An ongoing four-year project to replace timber sleepers in the two oldest MRT lines is affecting train speeds and lengthening journey times by as much as 40 per cent.
About 188,000 worn sleepers - thick rectangular planks on which the tracks sit - are being replaced on the North-South and East-West lines. Work started late last year and is expected to be completed by 2016.
Trains running over stretches where new sleepers have just been installed slow down as a precaution. This has reduced train speeds and increased journey times by up to 40 per cent.
A Land Transport Authority spokesman said "speed restrictions are temporarily imposed on sections of the track where sleepers have been recently replaced".
She added that these stretches are "monitored for a few weeks as a precautionary measure before speed restrictions are lifted".
Rail operator SMRT would not reveal how much the average speed has fallen, but said "journey time between terminals has increased by an average of 10 minutes". That works out roughly to a 40 per cent increase to 35 minutes in travelling time from Jurong East to Marina Bay.
And commuters are feeling it.
Stockbroker Cole Cheong, 46, who takes a train from Lakeside to Raffles Place for work, said the slower trains seem to worsen crowding during morning peak. And he is often late for work.
"It doesn't help much if I wake up earlier. So I get used to coming in late. As long as I get in before the market opens, it's fine."
Financial trainer Toh Teng Mok, 55, described the drop in speed as "bad", estimating that trains travel as slow as 30kmh - from the usual 70-80kmh. "This is an essential service," he said. "How did it come to this state?"
Other commuters said SMRT could have warned of the drop in speed and announced when normal service can resume. Finance director M.H. Tan, 60, said: "It's better to communicate to the public so as to avoid misconception that there is a technical problem. With proper communication, I'm sure people will understand."
SMRT had put up posters in stations and announcements on its website of the resleepering project - including a schedule of which parts of the network are affected and when. But it did not say the project would result in trains running slower.
An estimated 10 per cent of the 188,000 old sleepers have been replaced. But even as the remaining sleepers are being replaced, there are other engineering works to be done. These include replacing the power-supplying third rail as well as the signalling system, which determines service frequency.
SMRT would not say if these other projects - which will take up to 2019 to complete - will affect service for now.
Train speed was restricted after two major breakdowns in December 2011 as a safety precaution. Normal speed resumed in September last year, only to fall again when sleeper replacement started.
While SMRT has managed to reduce the number of breakdowns and noisy trains since 2011, observers said the slower trains mean service may get worse before it gets better.