Train disruptions yesterday, which affected tens of thousands of commuters during the evening peak hours, were blamed on a fault in a new signalling system being put through its paces.
Train operator SMRT and the Land Transport Authority (LTA) said the system is expected to "take a few more months to fully stabilise".
The entire North-South Line (NSL) went down just after 5pm. While SMRT engineers were able to get the line up again within 10 minutes or so, trains were moving noticeably slower - delaying journeys by as much as 30 minutes and causing crowding at several stations. It was about 7.20pm when SMRT said service had resumed fully.
A signalling fault on the Tuas West Extension - which opened just over a week ago - also affected service between Joo Koon and Tuas Link stations at the same time, although things were back to normal just after 6pm.
The LTA and SMRT said initial investigations pointed to a "failure in the radio communication network" of the new signalling system.
The day before, they had warned that in the coming weeks, intensive checks on the new system could lead to delays if fresh issues emerged.
They added yesterday: "Unlike new lines where the signalling system can be fully tested before being put into... service, we have to continue full-day checks on the existing NSL even as service is ongoing."