RAIL INTERLOCKING SYSTEM

1. Context 

2. Key points

• According to the Minister for Railways, stated to the Media that the electronic interlocking and point machine change led to the accident. 
• The Railway Board, the apex body of Indian Railways, also singled out "Signalling interference" in its preliminary probe, with senior officials indicating that possible sabotage and tampering with the interlocking system could have caused the mishap.

3. About Interlocking System.

• Railway traffic is controlled and managed by railway signalling. Interlocking, an integral part of it, involves a set of apparatus placed on a track to manage the safe movement of trains and track to manage the safe movement of trains and track configuration at stations and junctions.
• It prevents conflicting movements as a train gets a signal to proceed ahead only when its route is set, locked and detected as safe.
• The signal apparatus in an interlocking system may be interconnected mechanically or electrically with the tracks or both.
• Electronic interlocking (EI) is an advanced version of signalling that uses computer-based systems and electronic equipment to control signals, points and level-crossing gates.
• The Indian Railways defines it as "microprocessor-based interlocking equipment to read the yard and panel inputs; process them in a failsafe manner and generate required output.
• Unlike the conventional relay interlocking system, the interlocking logic in an EI system is managed via software and electronic components.
• It ensures all elements work together in proper sequence so that trains can move without coming in the way of one another.

Image source: The Hindu

4. Components of Electronic interlocking signal system

4.1. Signal

4.2. Point

• These are moveable sections of a track which allow a train to change track by guiding the wheels towards a straight or diverging line.
• For instance, if a train has to change lines, the point is activated ahead of time and locked.
• Electric point machines lock and unlock point switches in the desired position.

4.3. Track Circuit

• Electrical circuits are installed on tracks to detect the presence of a train between two points.
• These verify whether it is safe for a train to proceed over it.
• Electronic systems, communication devices that control signalling equipment and other components are kept in relay rooms with dual lock access control.
• All systems activities are recorded in a "data logger", similar to an aircraft's black box.

5. Working of the system

• The system receives a command, following which information is collected from the yard and processed to set a safe route.
• The determined route is aligned and signalling devices are interlocked at a particular position.
• A signal to pass is given based on which direction the track is set and whether the divergent track is set and whether the divergent track is free of obstruction.
• If a train is required to switch lines, the system will direct it to the empty track where two lines meet.
• Track circuits, meanwhile, prevent multiple trains from running on that block to avoid a collision.
• All points remain locked until the train has crossed a particular section of the track in use or the signal to proceed has been withdrawn.
• In case there is a failure in the system, the red light will be flashed, indicating that the route ahead is not clear or safe.

6. Causes for the Odish train crash

• A preliminary probe by Railways officials has found that a problem with the signal system could be the cause of the accident at Bahanaga Bazar railway station on the evening of June 2.
• The change that was done to the electronic interlocking led the Coromandel Express off the main line and onto the loop line where it crashed into a stationary goods train.
• The Bahanaga Bazar station has four lines two main lines which are primarily used by trains that don't have a scheduled stop and two loop lines for those trains that have to stop or halt at the station.
• At the time of the accident, two goods trains were stopped on the two loop lines, while the route was set for two mail express trains that were to pass the station via the main lines, as per Railway Board officials. The route, direction and signal were set.
• The Coromandel Express heading south (to Chennai) was given the green signal to enter Up Main line.
• The Yesvantpur Howrah Express heading north (to Kolkata) was to move on the Down Main Line.
• At the time of the accident, the Yesvantpur Howrah was running at a speed of 126 kmph and the Coromandel Express was travelling at 128 kmph both within the permissible limit of 130 kmph for the section.
• As the Coromandel Express was approaching the station, there was a signalling issue and the train move out of the main track and veered onto the adjacent track, the loop line, where it crashed into a parked freight train to carry iron ore, triggering the multi-train collision.
• The impact of the collision was such that the engine of the Coromandel Express and a few coaches jumped the tracks, toppled and hit the last two coaches of the Yesvantpur Howrah Express headed in the opposite direction.

7. Malfunction of the system

• Railway officials suspect that there was outside intervention or tampering because the affected stretch was equipped with the 'errorproof' EI system which ideally should not have taken the Coromandel Express to the loop line.
• The kind of tinkering done with the logic of the system can only be intentional.
• A senior officer, the flaws in the signalling system a few months before the Balasore accident.
• The officer raised the issue of trains getting into adjacent lines despite getting the green signal for another track.
• The official warned that if the signal maintenance system was not monitored and corrected immediately, it would result in serious accidents.