On 15th December 2011, SMRT Trains Ltd (company of SMRT Corporation Ltd) North-South Line experienced a major technical breakdown, said to be the worse in 24 years of history. Four trains, T133, 128, 139 and 134 experienced severe damage to their power collection device, known as the current collector shoe by SMRT.
A (healthy) current collector shoe as seen installed on Siemens 207F. Photo copyright Muhd Faizal, taken during 2007 Bishan Depot Open House with permission.
On MRTC/LTA (Mass Rapid Transit Corporation/Land Transport Authority) procured trains such as the first generation from Kawasaki Heavy Industry (KHI), current collector shoes are mounted on the motor and trailer car bogies. Each bogie has two shoes, one on each side. This was to avoid the need of inter-car jumpers and cables which supply power to an adjacent car which does not have access to the main power supply. Such systems are common in other countries (such as locomotive-hauled trains and overhead power (pantograph) systems). It is therefore true to say that each train carriage is self-sufficient for power, no matter if its the air-conditioning, lighting or traction system.
Such is the frequent passing of the shoes to the third rail; each train ‘passes’ over a part of the third rail 12 times as there are 12 bogies on a train. It was reported that no abnormalies occurred until T133 stopped at Braddell station at 1855 hrs when apparently the train could not move off. After failures in attempts to restore service, the train was taken out of service 24 minutes later. Eight minutes before, T134 (operated by KHI 067F) came to a halt in the tunnel between City Hall and Dhoby Ghaut stations, facing similar problems as T133. Passengers apparently had to wait 40 minutes as the train driver and Operation Control Center (OCC) sorted out the problem. Eventually, the passengers, exhausted and lack of air, were let out to walk 150 meters to Dhoby Ghaut station, with one woman feeling faint and sent to hospital. Jurong East bound service was finally restored around 2340 hrs almost five hours was lost.
A quick-thinking man on carriage 3067, seeing passengers feeling very ill, took the fire extinguisher at the gangway and smashed open a window on the carriage door, after which its picture went viral on the internet, clearly showing how serious the situation was to the passengers.
Article published on The New Paper on 17th December 2011 illustrates the trains’ positions and damaged shoes, from top to bottom, 1068 A2 (Motor Car 1), 3068 A2 (Trailer car), 1068 A1 (opposite of the first photo) and 2068 A2 (Motor Car 2). Particularly photo of 1068 A1, the shoe assembly had been pushed downwards considerably. Its entire shoe is missing as well. Others show linear damage (being dragged along) and also downward force. Forty meters of third rail was also found to be damaged, however it was varied at how its so, some reported that it dropped off, while others said the cover was off. It was apparent which component had went wrong, but LTA and SMRT said that more time and investigation is needed to find the actual cause. Its time frame came to a halt on Saturday, 17th December 2011 morning, when a similar incident happened again.
On Saturday morning, seven trains were affected, the earliest at 0650 hrs. It was reported that a four meter section of third rail had came off, just like Thursday, near Orchard station. The furthest damaged train reached Marina Bay station. Almost seven hours was spent to evacuate passengers, haul the damaged and immobilized trains back to Bishan Depot and fixing the rails before full service could be resumed at 1348 hrs.
SMRT came under heavy fire after the first disruption. One could say the public were displeased at SMRT for communication breakdown, instead of describing the first service disruption as a mechanical one, it could also be said as a PR disaster. Bridging buses were activated after an hour past the first signs that service cannot be resumed. Staff were also clueless as to where the shuttle bus pick-up points are. That night, there were already calls for the Chief Executive Officer, Ms Saw Phiak Hwa (57 YO), to resign. On Friday, there was a press conference where there was a simple explanation by Executive Vice President Train Operations on how the third rail could be involved in the disruption.
However the second disruption on Saturday morning confirmed the worst fear; it was the power component that knocked out the trains. There were even louder voices for the CEO to take up responsibility and step-down, which she hinted she would consider on Friday. The Online Citizen too hosted a session at 1600 hrs on Saturday at the Speakers’ Corner to request for the CEO to step down.
The Site Admin will not speculate directly on the causes, however he would list out possible factors that led to such a large scale disruption, why it took so long to restore service and what LTA and SMRT could have done to improve the situation when such a disruption occurs.
