Land Transport Authority (LTA) reported that the disabling of the software protection feature that resulted in the 15 November 2017 train collision arose when the faulty train was transiting between the old and new signalling systems.
Given this finding, LTA and SMRT have decided to isolate the operations of the Tuas West Extension for up to one month, which runs on the new signalling system, from the rest of the East-West Line, which runs on the old signalling system.
They stated that this will enable the engineers to carry out further assurance checks together with Thales, adding that as they need some time to prepare the commuters and their staff for this arrangement, the suspension of Tuas West Extension will continue till Sunday.
Commenting on this, Mr Khaw told the media, "Although Thales is confident, I am disturbed by the finding that a critical safety software could be disabled by a defective trackside device. Until this concern is fully addressed, we should not resume the link between Tuas West Extension and the rest of the East West Line."
He added, "I have told the team to keep separating the two sections of East West Line, if need be until the entire (line) is ready to run on the new signalling system. This way we avoid having trains transiting from one signalling system to another with its attendant safety risk."
In a Facebook post, LTA said that the whole-day suspension of the Tuas West Extension service on 16 November 2017 has been very useful for the Thales engineers to carry out detailed assurance checks on the new signalling system.
It reported that based on these checks, Thales has confirmed that the old and new signalling systems are respectively safe for operation.
LTA then announced that train service on the Tuas West Extension between Gul Circle and Tuas Link will resume operations on Monday, 20 November 2017, using the new signalling system. While, the rest of the East-West Line will continue to run on the old signalling system between Pasir Ris and Joo Koon.
From Monday, when the Tuas West Extension resumes service, bridging bus services will be available between Joo Koon and Gul Circle MRT stations.
The Tuas West Extension consists of Gul Circle, Tuas Crescent, Tuas West Road and Tuas Link stations.
On Thursday (16 November) morning, 33 buses were deployed on the bridging bus service between Joo Koon and Tuas Link MRT stations at headways of three to five minutes.
In addition, several bus trips were added to key trunk services in Tuas to better serve commuters in the area.
"Service was satisfactory. We will continue to provide bridging bus services between Joo Koon and Tuas Link MRT stations until Sunday evening," LTA and SMRT stated.
LTA stated that, along with SMRT, it will continue to investigate the incident together with Thales.
The project manager for the new signalling project in Singapore,Mr Peter Tawn, has stated on Wednesday that he disabling of the safety feature was the first occurrence for Thales anywhere in the world.