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Circle Line signalling problems caused by intermittent failure of signalling hardware on train




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The following is a joint-press release by Land Transport Authority (LTA) and SMRT.

After several weeks of investigations, a joint team comprising the Land Transport Authority (LTA), SMRT, the signalling system manufacturer Alstom, the Infocomm Media Development Authority (IMDA), the Defence Science & Technology Agency (DSTA), DSO National Laboratories, the Government Technology Agency of Singapore (GovTech) and electro-magnetic interference specialist Rohde & Schwarz, has traced the source of the signalling problems on the Circle Line (CCL) to an intermittent failure of the signalling hardware on one train, Passenger Vehicle 46 (PV46).

Between 2 and 6 November 2016, this intermittent hardware failure had caused Since early September 2016, there has been no occurrence of similar signalling faults until this morning, about 100 occurrences of loss of signalling communications on trains travelling in the proximity of PV46. The loss of communications on these trains resulted in their emergency brakes being automatically activated, which is a safety feature. Our ongoing investigations indicate a strong likelihood that intermittent hardware failure on PV46 was also the cause for the about 200 occurrences of loss of signalling communications on CCL trains between 28 August and 2 September 2016.

Investigation Findings

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An initial hypothesis was that interference from telecommunications signals may have caused the repeated activation of the trains’ emergency brakes. To test this, LTA, together with IMDA and the mobile network operators, suspended mobile telecom services across the entire CCL for two hours in the evening of 3 November 2016, and then for a full day on 4 November 2016. These tests showed that telecommunications signals were not the source of the interference.

Meanwhile, engineers and data scientists from DSTA and GovTech studied data collected from train logs and incident reports, and found that almost all of the faults occurred in the proximity of one particular train, PV46. On Sunday, 6 November 2016, we tested if PV46 was the source of the problem by running the train during revenue hours. We found that PV46 indeed caused a loss of communications between nearby trains and the trackside signalling system, resulting in the activation of emergency brakes on these trains. Before PV46 was put into service on that day, no loss of communications was observed on any CCL train.

Further tests on PV46 by engineers from LTA, DSTA and Rohde & Schwarz showed that faulty train signalling hardware on PV46 was emitting erroneous signals in addition to the ones it was supposed to emit. These erroneous signals occasionally prevented trains travelling in the vicinity of PV46, including in the opposite direction, from properly communicating with the trackside signalling system. This loss of communications led to the activation of the trains’ emergency brakes.

PV46 has been deployed for service since July 2015. Before being put into service, the train was tested extensively both at the manufacturing location as well as under local conditions. It is unclear at this point why the train’s signalling hardware has been experiencing intermittent failure. So far, no other train has been found to have the same hardware issue, but we continue to monitor closely.

PV46 has been pulled out of service while LTA and SMRT continue to work with Alstom on further investigations and rectification of its faulty hardware. LTA and SMRT will also conduct a thorough examination of the signalling hardware for the rest of the CCL fleet.

Mr Chew Men Leong, Chief Executive (LTA), said, “Following our earlier assessment that the signalling faults on the Circle Line were caused by an interfering signal, the joint team spent many weeks trying to trace the source. The sporadic occurrence of the incidents at different points along the Circle Line made it challenging for the investigators and I thank commuters for their patience during this period. I am also grateful for the collaboration with the other Government agencies and the cooperation from the telcos in helping us nail down the problem. In particular, I thank the engineers and data scientists from DSTA and GovTech respectively, without whom we would not have been able to theorise the possibility of a faulty train, and identify PV46.”

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