The railway industry around the world is not short of hiccups and problems just like any other man-made systems. Wear and tear, aging, glitches, and design errors are just some of the faults and problems that may occur. It is important that the team understand and learn from the train breakdown incidents by identifying the factors affecting the disruptions and ways to minimize them.
1.1 Case studies in Singapore and globally
1.1.1 Case Studies on Excessive Vibration
According to the incident report published by the Ministry of transport on the report of the committee of inquiry (COI) into the disruption on Dec 15 & 17, 2011 [1], Singapore’s SMRT faced a major disruption where the trains were unable to draw power from the third rail through Current Collector Device (CCD) shoes on the North-South line. Both incidents were concluded to be due to the sagging of the third rail which subsequently causing the CCD shoes to be damaged. The reason for the sagging was due to the dislodgement of multiple claws holding the third rail onto the tracked. Mr. Richard Greer, appointed by the Land Transport Authority (LTA) to investigate how railway vibrations may have caused the dislodgment. It stated in the investigation report (p.141) that the ‘outlier’ trains show that the high vibration is associated with very short duration transients that are superimposed on vibration time histories which are otherwise like typical revenue service trains. These transients are observed simultaneously at the base and top of the third rail bracket supports. This transient vibration is caused by wheel flats. This is tested in a laboratory and further reiterated by COI findings that the transient vibration of magnitude cause by ‘outlier’ trains with wheel flats is one of contributing factors to the dislodgement of claws.
In Hong Kong, Kowloon-Canton Railway Corporation investigated published an investigation report on the root cause of failure and cracking of underframe equipment support brackets on rail Mid-Life Refurbished (MLR) Trains on May 3, 2016 [2]. Stated in the report, on Dec 21, 2015, an MLR train was put to emergency stop due to an abnormal sound coming from the underframe of the train. Upon investigation, two out of three brackets supporting the compressor failed causing the flexible pipe-joints to open and release high pressured air. The root cause investigation established that excessive vibration from the car-body caused cracks and hence failure. Although the calculations made by the manufacture of the brackets were based on normal usage, the excessive vibration measured on the train increased the fatigue loading by twice their design limit. The source of the vibration through the car-boy was identified to be from the presence of minute undulation on the rail top on sections of the East Rail track where trains travelling along the section at 70-90 km/h may experience this. [pg5-9]
1.1.2 Case Study on Signalling Issue
Singapore’s MRT is commonly faced with multiple signaling integration faults. According to a news article published by the Straits Times on the Nov 16, 2017 [3], the Joo Koon collision on the East- West Line was caused by the signaling glitch which mistakenly profiling the stalled train as a three-car train. Additionally, according to another article by Today Online published on the 21 Jan, 2014 [4], on the same day, a south bound train was forced to stall about 500m away from a station due to signaling issues. It stated that when a train is faced with signaling issues, the train’s Automatic Train Protection (ATP) will be activated causing the service brakes to be engaged and stop the train.
Accordingly, to another article published on Aug 7, 2017 by the Straits Times [5], Hong Kong’s MTR trains were forced to travel slowly hence causing a service disruption of 10 hours where three computers controlling the rail signaling apparatus failed on 5 Aug 2017.
1.1.3 Case Studies on Coefficient of Friction
In London, during the leaf-fall season of 2016, several trains on the Piccadilly line had to be withdrawn from service due to flatted wheels. According to an investigation report led by David Crawley and team, published on May 5, 2017 [6]. Only about half of the total trains on that line could be offered for customer service. The cause of this incident was due to leaves from trees along the line resulting in low adhesion (as low as 0.02 COF for leaf mulch). If the forced used by the brakes on a moving train is much higher than what is required, the wheels will lock and side; if locked long enough while sliding, the wheels will become flatted by the abrasion against the rail head.
The issue of low coefficient of friction also caused a collision of a train and the end-of-line buffer stop at Cleveland Station, Queensland Australia on Jan 31, 2013. According to the incident report published by the Australian Transport Safety Bureau (ATSB) [7]. The report stated that the collision was a resulted from poor adhesion of the train’s wheels to the rail running surface from contaminants substance such as leaf tissue, iron oxide, a combination of natural oils and hydrocarbon oil, solid lubricant additive and woody particles found on the rail running surface upon examination. The contaminants resulted in the train to be unable to stop in time before colliding with the buffer stop.
A news article published by ctpost on Dec 6, 2017 warning commuters to expect crowded trains in the morning due to Metro-North, New York’s metro operator recalled several train cars due to bad weather the day before which caused slippery rail conditions [8]. Together with the combination of rain and fallen leaves that were crushed into gelatinous and slime-like substance on the rail head, trains were facing problems stopping normally. The safety system on-board perceived as slip-sliding and activated the emergency brake. This system causes the wheel profile to flatten due the dragging of wheel across the railhead when locked.
