SMRT said it is working with authorities to address security vulnerabilities found at its Bishan Depot, following a breach last month which resulted in a train being vandalised allegedly by two German nationals, reported The Straits Times.

In a statement on Thursday, the transport operator said that the original open design of the 30-hectare depot poses a number of unique challenges, due to its size and full visibility from adjacent buildings.

Following a vandalism breach in 2011, SMRT said that the 6.5km fencing perimeter has been enhanced with security features. In both the recent case and another graffiti incident in May, the fences were not breached, SMRT added.

Security in the depot perimeter had been further beefed up after the May incident, SMRT said. The operator also pointed out another vulnerability at the depot. Bishan Depot, it said is unique in that it is built on a concrete platform deck over swampy land which is the flood plain for the Kallang River and has a network of canals and drains running underneath.