The acd network is a Train Collision prevention system patented by

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The ACD Network is a Train Collision prevention system patented by Konkan Railway Corporation Limited (A Public Sector Undertaking of

Ministry of Railways, Government of India).[1] ACDs have knowledge embedded intelligence. They take inputs from GPS satellite system for position updates and network among themselves for exchanging information using their data radio modems to take decisions for timely auto-application of brakes to prevent dangerous 'collisions', thus forming a 'Raksha KavachTM' (meaning a '(Train) Safety shield').

ACDs fitted (both in Locomotive and Guard's Van of a train) act as a watchdog in the dark as they constantly remain in lookout for other train bound ACDs, within the braking distance required for their relative speeds. They communicate through their radios and identify each other. If they happen to find themselves on the same track and coming closer to each other, they automatically restrain and stop each other, thereby preventing dangerous head-on and rear-end collisions.

Loco ACD of a train also applies brakes to reduce the train speed either to 15 km/h if on approach it receives a message from other train bound ACD that has stopped in a block section on adjacent track (and driver of that train has yet not communicated that things are 'Normal') or to bring the train to a stop if train bound ACDs of other train are radiating 'train parted' message thereby preventing dangerous side collision that may occur due to infringement of adjacent track by a stopped or a 'parted' train, respectively.




Page No.








Need of A.C.D.



Features of ACD



Technology Used



Working Method For Anti Collision Devices



Accidents are prevented by ACD



ACD network can’t prevent a train collision



Benefits of the ACD system



Maintenance Support System (MSS)









Anti-Collision Device (ACD) is a self-acting microprocessor-based data communication device designed and developed by Kankan Railway.

When installed on locomotives (along with an auto-braking unit - ABU), guard vans, stations and level-crossing gates (both manned and unmanned), the network of ACD systems prevents high-speed collisions in mid-sections, station areas and at level-crossing gates.

The ACD uses both radio frequency and Global Positioning System (GPS) through satellites, whereby a train is automatically brought to a halt if the track ahead is not clear. The train starts braking 3 kms ahead of a blockade.
The Anti-Collision Device (ACD), also called `Raksha Kavach,' envisages setting up a network of "self-acting" micro-processor based communication devices which automatically apply brakes on trains that are unknowingly getting into a "collision-like situation," including before stations and at mid-sections. "At the mid-sections, where neither the protection of signals nor guidance is available to the driver, the ACD makes the loco intelligent and extends its capability to detect any collision-like situations in a range of 3 km, which the driver cannot detect on his own. Situations like collision between two approaching trains or between a derailed train on one track and an approaching train on the adjacent tract can thus be prevented," according to the KRCL official.

The "silent" network of ACD systems can be installed on the locomotives, guard vans and at stations, which could ensure that trains do not collide at while travelling at high speeds. Further, if the ACD systems are provided at the level crossing gates (both manned as well as un-manned), the project could provide protection to the lives of road users also. "We have tested the commercial prototypes of ACD system, which has been developed indigenously for the first time in the world. It has been technically proven during joint field trials with Research Design and Standards Organization, nominated by the Railways," the official said.

The ACDs are capable of multi functions. For example, while approaching a station, the Loco ACD gives the "station approach" warning to the driver about 2 km in rear of the first STOP signal of the station and in case the driver ignores the warning it will automatically regulate the train speed.

The pilot project implementation of ACD was successfully commissioned on the North-East Frontier Railway this year. Survey for expanding the system to another 10,000 km falling on the critical and busy sections of the network is almost complete.

The installation of this device will go a long way in preventing collision accidents. The application of this device has been refined to not only prevent mid-section collisions but also to pre-empt their occurrence in station yards.

The newly engineered solution is integrated with the signaling systems and interlocking to react appropriately in case collision-like conditions are perceived at the time of reception and dispatch of trains from a station. The design of crash-worthy coaches and tight lock couplers with anti-climbing features has been finalized and all future coaches are being made as per the new design. Despite the phenomenal increase in traffic, the number of consequential train accidents has come down from 464 in 2000-01 to 234 in 2005-06, a reduction of almost 50 per cent.

In 2006-07, the number of accidents came down to 195, the lowest-ever since the 1960s. Safety is the prime concern and all possible measures are being taken to ensure the safety of passengers.

The main modules of the ACD includes a GPS (Global Positioning System), which picks up signals from the constellation of GPS satellites that are being exclusively used for this purpose. The GPS submits the data to the Command and Control Unit (CCU) to extract the parameters related to the movement of locomotive like latitude, longitude, speed, angle, date and time. The antenna of the GPS receiver is fitted outside on the roof of the locomotive.

The user-friendly device helps the driver to know the various positions in the form of audio-visual indications, like Station Approach, SOS (for head-on, rear-end and side collision situations) and Gate Open. Another module is the radio trans-receiver, which transmits the information and commands generated by the CCU and receives the information being sent by other ACDs when the two systems are within the radio-range of 3 km.

