SINGAPORE: A software glitch that resulted in the Joo Koon MRT station train collision arose when the faulty train was "transiting between the old and new signalling systems", said the Land Transport Authority (LTA) in a statement on Thursday (Nov 16).
The collision was caused by a software glitch in the East-West Line (EWL) signalling system, authorities had said on Wednesday evening.
Operations on the Tuas West Extension were suspended for the entire day on Thursday for signalling contractor Thales to carry out checks on the new signalling system.
The Tuas West Extension runs on the new signalling system while the rest of the EWL runs on the old one.
Based on these checks, Thales confirmed that the old and new signalling systems were both safe for operation, said LTA.
"The disabling of the software protection feature that resulted in the Nov 15, 2017 train collision arose when the faulty train was transiting between the old and new signalling systems," the authority said.
Given this finding, LTA and SMRT have decided to "isolate for up to one month" the operations of the Tuas West Extension from the rest of the EWL, LTA added. This will enable further checks to be carried out.
"As we need some time to prepare our commuters and our staff for this arrangement, the suspension of Tuas West Extension will continue till Sunday," the statement said.
Though train services on the Tuas West Extension between Gul Circle station and Tuas Link station will resume on Monday, this part of the line will still be kept isolated from the rest of the line, which will continue to run on the old signalling system.
Bridging bus services will be available between Joo Koon station and Gul Circle station.
LTA added that 33 buses on Thursday morning had been deployed on the bridging bus service between Joo Koon and Tuas Link MRT stations "at headways of three to five minutes" and that "service was satisfactory". These bridging bus services will continue to be provided until Sunday evening.
Bus trips were also added to "key trunk services" in Tuas.
LTA and transport operator SMRT will continue to investigate the Joo Koon collision incident together with Thales, the authority added.
"DISTURBED" BY FINDINGS ON SOFTWARE GLITCH: KHAW BOON WAN
In a separate statement on Thursday, Mr Khaw said that he was "disturbed" by the finding that a "critical safety software could be disabled by a defective trackside device".
He said that until this was "fully addressed", the link between the Tuas West Extension and the rest of the East-West Line should not be resumed.
"I have told the team to keep separating the two sections of EWL, if need be until the entire EWL is ready to run on the new signalling system," he said. "This way we avoid having trains transiting from one signalling system to another with its attendant safety risk.”