A damaged power cable led to a series of events that caused a major MRT disruption affecting three train lines on Wednesday night - an incident which transport experts said could have been avoided.
Public transport operator SMRT Corporation - which runs the North-South, East-West and Circle lines which were hit - said in an update yesterday that the incident started with the breakdown of the insulation of a power cable.
The cable was between the Tuas Link and Tuas West Road stations on the East-West Line.
A circuit breaker at Tuas West Road station should have kicked in to isolate the fault, but it did not.
This caused the North-South and East-West lines' power system to trip, bringing down stretches of Singapore's two oldest and most-used train lines at 7pm, during the evening peak hour, and affecting thousands of commuters. The affected stations were between Woodlands and Jurong East on the North-South Line, and Queenstown and Gul Circle on the East-West Line.
The power fault caused blackouts at train stations and stranded commuters on trains along the tracks.
SMRT then tried to draw power from the Buona Vista Intake substation, which also serves the Circle Line. However, this was done without first isolating the initial fault.
This resulted in the Circle Line being hit at 7.30pm and more commuters being affected as there were no train services along a 16-station stretch, from HarbourFront to Serangoon stations.
SMRT said it is working with the Land Transport Authority (LTA) to conduct a full investigation into the "premature failure" of the components. The equipment manufacturers which supplied the parts are also being investigated.
Wednesday's train disruption was the worst of its kind to hit the MRT network since 2017, when stretches of the North-South and East-West lines were also disrupted due to a power fault.
The concurrent failure of three train lines is also rare.
The Straits Times understands that the fault on Wednesday is unrelated to ongoing power replacement works on the North-South and East-West lines. It originated from a stretch of the East-West Line that is relatively new and not involved in the replacement works.
The disruption was likely a one-off incident due to the confluence of factors that increased the scale of the disruption, said Assistant Professor Raymond Ong of the National University of Singapore, who researches transport infrastructure.
But he said SMRT has to relook how it reacts to faults: "There needs to be protocols in place to prevent one system from affecting another. This is critical. Wednesday's incident was avoidable."
He added that a better evacuation plan in the event of inclement weather is also necessary, as the elderly and sick will suffer during the prolonged wait.
The evacuation of some trains took nearly three hours on Wednesday, with the wet weather and lightning risks impeding progress.
Singapore University of Social Sciences transport researcher Park Byung Joon said it was easy with the benefit of hindsight to blame SMRT for drawing power from the substation without first isolating the fault, but it must be noted that a decision had to be made there and then with imperfect information.
"They were facing multiple failures and did not have the full picture," he said. "They should create a checklist so that they know what to do in case of multiple failures like this to prevent it from happening again."
Speaking on the sidelines of a press conference yesterday to announce that Hong Kong and Singapore had agreed to establish an air travel bubble, Transport Minister Ong Ye Kung said the incident was a reminder to him and transport operators not to be complacent.
"(The MRT network) is a complex system, every little part matters, just as every worker, every engineer, every station manager also matters," he said.
"(We must) continue to work hard together to make sure the system works as well as possible."
Wednesday's incident was the first major disruption the Transport Minister has had to face since he took over the portfolio in August.