‘Anti-Collision Device (ACD) Network’
- A Train Collision Prevention System (TCPS)
Ajaykumar A. Bhatt, IRSSE
Chief Signal & Telecommunication Engineer
M. Tech. (Communications Engg, IIT Bombay),
PG Diploma in Operations Management (PGDOM),
FIETE, MIRSTE, MCSI
ABSTRACT
Safety violations due to ‘human errors or limitations’ and ‘equipment failures’
occasionally result in Train collisions. Patented by Konkan Railway Corporation,
‘Anti-Collision Device Network’ (also called ‘Raksha KavachTM’, meaning
‘A Train Safety Shield’) is an on-board train collision prevention system.
Designed as a ‘non-signal’ system, it provides ‘non-vital’ ‘safety enhancement’
layer over the existing safety systems of train operations. ‘ACD Network’
therefore fills up ‘safety gaps’ left out due to limitations of existing ‘signal’ based
train protection systems.
‘ACD Network’ consists of mobile ACDs (on Locomotives and Guard’s Brake
Vans) and track-side ACDs (at Stations, Level Crossings, Locosheds, Sensors
based and Repeaters, en-route). Mobile ACDs take inputs from GPS satellite
system for position updates and network with track-side ACDs located within a
radius of Three Kms (using UHF radio modems); to activate brake(s) with the
help of on-board Loco ACD(s) through their Automatic Braking Units (ABUs),
whenever a collision-like situation is ‘perceived’. ‘ACD Network’ is likely to
prevent ‘head-on’ and ‘rear-end’ collisions in mid-sections, collisions at ‘high
speed’ in ‘station area’, ‘side collisions’ with derailed vehicles obstructing
adjacent line, collisions due to ‘train parting / jumbling’ and collisions with ‘road
vehicles’ at level crossing through ‘Train Approach’ warning and detection of
‘Gate Open’. Loco ACDs also give ‘Station Approach’ warning to drivers.
Moreover, using Manual ‘SOS’ buttons on their ACDs, Drivers, Guards and
Station Masters can also ‘stop’ trains when any unusual is detected.
A ‘pilot’ project of provision of ACDs on 1736 Kms of Broad Gauge route of
Northeast Frontier Rly zone of Indian Railways has been declared as
commissioned by Ministry of Railways (Railway Board) in June 2007.
Author is closely associated with development and field implementation of this
‘Anti-Collision Device’ (ACD) project of Konkan Railway Corporation Limited
(KRCL), since its beginning in August 1999.
1. EVOLUTION OF ‘ACD NETWORK’ – A BRIEF STORY
Serious head-on collision between two passenger trains on 2 nd August 1999 at
Gaisal station of Indian Railways, prompted Konkan Railway Corporation
Limited to seek and design a cost effective indigenous solution to prevent
dangerous train collisions, without replacing the existing signalling system.
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KRCL demonstrated the first working proto type of ACDs to Hon’ble Minister for
Railways in December 1999 on Konkan Rly’s double lines section between
Madgaon and Majorda stations.
Subsequently, Ministry of Railways (Railway Board) in January 2000
referred following TEN Train Collisions to KRCL for defining the ‘Scope’ of ACD
system:

‘Gaisal’ Accident on 02.08.1999 in Northeast Frontier Rly – Head-on
collision at Station (one train sent on ‘wrong’ track from ‘previous’ station)

‘Gwalior’ Accident on 05.07.1998 in Central Rly – Head-on Collision at
Station (after passing two home signals at ‘Red’)

‘Karna’ Accident on 05.01.1998 in Northern Rly – Rear-end Collision in midsection (due to subsequent train passing advanced starter signal at ‘Red’)

‘Faridabad’ Accident on 27.07.1997 in Central Rly – Rear-end Collision at
Station (after passing home signal at ‘Red’)

‘Firozabad’ Accident on 20.08.1995 in Northern Rly – Rear-end Collision at
Station (after passing home signal at ‘Green’)

‘Hodal’ Accident on 20.11.1997 in Central Rly – Rear-end Collision in midsection (due to driver of the train in rear not following the procedure for
passing Automatic Signal at ‘Red’)

‘Panskura’ Accident on 25.03.1999 in South Eastern Rly – Side-Collision at
Station (diesel ‘light’ locomotive standing on crossover portion, infringing the
‘fouling mark’)

‘Khanna’ Accident on 26.11.1998 in Northern Rly – Side Collision in
mid-section (with derailed back portion of a train, already ‘parted’ in
‘mid-section’)

