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Odisha Train Mishap: What's Electronic Interlocking? How Did It Cause the Crash?

"It happened due to a change in electronic interlocking,” the Railways Minister had said.

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Video Editor: Puneet Bhatia

On Sunday, 4 June, Union Railways Minister Ashwini Vaishnaw said that a change in electronic interlocking may have caused the horrific train accident in Odisha that claimed the lives of 275 people and injured more than 900 others.

"The commissioner of railway safety has investigated the matter and let the investigation report come but we have identified the cause of the incident and the people responsible for it... It happened due to a change in electronic interlocking," Vaishnaw told news agency ANI.

He added that "whoever did it and how it happened will come out during the detailed investigation."

What exactly is electronic interlocking? What is it used for? How did it cause the mishap? And why did the minister indicate that the electronic interlocking may have been 'tampered with'? The Quint answers these questions for you.

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What Is the Likely Sequence of Events?

The Chennai Central-bound Coromandel Express was passing through Odisha's Balasore station. But reportedly due to an 'incorrect signal', the train that was supposed to go via the main 'up line', changed tracks at a speed of more than 125 kmph.

This was allegedly due to an 'electronic interlocking' error. In other words, the signal for passing through the 'up line' was faulty, and as a result the Coromandel Express switched into the loop line from the main line, collided with a goods train that was parked there.

But it did not stop there. Then, the Coromandel Express derailed and some of the coaches crashed into the Bengaluru-Howrah Superfast Express train passing through the main 'down line'.

"It happened due to a change in electronic interlocking,” the Railways Minister had said.

What Is Interlocking?

An interlocking system is a safety mechanism that ensures the safe, efficient operation of train movements at railway junctions, stations, and signalling points. It is a combination of signals, points ( switches) and track circuits.

"The job of the interlocking system is to ensure that the points, which are movable sections of track that allow trains to change direction from one track to another, are properly aligned and locked in the correct position before a train can pass over them," a former Indian Railways employee explained to The Quint.

Track circuits are electrical circuits installed on the track that determines the presence or absence of a train. Once it determines whether a section of track is vacant or occupied, it enables the interlocking system to control train movements accordingly.

The interlocking system monitors the status of points, signals, and track circuits and combines these components to prevent unsafe situations from occurring. For instance, two trains attempting to use the same track simultaneously – which happened on the day of the Odisha tragedy, or conflicting movements at junctions.

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And What is Electronic Interlocking?

Electronic interlocking (EI) is a type of railway signalling system that utilises electronic components to manage and coordinate the signalling, points, and track circuits.

Such systems are designed to avoid train collisions by ensuring that signals are only cleared to proceed when the route ahead is clear. Essentially, the interlocking logic in the EI System is based on software and hence any change is easy without the need for any wiring changes.

A "change" in electronic interlocking, could have led to incorrect signalling or improper routing that forced the Coromandel Express off the main line.

The train, running at over 120kmph, took the loop line, or side track, colliding into a stationary freight train.

“The signals for a particular train movement can only be given once all the points and crossings for the movement have been correctly set, locked and verified that the route is free of any object (mostly a train),” VM Mathur, a former member traffic of the railway board told The Quint.

“At small stations (such as Bahanaga the site of the accident), the route is set from a central panel operated by the station manager on duty,” Mathur explained.

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Was Electronic Interlocking At Balasore Faulty?

Electronic interlocking systems have been provided at 347 stations during 2022-23, according to LiveMint.

Sandeep Mathur, principal executive director (signalling) of the Railways Board, however, told The Quint that very few stations, of the 7,000 across India, have non-electronic interlocking systems.”

The affected section in Balasore district was equipped with the electronic interlocking system, he confirmed.

As per a report in The Hindu, a preliminary investigation conducted by railway officials has revealed that the signal for the Coromandel Express was given for passing through the Up Main Line and then taken off. Why the signal was given and then taken off isn’t clear as of now.

story in The Print, showed that officials within the railway board had warned sought action against “serious flaws in the system”, especially raising concerns on failure of interlocking in February.

Vaishnaw had also added that added that “whoever did (the alleged manipulation – whether it was human error or system error) and how it happened will come out during the detailed investigation".

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