How does the rail interlocking system work? (GS Paper 3, Science and Technology)
Why in news?
- An electronic track management system used by the Railways has become the focus of investigation after the multi-train crash in Balasore district of Odisha on June 2, left nearly 300 people dead and more than 1,000 injured.
- The Railway Board, the apex body of Indian Railways, also singled out “signalling interference” in its preliminary probe, indicating that possible sabotage and tampering with the interlocking system could have caused the mishap.
What is an 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 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.
EI System:
- 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 a “microprocessor-based interlocking equipment to read the yard and panel inputs; process them in a ‘fail-safe’ 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.
The three components that form the basis of an electronic interlocking signal system are:
- Signal: Based on the status of the track ahead, light signals direct a train to stop (red light), proceed (green), or exercise caution (yellow).
- 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.
- 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 system activities are recorded in a ‘data logger’, which is similar to the black box of an aircraft.
How does the system work?
- 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 free of obstruction. If a train is required to switch lines, then the system will direct it to the empty track at the point 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.
What caused the Odisha train crash?
- A preliminary probe 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.
- A 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 main lines. The route, direction and signal were set.
- The Coromandel Express heading south (to Chennai) was given the green signal to enter the 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 moved out of the main track and veered onto the adjacent track, the loop line, where it crashed into a parked freight train carrying iron ore, triggering the multi-train collision.
- The impact of the collision was such that the engine of 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.
Did the system malfunction?
- An outside intervention or tampering is suspected because the affected stretch was equipped with the “error-proof” EI system which ideally shouldn’t have taken the Coromandel Express to the loop line. The kind of tinkering done with the “logic” of the system can only be “intentional”.
Role of electronic interlocking systems:
- While electronic interlocking systems in Indian Railways are designed to be highly reliable, like any complex technology, there is a possibility of malfunctions occurring. However, these systems are built with redundancy and fail-safe mechanisms to minimize the risk of failures and ensure safe train operations.
- For example if there is not proper sync between the signals or points or tracks, the system works to stop whichever train is coming, which means the signal would automatically turn red. This is also known as the ‘fail-safe’ system.
- Indian Railways has been implementing electronic interlocking systems across its network to upgrade its signaling infrastructure. These systems contribute to the overall safety and modernization of the railway network by facilitating smoother and more efficient train operations.
