The Online Citizen A Community of Singaporeans 
Land Transport Authority (LTA) has announced that the investigation has traced the source of the signalling problems which plague the Circle Line (CCL) to an intermittent failure of the signalling hardware on one train – Passenger Vehicle 46 (PV46).
It said that a joint team comprising LTA, Singapore Mass Rapid Transit (SMRT), the CCL signalling system manufacturer Alstom, the IMDA, DSTA, DSO National Laboratories, GovTech and electro-magnetic interference specialist Rohde & Schwarz found that the intermittent hardware failure had caused about 100 occurrences of loss of signalling communications on trains travelling in the proximity of PV46 between 2 to 6 Nov 2016.
It said that its ongoing investigations indicate a strong likelihood that this was also the cause for about 200 occurrences of loss of signalling communications on CCL trains between 28 Aug and 2 Sep 2016. The loss of communications on these trains resulted in their emergency brakes being automatically activated, which is a safety feature.
LTA stated that PV46 has since been pulled out of service while LTA and SMRT continue to work with Alstom on further investigations and rectification of its faulty hardware. They said that they will also conduct a thorough examination of the signalling hardware for the rest of the CCL fleet.
LTA said that together with IMDA and the mobile network operators, it suspended mobile telecom services on the CCL on the evening of 3 Nov 2016 and for the full day on 4 Nov 2016 to test if telecommunications signals could have caused the repeated activation of the trains’ emergency brakes. Tests showed that the telecommunications signals were not the source of the interference.
It also said that data collected from train logs and incident reports found that almost all the faults occurred in the proximity of one particular train, PV46.
On 6 Nov 2016, LTA tested if PV46 was the source of the problem by running the train during revenue hours and found that PV46 indeed caused a loss of communications between nearby trains and the trackside signalling system. Before PV46 was put into service on that day, no loss of communications was observed on any CCL train.
LTA noted that further tests on PV46 showed that faulty train signalling hardware on PV46 was emitting erroneous signals in addition to the ones it was supposed to emit. PV46 has been deployed for service since July 2015.
“Prior to this, the train was tested extensively both at the manufacturing location and under local conditions. It is unclear at this point why the train’s signalling hardware has been experiencing intermittent failure,” it wrote.
No other train has been found to have the same hardware issue. However, LTA said that it will check the rest of the trains.
LTA had stated that LTA, SMRT and Alstom are investigating the exact cause of the intermittent hardware failure.