‘Level Crossing’ Accident on 31.12.1995 in Central Rly – Collision with road
vehicle at Non-interlocked Manned LC Gate (due to road truck forcibly
entering on the track portion of Level Crossing gate)

‘Level Crossing’ Accident on 25.12.1998 in Eastern Rly – Collision with road
vehicle at Non-interlocked Manned LC Gate (due to road bus stranded on
the railway track portion of Level Crossing gate)
Based on KRCL’s presentation on ACD concept in Rly Board, a work of
‘Provision of Anti-Collision Devices on Northeast Frontier Rly’ was sanctioned
by Ministry of Railways as a pilot project on 25th February 2000.
Further, the Functional Requirements of this ‘Train Collision Prevention System’
(TCPS) using ‘ACD Network’ was formalized with the help of RDSO and Rly Bd
after analyzing the 128 collisions that occurred between April 1997 to Jan 2002
on Indian Railways, wherein it was concluded that about 105 (82%) train
collisions were preventable had ACD Network been in place and rest 23 (18%)
were non-preventable, even with any other available train protection systems.
‘ACD Network’ – A Train Collision Prevention System (TCPS)
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2. INTRODUCTION TO ‘ACD NETWORK’
ACD is ‘self-acting’ microprocessor-based data communication equipment
patented by KRCL that works ‘round-the-clock’. Different variants of ACDs when
installed on Locomotives (along with their Auto-Braking Units), Guard
Vans/SLRs, Stations and at Level Crossings (both manned as well as
un-manned), form an ‘ACD Network’.
ACD units (train bound as well as those fixed on ground) that are within a radial
range of 3000 metres, communicate with each other, and based on train
working rules programmed in them, take decisions automatically, without any
input from their users, triggering automatic brake applications (through Loco
ACDs) if two units are deemed to be at ‘risk of collision’, thereby preventing
‘dangerous’ collisions or minimizing the extent of damages that may be caused
by collisions in mid-sections and station areas resulting in saving the lives of
human beings. Further, added responsibilities have also been assigned to ACD
Network in the form of ‘administrative’ requirements namely, Loco ACD to ‘alert’
Driver on ‘Station Approach’ and also to trigger ‘Train Approach’ warning at
Level crossings for the road users.
For their operations, various ACDs derive inputs from locomotives, selfpropelled vehicles, existing signalling systems, speedometers, devices that
provide ‘open’/‘closed’ status of Level Crossing Gates etc.
Users of ACDs, namely Drivers, Guards, Station Masters and Gatemen neither
depend on it while performing their normal duties related to ‘Train operations’
and ‘Train passing’ nor give any ‘Manual inputs’ to ACDs for their ‘operations’.
‘ACD Network’ – A Train Collision Prevention System (TCPS)
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ACDs however empower Drivers, Guards and Station Masters to ‘stop’ trains by
pressing of ‘Twin SOS’ buttons provided on their respective consoles, in case
they perceive ANY type of danger in train operations.
This ‘Train Collision Prevention System’ (TCPS) thus ‘enhances safety’ in train
operations by providing a ‘NON-SIGNAL’ additional ‘safety overlay’ over the
existing signalling system, without replacing any of them and nowhere affects
the vital functioning of the present safety systems deployed for train operations.
3. PRE - REQUISITES FOR ‘PROPER’ WORKING OF ‘ACD NETWORK’

Surveying of ACD routes for availability of both GPS reception and
inter-ACD radio communication range of 3000 metres to identify the ‘GPS
reception shadow zones’ and to work out the requirements of ACD
repeaters en-route (where continuous inter-ACD radio communication for a
distance of more than 200 meters is not available), respectively.

Mapping of locations of Stations (along with their yard layouts, including
Locosheds if any), Level Crossings, ACD Repeaters and other fixed ACDs
en-route, during the ACD survey, to decide locations for fixing of these
permanent ACDs and also storing this information in the memory of train
bound ACDs as well as concerned Station ACDs.

'Adequate' brake power is available in trains, fitted with Loco ACDs.

'Adequate' braking distance is available for a train fitted with ACDs,
whenever ACD Network perceives a ‘collision-like’ situation.

