What is electronic interlocking system that led to Odisha train accident? Know its significance

The electronic interlocking system forms the nerve-centre of the Indian Railways’ signalling apparatus.

Union railways minister Ashwini Vaishnaw on Sunday said that the train accident in Odisha’s Balasore may have been due to a change in the electronic interlocking system, even as the commissioner of railways safety continues an investigation into the country’s worst rail tragedy in nearly three decades.

Restoration work underway at Odisha’s Balasore district on Sunday. (PTI)

Read here: Ashwini Vaishnaw prays as train movement at Odisha crash site resumes| 10 points

The electronic interlocking system forms the nerve-centre of the Indian Railways’ signalling apparatus. It is an interconnected system of signals, crossings and points – the three elements that comprise the signalling set-up – and ensures that trains across the railways’ expansive 120,000km network travel seamlessly and do not come in each other’s way.

A point is a moveable piece of track that changes a train’s direction. These are moved using switches operated from a control panel. A crossing, usually installed at a junction, performs a similar function.

Points, crossings and signals communicate with each other electronically in the interlocking system. Points along a line are “interlocked” and operate in sync with signals to ensure trains running on the same track do not collide and that a train does not enter an already occupied line – as happened on Friday evening. So, if a train is travelling down, or stationary, on one path and a second is approaching it, the system is automatically programmed to change signals, or points, to slow down or divert the latter train.

The Chennai-bound Coromandel Express rammed into an iron ore-laden goods train on the loop line near the Bahanaga Bazar station in Balasore on Friday evening.

Read here: CBI probe recommended into Odisha three-train collision, says Ashwini Vaishnaw

A loop line is a railway track that diverts from the main line and rejoins it at a further distance. They essentially serve as service lanes for trains to make stoppages or overtake manoeuvre without affecting other trains.

The Coromandel Express had been shifted to the loop line seconds earlier, even when it was not scheduled to stop at the Bahanaga Bazar station and was travelling around its permitted top speed of 130km/hr.

A change in the system, as Vaishnaw said on Sunday, would imply human interference to keep the electronic network from operating as intended.

“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 obstruction (mostly a train),” VM Mathur, a former member traffic of the railway board said.

Track circuits (an electrical system that detects the absence of a train on a section of track) are used to verify that a route is not occupied.

“At small stations (like the one involved in the accident), the route is set from a central panel operated by the station manager on duty,” Mathur said.

As HT reported on Sunday morning, this could imply that the point on the track was incorrectly changed, leading the passenger train on to the occupied loop line. An expert also indicated a third possibility – that the Coromandel Express derailed before hitting the freight train.

Sandeep Mathur, principal executive director (signalling) of the Railways Board said, “Very few stations, of the 7,000 across India, have non-electronic interlocking systems.”

The affected section in Balasore was equipped with the electronic interlocking system, Sandeep Mathur confirmed, which means that it did not require manual intervention and operated automatically.

Explaining the functioning of the system Sandeep Mathur said, “If a train has to go to a loop line, then there is a point that has to be operated to direct the train. If the train has to go straight and the tracks are not occupied and the points are correctly set then the signal is displayed to be ‘green’ indicating to the loco pilots that they can continue running on the same track. However, if a train has to change its track and enter a loop line, then the signal is displayed to be ‘yellow’.

Read here: How Coromandel Express derailed, set off triple-train collision, explains Railway Board

“Even if this system fails, the signals will automatically turn red, not allowing the train to continue running at the same speed,” said Sandeep Mathur.

However, experts underlined that there is little possibility the system failed.

“It is unlikely for a system like this to fail. In my opinion, the Chennai-bound train either derailed first and then rammed into the goods train, or there was some kind of sabotage,” VM Mathur said.