The signalling issues behind recent MRT delays will continue to pop up occasionally over the next two years at least, which is the minimum time it would take to overhaul the system, said SMRT.
This year, the rail operator has been hit by at least three instances of faulty signalling on the North-South Line, leading to trains slowing down significantly. One occurred at the end of last month, and was followed by two more on Monday and Tuesday.
SMRT spokesman Alina Boey yesterday said a programme to upgrade the signalling system will "address many of the signalling-related incidents that we are facing today".
But the upgrade, which will allow trains to run more frequently, will be completed only in 2016 for the North-South Line and 2018 for the East-West Line.
Signalling faults accounted for nearly a quarter of the SMRT trains pulled out of service last year on these two lines.
On Monday morning, a track circuit failure between Yew Tee and Kranji stations caused trains to slow down. This held up service on stretches of the line on either side of those stations, resulting in thousands of commuters being late for work and school.
The next evening, a code generator fault along the track at Marina Bay station added about 20 minutes of travelling time for commuters going from Ang Mo Kio towards Marina Bay.
Code generators tell trains how fast they can travel. Tuesday's problem meant trains on the affected stretch had to run at slower speeds while SMRT engineers replaced the generator, said Ms Boey.
SMRT is working on interim measures to minimise such incidents even as upgrading works take place, she added.
These include refurbishing train tachogenerators, which indicate how fast a train is going. Faulty tachogenerators provide inaccurate speed readings to the signalling systems, and can cause signalling issues.
SMRT has previously said that such measures would also take about two years to roll out.
Ms Boey added yesterday: "Despite our best efforts, there will still be delays, as it takes time for us to implement these enhancements over the more than a thousand track circuits on the North-South and East-West lines."
Adjunct associate professor Gopinath Menon of Nanyang Technological University pointed out that rail operators have short windows to work on upgrading overnight, when trains are offline.
He also highlighted how the network is still not extensive enough for commuters to hop onto another line when disruptions happen, although this will change in the future. For instance, the Downtown Line will provide another east-west option when completed in 2017.
"Once the network grows, there will be less effect when something breaks down," said Prof Menon.