CBTC Implementation: A review

In recent months, signalling system tests have been the consternation of many commuters. The rollout of the new Communications-based Train Control signalling system, CBTC for short, has been particularly rough, with regular delays and faults across the North South Line (NSL) and East West Line (EWL)

This article will attempt to delve deeper into the technical workings of the CBTC system and how certain working aspects of the system have led to the regular service delays faced by commuters. We will also discuss the policy side of the issue, from the implementation of the CBTC, and what lies ahead for the full commissioning of the system.

Key Milestones:
  • 2012: Signalling upgrade starts, projected commissioning in 2016
  • 2016 (Aug): Trial runs commence on the NSL during off-service hours
  • 2016: Opening of Tuas West Extension delayed for more rigorous testing of the CBTC 
  • 2017 (28 Mar): CBTC live tested on the NSL for the first time, during the last hour of revenue service
  • 2017 (16 Apr): Full-day CBTC testing on the NSL commences on Sundays
  • 2017 (29 May): Daily full-day testing of the CBTC commences on the NSL 
  • 2017 (18 Jun): Opening of the EWL’s Tuas West Extension and partial CBTC implementation 
  • 2017 (Jul): Trial runs commence on the EWL during off-service hours
  • 2017 (Dec): Projected live testing on the EWL
  • 2018 (Mar): Projected full commissioning on the EWL
Background
North South Line near Woodlands
North South Line near Woodlands

The North South Line (NSL) and East West Line (EWL) are the two oldest metro lines on the Singapore Mass Rapid Transit (MRT) network, which opened in stages between 1987 and 1990. The legacy signalling system fitted to the NSL and EWL since its introduction in 1987 was the Westinghouse FS2000 supplied by British company Westinghouse Signals Ltd (now part of Siemens). It relied on a fixed-block system that divided the track into ‘blocks’ which could only be occupied by one train at a time. Automatic Train Control (ATC) was supported through its ATP, ATO, ATS subsystems, along with relay interlockings.

As part of the resignalling upgrade, French company Thales is installing its SelTrac Convergence CBTC system to upgrade the legacy Westinghouse signalling system, along with its NetTrac MT management system. The signalling upgrade is part of a multifaceted expansion and upgrading of ageing infrastructure on the rail network, which includes sleeper replacement, third rail and power system upgrading, installation of noise barriers, and the purchasing, refurbishment and replacement of rolling stock. 

Thales touts its radio-based CBTC system as being highly reliable and advanced. It has previously provided CBTC for other rapid transit systems around the world, including the Kuala Lumpur Rapid Rail, Hong Kong MTR, London Underground, New York City Subway, Shanghai Metro and the Vancouver SkyTrain.

Tuas West Extension of the East West Line
Tuas West Extension of the East West Line

While the North South Line has fully transitioned to CBTC, a part of the East West Line (EWL) also operates on CBTC (between Pioneer and Tuas Link). All trains heading westbound switch from the legacy Westinghouse to the new Thales CBTC signalling systems at Pioneer station, and switch back to the legacy Westinghouse signalling system when heading eastbound from Pioneer towards Pasir Ris.

The rollout of the CBTC is closely coordinated between the Land Transport Authority (LTA), the statutory board that owns all rail assets; SMRT Trains, the operator of the NSL and EWl, and Thales, the system supplier.

But first, what is CBTC?

Main Article: Communications-based Train Control

In a Moving Block signalling system, the braking parameters are communicated to each train in real time, based on the train in front
In a Moving Block signalling system, the braking parameters are communicated to each train in real time, based on the train in front

Communications-based train control (CBTC) is a moving block type railway signalling system that relies on continuous telecommunications between the train and trackside equipment for train management and control. The CBTC system on a train communicates real-time location and speed data with the trackside computers, which establish a safety envelope in which a train is allowed to operate. Before it gets too technical, in layman terms, the CBTC allows trains to operate closer to each other while maintaining a safe distance

In Singapore, the CBTC signalling system is used on the North East LineCircle Line and Downtown Line. The North South Line and East West Line, being the oldest lines in the network, are being upgraded from a speed-signalled Fixed Block signalling system to a new CBTC signalling system, expected to be commissioned in Year 2017 and 2018 for both lines respectively.

The CBTC system on a train communicates real-time location and speed data with the trackside computers, which establish a safety envelope in which a train is allowed to operate. This is in contrast to the legacy Westinghouse signalling system which uses divides the track into segments called ‘blocks’, which only can be occupied by one train at one time.

Readers keen on learning more about the general working principles of the CBTC contrasted with that of the legacy Westinghouse signalling system are highly encouraged to visit the main CBTC article, Communications-based Train Control.

While ‘CBTC’ is frequently used as an all-encompassing term for the new signalling system, Communications-based Train Control is, strictly speaking, is just the train separation component of the upgraded signalling system. The system contains, Automatic Train Operation (ATO), Automatic Train Protection (ATP) and Automatic Train Supervision (ATS) subsystems, which work together to offer Automatic Train Control (ATC) capabilities.

How does CBTC compare with the old signalling system?

The CBTC system uses existing track space more efficiently, safely reducing the space between trains, making room for additional services. On the North South Line and East West Line, the CBTC upgrade brings down waiting times 120 seconds to 100 seconds, allowing for a 20% increase in capacity, and a maximum of 36 trains per hour over the current maximum of 30 trains per hour.