Only ‘working’ (both Loco as well as Guard) ACDs fitted trains ply inside the
ACD territory.
4. FUNCTIONING OF ‘ACD NETWORK’: TRAIN COLLISON PREVENTION
UNDER ‘VARIOUS’ TRAIN WORKING SCENARIOS
4.1. PREVENTION OF ‘HEAD-ON’ COLLISION
Loco ACD of a train applies brakes to bring it to a stop using its ‘Intelligent
Braking Logic’ (IBL) when it approaches a Loco ACD of another train on the
same track, which is approaching it from opposite direction or waiting and/or
stationary.
When a train is waiting and/or stationary on a main line at a station, the Loco
ACD of a train approaching this station will only reduce its speed to ‘maximum
speed permissible over mainline turnout’, in case route for it is not set to main
line, thereby fulfilling the dual requirements namely, of reception in loop line (for
which the route might have been set and signal cleared) as well as to reduce
the impact of collision in case driver enters an ‘occupied’ loop line, may be after
‘Passing a Signal showing ON aspect’ OR ‘Passing a Defective signal showing
OFF aspect’.
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4.2. PREVENTION OF ‘REAR-END’ COLLISION
Loco ACD of a train applies brakes using its IBL for maintaining safe distance
from the Guard ACD of a train ahead on the same track, moving away from it or
waiting and/or stationary.
4.3. PREVENTION OF ‘SIDE COLLISION’ IN BLOCK SECTION
Loco ACD of a train applies brakes using its IBL for reducing its speed to
15 Km/hr when it approaches a Loco ACD of another train that had already
stopped in the block section but the driver of that stopped train did not press
‘CANCEL’ push button (on Driver’s console) to indicate that his train is
‘NOT INFRINGING’ the adjacent track. In such cases, the train will be able to
resume its ‘NORMAL’ speed only after crossing the stopped train in block
section. In case of multiple lines sections, the trains that are operating on
‘adjacent’ tracks and approaching the stopped train will only be affected.
4.4. PREVENTION OF COLLISION DUE TO TRAIN ‘PARTING’/‘JUMBLING’
Guard ACD of a train detects train parting / jumbling when its train length
exceeds / reduces by 100 metres from the ‘pre-deduced’ train length,
respectively.
Guard ACD of a train detects train parting / jumbling, irrespective of whether it
takes place when the train is in motion or after it comes to a stop.
Subsequently, both Loco and Guard ACD of the parted / jumbled train radiate
the train parting / jumbling, till such time its driver presses ‘CANCEL’ button in
‘train stopped’ condition OR ‘original train length is restored’. Loco ACD of any
train that approaches this parted / jumbled train applies brakes using its IBL to
bring it to a STOP, thereby preventing side collision due to train parting /
jumbling.
Guard ACD also detects ‘train parting’ of a train in Station area, provided ‘after
the train comes to a stop and its Guard ACD is not switched off’, prior to
detaching its Loco. This ‘unwarranted’ generation of ‘Train parting’ condition can
however be avoided, if Guard ACD is switched off prior to detaching the Loco
from this train.
4.5. PREVENTION OF COLLISION DUE TO ‘FOULING’ OF LINES IN
‘STATION AREA’
While approaching a station, Loco ACD of a train applies brakes using its IBL to
bring it to a STOP if it detects Loco ACD/Guard ACD of another train radiating
fouling of the track in the station area, on which it is approaching. This also
applies to the lines that have been fouled simultaneously by a train including
‘intermediate two lines’ that are neither occupied by the Locomotive nor the
Guard van of the train at that time.
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4.6. PREVENTION OF COLLISIONS AT A STATION –
4.6.1. While approaching a Station, Loco ACD of a train gives an ‘ALERT’ to the
Driver through a continuous audio-visual warning from the location when
it is about 1600 metres away from the First Stop Signal (FSS) of the
Station. Whereas Audio warning stops automatically after 10 seconds,
the visual warning disappears after crossing the FSS. This ‘ALERT’ of
‘STATION APPROACH’ helps the driver in ‘foggy’ season or in weather
conditions that do not permit ‘clear visibility’, while approaching a Station.
4.6.2. While approaching a Station, if Loco ACD of a train does not
receive any communication from a Station ACD; it will display
‘NO COMMUNICATION’ (from Station ACD) message and give audio