Possible Factors:
Damage/disturbance of third rail components
As the third rail is accurately aligned to the loading gauge in terms of height and distance, any large deviation would cause an outage of power to the train. With low line voltage, the emergency brakes will be kicked in and train will be stopped; a safety feature. In this case if the third rail is dislodged, it will sag and come resting on the current collector shoes as the train passes by. The mechanism of the shoe exerts 130 N (Newtons, about 13 kilograms) of force upwards onto the rail to ensure adhesion, a similar method to overhead power system/pantograph arm. This added force, adding on to the kinetic forces as the train is moving, may shear off the current collector shoes. As third rail is only fitted on one side of the tracks, the loss of shoes on one side will mean a cut-off of power, stalling the train.
On early Sunday morning, LTA and SMRT staff found 21 of these clamps fell off the third rail support. The third rail support is bolted to sleepers, which are made of timber on overhead viaducts and roadbed sections, and concrete in tunnel sections. On the other side of the support is the clamp assembly, which holds on to the third rail at 6.3 meters interval. Missing clamps would mean the third rail is free to droop with gravity, interfering with the kinematic envelope of the current collector shoe and the train. What follows would be as described above.
There would be a consideration that trains introduced to service recently, either as new stocks or as repaired ones, have train-board components exceeding the kinematic envelope, and hence caused disturbance to the third rail. However the Site Admin would consider this as very remote as kinematic envelope checks are carried out before a train leaves workshop, as for repair/rectification trains, every time before they leave the depot.
- Why would the clamp come lose?
For this, only personnel inside would know. It would be easy for all to speculate that aging, lack of maintenance, recent repairs of the third rail etc.. It is advised to wait for the official report on why this would happen.
Why It Took So Long?
Damage to train-side/way-side components that led to further immobilization of the trains
Damage to components of the train can mean they get into the way of surrounding items. A train is allowed to travel, move on the latitude and longitude planes and this is known as its Kinematic Envelope. As our trains are long (22 to 23 meters), there is considerable ‘throw’ of the car, where the front and middle of the car is concerned, the front will ‘extend’ outwards more, and the middle will move ‘sideways’, when negotiating a curve. The third rail is particularly close to the middle of the train and its components when it comes to a curve, and hence any damage, no matter if its the cover alone or the entire assembly, may get in the way of the train. Even if the train can be hauled away, these damaged components intruding the kinematic envelope will prevent a successful extraction to be carried out, hence time is needed to move any damaged components, at the track or on the train, out of the way before the train can be pushed/pulled away from its position. Furthermore the damaged current collector shoes may interfere with healthy third rail sections while the train is moving to the depot; further care is required to remove them.
Absence of power at/in the sector leading to damaged trains
As with the Thursday incident, some forty (40) meters of third rail was found dislodged. This would effectively mean that traction power cannot be supplied to rescue trains. MRTC designed the system to use other revenue 6-car stocks to act as rescue train in hauling/pushing defective trains, 3-car is also shown to be possible. An illustration of a 12-car rescue operation is shown here with a video by Lim Wen Jie.
Time is needed not only to organize such trains, but because of limitation in the signalling system the rescue train can only, if approaching from the opposed direction of travel, travel below 18 km/h on Restricted Manual mode. For T134 on Thursday’s incident, the nearest crossover (switch) from the north would be at Newton, to the south, Raffles Place. Consideration for the lack of power, position of the damaged third rail would follow. The use of diesel locomotives would have sped up the process; the Site Admin is not sure if this is carried out, but SMRT should consider the use of non-electric units in the case of suspected traction power failure to avoid getting an additional train damaged/stalled in the tunnel.
Rectification of the third rail
Rectification work does need time; the shifting of resources, organizing of manpower and access to the tracks after the damaged train sitting near it is removed. Thereafter a test train would travel over before revenue service can resume. Then again the Site Admin did not receive information whether a test vehicle is deployed, but this is the practice in worldwide systems and SMRT would likely do the same.
What could have LTA/SMRT done?