This will be accompanied by the delivery of 57 new trains (45 C151B and 12 C151C trains) for both lines by 2019, greatly reducing peak hour congestion on these lines in the years to come. It is also supported by modernised ATP, ATO and ATS subsystems.

The system can also adjust train speeds, reducing train bunching and recover from delays. Trains are also able to operate on all tracks in both directions safely. This offers more flexibility for trains to switch between tracks when there is a fault on one stretch of track. 

Under CBTC, trains can travel much more closely together
Under CBTC, trains can travel much more closely together

On the North South Line and East West Line, trains on fixed-block signalling use Semi-automatic Train Operation (STO), with the driver closing the doors at every station and operating the train manually during a disruption. After the CBTC upgrade, both lines will use Driverless Train Operation (DTO), where doors will close automatically. The system will not require input from the driver unless in the event of a disruption.

The CBTC is advantageous even in wet weather, where trains will automatically adopt a suitable wet weather braking profile when the rails are wet, without the need for manual driving. In the old signalling system, the braking forces demanded by the Automatic Train Control (ATC) are optimised for dry weather and would cause the wheels to slip during wet weather, resulting in platform overruns. As such, Train Operators manually drive the train in Coded Manual, CM (also known as Protected Manual Mode, PMM), resulting in a more jerky ride. Under CBTC, trains in wet weather will adopt a more gentle braking profile to avoid wheel slippages, and the additional time taken between stations are automatically factored into the scheduling system.

Hardware and Software upgrades
Trackside CBTC Antenna
Trackside CBTC Antenna

The new signalling system involved the installation of additional signalling equipment on board every existing train on the North South and East West Lines. As such, two seats were removed from both ends of each train and a signalling equipment housing unit was installed in its place. The unit houses the Vehicle On- board Computer (VOBC), and includes ATC equipment as well as relays. Two units are installed on every train, offering redundancy as each computer can assume the working role of the other in the event of a system fault. In addition, the train operator’s console had to be modified to accommodate the human-machine interface (HMI), the CBTC display unit.

New infrastructure was also installed. New trackside equipment such as antennas and associated cabling were installed along the tracks, and wayside controllers (new computer systems) had to be fitted to existing train stations. 

While the CBTC no longer requires existing track circuits for operational use, they are still retained to be used as a backup system for train detection and for broken rail detection. Although not equipped with the fixed-block signalling system, the Tuas West Extension is also fitted with track circuits for this reason.

Implementation Timeline & Challenges

Resignalling projects present a unique difficulty as since signalling systems are critical to the operation of trains and rely on the near-flawless operation of its many constituent components to operate smoothly. Minor software glitches or hardware issues can cascade into long delays. As such, rigorous testing is crucial to the successful rollout of a new signalling system.

CBTC antenna and lineside equipment along the NSL
CBTC antenna and lineside equipment along the NSL

In February 2012, Thales was awarded Contract 1652A – Replacement Signalling System for the North -South And East -West Lines and Contract 1652B – Signalling System for Tuas West Extension for S$195 million and S$40.3 million respectively. Resignalling work was coordinated among SMRT, LTA and Thales engineers. The upgrading work would be carried out across 95km of tracks, 141 trains, 54 stations, 1 main operation control centre, and 3 depots (Bishan Depot, Ulu Pandan Depot, and Tuas Depot) from which trains are deployed.

As a brownfield application of the CBTC, re-signalling an operational line presents significantly greater challenges than a greenfield application (i.e. on new lines). Previous applications of the CBTC in Singapore (on the NEL, CCL and DTL) involves intensive daily testing for several months prior to the opening of the line. 

SMRT's newest train, the C151B, is only equipped with CBTC
SMRT’s newest train, the C151B, is only equipped with CBTC

On the NSEWL, the signalling upgrade started in 2012 and was intended for commissioning by 2016. That deadline was missed and pushed back to 2017. In the meantime, the opening of the Tuas West Extension was pushed back to 2017 for more rigorous testing of the new signalling system. While the reasons for the delay were never made public, there was a possibility that other upgrading work, such as sleeper replacement, took priority over the resignalling. 

Much of the testing work was carried during off-service hours. In addition, the delays affected the launch of SMRT’s newest trains, the Kawasaki Heavy Industries & CSR Qingdao Sifang C151B (or simply C151B), of which all 45 units had been delivered. The new C151B train is easily identified by its white exterior and is only equipped with the CBTC signalling system and as such, requires the CBTC signalling system to be active in order for it to be deployed on the line.

The opening of the Tuas West Extension was indirectly affected by the launch of the C151B trains. As CBTC was not commissioned on the EWL, only older trains (equipped with both the legacy fixed-block and new CBTC signalling systems) could ply the full stretch of the line. These trains would be freed up by redeploying them from the NSL, but only after C151B trains were introduced cover the shortfall on the NSL. Hence, when the Tuas West Extension opened three weeks after full-day CBTC testing began on the NSL, at least 10 C151B trains were already in service on the NSL. To a smaller scale, the additional trains also helped to accelerate the body shell replacement of the older C151A trains which were being sent back to China for repairs.

Implementation Process
Workers install lineside CBTC equipment during engineering hours (Photo: LTA)
Workers install lineside CBTC equipment during engineering hours (Photo: LTA)

Much of the testing work was carried during engineering hours, limited to between 1.30am and 4.30am. This three-hour window was crucial, as beyond that, time was need to prepare stations and trains for the start of revenue service at 5:30am. Apart from over 1,300 tests required to ensure the core functionality of the signalling system, the CBTC was also run in ‘shadow mode’ during regular operating hours, where it was turned on for monitoring and data recording purposes. This mimicked an actual operating scenario whilst the trains remained driven by the old signalling.

