Why Coromandel Express crashed in Odisha

The CBI has been asked to investigate the crash, alongside the statutory inquiry by the Commission of Railway Safety (CRS).

Here are the basics of how the system works.

 

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First, what is meant by ‘interlocking’ in railways?

Interlocking in railway signalling systems is a crucial safety mechanism that ensures train movements continue without any conflicts, thus preventing accidents.

There are three main components of the interlocking system: point, track occupancy sensing devices, and signal. The interlocking system coordinates the functions of these three components to control train movements.

The digital interface of this system is a computer screen (or multiple screens) that shows the full view of the station layout, the real-time movement of trains, the signals, and the position of the points. This computer interface is called a data logger.

What is the function of each of these three main components?

* Signals (which are lights of green, red, and yellow colour) are installed along the tracks to indicate the status of the track ahead.

* Track circuits are electrical circuits (also known as track-occupancy sensing devices) that detect the presence of trains.

* Points allow trains to change tracks. The Coromandel was supposed to go through Bahanaga Bazar on the ‘Up’ main line, but the point just before the station switched the express on to the loop line that was occupied by the stationary goods train.

And how do the points work?

The points, also called switch rails, are movable rails that are typically placed at the point of divergence of two tracks going to different directions. Once the direction of a train is determined, the point gets locked at a particular position, and cannot be budged until the train has passed. The driver, or loco pilot, has no say in this matter.

How does the system sense whether a track is occupied?

There are various kinds of track-occupancy sensing devices. Generally, sensors are installed on the tracks that detect the passage of wheels on the rails. These are called axle counters. They count how many sets of wheels or axles have passed over them in order to determine whether the entire train has passed through.

So how is this whole system configured?

A ‘sound logic’ of what is safe train operation is fed into the interlocking system, which is controlled remotely from the station.

Earlier, when technology was more basic, this job would be done manually, wherein a pointsman would physically operate the point to change its direction for an incoming train, and to lock it. Someone would then physically show a green flag or signal to the train after checking that the track was clear of obstacles. The driver would see the flag/ signal and proceed.

Today, out of the 7,000-odd stations in the Indian Railways network, only around 100 small stations still have manual levers to control these points. The rest operate electronically, even though the basic principles of the logic are taken from the old and time-tested standard operating procedure for safety.

In the case of the Coromandel, the logic in the computer would be that if the Up line (on which the Coromandel was) is vacant, and if the point is directed to the Up line and is locked for the Coromandel, then the signal to the train should be green.

How safe is this system?

If any of the three components (signals, points, and track occupancy sensors) does not correspond to the overall ‘safe’ logic fed into the computer, the system will work to stop the oncoming train. This means if the point is not locked, or not set to the desired direction, and/ or if the sensing device detects that the track is not clear, the signal will automatically turn red — indicating to the oncoming train that something is wrong and that it should stop.

This is called a “fail safe” system — one that errs on the side of safety.

Who operates and monitors the interlocking signalling system?

The interlocking system is usually operated and monitored by trained personnel from the signalling and telecommunications department in Railways, often known as ‘signallers’ or signal operators. They are responsible for setting the signals, monitoring track circuits, and ensuring the safe movement of trains.

Are interlocking signalling systems used worldwide?

Yes, interlocking systems are used in railway networks worldwide. Countries may have variations in their signalling practices and technologies, but the underlying principle of preventing conflicting train movements remains the same.

How are these systems secured against interference?

The relay room — which is the place from where the entire interlocking/ signalling apparatus can be controlled or manipulated — is locked with double locks. One key is with the station master; the other is in the custody of the signalling staff.

To open the relay room for any maintenance the station master’s approval is required, and every entry and exit is logged in a register.

As technology improved over the years, the Indian Railways put in place a system in which the opening and closing of the relay rooms were connected electronically to the data loggers. Every such event is not only registered on the servers, but it also triggers an SMS that goes to the officials concerned.

This is done to prevent unauthorised access. Since relay rooms (or huts or cabins) are places from where signals can be manipulated, their access protocol is strictly codified and guarded.

Can this system be tampered with?

The system is designed to be fail-safe. However, as Railway Board Member (Operations and Business Development) Jaya Varma Sinha said on Sunday, any machine is “prone to failure even if it runs smoothly 99.9% of the time”.

She said things like digging work may snap cables, wear and tear and short circuit etc can cause failures. “Generally these things don’t happen. But that 0.1% possibility of failure due to any reason is always there in any kind of system,” Sinha said.

However, railway operations and maintenance is replete with instances wherein signal maintainers at stations have been found trying to bypass the system locally to rectify what they believe would be minor jobs that could be done without accessing the relay room.

As it now appears in the case of this accident, a signal maintainer or technician of the signalling department at the Bahanaga Bazar station did open one of the location boxes at the station to “loop” the circuit and achieve a “clear path” (or a green signal) for the Coromandel Express.

Location boxes are the junctions of cables from various hardware meeting circuits to work in the pre-set safety logic.

This safety override is usually unauthorised. This is because in normal circumstances, signal maintainers would have to furnish a disconnection memo to the station master in order to do anything to the interlocking system.

Once anything to do with the interlocking is disconnected, every aspect of signalling would have to be done manually following laid-down procedures of safety — flagging the signal after ensuring the line is without obstacles, manually setting the point, and so on. For longer durations, if the maintenance job is major, a temporary “traffic block” — when no train operation on the line would be allowed for some time — is to be effected.

Are the Railways doing anything to prevent such unauthorised maintenance work?

Yes, checking such unauthorised “off the book” maintenance activity is a continuous activity. Regular safety drives are conducted to make sure everything is as per laid-down protocols. On Monday, the Railway Ministry ordered a weeklong drive to check whether all signalling equipment across India are in perfect order. This includes checking the security protocol around access to relay rooms and other signalling infrastructure.