1.1.4 Case Studies on Derailment
On the May 6, 2011, a bogie on freight train travelling towards Adelaide, South Australia had derailed as it approached a bend. According to the investigation report by the ATSB [9], the derailment caused track components and signaling circuits to be damaged. Investigation test started on the train wagons on bogie examination, weight loading, design performance and static twist test but nothing wrong could be faulted. The investigation was then conducted to the tracks and high level of metal loss from the head and gauge face could be seen visually. Upon actual inspection, the head loss was 47.3% which was more than the upper limit of 34%. Although not the main contributory factor, it was tested and did not meet safety standard. (p. 13)
Taken from a news article written by Reilhac on Nov 19 2015 on Reuters [10]. It stated, on Nov 14, 2015, a high-speed French TGV1 train from Paris to Strasbourg derailed due to entering a bend at excessive speeds (265km/h instead of 176km/h). The centrifugal force destabilized the TGV causing it to derail. The incident occurred while the train was on its testing phase along a new service route.
1.2 Innovative ways to reduce disruptions
In Singapore, the use of Multi-Functional Vehicle (MFV) which provide condition monitoring are fitted with technologies such as Linear Variable Transducer for monitoring the third rail sag, “RailVision” which is an image capturing and detection system for track faults, ultrasound technologies to detect rail conditions and lastly, Laser Trolley to measure both rails simultaneously [12]. Early this year in 2018, SMRT partnered with McLaren Applied Technologies to integrate their high-speed data loggers, used in Formula 1 Race cars to the train system for data gathering. Data will be used to track and predict the performance of trains [13].
To prevent flatted wheels, most trains are fitted with Wheel slide protection (WSP), similar to motor vehicles’ Anti-Lock Brake System (ABS). The micro-processor controls the braking system whereby if a slide is detected, it alters the braking on/off in pulses [14]. Additionally, sanding is also commonly integrated together with the system. Locomotive is equipped with a sandbox in front of the wheels which delivers dry sand for the wheels to gain traction. It works together with the WSP in detection of wheel slide and activation. Sanding is also used to assist in slip conditions [15].
The problem of wheel sliding also incurs embrittlement of the wheels making them susceptible to cracking and instant failure due to the heat generated by sliding. The heat generated can alter the micro-structure of the wheels. Different types of steel used for manufacturing the wheels are tested and studied to improve the wear rate of wheels [16].
In United Kingdom (UK), the MFVs are fitted with high pressure washers to wash and clean the railheads off the contaminants. The railhead is also coated with sandite4 to assist and provide adhesion [17].
In Japan, signal analysis is used for fault detection. Probes are used to pick up signals for multi-resolution analysis (MRA) whereby Fourier analysis is used for signal conversion. Track irregularities are measured from the vertical and lateral acceleration of the car body and the roll angle calculated by a rate gyroscope. Cabin noise is recorded and analyzed for rail corrugation using the spectral peak calculation. A GPS is then used to determine its location [18].
1.3 Ways to enhance existing system in Singapore
The MFV used in Singapore’s railway for fault detection and identification is manually operated. Considering the factors of human errors coming into play, a report from the School of Engineering Electronics in VIT University, India proposed the used of autonomous vehicle for fault detection which helps to reduce the engineering hours and manpower. The vehicle is fitted with multiple infrared sensors to detect obstacles on track, discontinuity and the absent of nuts and bolts. The sensors run across the track to identify an anomaly in the receiving signal. Additionally, the vehicle is also fitted with ultrasonic sensors which detects the misalignment of track similarly by comparing the receiving signal with a set datum [19]. The team feels that by incorporating the ultrasonic sensor to identify misalignment onto the passenger trains in Singapore, the operators will be able to pick up much more data to promptly identify and rectify the fault before escalation to a bigger problem.
Rail lubrication also plays a crucial role in maintaining the lifespan on railheads and wheels. In UK and North America, friction modifiers or traction enhancers are added to the top of the rail for lubrication. The function of these modifiers has effects on reducing wear on both railhead and wheels, flanging contact noises in curve and increased fuel efficiency [20]. Portec Rail Group, UK, has a water based liquid Friction Modifier called “Keltrack” which promotes on shorter braking distance, noise level reduction and extended rail life with no effect on the signaling components [21]. These friction modifiers may or may not be used in the Singapore’s context due to its environmental conditions which may affect the properties of the lubrication. Having better lubrication should assist in the traction of the train preventing wheel flats leading to excessive vibration of the train.
In addition to the detection of flat wheels, the case of Metro North recalling multiple train cars [9] has led the company operator to look for alternative solutions other than visual check approach. The company has adopted an Automatic Inspection System (AIS) in the form of WheelChex® consisting of 32 Vortok MultiSensors 5 which is a system different from the traditional AIS. These sensors measure the force profile of each wheel as it passes over the system and the acquired data is used to identify the roundness and smoothness of each wheel by observing the mean weight and peak force of the wheel [22].
Signaling issues happens commonly in the railway sector, for safety reasons, trains are forced to come to a standstill when there is a signaling fault is encountered causing disruptions. In the UK, measures such as introducing uninterrupted power supplies (UPS) which takes over the main supply when it is cut due to, for example, a blown fuse. Replacing aging cables, wireless monitoring with annual inspected [23]. There are incidents where the trains in Singapore faced with power outages which cause the signaling system to fail. Hence a UPS or backup power supply may be feasible to be implemented in the system.