Brief Timeline – North South Line:

CBTC Live Testing began in the late hours of 28 March 2017, during the last hour of revenue service, when all trains were stopped at around 11pm to facilitate the switch to the new system, up till the end of revenue service hours past midnight. These tests were carried out across the next few days, for a total of 10 rounds of testing. Full-day testing of the system commenced on 16 April 2017 (Sunday) and continued every Sunday for the next two months for a total of 7 rounds of testing. 

With no major issues found during these live tests, the decision was made to proceed with full-day weekday testing (akin to full implementation) of the CBTC system, which commenced on 29 May 2017, deliberately timed with the start of the month-long June school holidays to lessen the inconvenience on students.

Brief Timeline – East West Line:

After the open house two days prior, partial implementation of the CBTC commenced on 18 June 2017 with the opening of the Tuas West Extension. Trains switched from the old Westinghouse fixed-block system to the Thales CBTC system at Pioneer Station (in both directions).

Other Challenges

Unlike the North East LineCircle Line, or Downtown Line, which operates on a single type of train (Alstom Metropolis for the NEL and CCL, Bombardier MOVIA for the DTL), the North South Line and East West Line operate on four distinctly different type of rolling stock, namely the Kawasaki Heavy Industries C151Siemens C651Kawasaki-Nippon Sharyo C751B and the Kawasaki-Sifang C151AC151B. A total of 141 trains were upgraded with the Thales CBTC signalling system.

Each of the four fleets of trains is different on a technical level, with different types of traction motors and existing on-board equipment, so the signalling had to be adapted for each type of train. Moreover, in contrast to the fully-underground new lines, the NSL and EWL runs on viaducts, at-grade sections and underground tracks, hence the challenge of adapting the system for all these different types of trains in different track conditions (i.e. dry and wet weather). During wet weather, trains adopt a modified braking profile with a greater braking distance to compensate for the reduced track adhesion during wet weather.

In addition, the signalling system had to be adapted to interface with existing technologies such as the Rail Travel Information System (RATIS) screens at stations and multiple types of Platform Screen Doors (PSD) installed across the line. With the introduction of the CBTC signalling system came the challenge of integrating these existing technologies to work with the new signalling system.


Faults and Failures

The CBTC implementation resulted in many recent faults and delays with both the NSL and EWL.

Train bunching as a result of CBTC
Train bunching as a result of CBTC

On the North South Line, regular signalling faults and delays caused long headways and instances of very close ‘bunching’ along the line. While the CBTC system proved effective in running trains together at very tight intervals, the cause of such ‘bunching’ incidents was often the CBTC system itself, when minor signalling issues often delayed individual trains and causing long headways followed by a quick succession of ‘bunched’ trains (trains arriving in quick succession). 

Despite the relatively fault-free performance of CBTC on the EWL (after all, the Tuas West Extension was the most rigorously tested stretch of line prior to implementation), the signalling change point turned out to be a significant weak link. The changing of signalling systems at Pioneer was supposed to take 2 minutes, but frequent delays (especially during the peak hours) led to significant backlogs east and west of Pioneer Station. Westbound congestion often stretched to Lakeside and beyond, even reaching to Jurong East in extreme circumstances.


Scenarios Faced – NSL Jurong East bottleneck

With trains operating at higher frequencies under the CBTC, train bottlenecks regularly occur at Jurong East, one of the terminating stations of the North South Line. As a result, commuters frequently face additional travelling time between Bukit Batok and Jurong East during the peak hours, as trains queue up to enter Jurong East.

The turnaround duration at Jurong East is determined by the CBTC signalling system, as is the automated door closing at every other station. As such, there is a risk that commuters might get struck by closing doors especially while transferring from East West Line to the North South Line. Previously, Train Captains would manually close the doors at an appropriate moment by monitoring the platform situation through CCTV monitors, while also holding the doors for commuters transferring from the East West Line.

Ulu Pandan MRT Depot
Ulu Pandan MRT Depot

Fresh trains from Ulu Pandan Depot would also require a switching of signalling systems. On the North South Line, trains are launched from both Bishan Depot and its Ulu Pandan Depot. Bishan Depot is located along the NSL, which means trains coming from there continue to operate on the new signalling system. However, Ulu Pandan Depot is on the EWL, which means that when trains are launched from Ulu Pandan to Jurong East station, trains have to be switched from the old signalling system to the new one.

As explained during a media briefing on 14 July 2017, the signalling switch at Jurong East station takes about one-and-a-half minutes, and in the morning with a headway of about two minutes, it causes delays and congestion which impacts a commuters’ journey.

Scenarios Faced – EWL Pioneer bottleneck

All westbound East West Line trains, terminating at either Joo Koon or Tuas Link, have to switch to the new signalling system at Pioneer MRT Station (Platform B). This is because Joo Koon-bound trains turn around at a cripple siding west of Joo Koon Station, built as part of the Tuas West Extension which is equipped only with the CBTC signalling system. 

