21 November 2017
Investigation Findings on Train Collision at Joo Koon MRT Station & Shorter Operating Hours along NSEWL in December
The Land Transport Authority (LTA), operator SMRT and signalling system provider Thales have ascertained that the train collision on 15 November 2017 was caused by an unexpected disabling of a protective feature on the train that was hit, when it earlier passed by a trackside device at Clementi, which had yet to be modified for compatibility with the Communications-Based Train Control (CBTC) system.
2. When the train was travelling eastwards from Ulu Pandan Depot to Pasir Ris MRT station and then westwards from Pasir Ris MRT station to Pioneer MRT station, it was controlled by the old signalling system with the new CBTC system in passive mode. The CBTC system took over active control once the train entered the CBTC-controlled area west of Pioneer MRT station. Investigation findings indicate that on 15 November, an abnormal condition on a train-borne CBTC signalling equipment disabled a feature designed to apply a protective “bubble” around the affected train to ensure safe distances between trains. When such an abnormal condition occurs, the CBTC system is designed to immediately apply a second protective bubble (known as a “Non-Communicating Obstruction (NCO)”), to replace the first protective bubble. However, this second bubble was unexpectedly disabled when this train passed by a trackside device at Clementi which had yet to be modified for compatibility with the CBTC system.
3. This did not affect the safe operation of the train as it continued to travel under control of the old signalling system along the EWL, eastwards towards Pasir Ris MRT station and then westward to Pioneer MRT station. When the train arrived at Pioneer MRT station where it transitioned to the new CBTC system on the TWE, the train captain correctly detected the abnormal condition on the train-borne CBTC signalling equipment and reported it to the Operations Control Centre (OCC). The OCC then directed the train towards the next station, Joo Koon MRT station to alight passengers before withdrawing the train from passenger service. By design, the train was no longer allowed to move in Automatic Mode after the abnormal condition had been detected. As such, the train moved towards Joo Koon MRT station in Restricted Manual mode with a system-imposed speed limit of 18 kilometres per hour. The same speed limit was automatically imposed on the second train for safety reasons.
4. When the first train stopped at Joo Koon MRT station and the platform screen doors were manually opened, the “closed track” protection was automatically activated to prevent other trains from entering or leaving the platform. Data logs have confirmed that the second train stopped about 36 metres behind the first train. Once the platform screen doors were closed, the “closed track” protection around the platform was automatically lifted to allow the first train to leave the station. At this point, the second train started to move forward automatically as it could not sense any protective bubbles around the first train. This resulted in the collision at 8.20am.
5. Since 20 November 2017, the signalling systems of the TWE have been separated from the rest of the EWL to reduce the complications of operating two different signalling systems concurrently on an extended line. This separation will continue until the EWL re-signalling works are completed next year, when the entire EWL, including TWE, can be operated on the new CBTC signalling system.
6. Thales has also given its assurance that the CBTC signalling systems used on the North-South Line (NSL) and TWE are safe and robust. Thales is also confident that the re-signalling works for the NSL is on track to be completed by next month.
Early closure and late opening on NSEWL
7. LTA, SMRT and Thales have worked closely together on a revised engineering schedule for the North-South and East-West Lines (NSEWL). This enables us to accelerate the re-signalling works on the EWL so that train services on the entire line, including TWE, can run seamlessly on the new CBTC system, and also provides more time for other renewal projects and maintenance works to improve overall reliability on the NSEWL. With extended engineering hours from December 2017 onwards, the completion of re-signalling works on the EWL will be significantly accelerated from end-2018 to June 2018.
8. From Friday, 8 December to Sunday, 31 December, 17 EWL MRT stations (from Tiong Bahru to Tuas Link stations) and two NSL MRT stations (Bukit Batok and Bukit Gombak stations) will close earlier on Fridays and Saturdays, and open later on Saturdays and Sundays. This arrangement will more than double LTA and SMRT’s engineering and track access time from 3 hours to 7.5 hours each night. There will also be full Sunday closure on these stretches on 10 December and 17 December (please see Annex for a summary). The NSL MRT stations at Bukit Batok and Bukit Gombak are also affected as the works will extend to Jurong East MRT station, which is a heavily used intersection of the NSL and EWL.
9. Reduced train service hours will also be implemented along other stretches of the NSEWL in the first half of 2018, to facilitate re-signalling and other renewal and maintenance works. LTA and SMRT will work together to minimise inconvenience to commuters and ensure that commuters are informed of reduced train service hours in a timely manner.
10. Parallel shuttle buses will be provided along affected MRT stations during affected hours. As per past planned closures, fares for these shuttle bus services will follow the rail fare structure. Commuters can also continue their travel on alternative rail lines such as the Circle Line and Downtown Line.
11. Said LTA’s Chief Executive, Mr Ngien Hoon Ping: “The additional engineering hours is very precious to LTA, SMRT and Thales. This will substantially accelerate the implementation of the new signalling system for the EWL and provide additional maintenance hours for the entire NSEWL network. More engineering hours will also be needed in the first half of 2018 as we work towards the completion of the re-signalling works on the NSEWL. We will announce more details at a later date and work with public transport operators to ensure that there are alternative options for commuters who need to travel along affected stretches. When re-signalling is complete, commuters will be able to look forward to shorter headways and increased capacity on the NSEWL. We seek the patience and understanding of commuters.”
12. During this period, station staff will be deployed to assist and guide commuters. More details on the first and last train timings at affected stations will be provided by SMRT over the next few days.