From precision to peril: Role of signalling in train accidents

How does railway signalling work?

It has two main parts: one dealing with the movement of trains between stations and another within a station. Movement of trains between two stations is governed by ‘block rules’—the track is divided into blocks electronically, with signalling at both ends of the block. Within stations, movement is regulated by ‘interlocking’ that ensures trains aren’t set on collision course with the right signalling and alignment of points—the place where a train change tracks. If a part of the track or the loop line is already occupied by a train, the interlocking system ensures the signal for the approaching train is not cleared.

What can go wrong with the system?

The signalling system in India is automatic. There is little manual intervention now. Though automatic signalling is being used across the railway network, the systems vary at different places. Indian Railways is moving to a uniform signalling system called ‘electronic interlocking (EI)’— a network of signals and switches—which would control the movement of trains. But problems could arise due to external interference (like sabotage), system lapses and software glitches. Also, electrical signalling derives its power using underground cables. Faults there could alter EI functioning.

Is signalling mostly at fault in train collisions?

As per a report by the Comptroller and Auditor General last year, out of 2,017 train accidents between 2017-18 and 2020-21, 1,392 or 69% were due to derailment. And an analysis of 1,129 ‘inquiry reports’ of derailments revealed 24 factors, including incorrect setting of points at stations, and system and technological deficiencies in signalling systems.

So, what went wrong in Odisha?

The train accident is still being investigated and the Railway Board is seeking a CBI enquiry. But preliminary investigation points to a signal failure. Coromandel Express, entering Bahagana station, was green signalled to enter the main line but this was taken off, so the train entered a loop line where an iron ore-laden goods train was parked. Railway minister Ashwini Vaishnaw has blamed a change in electronic interlocking, pointing toward human intervention and sabotage.

How can train travel be made safer?

In 2022-23, 530 km of tracks were upgraded with automatic signaling as compared to 218 km in 2021-22, an increase of 143.12%. These are the best figures for automatic signalling in the history of Indian Railways. A large number of digitally interlocked stations have been created. The Research Designs & Standards Organisation, along with manufacturers, has developed an automatic protection system named ‘KAVACH’. This activates the brakes if the pilot fails to control the train as per signal or speed restrictions.