The signalling switch over is said to take about 2 minutes. However, the actual time required to switch between signalling system varies from as fast as 30 seconds to 5 minutes and much longer should a train or signalling fault occur. With the peak hour train frequency of about 2.5 minutes, delays in the switching of signalling system at Pioneer in either the Eastbound or Westbound direction regularly causes bottlenecks as trains queue up to enter the station.

As a result, commuters may have likely encountered slow-moving trains and “stop go stop go” scenarios from Lakeside and Pioneer as trains bunch close together. In the Eastbound direction, commuters may face long wait times for trains if there is a delay in switching signalling systems, giving rise to long headways and overcrowded trains.

Jurong East crossover wait point

One scenario observed at Jurong East is the location at which trains stop to wait for the front train to exit the station. When CBTC was first implemented on the NSL, trains heading into Jurong East stopped before the first crossover point which directs Platform A and Platform D, which is around half the distance between Jurong East and Bukit Batok. Trains would then proceed to wait there until the front train occupying either Platform A or D left the station. This scenario left a lot of unoccupied track before Jurong East, increasing the amount of time when between train departures/arrivals at Jurong East Platforms A/D and thereby decreasing the rate of train turnarounds.

After a while, the system was updated to allow trains heading into Platform D to stop just before the crossover point that leads to the eastbound East West Line (Jurong East Platform B/C), as illustrated in the scenario diagram above (NSL Jurong East bottleneck).

While the reason for this scenario is unclear, a brochure for the Thales NetTrac MT central control system reveals a feature known as Automatic Deadlock Prevention, which prevents deadlocks in a bi-directional single-track travel area. It works by preventing the issuing of route request until a train at the terminal is at a location where it will clear the interlocking just before the second train required the route to be set. There is a possibility that this system prevents a train from entering what is perceived to be a bi-directional track and thereby preventing an incoming train from entering the sector before an exit route has been finalised for the front train occupying the platform at Jurong East.

Trains entering wrong sections of track

Another scenario observed was where trains abruptly entered sections of track when they are not supposed to, resulting in obstruction of other trains on the line and subsequently delays. For example, a train waiting to enter Jurong East would overshoot its waiting position, pass over the final crossover point and come to a stop just before the platform, blocking the train at the platform from exiting the station. Delays resulted as the offending train had to reverse, to allow room for the train at the platform to leave the station.

Another scenario observed was during bunching at Choa Chu Kang towards Jurong East, where a southbound train abruptly crossed over to the northbound track after leaving the station. While safety mechanisms prevented a collision with a northbound train on the same track, the offending train had to be reversed back onto the southbound track. 

Other faults

Platform overrun and reversing
Overrun scenario on the North South Line (CBTC Operation)
Overrun scenario on the North South Line (CBTC Operation)

Under CBTC operation, trains occasionally overrun the station and have to reverse, regardless of wet or dry weather. As a result, trains are made to reverse back into the station, resulting in minor delays. Many possible factors include incorrect detection of the alignment device, or a braking curve not ideal for the weather scenario. Progressive software updates have reduced the speed of trains on rainy days.

Train doors do not open, skips station

Trains occasionally stop at the correct position but then proceed to the next station after a short dwell period without ever opening the doors. Complaints about this scenario often appear on SMRT’s social media platforms. This scenario is likely caused by the Vehicle On-board Computer (VOBC) unable to detect the presence of the alignment device at the end of each platform. 

Doors close too fast / without announcement

Under the old signalling system, the timing of the “Doors are closing” chime is controlled by the Automatic Train Supervision (ATS) – the ATC subsystem that governs schedule adherence – and automatically plays before the scheduled departure of the train from the station. It is then the job of the Train Operator to close the doors at an appropriate moment to avoid closing the doors on passengers, before setting the train in motion.

However, under the new CBTC signalling system, the “Doors are closing” chime, doors closing action and actual departure timing of the train are all governed by the signalling system. Occasionally, the system may leave too little time for boarding and alighting activities especially at interchange stations, which is a source of complaints. 

Interfacing between Platform Screen Doors & Train Door
Unsynchronized Platform Doors
Tuas West Extension – Unsynchronized Platform Doors

With CBTC, train doors and platform screen doors are designed to open and close in sync, instead of the short lag time between the opening and closing of both the platform screen doors and train doors under the legacy Westinghouse signalling system. Issues affecting the interfacing between the train doors and platform screen doors will lead either set of doors to fail to open or close, resulting in delays as the train is unable to move off the station until the CBTC signalling system confirms that both doors are closed.

A prominent example of this scenario happened during the revenue service launch of the C151B train (Set 601/602), when the North South Line was undergoing Sunday full-day trials. At City Hall station (towards Jurong East), the train was delayed for around eight minutes as the system failed to detect that both sets of doors were closed, resulting in a backlog of trains.

Abrupt braking during normal operations

Under CBTC operation, trains engage the emergency brakes as a safety measure when there is a loss in radio communication between the train and wayside controllers, or any form of incorrect or conflicting signals are received. This occasional glitch is the reason for the out-of-the-blue abrupt braking scenarios that some commuters might have experienced.

A computer system leading to incorrect/conflicting signals was the cause of the island-wide train disruption on 28 June 2017. It was blamed on a system error caused by Thales engineers missing a step while loading a new radio software. The system error disrupted radio communications between trains and lineside antennas, and all trains along CBTC-equipped sections of the NSL and EWL came to a standstill.

