To allow fresh concrete to "cure and reach full strength" as part of ongoing track improvement works, some trains will be running slower than usual as temporary speed restrictions have been imposed on affected tracks on the North-South Line (NSL), said SMRT.
This resulted in slower trains and delays yesterday morning which lasted over 11/2 hours.
In a statement yesterday evening, SMRT said it has been carrying out track improvement works during non-operational hours in the NSL south-bound tunnel near Raffles Place MRT station.
These works are slated to be completed by next month, and involve replacing parts of the existing concrete track bed that support the running rails.
On nights when fresh concrete is cast on the track bed, several hours are needed for the concrete to cure.
SMRT's vice-president for corporate communications, Ms Margaret Teo, said: "As a result, some commuters travelling on the NSL towards Marina South Pier MRT station would have experienced slower-moving trains over a 300m stretch between City Hall and Raffles Place MRT stations."
She added that the speed restrictions can cause congestion during peak hours when trains, running at two-minute intervals towards the city, need to maintain a safe distance from one another.
"As such, some commuters may experience trains stopping between stations, or longer waiting times at station platforms," said Ms Teo.
SMRT will progressively lift these speed restrictions in the coming days.
Ms Teo said commuters should, in the meantime, cater up to 15 minutes of additional travelling time on the NSL towards Marina South Pier station during peak hours.
There was also a delay of four hours on the NSL last Wednesday morning for similar reasons and track maintenance works could not be completed before trains started operating.
Marketing strategy consultant Clement Law, 26, was travelling from Admiralty station to Newton station at about 8.30am to get to work when he got caught in the delay.
"Luckily, many people are still on leave from the Chinese New Year break, so the impact wasn't as bad as it would have been otherwise," he said.