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Faulty train in Joo Koon collision had safety feature disabled twice

SINGAPORE — In the most detailed explanation to date of events leading up to the collision at Joo Koon station, rail operator SMRT and the Land Transport Authority (LTA) disclosed on Tuesday (Nov 21) that two protective features that would have kept the trains safely apart got disabled in succession.

The train collision at Joo Koon was caused by two faults that knocked out a safety feature to keep trains apart, LTA and SMRT have said. Photo: Low Youjin/TODAY

The train collision at Joo Koon was caused by two faults that knocked out a safety feature to keep trains apart, LTA and SMRT have said. Photo: Low Youjin/TODAY

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SINGAPORE — In the most detailed explanation to date of events leading up to the collision at Joo Koon station, rail operator SMRT and the Land Transport Authority (LTA) disclosed on Tuesday (Nov 21) that two protective features that would have kept the trains safely apart got disabled in succession.

Trains on Singapore’s rail network are kept at a safe distance from one another by so-called “protective bubbles”. While the network had previously experienced instances where one set of “protective bubble” failed, prompting a back-up to kick in, the incident on Nov 15 marked the first time that the primary and secondary safety feature both failed.

The collision injured 38 people, including two SMRT staff. One female commuter remains in hospital, where she is under observation for neck and back pains. 

Transport Minister Khaw Boon Wan acknowledged that the incident had “shattered” public confidence, but maintained: “It (has) happened ... so we have to just get (it) over with and regain the public confidence.”

Senior officials from the LTA, SMRT, and signalling equipment provider Thales used detailed graphics at a briefing on Tuesday to explain the chain of events leading up to the collision at Joo Koon.

The first glitch happened as the faulty train, the one that was eventually rear-ended, left Ulu Pandan Depot to start its east-bound service that morning.

Unknown to anyone at the time, an “abnormal” loss of communication between the train’s on-board computers disabled the first “protective bubble” around the train.

While a second, back-up protective bubble kicked in immediately, this was knocked out as the train passed a trackside device at Clementi that had not been modified for the new signalling system — which presently runs between Pioneer and Tuas Link at the western end of the line.

The East-West Line is running on two different signalling systems, with the old system in use from Pasir Ris to Pioneer stations.

According to SMRT Trains’ chief executive Lee Ling Wee, some trains departing the depot had previously seen their first protective bubble disabled. Some instances of this had been observed since the Tuas West Extension kicked off in June, though the back-up bubble kicked in and no safety incidents occurred as a result.

“The reason the collision was possible this time is because, on top of all these things, there was on-going work near Clementi and that actually caused the (second) bubble to be removed,” said Mr Lee.

The removal of the second protective bubble was unprecedented. LTA chief executive Ngien Hoon Ping added: “What Thales had not anticipated in the Nov 15 incident was that (the second safety feature) became disabled because of that incomplete modification ... in Clementi.”

The faulty train, however, was able to run without a hitch to Pasir Ris and turn around towards Tuas Link, because it continued to run under the old signalling system. The new signalling system had been running in the background in a “passive” form.

The removal of the first protective mechanism went undetected until the train reached Pioneer station, where the East-West Line transits between the two signalling systems.

As the train switched to the new signalling system, the captain noticed the problem and alerted SMRT’s operations control centre to it. He was directed to drive off in a restricted manual mode - which caps his speed at 18kmh – and disembark all passengers at Joo Koon, the next station, before withdrawing it from service.

Things went as planned until the driver shut the platform screen doors at Joo Koon station, which lifted a “closed-track” message to incoming trains.

A second train that had stopped about 36m behind, operating under fully automatic mode, began moving forward. It then rear-ended the faulty train, which had not moved off and had no “protective bubble” after the feature was disabled twice.

Officials at the briefing clarified that the distance between the trains that day was about 36m, and not 10.7m as they had previously told the media. The longer distance was based on actual logs, while the 10.7m gap had been given based on estimates from video footage of the incident.

Transport experts said the explanation given by the officials on Tuesday was informative, but also raised more questions.

Dr Walter Theseira of the Singapore University of Social Sciences (SUSS) said more analysis and tests needed to be done to ascertain the root causes and chain of events leading up to the event.

“Train signalling systems are comprehensively tested before they are pushed out, clearly. If both protective features had failed, somewhere earlier down the line, a root systemic cause might have contributed to it,” he added.

Dr Park Byung Joon, who is also from the SUSS, said he was concerned about contingency plans in the event that such protective systems failed.

Thales had said the two protective features are “standard” in the company’s system and are consistent with other systems worldwide.

Said Dr Theseira: “To be fair, engineering systems are complex and difficult, but in the event that such a failure was foreseeable, and hence, the collision could have been prevented, then the public needs to be given an explanation in due course.”   

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