Information Screen bugs
The common 'next station' bug on the RATIS
The common ‘next station’ bug on the RATIS

The Rail Travel Information System (RATIS) screen on platforms, which indicate the arrival time and destination of the approaching train, tends to glitch by displaying the subsequent station as the destination rather than the actual terminating stop of the train. For example, a train at City Hall heading towards Marina South Pier might display “Raffles Place” for any amount of time, as shown in the picture on the right. Passengers are encouraged to just board the train regardless of the destination shown as the destination may be incorrect. 

During the early days of CBTC testing, the RATIS would also not indicate the platform at which the train will arrive Jurong East at (either Platform A or Platform D). This issue has since been resolved.

Other scenarios

Changi Depot not CBTC equipped

While Bishan DepotUlu Pandan Depot, and Tuas Depot were installed with CBTC, Changi Depot is the only depot to be not fully upgraded to CBTC. This is because the depot will be replaced by the future East Coast Integrated Depot which is targeted for completion in Year 2024.

PMSM trains redeployed to Changi Airport Line

For several weeks after the opening of the Tuas West Extension (18 June 2017), C151 trains upgraded with IGBT-VVVF Permanent Magnet Synchronous Motors (PMSM) from Toshiba were fully redeployed to the Changi Airport Line between Tanah Merah and Changi Airport, away from entering the CBTC equipped sectors west of Pioneer. While the reason for this redeployment is unclear, there might have been the desire to avoid initial complications. PMSM-equipped C151 trains returned to the mainline EWL since early July 2017.

Friction Brake usage

Commuters may notice a pungent metallic smell similar to a burning smell at stations when travelling on the NSL and EWL, but especially on CBTC-equipped sections of track. That is the smell of the friction brakes.

Under normal operating conditions, trains use the traction motors to slow down from higher speeds in a process known as regenerative braking, returning current to the third rail at the same time. However, under the CBTC, the friction brakes engage more frequently as the trains often engage in more abrupt braking, and when they start to overheat, the smell is produced. This scenario is most prevalent in the first-generation C151 trains, where fine regenerative braking control is less strong that other types of rolling stock.

Another scenario of heavy friction brake usage is during wet weather, where trains frequently engage friction brakes to stop the train in their precise stopping positions.


Fine-tuning the system

Since the start of the CBTC revenue service trials, engineers from LTA, SMRT and Thales have been continuously fine-tuning the system to suit local conditions and ironing out existing glitches.

A software update was installed on the new signalling system on the North-South Line (NSL) after passenger service hours on Friday, 14 July, to further fine-tune the ongoing testing by the Land Transport Authority (LTA), SMRT, and system supplier Thales to stabilise the system after having undergone full-day testing since 29 May 2017.

Incident Management

Crowd at Kranji on 2nd June 2017 during a signalling fault
Crowd at Kranji on 2nd June 2017 during a signalling fault

During a fault with the CBTC signalling system on the North South Line as well as the Tuas West Extension, SMRT would activate its Rail Incident Management Plan (RIMP) to deal with the incidents. Delay announcements would be broadcasted across NSL and EWL stations, along with updates to social media platforms. 

In the case of prolonged delays, free bus boarding at affected stations, as well as stations leading up to the affected stretch (which are indirectly affected due to train bunching, are activated. Depending on the severity of the incident, rail bridging bus services may be offered as well. 

SMRT also offers printed guides on alternative travel arrangements, which are available at all stations and distributed in the event of a disruption. Commuters can get a refund for an incomplete journey at any TransitLink Ticket Office up to 7 days after a disruption.

Future Plans

The EWL will soon be operating with CBTC
The EWL will soon be operating with CBTC

Despite the issues, SMRT expects the CBTC signalling system on the North South Line to stabilise by November 2017 – January 2018, and should be fully operational by May 2018, a year from when testing during passenger service started. A similar timeline was reported during resignalling works on the London Underground’s Jubilee Line, requiring about 6 months to bring the failure rate down to acceptable levels.

As confidence in the new signalling system grows, only then will SMRT add more trains to the line during the peak hours to maximise the benefits of the CBTC signalling system. After being fully commissioned, the legacy Westinghouse signalling system will be decommissioned, and associated hardware will be uninstalled.

For the East West Line, CBTC testing on certain stretches has begun in July 2017 across several stations. Live testing of the CBTC on the EWL is projected for December 2017, again coinciding with the month-long school holidays for minimum disruption to students.


Our Take

A common topic in public discourse is how the CBTC signalling system could have been better implemented to reduce its impact on commuters. Unfortunately, there is no easy answer to this question. While many lessons have been learnt from implementing CBTC overseas, no two metro systems are identical, and each resignalling project is a challenging endeavour for engineers. 

Difficulty of resignalling projects

Resignalling projects tend to be difficult to manage, as is the experience with other metro systems such as London, New York and Kuala Lumpur. As such, metro systems tend to proceed cautiously and roll out upgrades in phases before full commissioning. 

Signal fault on the NSL
Signal fault on the NSL

However, this was not the case with the North South Line. Rather than proceeding in stages (e.g. expanding testing to weekends, off-peak hours, and finally peak hours), the decision was made to jump straight into full-day weekday testing despite just 7 days worth of weekend testing. And as faults unravelled one after the other during weekday testing, so did the consternation of many passengers. 

