Three out of six major renewal programmes for the North-South and East-West MRT lines will be completed by the middle of this year, with the remaining three slated for completion by early 2020s.
As such, commuters should expect early closures and late openings of the train network to continue beyond June to give engineers more time to carry out such upgrading work.
In a joint statement yesterday, the Land Transport Authority (LTA) and rail operator SMRT said programmes to replace the rail sleepers and power supplying third rail have been completed.
A programme to replace the signalling system on the North-South Line has wrapped up, while that for the East-West Line is "more than 90 per cent" done and will be completed by June.
Three other programmes will be rolled out soon: upgrading the power supply system to cope with the higher train load; replacing the track circuit system (a system related to the signalling system); and the replacement of 66 first-generation trains.
Elsewhere, the LTA has awarded Bombardier, builder of the Bukit Panjang LRT, a $344.25 million contract to overhaul and improve the light rail transit system.
Speaking during his ministry's budget debate yesterday, Transport Minister Khaw Boon Wan said: "We are determined to make our system among the best in the world. Until all the ageing assets are fully replaced and upgraded, we may still encounter some delays or disruptions.
"But we are doing our best to eliminate such risks and should they happen, to minimise inconvenience to commuters."
He added that the shorter operating hours on Fridays and weekends will continue, but did not say when they will end. Mr Melvin Yong (Tanjong Pagar GRC) had asked on Tuesday if these shorter hours will become "a permanent feature".
In response to press queries, a spokesman for Hong Kong's MTR said all its engineering and upgrading works, including the ongoing resignalling programme, are done after operating hours.
Implementing shorter operating hours, he added, was done only once in 2011, when track realignment was necessary.
In that instance, Sheung Wan station (then the western terminus of the Island Line) was closed for 54 hours from end of service on a Friday to start of service on a Monday to adjust the track alignment as part of the West Island Line project.