and proposed a plan to open up the concrete at some areas of the stations to inspect the construction quality. The investigation also revealed further incidents of substandard work and missing construction records. For example, 40% of Request for Inspection and Survey Checks forms for the northern approach tunnels are missing. Construction and facility enhancement New railway lines and track The 11-kilometre tunnel of the East-West Corridor was fully broken through in August 2016. As of February 2017, construction and tunnel boring is underway for the sections between the Exhibition Centre station and Causeway Bay, and between Causeway Bay and Kowloon. MTRC has set up an Immersed Tube Tunnel Casting Yard at the site of the former Shek O Quarry at the south side of the Hong Kong Island to pre-assemble sections of the tunnel tubes, which will be then transported by sea and immersed in place. As June 2017, the first Immersed Tube Tunnel units was installed in Victoria Harbour, marking the beginning of constructing the fourth harbour-crossing railway tunnel in Hong Kong. 11 tube tunnel units in total will be constructed and placed for the harbour crossing section. New signalling systems and station facilities Both of the new corridors will receive new signalling systems as part of the Sha Tin to Central Link project. The technology, known as communications-based train control (CBTC), will minimise train intervals while complying with existing and future infrastructure, such as platform doors/gates. The East West Corridor are now using SelTrac CBTC supplied by Thales. This is an updated, more modern version of the Seltrac IS technology already installed on the West Rail line, Ma On Shan line, and Kowloon Southern Link. New on-board computers are being retrofitted to the existing SP1900 trains as part of their modifications to form 8-car trains, supplemented with newly acquired 8-car trains delivered with the new computer already installed. All stations on the Ma On Shan line have also received half-height platform gates in conjunction with the upgrade, and new underground stations will have full-height platform doors installed. The North South Corridor will have the TBL train protection and Alstom's ATO system in use on the current East Rail line including the Lok Ma Chau Spur Line replaced with Trainguard MT CBTC supplied by Siemens. (AWS used by intercity trains on the East Rail line is not expected to be affected.) At the same time, all platforms would