In particular, signalling systems rely on the reliable function of its many component parts to deliver a reliable, working system. As such, the minor technical glitches escalated into major delays that brought peak hours chaos during the early weeks of full-day weekday CBTC testing on the NSL. The question of reliability often surfaces, and despite what LTA/SMRT have said about the multiple redundancies of the signalling system, understandably left many questioning the reliability of the signalling system. In the bigger picture, the rushed rollout of the signalling system (likely to coincide with the June school holidays) could have left underlying issues not fully assessed before peak hour testing.

Despite public suggestions to confine signalling tests strictly to off-peak hours, peak hour testing is necessary to ‘stress test’ the system, as there is no effective way of simulating such conditions during off-peak hours. Apart from the short headways between trains, the signalling system has to cope with high passenger loading on trains, which affects the performance characteristics and braking profile under automatic operation. Factoring in the unique characteristics of four different types of trains on the NSL, coupled with the chance of wet weather along certain stretches of the line, putting the new CBTC signalling system through its paces must be conducted in a challenging environment such as that presented during peak-hour testing.

C151B Deployment
The C151B train
The C151B train

Furthermore, the deployment of the of the C151B trains on the NSL essentially gave LTA/SMRT no room to back out of CBTC testing. As explained in an earlier section (Implementation Timeline & Challenges), the new C151B trains were only equipped with the CBTC signalling system and had to be deployed on the NSL, otherwise, there would be insufficient trains for the Tuas West Extension.

This also meant that it was not practically feasible to revert back to the legacy Westinghouse signalling system in the event of a major disruption, as the C151B trains were incompatible with the legacy Westinghouse signalling system. They would have to be stabled at an available siding or a depot, away from the main line before a signalling switch can be put into effect. In essence, it would be very difficult to pull off a signalling switch during operational hours owing to the difficulty of taking the C151B trains out of service. By June 2017, there were more than 10 such trains deployed on the North South Line daily.

Partial Line Implementation

Partial line implementation could have been rolled out on the NSL to more rigorously test the CBTC, similar to what was done for the Tuas West Extension, with trains switching signalling systems at a certain station along the line. However, that would affect plans to deploy C151B trains on the North South Line, which can only operate on CBTC-active sections of track. This would make partial implementation difficult.

Another alternative would be to operate a shuttle train service with commuters having to change trains at a certain station (e.g. Ang Mo Kio) and not having to switch signalling systems. Such an approach was taken at Kuala Lumpur during the CBTC rollout of the LRT Ampang / Sri Petaling Line where one set of trains were equipped with the legacy system only and another set of trains with the newer CBTC system only. The line had to be operated as a shuttle service, with commuters having to change trains between CBTC and legacy system-equipped sections of track.

However, this approach would be inconvenient and cause unnecessary trouble, for C151B trains comprise a very small part of the NSL operating fleet, and SMRT/LTA might not have seen the need for more rigorous testing of different sections of track when no issues were detected early in the testing phase. Combined with the rushed implementation of a signalling system already behind schedule, such an approach was not taken. In hindsight, the initial complications with switching signalling systems as surfaced during the Tuas West Extension rollout (where trains switched signalling systems at Pioneer) might have defeated the purpose of partial implementation.

Weekend closures for smoother implementation?

A key advantage to Thales’ resignalling proposal was the promise of no passenger service closure. It was a promise that won the contract over several major international rail systems providers, such as Alstom, Bombardier, Invensys, Ansaldo STS and Siemens. 

London commuters during a rail disruption (Photo: Mirror UK)
London commuters during a rail disruption (Photo: Mirror UK)

Such was the scenario when Thales was implementing the CBTC signalling system on the London Underground’s Jubilee Line. Upgrading and testing work necessitated the closure of sections of the Jubilee line each weekend during 2009. Although the project was due for completion in March 2010, the closures continued through 2010 and only finished in spring 2011. The programme of temporary closures for engineering work was criticised by many, and patrons to large event venues such as Wembley Stadium and The O2 had to rely on limited-capacity rail bridging buses. 

As a major transport link serving the north of Singapore, any form of planned weekend closures would be very unpalatable to many commuters. Unlike the Jubilee Line, the lack of duplicity of the North South Line would affect many commuters and require many bridging buses to cover affected sectors. As such, weekend closures were not carried out on the NSL CBTC implementation and will likely remain so for the EWL implementation.

Conclusion

Taking these factors into consideration, along with the relative success of the CBTC during weekday testing, the decision was made to jump straight into full-day testing for the North South Line, and that was when the problems started. Despite many factors working against SMRT and LTA, compounded by LTA’s rushed schedule for CBTC implementation, made an unfavourable situation worse. It was only through multiple glitches and disruptions on the NSL that a more robust system was established.


Our take on SMRT’s Incident Management

During a delay, it was clear that SMRT’s rail incident management plan (RIMP) left much to be desired. Delay information was not being well disseminated to commuters in a timely manner. Delay estimates did not accurately reflecting actual travel time and did little to soothe the nerves of passengers at overcrowded stations who were late for appointments. Furthermore, in a delay, commuters were left in the lurch with regards to when services are expected to be restored, leaving them stranded at train stations without enough information to plan an alternative route. 

Commuters boarding bridging buses during a NSL Signalling Fault
Commuters boarding bridging buses during a NSL Signalling Fault

Furthermore, SMRT does not announce instances of delays under 10 minutes on their social media platforms. This leaves commuters unable to substantiate their delays when rushing late for work or being late for appointments. Although commuters can request for delay chits at the Passenger Service Centres at affected stations, these offices would frequently be unstaffed or understaffed as staff members are busy attending to train service disruption/delay and guiding commuters. One can imagine the queue in the City if every office worker lines up to get a delay chit during the rush hour.

