An interfering signal in the Circle Line tunnel is the possible cause of a signalling glitch that has plagued the MRT line since last week.
More investigation is required, and further temporary shutdowns of mobile services on the line are possible. "This interfering signal could be a possible cause of the intermittent loss of train-to-track communications," SMRT and the Land Transport Authority said. "However, experts have not been able to verify the source."
The signal is "within the operating frequency band of the signalling system", SMRT said in a statement yesterday evening.
Mobile signals in four Circle Line stations - Kent Ridge, Haw Par Villa, Pasir Panjang and Labrador Park - were shut down for two hours on Friday evening to investigate the matter.
Further tests were conducted between 1am and 4am, and investigations are continuing, said SMRT.
Should and when an incident recurs, telecommunications signals along stretches of the Circle Line will be suspended for short periods for tests.
"If temporary telecommunication signal suspensions have to be carried out, there will be in-train and station announcements along the affected stretches," said SMRT.
"We seek commuters' understanding and patience as we press on in our investigations."
Chew Hui Min