Adoption of Short Messaging Service (SMS) alerts to commuters
With mobile phone a common item to a traveling Singaporean, it would only be sensible to send messages about disruptions to them before they step into the station so they can find alternate transport, before they step out of their homes so they can plan ahead. The best aim would be to alert a potential commuter before he leaves home, however this may not be the case all the time. Operators and authority should set a timing at which the alert will be given, 5, 10 or 15 minutes of delay would require a heads-up? This depends on the traveling pattern of a commuter, but for situations of above 10 minutes delay a heads-up is a must.
Review of the communication system between OCC/HQ and Stations
Staff were seen by commuters to be clueless during the disruption. Many did not know when trains are running again, neither some know about where to take the shuttle buses. Presently communication by phone is insufficient in such scenarios. Japanese operators for example uses land lines, mobile lines and facsimile to communicate information. There would be little clutter as facsimile can be sent to all stations along the line at one go.
Instead of depending on two-way radios in the case of train drivers, mobile phones can be used instead. This is aided by the fact that tunnels have at least 2G reception, with full upgrade to 3.5G already on the way. Mobile phones would be owned by the company, and calls two and fro the OCC would be on secured lines if need be. The existing Singtel Grid (walkie-talkie phones) is also an existing technology to be tapped upon.
Commuters would tend to ask the following questions during a disruption; staff on all levels should be trained to answer them, and OCC/HQ personnel should tackle such questions first.
Why is the train stopped? (Why is the train late?)
When will the train move off? (When will the next train arrive?)
Should I just wait here for the train? (Should I take a detour?)
What time will I arrive at my destination?
These are examples taken from a professional publication for dealing with railway diagram (schedule) disruptions by a society in Japan that discusses ways to improve urban transport. For examples 1 and 2, operators (in Japan) are using IT and that includes mobile phone services to provide the latest information to commuters. For point 3, the method of taking a detour may be provided, but the best detour route cannot be done; it is up to the commuter to choose his best method. For point 4 however, is a barrier about absolutely accurate information which no one can provide at detail now.
Besides communications, commuters were also seen to be asking staff about refunds. In the case of a disruption, paid passengers should not be bothered about their fares at that moment. Simple; spare a thought about those people trapped in trains in the tunnels, they are struggling to stand against the heat and lack of air! Would they care about their fares then? Commuters at stations should only inquire staff about connection/shuttle bus, and not to go in-detail about refunds which can be made within three working days from a disruption.
LTA announced on Saturday night that trains will be running later on Sunday to cope with extra checks throughout the NSEWL system; service resumed at 11 am with some stations up to 45 minutes later. Shuttle buses were deployed, however still irked many commuters who found buses arriving later and drivers losing their way as many were pulled out with haste from workshop and operations.
Trains will also be running slower along tunnel sections with ‘floating slab tracks’. Floating slabs mean that the tracks are installed on concrete roadbed which is padded with rubber before installed on the tunnel floor, designed to reduce vibrations caused to nearby buildings. The area which the incidents happened (City Hall to Dhoby Ghaut, Orchard) feature tunnels with such design. Hence from service resumption on Sunday noon trains run below 40 km/h instead of the usual 78 km/h for these sections. Operation method is not changed (ie. Auto mode in tunnels with speed restriction).
On June 15th 2011, the Site Admin published an article about making the public transport better, and such ideas were put forth. Had LTA and SMRT considered them at that time, it may be different for commuters during this chain of disruptions. Of course, the Site Admin is not the only person in Singapore with these views; many commuters and netizens, transport enthusiasts or not, too share these views. Whether LTA or SMRT wants to take up these ideas or not will be up to their budget and feasibility. If other countries can, we sure can, as we work towards having a World Class Transport (we are not there yet!).
References:
鉄道ダイヤ回復の技術 (電気学会・鉄道における運行計画・運行管理業務高度化に関する調査専門委員会, オーム社)
ISBN-13: 978-4274209147
電気鉄道概論; 改訂増補版 “a Survey of Electric Railway” (安藤 信三)
ISBN-10: 442-5925025
Mass Rapid Transit System : Proceedings of the Singapore Mass Rapid Transit Conference
ISBN 9971-84-636-5
The Straits Times 19th December 2011 Edition
The New Paper 17th December 2011 Edition