A better alternative is the prompt dissemination of delay information on dedicated social media channels such as MTR Updates (Facebook / Twitter), which is run by the Hong Kong MTR. Like many overseas rail operators, it also issues delay certificates online in PDF form on their website, where affected commuters can download as proof of their delay.

With regards to free bus boarding, Bus Captains are also unfamiliar with the Standard Operating Procedures such as disabling all entry EZ-Link readers instead of verbally telling commuters that the ride is free. Many commuters continue to tap their cards when boarding buses when free bus boarding is activated.

Despite all of SMRT’s RIMP shortcomings, its active deployment of Service Ambassadors (SAs) at station platforms is a welcome move to better assist commuters and reassure commuters during the CBTC testing period. It is also helpful to have more manpower on hand in the event of a rail disruption. In all, SMRT’s RIMP leaves much room for improvement and it is hoped that greater transparency and public outreach efforts can pacify commuters during this difficult implementation period.


Factfile

  • All trains equipped with both legacy Westinghouse signalling system and new CBTC signalling system – but C151B trains are only equipped with the CBTC signalling system
  • All lines equipped with both legacy Westinghouse signalling system and new CBTC signalling system – but Tuas West Extension is CBTC equipped only 
  • Traction motors on trains:
    • C151 (61 trains): 4-quadrant/GTO chopper control (Mitsubishi Electric) / 5 trains with IGBT-VVVF (Toshiba)
    • C651 (19 trains): GTO–VVVF PWM (Siemens) / IGBT–VVVF (Toshiba) after refurbishment
    • C751B (21 trains): IGBT-VVVF (Fuji Electric)
    • C151A & C151B (80 trains) – IGBT-VVVF (Fuji Electric)
  • 3 Forms of driving modes on all trains
    • ATO: Automatic Train Operation
      Used during normal operating conditions (Both Westinghouse and CBTC). Under Westinghouse signalling, train operators only control door operations and setting the train in motion. Under CBTC, ATO mode covers most or all aspects of normal operation without the need for driver input.
    • CM: Coded Manual
      Also known as Protected Manual mode. Under CM, trains are manually driven within the limits of the safe operation with all safeguards in place. Frequently used during wet weather under Westinghouse signalling. Can be identified by a steady orange/yellow light at the front of the train.
    • RM: Restricted Manual
      Under RM, trains are driven on-sight without safeguards in place, but limited to a very slow speed. Frequently used during shunting operations. Can be identified with a flashing orange/yellow light at the front of the train.

Summary

  • CBTC implementation fell behind schedule from the start
  • CBTC had to be implemented on the NSL before the Tuas West Extension could be opened, owing to limited number of trains
  • C151B trains on the NSL allowed for older trains to be reallocated to the EWL
  • Pace of implementation worked against LTA; faults occurred often on the NSL
  • Signalling system is constantly being fine-tuned and is expected to stabilise several months after implementation

Case studies – London (Urban Metros)

Perhaps the most well-known rapid transit system in the world, the London Underground experienced many difficulties when it implemented moving-block signalling systems. All these systems utilise TBTC (Transmission Based Train Control) rather than radio-based CBTC owing to the reliability of track loops over radio communications. In this section, TBTC and CBTC are used interchangeably.

London Underground chose not to adopt radio-based CBTC in line with general CBTC advancement as the untested technology was deemed as too risky. The same technology is used by the Victoria Line, Jubilee Line, Northern Line, and other rapid transit systems including Vancouver’s SkyTrain, Toronto’s SRT, San Francisco’s Municipal Railway (MUNI) and Hong Kong’s MTR. Fast-forward several years, LTA has opted for the radio-based CBTC on likely because of the reliability it experienced with radio-based CBTC on the NEL, CCL and DTL.

London Underground Northern Line (Photo: The Independent UK)
London Underground Northern Line (Photo: The Independent UK)

The first CBTC-upgraded Underground line was the Jubilee Line, of which Thales supplied the signalling equipment (the Docklands Light Railway was upgraded to CBTC several years prior). Upgrading and testing work required the closure of sections of the Jubilee line each weekend during 2009. Although the project was due for completion in March 2010, the closures continued through 2010 and only finished in spring 2011. The programme of temporary closures for engineering work was criticised by many. Similar difficulties were encountered during the Victoria Line signalling upgrade, necessitating weekend closures before a phased introduction could take place. Many issues were encountered before the two lines finally achieved commissioning in 2011 and 2012, in time for the 2012 London Olympics.

With the lessons learnt, the CBTC upgrading of the Northern Line was much smoother despite the greater complexity of the line. Migration strategy centred staged implementation, and a six-month period of ‘shadow-running’ before live implementation of the system. To eliminate organisational issues, both teams from London Underground and Thales occupied the same premises in Canary Wharf, allowing engineers to work much more closely together for the successful implementation of the new signalling system.

London’s complicated Sub Surface Lines (comprising the Circle, District, Metropolitan and Hammersmith & City Lines) are also being resignalled by Thales. It was awarded a £760m contract to renew the signalling and train control systems by implementing a radio-based CBTC system, with the ‘main benefits’ to be delivered by Year 2022. The new contract replaces an older £345m contract awarded to Bombardier in June 2011 but terminated in December 2013, with the company unable to deliver a system suited for the complex nature of the network.

