The Land Transport Authority (LTA) and Singapore Mass Rapid Transit (SMRT) has issued a joint statement on investigations into the cause of the intermittent loss of signalling communications between the trains and tracks on the Circle Line (CCL) which had led to the automatic activation of the trains' emergency brakes.
They stated that a series of tests had been conducted with the train manufacturer Alstom and concluded that an interfering signal could have disrupted the trains’ signalling systems and leading to the loss of communications.
Engineers have tried to establish the source of the interfering signals over the past two weeks. However, as the incidents had ceased by the afternoon of 2 September 2016, they were unable to determine the source.
LTA and SMRT said that it would install spectrum analysers within the CCL tunnels to detect the presence of any interfering signal. This measure will be extended to the North East Line, which has the same signalling system.
They added that an electromagnetic shield would be placed on trains to minimise the impact of interfering signals as part of feasibility studies to strengthen the existing signalling communications network. The possibility of changing the signal system frequency and/or modifying the system in the event of signal interference would also be explored.
Between 29 August to 2 September 2016, the CCL experienced intermittent signalling issues for five days in a row which caused a build up of commuters at stations and delay in travel times. On the first day, SMRT also alerted passengers to hold onto handrails as trains may experience intermittent braking.
On 2 September, SMRT announced that mobile networks for Circle Line (CCL) would be shut down for two hours to check for possible interference between the telecommunications network and train signalling system during peak hours when most of the incidents had occurred.
However, the fault still could not be found. So the SMRT and LTA are attempting to use the electromagnetic shield on trains in an attempt for forestall signal interference. But without establishing the cause, means the fault may reoccur as it did on 20 September when trains experienced 15 minutes slower traveling time which again caused delays.