Commuters on the East-West Line faced more disruption yesterday due to a track circuit fault at Buona Vista.
Between 8.30am and 1pm, trains moved more slowly than usual, resulting in delays of between five and 25 minutes for commuters.
Rail operator SMRT, which runs the line, first tweeted at 8.13am that there would be an additional 15 minutes of travelling time between City Hall and Dover MRT stations.
Nineteen minutes later, another tweet warned commuters to expect an additional 25 minutes of travelling time between the two stations.
SMRT announced at 12.55pm that normal service had resumed.
Track circuits help send signals to the operations control centre to monitor the speed, location and identity of trains.
Faulty track circuits were also the cause of at least six disruptions between the Clementi and Joo Koon stations on the East-West Line in the first two months of the year.
SMRT had previously said the upgrading of the signalling system on the 30-year-old East-West line, expected to be completed by the end of next year, would help alleviate such track circuit faults.
Testing of the new communications-based train control signalling system began on the North-South Line in March.
This system allows trains to run closer together and arrive at intervals of up to 100 seconds during peak hours, instead of the 120 seconds currently.
On Monday, commuters travelling between Choa Chu Kang and Jurong East experienced delays of up to 20 minutes due to a signalling system fault.
Earlier this month, the Land Transport Authority and SMRT warned that there could be more delays as testing of the new system continues.
National University of Singapore transport researcher Lee Der- Horng described faulty track circuits as a "major issue" facing railway systems worldwide. Upgrading the signalling system would help resolve this problem, he said.
Treasury analyst Stanley Soh, 35, was on his way to work from Queenstown station when he was hit by a 15-minute delay during yesterday's disruption. He said: "Of course, I am frustrated."