The final module in the system is the braking mechanism, which envisages the CCU to take a decision for applying either the normal brake or the emergency brake on the locomotive as the situation required. "The electro-pneumatic braking is then applied through suitable solenoid interface installed for this purpose in the cab of the locomotive," the official explained.

ACD is an intelligent friend to the engine driver, which can act on its own without any human intervention. It comprises a Command and Control Unit (CCU), a GPS Receiver, Radio Transmitter and Crew Interface. The CCU, which is the heart of the ACD, is a microprocessor-based module which processes the data and generates commands. The GPS Receiver picks up signals from GPS satellites and submits the same to the CCU to extract parameters related to the movement of the locomotive such as latitude, longitude, speed, angle, date and time.

ACD prevents the head-on collision of two speeding trains, which accidentally happen to be on the same track. An ACD mounted on a train constantly looks out for signals from another ACD in a 3-km range. The moment both the trains are within the required breaking distance, the ACDs, after analysing the data from the GPS, deduce that they are on the same track and are heading for a collision. Then the ACDs automatically apply the brakes, bringing both the trains to a halt without the intervention of the driver.

The ACD can be used not only for avoiding head-on collisions but also to detect if a train has accidentally stopped on the same track as another, preventing a following train telescoping into its rear. Also, if two trains are moving on the same track but the separation distance is less than 2 km, the ACD will automatically regulate the following train's speed. It can also detect when the bogies of a train from an adjacent track derail on to a train's path. Konkan Railways has tested out 11 accident scenarios with the ACD.

The ACD can be mounted not only on trains but also be installed at railway stations, level crossing gates (both manned and unmanned), and on guard vans. If a station is equipped with an ACD, the driver will receive the ``station approach'' warning as the train approaches the station. Also, the ACD can sense whether a level crossing gate is open or damaged and warn the driver, besides regulating the train's speed.

Features of ACD

The principal object of the present invention is to overcome these disadvantages and provide an anti-collision safety device for vehicles travelling on tracks, without any driving personnel, that is to say, a device which itself can estimate risks and react in consequence.

More generally, the invention is intended to provide a device comprising means of observation and making decisions for safe operation, using in particular the principle of deformable movable blocks.

To this end, the present invention relates to an anti-collision safety device of the type indicated above, characterized in that it comprises means for detecting and counting reference points provided along the track, means for calculating the distance of a vehicle from a given zero point, and means for converting this distance into a time with a time reference constituted by a synchronization pulse received by all the vehicles. The device further comprises means for generating a series of position pulses, emitted by all the vehicles and received by all the vehicles, the distance between a vehicle and the vehicle immediately preceding it being determined by comparing the position pulses; further, the safety device of each vehicle compares this relative distance with its stopping distance and causes the vehicle to stop when the relative distance is smaller than the stopping distance.

According to another characteristic feature of the invention, the stopping distance is determined from the actual speed of the vehicle, which may be obtained by a tachometer (e.g., a phonic wheel) supplying speed signals to a function generator which is initialized by the position pulse and which furnishes an output signal as soon as the function generator has reached the actual vehicle speed, the vehicle being caused to stop if the signal from the function generator does not lie within the distance between the vehicle and the vehicle immediately preceding it (relative distance window).

According to another characteristic feature of the invention, an alarm is given by a position alarm device set off separately or in combination by a breakdown of the reference point detector, a beakdown of the reference point counter, or a transmission breakdown. This alarm is transmitted to the central control station (PCC) by the emission of a pulse characteristic of a vehicle, and the central station PCC then distributes a general brake or line emergency stop signal that stops all vehicles on the line.

According to another characteristic feature of the invention, the safe operation of the loop functions (calculaton of position, calculation of stopping distance) is controlled by the signals supplied by duplicate breakdown detecting circuits, the output signals from the means checking for intrinsic safety the coincidence of the output signals of the duplicate circuits, the absence of coincidence characterizing a breakdown or a risk of collision and causing stopping
Technology used in ACDs:-

The heart of the ACD is an Intel 80386 processor that uses the DM&P M617 Intel chipset. It [ACD] has an integrated digital radio modem and works on the VxWorks Real Time Operating System (RTOS). Raja ram adds, “VxWorks, as a platform, is most suitable for real-time applications.”

The working of Anti Collision Devices (ACDs) in Indian Railways

The working of Anti Collision Devices (ACDs) in Indian Railways is described as:-
The loco a.c.d is the heart of a.c.d network. In the a.c.d the radio single from the consolation of Global Positioning System (G.P.S) satellite or received by GPS receiver through by antenna. This signal is sent to the command and control unit that is C.C.U. of the ACD the C.C.U is micro processor based module. And as like a brain of the acd system.

