The Land Transport Authority noted that the Joo Koon train collision last month was caused by a “software logic issue” and a “confluence of failure conditions,” as it concluded its investigations into the incident yesterday.
In a press release, the statutory board reiterated that the collision – where at least 38 individuals were injured – to complications from operating two signalling systems concurrently on a single line. It also attributed the crash to the following unexpected failures:
“The train develops an abnormal condition with its train-borne CBTC equipment which prevents it from communicating with the trackside CBTC signalling equipment. When this occurs, the CBTC system will, by design, apply a Non-Communicating Obstruction (NCO) protective “bubble” around the affected train to ensure its safety. This was the requisite start state for the incident; and
“The train crosses the only track point that has not yet been fully modified for compatibility with the CBTC system; and
“The NCO protective “bubble” is unexpectedly disabled by the CBTC system, as the software logic cannot correctly process a track point that has yet to be fully modified for compatibility with the CBTC system when running in passive mode. This is not an issue when the CBTC is running in active mode on the North-South Line and the Tuas West Extension (TWE) as they are fully on the CBTC system.”
LTA also said the failure conditions arose as a result of complications from operating two signalling systems concurrently on a single line.
The LTA added that signalling system provider Thales has completed circuit modification works for the previously incompatible track point and will be setting up a CBTC simulation facility in Singapore to “strengthen testing processes” for the signalling system in the North-South and East-West Lines.
Besides this, the authority told reporters that it “reserves the right to take appropriate action against parties involved in the collision,” noting that Thales has accepted responsibility for the incident and apologised.
LTA added:
“LTA’s immediate priority is to ensure the timely delivery of the multiple asset renewal works in the pipeline so as to improve rail reliability.
“We will continue to work closely with SMRT and Thales to safely complete the upgrading of the signalling system for the North-South and East-West Lines as soon as possible.”