Train commuters heading to the western end of Singapore will not be able to use the four stations on the Tuas West Extension (TWE) until Monday. While the four stations on this extension - Gul Circle, Tuas Crescent, Tuas West Road and Tuas Link - will reopen after the weekend, the authorities will keep service between Joo Koon and Gul Circle stations suspended for up to a month.

The move comes as the authorities continue investigations into Wednesday's SMRT train collision at Joo Koon following a signalling glitch, which left 36 people injured. The debacle is the latest in a slew of rail woes, following last month's MRT tunnel flooding. Delays also struck the Circle Line and North East Line on Wednesday and yesterday, respectively.

During the suspension of service on the TWE, bus services will be provided for commuters travelling on this section of the East-West Line (EWL). Come Monday, those who have to break up their journey by taking a bus bridging service between Joo Koon and Gul Circle will not be charged for a separate trip when they rejoin the train network. As many as 100,000 commuters who use the 7.5km extension that opened in June may be affected.

The Land Transport Authority (LTA), in a statement yesterday, said that after suspending service on the TWE, French firm Thales found that both the new communications-based train control system on the TWE and the old fixed-block signalling system used on the rest of the East-West Line were safe for operation. Thales is providing the new signalling system which is already fully operational on the North-South Line and allows for trains to run at shorter intervals.

"Given this finding, the LTA and SMRT have decided to isolate for up to one month the operations of the Tuas West Extension, which runs on the new signalling system, from the rest of the East-West Line, which runs on the old signalling system," said LTA.

The collision had occurred when a train passed a faulty circuit as it was transitioning between the two signalling systems. The train gave out the wrong information to the one behind, which then lurched forward upon misreading the distance between itself and the stationary train.

Transport Minister Khaw Boon Wan said yesterday, "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."

"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. This way, we avoid having trains transiting from one signalling system to another with its attendant safety risk."

Assistant Professor Andrew Ng, of the Singapore Institute of Technology's engineering cluster, said isolating the two signalling systems was the 'right move'. He said, "This isolation is not sustainable in the long run, as commuters will want to have a seamless journey. But it is understandable that investigations have to be carried out."

Government Parliamentary Committee for Transport member Yee Chia Hsing said installing the signalling system is a very complex engineering endeavour, as it is being implemented in different generations of trains. "I hope they can solve this problem before the one month and bring (service) back onstream," he said.