1.  LTA and SMRT have been undertaking investigations into the cause of the intermittent loss of signalling communications between the trains and tracks on the Circle Line (CCL), leading to the automatic activation of the trains' emergency brakes.

2.  Following a series of tests, LTA, SMRT and train manufacturer Alstom have assessed that an interfering signal could have disrupted the trains’ signalling systems and led to the loss of communications. Over the past two weeks, engineers have tried to establish the source of the interfering signals. However, as the incidents had ceased by the afternoon of 2 September 2016, they were unable to determine the source.

3.  Notwithstanding this, LTA and SMRT will 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.

4.  We will also commence feasibility studies to strengthen the existing signalling communications network, for example, by placing an electromagnetic shield on the train to minimise the impact of interfering signals. We will also explore the possibility of changing the signal system frequency and/or modifying the system to provide redundancy in the event of signal interference.  (The signalling systems on newer rail lines such as the Downtown Line (DTL) and current lines undergoing upgrading such as the North-South and East-West Lines (NSEWL) are already equipped with new features that provide redundancy in the event of signal interference.)

5.  LTA and SMRT will continue to closely monitor the performance of the CCL.