warning till such time it is acknowledged. In case Driver does not
acknowledge this warning manually by pressing of ‘CANCEL’ button (on
Driver’s console), Loco ACD will apply brakes after 10 seconds to bring
the train to a STOP prior to reaching the FSS.
4.6.3. While approaching a Station if Loco ACD does not receive any
communication from the Station ACD but receives communication
directly from a Loco ACD (or Guard ACD) of a ‘STATIONARY’ train on
the ‘MAIN LINE’, it reduces its speed to ‘Maximum speed permissible
over first main line turnout’ before it reaches the same. This is done in
order to permit signaled reception of the train on a loop line when
‘MAIN LINE IS OCCUPIED’ (MLO).
4.6.4. While approaching a Station if Loco ACD receives a communication from
Station ACD stating that ‘ROUTE IS NOT SET TO MAIN LINE’(RNSML),
it reduces its speed to maximum speed permissible over first main line
turnout before it reaches the same. This is done in order to prevent
dangerous collision with a train on a ‘LOOP LINE’, for which the route
has been set, ‘erroneously’ (irrespective of fact whether main line at that
time is occupied or not).
4.6.5. While approaching a Station on ‘MAIN LINE’ if a Loco ACD of the train
receives a communication from Station ACD that a ‘stabled load’ or a
‘train not fitted with ACD’ has occupied the main line that is
track circuited, it applies brakes to bring its train to a STOP short of first
facing point on approach of that main line.
4.6.6. Where the ‘MAIN LINE’ is not track circuited, the Station ACD declares
main line as ‘OCCUPIED’ as and when an ACD Train / ACD fitted
Locomotive STOPS on that ‘MAIN LINE’, thereby taking care of
‘STABLED LOADS’ getting formed out of such ACD train.
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4.7. PREVENTION OF COLLISIONS AT ‘DANGEROUS’ SPEEDS WHEN
‘CORRECT’ TID IS NOT KNOWN
Loco ACD of a train carrying TID-FS (Track-ID ‘Fail Safe’ mode) status imposes
a speed limit of 25 Km/hr on self as well as on another train that approaches it
(through its Loco ACD, irrespective of the fact whether the other train carries
TID-FS status or not).
The speed limit imposition is removed once these trains cross each other.
‘Self-correction’ of TID-FS of the train in ‘DOUBLE LINE’ sections takes place
‘automatically’ after it crosses the other train that is carrying a valid TID of the
section. TID-FS status does not get corrected if both trains carry TID-FS.
4.8. PREVENTION OF COLLISIONS WITH ‘ROAD VEHICLES’ AT LEVEL
CROSSINGS (LCs)
4.8.1.
Loco ACD of a train activates audio-visual ‘TRAIN APPROACH’
warning for Road users at MANNED and UNMANNED LEVEL
CROSSINGS when it is 2000 metres away from it. This warning stops if
train stops on approach (but again reactivates when it starts) or finally
crosses the Level Crossing.
VISUAL warning changes from ‘NO LIGHT’ to ‘FLASHING RED’
(continuous visibility of 400 metres except on curves) and
AUDIO warning is in the form of a ‘HOOTER’ (audibility up to a distance
of not less than 30 metres in a direction where the sound waves are not
obstructed on a clear day, with the wind velocity and the extraneous
noises being negligible).
4.8.2.
Loco ACD imposes speed limit of 30 Km/hr while approaching a
MANNED (NON-INTERLOCKED) LC gate when it detects it in 'OPEN'
condition through its Gate ACD. This restriction however is removed
either when locomotive crosses the LC gate or it receives the
'GATE CLOSED' information from the Gate ACD, whichever is earlier.
4.8.3.
Suitable ‘DISCLAIMER’ BOARDS (in Regional, Hindi & English
languages) for the information of Road users are provided at
UN-MANNED Level Crossings (one each on either side of tracks) to
protect the Railway's legal right of way.
4.9. PREVENTION OF ‘UNUSUAL’ THROUGH ‘MANUAL’ SOS SENT BY
ACD USERS
Loco ACD applies emergency brakes to bring the train to a STOP when the
‘Twin SOS’ buttons provided in Loco (self or other) or Guard or Station ACD that
is within the radial distance of 3000 metres from it, are pressed simultaneously.
After stopping, Loco ACD permits movement of the train at a speed not
exceeding 15 Km/hr after driver presses ‘CANCEL’ push button. This speed
restriction however continues till such time either the source (that has generated
SOS) cancels ‘SOS’ or the Loco ACD moves away from the source (that
generated SOS) by more than 3000 metres, whichever is earlier.
