New Delhi: A day after a passenger train rammed into a stationary freight train near Chennai, experts and union leaders said according to the data-logger video, the Mysuru-Darbhanga Express train was given a green signal to pass through the main line, however, it entered a loop line already occupied by the freight train.

Train number 12578, Mysuru-Darbhanga Bagmati Express, collided with the stationary goods train at the Kavaraippettai railway station in the Chennai rail division in Tamil Nadu at around 8:30 pm on Friday, leading to injuries to nine passengers.

The data logger is a device placed in the station area to capture train movements and signal aspects, among other things.

This data logger's yard-simulation video has been circulated among senior railway officials' WhatsApp groups since Saturday morning, prompting them to draw a parallel between the accident and the Balasore train collision of June 2, 2023.

When contacted, the chief public relations officer (CPRO) of the Southern Railway said he is not aware of any such video and that multiple investigations have already been initiated into the collision.

In a press statement released late on Friday, the Railway Board also admitted that the passenger train was given a green signal for the main line but it experienced a jerk and entered the loop line, resulting in the collision with the freight train. A high-level enquiry has been ordered into the incident.

The board said on Saturday that the commissioner of railway safety will conduct a detailed investigation as he visited the accident site in the morning.

In Balasore, the Howrah-bound Coromandel Express was given a green signal for the main line. However, due to the wrong interlocking of tracks, it entered a loop line and collided with a stationary goods train.

"Based on the information available in the public domain, it appears that this collision almost repeats the Balasore train collision of June 2, 2023. The railways should take a serious approach to remove the anomalies in the signalling system," R Kumaresan, president, All India Loco Running Staff Association (AILRSA), Southern Railway, said.

According to safety experts, in an automatic-signalling system, the signal aspect follows the interlocking of tracks. It means if the signal is green for the main line, the interlocking will automatically be set in such a way that the train comes on the main line.

"The lack of coordination between signal aspect and interlocking happens due to some fault in the signalling system. Prime facie, it appears to be some kind of a technical glitch," a safety expert said, requesting anonymity.

Sanjay Pandhi, the working president of the Indian Railway Loco Runningmen's Organisation (IRLRO), expressed surprise as according to him, all previous trains passed through the said station "without any abnormalities in the signalling and interlocking system".

"In Balasore, the collision happened soon after the signal-repair work was over. Contrary to that, there was no such thing reported at the Kavaraippettai railway station and train operations were normal.

"So it appears that some malfunction, which could be corrosion of mechanical equipment etc., might have happened, leading to a coordination break of signal and interlocking," Pandhi said.

K P Arya, who retired as the chief signal and telecom engineer/information technology in the Northern Railway, said, "The data logger's yard-simulation video shows that the train concerned is going on both the main line as well as the loop line, which is not possible." "So there is a possibility that the train might have derailed at the interlocking point and while the engine and some coaches headed towards the loop line and collided with the freight train, the remaining coaches scattered all around, infringing the main line as well," he added.

Arya said it is a widely-known (but never officially acknowledged) engineering defect of tracks and interlocking-point mechanisms, which can cause such a derailment.

"I have gone on highlighting this aspect during my various tenures to the Railway Board as well as to the commissioner of railway safety," he said.

The experts said a clear picture would only emerge after a thorough investigation, which is already on.