Updated at 5pm, Nov 2:
Train services have resumed on the Circle Line (CCL), after nearly three hours of disruption caused by a signal fault during the peak hours of Wednesday morning (Nov 2).
But what caused the signal fault?
Preliminary investigations indicate that "an interfering signal could have disrupted the communications", said LTA and SMRT in a joint statement today.
The nature of the faults could be similar to the series of week-long delays that occurred on the same MRT line in September this year.
When the delays occured then, SMRT explained that the fault had to do with "intermittent loss of wireless communication between the signalling equipment on the trains and signalling equipment on the track".
As to what is interfering with the signal? SMRT still doesn't know.
"The source of the interfering signals could not be conclusively established as the incidents subsequently stopped," SMRT said today, adding that there has been no occurrence of similar signalling faults until this morning.
So what is LTA and SMRT doing?
1. LTA and SMRT have arranged with the Infocomm Media Development Authority (IMDA) and mobile network operators to suspend telecommunication signals along stretches of CCL for short periods of time to assist in investigations, should similar signalling faults recur.
If temporary telecommunication signal suspensions have to be carried out, there will be in-train and station announcements along the affected stretches.
2. All CCL trains will be manned during evening peak hours for faster response and recovery. SMRT will also deploy additional manpower at train stations to assist commuters.
3. Following the CCL incidents in September, LTA and SMRT had commenced feasibility studies to strengthen the existing signalling communications network, including exploring placing an electromagnetic shield on the train to minimise the impact of interfering signals, and changing the signal system frequency and/or modifying the system to provide redundancy.
What happened today (Nov 2)
SMRT first tweeted at 7.37am, informing commuters of 10 minutes of additional waiting time between Pasir Panjang and One North stations.
Shortly after the tweet, SMRT said in an update that the signal fault had been resolved.
However, more updates followed, announcing that trains travelling towards Harbour Front would be delayed by about 10 minutes, and that its engineers were investigating the fault.
An hour after the start of train service disruption, SMRT said that the waiting time on the Circle Line was extended to 30 minutes and that free bus services had been made available at all Circle Line stations.
At 9.06am, the transport operator added there was no train service between Botanic Gardens and Serangoon stations.
Regular train services were finally resumed at 10.27am, with buses plying routes between Bishan and Paya Lebar stations.
On social media, commuters also shared their frustration after being left stranded in crowded train stations affected by the service delay.