schematic above, the Locomotive ACD comprises of -

Global Positioning System (GPS) Receiver -
It picks up signals at every ONE second from the constellation of GPS Satellites (minimum 'three', at a time) and submits the same to Command and Control Unit (CCU) of ACD. The CCU, in turn, extracts the parameters related to the movement of locomotive like latitude, longitude, speed, date and time etc. from the 'real-time' data stream received from this GPS receiver. The antenna of the GPS Receiver is fitted in a 'secured' manner on 'roof-top' of the locomotive.

Command and Control Unit (CCU) -
CCU consists of an Intelligent Programmable Central Processing Unit that is the 'heart' of the ACD system. It processes the data and takes decisions for 'alerting' its USER through generation of 'Audio-Visual' signal or 'Action' in the form of 'braking' or 'whistling' of Locomotive.

The CCU thus -

• Receives Inputs from GPS Satellites (through GPS Receiver) & other ACDs (through UHF Radio-transceiver)


• Processes its 'Decision making' Logic using the 'data' & 'commands' received

• Initiates protective actions in the form of 'Audio/Visual/Text' 'Indications' to the USER or 'Actions' like 'Loco Braking' or 'Whistling' or generation of 'Auto-SOS' etc., without waiting for the USER to respond

• Transmits its own 'data' & 'commands' to other ACDs, through UHF Radio-transceiver

• 'Programmable' to effect ANY changes in its 'logic' of working, to cater for any change in the rules related to train working

Wireless Transceiver for 'Inter-ACD' Communication -
It 'transmits' the data and information (in the form of commands), being generated by its own Command and Control Unit. Similarly, it 'receives' the data and information (in the form of commands), being sent by other ACDs, when the same is within the 'radio-range' of about 3Kms. The 'Omni-directional' antenna for the wireless transceiver is fitted in a 'secured manner' on the 'roof-top' of the locomotive cab at a convenient location. Similarly, the antennae for Guard's SLR/Brake Van, Station, LC Gate and Repeater ACDs are also fixed at an 'appropriate' locations. The 'inter-ACD' communication is characterized as under:

• UHF spot frequency is selected in the 440-470 MHz band

• Radio-range of UHF transmission is limited to THREE Kms, to cater for the braking distances of trains which may approach each other with full speed from opposite directions


• Only 'Loco ACD' broadcasts 'continuously' - Other ACDs remain in 'receive' only mode, most of the time, unless triggered for action by Loco ACDs present in their 'radio-range' of influence. In case of failure of 'Loco ACD' on run, the 'Guard ACD' starts broadcasting continuously

Braking Mechanism for Speed Control of the Locomotive -
On the basis of its 'internal' processing or the 'information' received from other ACDs, the CCU takes a decision to send the 'command' for applying brakes through its Auto-Braking Unit (ABU), interfaced 'suitably' with the braking system of the locomotive. The ABU thus applies 'Electro-pneumatic' braking, 'automatically', without waiting for 'manual' intervention by the driver.

Crew Interface Panel of ACD -
It consists of a Text Message Display Panel, Keyboard and Audio-Visual indications for the USER interaction.

Other ACDs -

• Guard ACD - Similar to Loco ACD, except the following

1. No braking interface

1. Own 're-chargeable' battery (replaceable, on-run)

(iii) 'Portable' instead of 'Fixed'

• Station ACD & Gate ACD - Similar to Loco ACD except the following

(i) No 'GPS' Receiver
(ii) No braking interface

1. Own re-chargeable battery, with battery charging arrangement

(iv) Gate ACD do not have 'data entry key pad'

• Repeater ACD - Most simplified, 'Store & Forward' device working on 're-chargeable' battery, used only when 'minimum' radio-range of 3Kms is not available due to 'terrain' conditions. It does not have user 'Interface' Panel, 'GPS Receiver' & 'data-entry key pad'

'Unusuals' in Train Operations - Handled by 'Networked' ACD System

'Networked' ACD system consists of ACDs fitted on Locomotives, Guards' SLRs / Brake Vans, Stations, Level Crossing Gates (both un-manned as well as manned) and Fixed Repeaters en-route, where minimum radio-range of THREE Kms is not available between two mobile Locomotive ACDs.

This 'Networked ACD System' can provide 'Additional Safety Shield' to the users against the 'Collision-like' situations that may result into ACCIDENTS of following nature -

• 'Head-on' Collision

• 'Rear-end' Collision

• 'Side' Collision

The 'Networked ACD System' will also 'EMPOWER' its users to send a 'DISTRESS' signal in the form of 'SOS' to STOP the train, whenever a 'collision-like' situation is perceived, for example,

• 'SOS' by Driver - when derailment of its own train is noticed, which may endanger the movement of train(s) on adjacent track(s)

• 'SOS' by Guard - when a train approaching on the same track from behind or Dragging of derailed Coaches/Wagons close to the SLR/Brake Van is noticed

• 'SOS' by Station Master - when any unusual like 'hot-axle'/'flat tyre'/'fire' etc. is noticed while performing train passing duties

• 'SOS' by Gateman - when an infringement of track portion from Road Vehicle is noticed in the face of an approaching train

In addition, ACD System can also perform the following functions to check the 'alertness' of train crew in a 'limited' manner, namely,

• 'Alerting' the driver while approaching a Station and applying brakes 'automatically' to control the train speed, in case driver fails to 'timely' respond to the 'Audio-Visual' warning, generated by the Loco ACD.

• 'Guard Missing' or 'Not being Alert' which can be checked by 'Loco ACD' automatically, by monitoring the manual 'Acknowledgement' sent by Guard through the 'Guard ACD', at 'pre-defined' time intervals

Networked ACD System - Various Scenarios in Action

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ACD Project - Beneficiaries
The 'Networked' ACD System being developed by Konkan Railway will not substitute any of the existing train working rules, which ensure safe running of trains on Railways. It will work 'silently' without interfering in train operations and shall act to 'alert' train crew or 'apply' brakes when 'collision-like' situations are 'perceived' either 'electronically' or through 'SOS' sent by human agencies, involved in train running and train passing duties.

The Passengers travelling by the trains and the Road Users of the Level Crossing Gates will be the ultimate beneficiaries who will get the 'electronic' protection from this Additional Safety Shield.

Konkan Railway is thus 'hopeful' and also 'confident' of making the 'train travel' safer for the 'public' by implementing the concept of 'Networked ACD System' in train operations, soon.

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