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This is a useful feature of ACD that empowers its USERS (Driver, Guard and
Station Master) to stop train(s) in their vicinity (within a radius of 3000 metres)
when any of them detect any dangerous situation affecting ‘safety’ of train
operations like FIRE, DERAILMENT, ‘ROLLING STOCK DEFECT’ etc.
5. ACD PROJECT: MILESTONES ACHIEVED
5.1. IMPLEMENTATION OF ACD PROJECT ON INDIAN RAILWAYS (IR)
Ministry of Railways included provision of ACD system on its Broad Gauge
routes in the CORPORATE SAFETY PLAN OF INDIAN RLYS (2003-2013)
as under:
 ACD works already sanctioned on 3419 Route Kms, to be completed by
2007-08.
 ACD works included for covering 52600 Route Kms, to be completed by
2013-14.
5.1.1.
ACD SURVEY COMPLETED BY 30th SEPT 2003
 Covering 3455 Route Kms having 398 Stations of nominated BG routes
of Northern Rly, South Central Rly, Southern Rly, South Western Rly
and Northeast Frontier Rly.
 Ministry of Railways (Railway Board) has also sanctioned ACD Survey
over additional 10000 Route Kms of Indian Railways. The same will be
undertaken after the Composite Field Trails of ACDs in suburban
section of Western Railway are completed.
5.1.2.
IMPLEMENTATION OF ‘PILOT ACD PROJECT’ OF ‘NF RLY’
 National project of implementing ACD Network launched by Hon’ble
Minister for Railways on 20th January 2004 at Kishanganj station in
Katihar Division of Northeast Frontier Rly, covering 1736 Route Kms.
 Ministry of Railways (Rly Bd) declared this ‘ACD Network’ as
‘COMMISSIONED’ on 25th June 2007.
5.2. IMPLEMENTATION OF ‘ACD PROJECT’ OF ‘KONKAN RAILWAY’
 Sanctioned by Rly Bd on 17th December 2003 under the Corporate
Safety Plan of KRCL.
 ACD Survey covering 760 Route Kms (BG) having 53 stations,
completed on 19th December 2003.
 ACD Network will get commissioned (after carrying out Site Acceptance
Test), in September 2007.
‘ACD Network’ – A Train Collision Prevention System (TCPS)
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6. SUMMARY
6.1. ‘ACD Network’ is NOT a Signalling System and hence does not cater for
any ‘safety critical’ functions that are being performed by existing
Signalling system and the staff involved in ‘train running’ and ‘train passing’
duties on Railways. It actually acts as an ‘ADDITIONAL SAFETY
OVERLAY’ with the prime objective of preventing dangerous train
collisions that normally results in heavy loss of human lives.
6.2. While at stations adequate signaling systems that permit safe train
movements by Station Masters are already in place so long as all the
interlocking circuits are in position - the same cannot be said of the
Drivers.
‘ACD Network’ steps in to convert the ‘SIGNALLED’ system to a
‘CONTROLLED’ system - giving Drivers also a continuous protection
against the unusually behaving accident-prone train, ‘approaching’ or
‘ahead’ or ‘infringing’ its track (may be after derailing and parting),
including fouling and occupation of the main lines at stations. Thus
evolution of this ‘ACD Network’ - is a watershed, filling the void by
‘enhancing’ the safety in train operations.
6.3. At Level crossings too – ‘ACD Network’ provides the ‘TRAIN APPROACH’
warning to Road users and regulates the train speed ‘automatically’ if Loco
ACD receives ‘Gate Open’ message from Gate ACD of a ‘Non-interlocked’
Manned LC gate.
6.4. ACD system, though being a ‘NON-SIGNAL’ system also helps in a limited
manner to prevent dangerous collisions with ‘stabled load’ (not fitted with
ACD or a non-ACD fitted train) occupying the ‘MAIN LINE’ and with a train
standing on loop line if ‘ROUTE IS NOT SET TO MAIN LINE’, provided
Station ACD passes on such information in advance to Loco ACD of an
approaching train to enable it to reduce the speed prior to reaching the first
point of the station.
Thus this ‘ACD Network’ ‘bridges’ gaps in ‘safety’ of train operations caused
‘occasionally’ by ‘human errors or limitations’ and ‘equipment failures’, while
performing the ‘train operations’ and ‘train passing’ duties and also by road
users while crossing the level crossings.
Advent of this microprocessor based ‘knowledge embedded’ Train Collision
Prevention System (called ‘TCPS’, ‘ACD Network’ or ‘Raksha Kavach TM’), has
now opened a new chapter of introspection in Railways’ perspective and
understanding of ‘Safety’ in Train Operations.
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