While emergency brakes can be applied on trains travelling in automatic mode, SMRT staff could not have anticipated the software glitch that led two trains to collide at Joo Koon Station last November, Transport Minister Khaw Boon Wan said on Wednesday (Jan 10).

Both the staff at the Operations Control Centre and the train captains in question did not know the protective bubble to keep trains a safe distance apart could be deactivated, and hence could not react to prevent the incident, he said, reiterating that the incident was unprecedented.

“Thales, the supplier of the CBTC (communications-based train control signalling system), had not anticipated such a scenario. This was an isolated case with no precedent, even for Thales,” said Mr Khaw, who was responding to Non-Constituency Member of Parliament Dennis Tan’s questions on the incident in Parliament, including whether the captain of the second train could have applied brakes in time.

“Had they been aware, the train captain on the second train could have switched from Automatic to Restricted Manual Mode to drive the train manually or, as a last resort, engaged the emergency stop button to keep the train from moving,” he added.

On November 15, a train rear-ended another at Joo Koon MRT station, injuring 38, including SMRT employees.

“Based on train logs, the train captain in the second (incoming) train was unable to engage (the) emergency brakes in time to avert the collision,” he said.

“So I think on hindsight, one can blame the captain but I don’t, because he was mentally not prepared and never trained to react for that kind of scenario. So, whatever it is the flaw, Thales has accepted full responsibility, apologised, and the flaw has been rectified,” he said.

The Land Transport Authority’s investigations into the incident found that the first train developed an “abnormal condition” with its on-board signalling equipment, which prevented it from communicating with the trackside signalling equipment.

When this happened, the system developed a “protective bubble” around the affected train to ensure its safety. But this safety feature was unexpectedly disabled when the train crossed a point on the track that had not yet been fully modified for the new signalling system. That was why the second train, operating in automatic mode, had moved towards the first at Joo Koon Station, and collided into it.

The East-West Line runs on two different signalling systems, with the old one in use from the Pasir Ris to Pioneer stations while the new one runs between the Pioneer and Tuas Link stations — a protocol which has “introduced complications” to the infrastructure, said Mr Khaw on Wednesday.

As an “added precaution”, train operations from the Joo Koon to Tuas Link MRT stations have been separated from the rest of the East-West Line since Nov 20. Thales has also completed its circuit modification works for the incompatible track point and is modifying the software logic of the signalling system to prevent future disabling of the protective bubble.

Source:
courtesy of TODAY

by Kelly Ng

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