SINGAPORE - To allow fresh concrete to "cure and reach full strength" as part of ongoing track improvement works, some trains will be running slower as temporary speed restrictions have been imposed on affected tracks on the North-South Line (NSL), said SMRT.

This resulted in delays and slower trains on Monday (Feb 19) morning which lasted over an hour and a half. On Twitter, SMRT had said track improvement work meant that commuters had to add 15 minutes of travelling time from Ang Mo Kio station to Raffles Place station on the NSL

In a statement on Monday evening, SMRT said that 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 near Raffles Place MRT station are slated to be completed by March 2018, 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 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 300-metre stretch between City Hall and Raffles Place MRT stations."

She added 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.

In the meantime, Ms Teo said commuters should 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 (Feb 14) for similar reasons and track maintenance works could not be completed before trains started operating. Journeys took 20 minutes longer from 6am to 10am.