Land Transport Authority (LTA) announced that, according to its preliminary investigation, the collision between two trains incident which took place at Joo Koon Station on Wednesday (15 November) morning was due to the "inadvertent" disabling of a software protection feature.
In its earlier statement, LTA stated the incident resulted in 23 passengers and 2 SMRT staff sustaining light to moderate injuries, and being conveyed to Ng Teng Fong Hospital and National University Hospital.
It stated that a train heading in the direction of Tuas Link Station stopped at Joo Koon Station to detrain passengers due to an anomaly in the train signalling system at about 8.18am.
Unfortunately, at 8.19am, a second train stopped 10.7 metres behind the first stationary train, which is in accordance with the safety protocol of the signalling system protection that ensures safe stopping distance between two trains.
At 8.20am, after detrainment, the first train’s doors closed and before this train could move off, the second train, activated by the signalling system, moved towards the first train and hit it.
"Thales (the French company which supplied the new signalling system), LTA and SMRT are investigating the incident," the statement wrote.
LTA notes that the preliminary finding was that the first train departed Ulu Pandan Depot with a software protection feature, but the feature was inadvertently removed when the first train passed by a faulty signalling circuit. This train then arrived at Joo Koon station without the feature.
It added that the removal of this feature resulted in the first train giving off a train profile on the new signalling system of a three-car train instead of a six-car train. As a result, the second train detected the first train as a three-car train and misjudged the distance between the two trains, therefore resulting in the collision.
According to LTA, Thales has confirmed the old and new signalling systems continue to be safe for operation. The East-West Line is currently running on the old signalling system from Pasir Ris to Pioneer, and the new signalling system from Joo Koon to Tuas Link.
As a precautionary measure, trains will go through an additional layer of control measures and manual checks before they are deployed.
It said that operations from Joo Koon to Tuas Link will also be suspended on 16 Nov 2017, while it conducts assurance checks with Thales, adding that bus bridging will be deployed for the affected stretch for the duration of the suspension.
LTA deputy chief executive of infrastructure and development Chua Chong Kheng said at a joint press conference held later Wednesday that the trains will also go through an additional layer of control measures and manual checks before they are deployed.
Mr Alvin Kek, SMRT Trains’ senior vice president of rail operations for the North-South and East-West Lines (NSEWL), said that these include instructing drivers to be more alert and vigilant, even when their trains are in automated mode.
He told reporters that the rail operator would also increase the timed separation of trains arriving at NSEWL stations, up to between 2.5 and three minutes from the present two, until they were satisfied with findings from the ongoing investigation.
Mr Chua, however, stressed there was no indication that the removal of the software protection feature was due to human action as he expanded on his use of the word "inadvertent", saying that the new trackside signaling circuit is still a work-in-progress and as the train passed by, we observed this (software protection) feature got removed.
He then added that a thorough investigation was being conducted to get to the root cause.
Talking about the trains which halted 10.7 metres behind the first train, authorities were asked if the rear train driver - subsequently injured in the collision - could have overrode the signalling system and prevented his train from moving forward at an estimated speed of 16km/h.
Mr Kek responded, "10.7 metres away is relatively close, the movement before coming into contact with the first train took only 10 seconds. The driver can override the system, and apply the manual brake, but he didn’t. It is now subject to the investigation."
Meanwhile, Thales representative Peter Tawn said this was the first incident of such a nature, saying, "We are very confident our system is safe. The Thales system is on record one of the safest there is. We've never had a collision.”
Mr Chua then said, "Obviously the situation is not satisfactory, we are concerned and will work closely with SMRT on this. There’s also a technical bit here and we must be clear about responsibilities. This incident involve technical aspects and we need to iron those out with Thales."
"But ensuring the safety of our commuters remains our priority," he added.
One of the trains involved in the incident was pulled away in the direction of Tuas Link MRT station at about 3.20pm. While, the second train was moved out around 40 minutes later, at about 4.05pm.
23 passengers and two SMRT staff sustained "light to moderate injuries". They were taken from the scene of the incident to Ng Teng Fong Hospital and National University Hospital (NUH) in the morning.
Three other walk-in patients went to Ng Teng Fong General Hospital later in the afternoon.
According to the media reports, the three patients remain warded for observation, two at Ng Teng Fong General Hospital and one at National University Hospital.
In all, 22 patients received treatment and were discharged, one declined treatment and returned home, two are still being treated.