From June 5 to Dec 18, train services at 13 stations along the North-South and East-West MRT lines will start at 7am on Sundays - about 90 minutes later than usual.
This is to allow more time for track maintenance and renewal works on the western sector of the network, SMRT said yesterday.
The stations are from Joo Koon to Queenstown on the East-West Line, and Jurong East to Bukit Gombak on the North-South Line.
To minimise inconvenience to commuters, a new parallel bus service will ply from Joo Koon MRT station to Bukit Gombak MRT station (via Jurong East MRT station) in both directions. The service will operate with a 10-minute interval between 5.30am and 7am on Sundays when train services are not available. Fares will be similar to train fares for the same distance. Train, bus and hybrid concession passes will be accepted, SMRT said.
Existing bus services are available for journeys between Jurong East and Queenstown MRT stations.
SMRT said affected commuters can also travel to stations on the Circle and Downtown lines to get to the city.
SMRT has also been closing stretches of the East-West Line - between Tanah Merah and Pasir Ris stations, and between Joo Koon and Jurong East stations - half an hour earlier. The early closures, which will last till end August, are from Sundays to Thursdays.
Last month, SMRT said it had replaced half of the 92,000 timber sleepers on the East-West Line with concrete ones. Sleepers help to hold tracks in place.
An earlier project to replace 96,000 sleepers on the North-South Line was completed last April.
An ongoing project to upgrade the signalling system on both lines is past the halfway mark. Upgrading the signalling system allows trains to run at intervals of 100 seconds during peak hours instead of 120 seconds now.
The power-supplying third rail is also being replaced, but this project is still in its early stages.
Meanwhile, the Land Transport Authority said it is also building a new power intake substation and upgrading the existing power system to increase the network's power supply capacity. But it did not say when this will be done.
Power-related breakdowns have been rising in frequency and severity in recent years.
Said SMRT: "Starting train services at 7am on Sundays at the 13 NSEWL stations will give our project teams, track patrol teams and maintenance teams 29 additional work nights over the six-month period. We seek the understanding and patience of commuters."
Stockbroker Cole Cheong, 49, a Jurong resident who has been using the MRT to get to work for more than 20 years, said: "No choice. They need this extra time to renew the system. The public should have some understanding if it leads to better service in the long term.
"They should have better information about bus services as train commuters who are affected may not be familiar with bus routes," he added.