UPDATED [5:41pm 30 April 2013, adding statement from SMRT]
A track fault on the North South Line that caused long train delays Monday evening was traced to a rail crack.
The affected rail was replaced Tuesday morning before train services began, transport operator SMRT said.
In a statement Tuesday afternoon, SMRT vice-president for corporate marketing and communications Kalai Natarajan said the reason for the rail crack was still being investigated.
The crack, which was found on a rail joint on a stretch of track between Somerset and Orchard stations, resulted in a track circuit break, which in turn activated a safety mechanism in the signalling system, Kalai explained.
The rail crack in the welded area between two rails was spotted and at 8.30pm and 9.19pm Monday, and engineers temporarily installed G-clamps to secure the rail joint.
Trains travelled over the affected stretch at a slower speed as a safety precaution so as not to put pressure on the G-clamps.
The track fault on Monday affected northbound service between Somerset and Orchard stations.
Trains were travelling slower over that stretch as a safety precaution, it added.
Several northbound commuters on the line reported travel times of double the usual period as trains kept stopping.
Twitter user ijiann said it took one hour to get from Raffles Place station to Toa Payoh stop.
Another Twitter user, Teridoll, recounted being on the train from Marina Bay station past 6pm and only reaching Orchard around 8:22pm.
Peggy Lim, who took the train from City Hall to Somerset, said the train was stuck for more than five minutes, moved slowly, stopped again and then started moving at a very slow speed until she finally reached her destination.
"I'm so annoyed they wasted my time," she said.
Even southbound commuters said they experienced train delays.
"I got on the train at Toa Payoh around 6.55pm. I was heading towards City Hall. The train stopped for a few minutes at each station before finally reaching City Hall at 7.30pm," said Melissa Pang.
President Tony Tan Keng Yam has voiced deep concern over the violence in Little India on the night of 8 December, a rare incident in the usually peaceful city-state. …