1. The Land Transport Authority (LTA) and SBS Transit (SBST) have formed a joint team in October 2012 to further enhance the service reliability of the North East Line (NEL) and Sengkang-Punggol Light Rapid Transit (SPLRT). This is similar to the LTA-SMRT Joint Team set up earlier to improve the reliability of the North-South Line, the East-West Line and the Circle Line.
2. The LTA-SBST Joint Team will, as a priority, focus its attention on reviewing the underlying causes of and contributory factors to the recent service disruptions on the NEL due to component failure in the Overhead Catenary System (OCS) that supplies power to the trains, and identifying appropriate measures to address them.
Cause of Recent NEL Disruptions
3. The LTA-SBST Joint Team has established that stress corrosion cracking (SCC)1 is the cause of the NEL incidents in March 2012, August 2012 and January 2013.
4. For SCC to take place, three factors must be present, namely material susceptible to SCC, a corrosive agent, and sufficient tensile stress to induce SCC. The Joint Team has established that chloride from tunnel water seepage is the corrosive agent in the failure of the Balance Weight Anchor (BWA)2 wires that broke during the March 2012 incident, while chloramines are the corrosive agent in the failure of the U-bolts3 in both the August 2012 and January 2013 incidents. Preliminary environmental testing concluded that chlorine and traces of ammonia are found at the affected stretch of tunnel (between HarbourFront and Outram Park stations). Further investigations are ongoing to locate the source of the corrosive agents for the August 2012 and January 2013 incidents. There is no indication at this stage to suggest that it is a system-wide problem.
Immediate Steps Taken to Prevent Recurrence of Similar Incidents
5. In the interim, SBST has taken immediate precautionary steps to prevent a recurrence of similar incidents. Specifically, SBST has:
- changed out all BWA wires along the stretch of tunnel between HarbourFront and Outram Park Stations.
- commenced the replacement of all 1,600 U-bolts along the stretch of tunnel between HarbourFront and Outram Park Stations. Half of the U-bolts along this stretch have been changed out, and SBST will complete replacing the remaining 800 U-bolts by mid-April 2013.
- intensified checks for any tunnel seepage water that drips onto the BWA wire ropes by increasing the number of visual inspections from once to twice weekly by track patrolmen.
- shortened the 3-monthly U-bolt inspection to 2-monthly, including physical checks and cleaning of the U-bolts.
6. To ensure the health of the entire NEL, the LTA-SBST Joint Team is also carrying out sample testing of the U-bolts beyond Outram Park station, to determine the conditions of these U-bolts and have them replaced where necessary.
Long-term Plans to Improve Reliability
7. The LTA-SBST Joint Team has also formulated plans to improve the reliability of the NEL in the longer term. Specifically, the Joint Team will:
- seek to replace all U-bolts with corrosive-resistant materials that are more suitable for the current NEL tunnel environment.
- study new materials for all 182 BWA wires, and will commence replacement works after completing the study in May 2013. The replacement works for all BWA wires is expected to be completed by mid 2014.
- study ways to improve the OCS such that normal train operations can continue in the event of BWA wire failure. The modification works for the OCS to enhance its resilience, if feasible, are expected to commence in mid 2013.
- engage an independent consultant to conduct a comprehensive review to enhance the overall NEL OCS, its maintenance regime, and recovery measures to allow for faster recovery from OCS incidents. The consultancy study will likely be concluded by mid 2014.
Addressing Train and Signalling-related Issues to Reduce Service Delays and Train Withdrawals
8. In 2012, the number of unplanned train withdrawals for every 100,000 kilometres on the NEL stands at 0.7. About half of the service delays and train withdrawals on the NEL and SPLRT result from faults related to trains and signalling systems. Working Groups have been formed to identify preventive measures to further reduce service delays and train withdrawals. For example, air conditioning faults caused a significant number of service delays and train withdrawals in 2012. SBST has already implemented measures, e.g. fleet wide replacement of faulty air conditioning CPU cards, and is closely monitoring the situation. The Joint Team will look into how service reliability can be further enhanced, and ensure that the maintenance regime keeps pace as the system ages so that service reliability will not deteriorate over time.
About the LTA-SBST Joint Team
9. The LTA-SBST Joint Team comprises engineering and maintenance experts from both organisations, and is headed by Mr Chua Chong Kheng, Deputy Chief Executive of LTA and Mr Wong Wai Keong, the Executive Vice President (SBST, Rail) and reports to the Chief Executives of LTA and SBST.
1 It has also been established that triggers for, and the nature of, the SCC on the Balance Weight Anchor (BWA) wires, differ from that for the U-bolts. For the former, it is inter-granular SCC triggered by chloride, while for the latter, it is trans-granular SCC triggered by chloramines.
2 BWA wires are responsible for holding the OCS wires in place.
3 U-bolts are responsible for holding the OCS cantilever arms in position.