The GPS submits the data to the Command and Control Unit (CCU) to extract the parameters related to the movement of locomotive like

  • Latitude.

  • Longitude.

  • Speed.

  • Angle.

  • Date and time.

It processed the data and generated the commend from the acd. A part from the GPS receiver there is a radio Trans receiver inside the acd. A transmits information such as:

  • Identification no.

  • Speed

  • Location in terms of Latitude, Longitude, and status of it working with the help of sprats radio antenna.

It also received the information being send by other acd range within range 3 Km. this information also send to the C.C.U. for processing all receiving the information from the other acd and the data from the GPS receiver. The C.C.U unit take a design for apply either a normal & emergency break or the locomotive break as the case may be.

This is active with the help of the auto breaking unit of the loco on board mobile loco ACD and guard room acd have both a GPS receiver and radio trans receiver. The GPS receiver received the data from the satellite and radio trans receiver communicate with the other GPS. Within range of 3.Km. the tracks side and sates nary module. Such as :- station ACD, level crossing ACD, and loco side ACD.

Both mobile and stationary ACD exchange information and take decision base on trans working rule. And embedded soft ware to a apply breaks automatic with art any input users. All the ACD work on the principle of distributed control system. It’s very simply but it two ACD on locomotive within pre define distance and proceed and risks on collision system. Automatically active the breaking to the train and prevent collision relay in accident.

Unit for Locomotive

( L:- 435 x, W:- 203 x, H:- 342 mm )‏

The Following Accidents are prevented by ACD:-

  • Detection and Prevention of Head-on, Rear-end and Side Collisions: – Only system in the world to provide these UNIQUE features even when a train is not protected by a signal, as in a block section.

  • Detection of fouling and prevention of collision due to fouling:- Except when a Train on main line overshoots the ‘Fouling Mark’

  • Detection & generation of Train parting / Jumbling: - Consequently bringing any approaching train on the adjoining line to a dead stop.

  • Station Approach Warning to Drivers: - Can result in saving of Manpower for deployment of detonators during foggy weather, Provided 100% coverage of ACD fitted trains is available on the

  • Concerned ACD route.

  • Speed limit imposition:- Based on ‘preset’ conditions in FRS of ACD

  • Train Approach’ Warning for road users at Level Crossings both manned and unmanned :- In addition, at manned non-interlocked level crossings, reducing the train speed to 30 Kmph in case the gate is detected in ‘open’ condition through Gate ACD.

  • Manual SOS functionality available for Drivers, Guards and Station Masters: - To bring all trains to a halt within a radial distance of 3 Kms, in emergencies

The situations in which ACD network can’t prevent a train collision:-
An analysis of ‘preventable’ and ‘non-preventable’ accidents by Safety Directorate of Railway Board of a total of ‘128 train collisions on Indian Railways’ during the five years period namely, from April 1997 to January 2002, indicated that 82% of these collisions were preventable by ACD. The balance 18% of the collisions were ‘non-preventable’ in any case due to various reasons like failure of brake power of train, inadequate reaction time, insufficient braking distance, etc.
Various collisions/situations which are not preventable in any case, with or without ACD network, are enumerated below:

  • Other train is a ‘NON’ ACD Train – ACD functions by reacting to another ACD, as such if one of the two trains is a non-ACD train, the protection against collision will be missing.

  • Adequate’ braking distance at that speed is not available when a ‘dangerous’ collision-like situation arises suddenly – However, severity of the collision would be reduced as a function of the reaction time.

  • Train derails and its wagons/coaches dash with another Train, already on ‘adjacent’ track – No reaction time situation

  • Failure’ of brake power of the Locomotive/train

  • Rolling backward/forward of a ‘Stabled load’

Benefits of the ACD system

  • Very economical and cost effective.

  • Easily adaptable and expandable.

  • Does not degrade the existing safety level.

  • Employs state-of-art hardware and software technology.

  • No way had side equipment required, hence no requirement of Power.

  • No cabling on the track required (which is more expensive and cumbersome)‏.

  • Less susceptible to Vandalism.

  • It does not require any inputs to be fed by the crew at the start of journey, thus human error is eliminated.

Maintenance Support System (MSS)

  • Daily Reports of incidences of Warning to the Driver due to Gate OPEN or Obstruction.

  • Date wise Report of incidences of Warning to the Driver due to Gate OPEN or Obstruction.

  • Daily Maintenance Report – Failure of Loco Unit and Gate Unit.

  • Date wise Maintenance Report – Failure of Loco Unit and Gate Unit.


1. ACDs can be implemented in railways to prevent collisions and to decrease the timing between two consecutive trains running one after another.

2. It can be used in heavy vehicles like cranes, earthmovers etc to prevent accidents and for their safe working in public places.
3. ACDs can be used as a tracking device.








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