'Software logic issue' was root cause of Joo Koon train collision: LTA

SMRT staff inspecting at a platform of Joo Koon station on the morning of 15 November 2017 after a moving train hit a stationary train at the station, causing injuries to 28 persons.  (Yahoo News Singapore file photo)

A “software logic issue” with the new Communications-Based Train Control (CBTC) signalling system that is being installed on the East-West Line (EWL) was the “root cause” of last month’s train collision at Joo Koon MRT station.

The Land Transport Authority said on Monday (18 December) that its latest findings are consistent with its initial investigations, which were presented to the media on 21 November.

In its news release, the LTA said it had corroborated its findings with CBTC system supplier Thales and that extensive tests and analyses – conducted by the authority, SMRT and Thales – had confirmed the confluence of various “failure conditions” that led to the collision.

This included an “abnormal condition” in the train-borne CBTC equipment, which prevented the train that was hit from communicating with the trackside CBTC equipment. Under normal conditions, such an occurrence would trigger the activation of a protective “bubble” that would ensure the affected train’s safety.

That day, however, the affected train crossed the only track point that had not been fully modified to be compatible with the CBTC system. This led to the train’s protective bubble being deactivated, which subsequently led to it being hit by the train behind it at Joo Koon station.

Moving forward

The LTA said the failure conditions stemmed from operating two signalling systems along the same line. As a precaution, train services along the Tuas West Extension – which operates on the new CBTC system – have been separated from the rest of the EWL since 20 November.

Thales has also completed its modification work on the incompatible track point and has tweaked the software logic of the CBTC system to prevent any future inadvertent disabling of a train’s protective bubble.

The French multinational company will also be setting up a CBTC simulation facility in Singapore to strengthen its testing processes along the North-South Line and EWL.

“This new facility will allow us to perform additional simulation tests which are tailored to the environmental and infrastructural conditions of the rail network in Singapore,” said the LTA.

The facility will be built in two phases, the first of which will be completed by the first half of 2018. This will enable off-site testing of the EWL’s CBTC signalling system before it is rolled out for passenger services.

The second phase, due to be completed by the end of next year, will augment the facility’s CBTC system testing capabilities.

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