Case studies – Japan (Suburban railways)

In Japan, CBTC technology is not prevalent but a similar system, ATACS, has been developed by East Japan Railway Company (JR East) and entered live trials on an 18-kilometre stretch of the suburban Senseki line between Aoba-dori and Higashi-Shiogama, serving the city of Sendai.

JR East Senseki Line (Photo: Getty Images)
JR East Senseki Line (Photo: Getty Images)

ATACS stands for Advanced Train Administration and Communication System, and is a radio-based moving-block system which offers cab signalling with full train protection. It is primarily intended for suburban passenger networks and mixed-traffic railways which utilise a mix of rolling stock designs. The brake profile is then calculated for each type of train and its position, and also factors in the location and activation of railroad crossings.

Although the March 2011 Tohoku Earthquake damaged critical infrastructure, the ATACS system was repaired and introduced in October 2011. It has achieved stunning reliability figures – up till 2016, an availability of 99.99999% was achieved, with a radio interruption caused a 10-second failure in one six-month period.

JR East is scheduled to roll out ATACS on the Tokyo suburban network with the 37-kilometre Saikyo Line between Ikebukuro and Omiya, scheduled for the autumn of 2017. It 2014, it also selected Thales to design and install a CBTC for the 30-kilometre Joban Line between Ayase and Toride, which would then allow JR East to compare ATACS with European CBTC. JR East intends to equip ATACS on the Koumi Line by 2019 and the entire Tokyo metropolitan area by 2036.


Conclusion

The CBTC upgrade is an overdue and necessary major upgrade to boost capacity on our rail network and disruptions are an inevitable part of this transition. As SMRT, LTA and Thales engineers continue to iron out issues with the new signalling system, commuters are urged to be patient during the transition period and plan for additional travel time and alternative travel routes. 

Along with additional trains purchased by LTA, commuters can expect shorter headways and smoother and less crowded journeys when the Thales CBTC signalling system is fully commissioned on the NSL and EWL.

This article has been written from the perspective of an industry outsider, and the content covered here is likely just the tip of the iceberg in regards to technical and policy details. With LTA and SMRT’s traditionally guarded stance against the disclosure of such details to the public, it remains difficult for the public to gain a better knowledge of the CBTC implementation process apart from the limited information contained in LTA’s official press releases. 


Annexe: List of signalling faults attributed to the CBTC
  • June 30, 6.32am: ‘Signal track fault’ at Ang Mo Kio
    Additional 10 minutes of travel time from Woodlands to Ang Mo Kio, revised to 15 minutes at 7 am. Cleared at 8.50am.
  • June 28, 5:22pm: Signal fault across entire TWE sectors
    Attributed to Thales engineers missing a step while loading a new radio software, causing a system error that disrupted radio communications between trains and lineside antennas, and all trains came to a halt as a safety feature 
    No train service between Joo Koon and Tuas Link, restored 45mins later
  • June 28, 5.15pm: Signal fault across entire NSL / TWE sectors
    Additional 30 minutes of travel time across the entire line, later changed to no train service until further notice (5.37pm), partial followed by full restoration 2 hours later
    Attributed to Thales engineers missing a step while loading a new radio software, causing a system error that disrupted radio communications between trains and lineside antennas, and all trains came to a halt as a safety feature 
  • June 11, 6.10pm: ‘Signalling system fault’
    Additional 20mins travelling time between Choa Chu Kang and Jurong East with free bus services activated. Restored at 6.50pm.
  • June 2, 5:05pm: Signalling system checks’
    Additional 15mins travelling time due to ‘signalling checks’ could cause delays of up to 15 minutes, updated to additional 30mins travelling time between Yishun and Yew Tee with free bus boarding and bridging buses offered. Resumed at 8pm.
  • June 1, 6.47pm: ‘Signalling system fault’
    Additional 20mins travel time between Jurong East and Marina South Pier, free bus services available between Jurong East – Choa Chu Kang and City Hall – Ang Mo Kio. Updatd to 15mins at 7:17 pm. Restored at 7:41pm, free bus services ceased.
  • May 29, 6pm: ‘Signalling fault’
    Additional 20mins travelling time between Choa Chu Kang and Jurong East with free bus services activated. Restored at 6.25pm
  • May 28, ‘Signalling fault’
    No train service between Marina Bay and Marina South Pier for around 3 hours, free regular bus services activated

This list only covers delays officially reported by SMRT.


Annexe: Timeline of CBTC events
  • 2012: Signalling upgrade starts, projected commissioning in 2016
  • 2015 (Dec): 91% and 41% of installation complete on the NSL and EWL respectively
  • 2016 (Aug): Trial runs commence on the NSL during off-service hours
  • 2016 (Oct): Launch of CBTC on the NSL delayed to 1Q 2017, 93% of testing complete on NSL, installation on EWL ‘more than 80% complete’
  • 2016: Opening of Tuas West Extension delayed for more rigorous testing of the CBTC 
  • 2017 (Jan): NSL live testing announced for March 2017, ‘more than 85%’ installation complete on the EWL
  • 2017 (28 Mar): CBTC live tested on the NSL for the first time, during the last hour of revenue service
  • 2017 (16 Apr): Full-day CBTC testing on the NSL commences on Sundays
  • 2017 (29 May): Daily full-day testing of the CBTC commences on the NSL 
  • 2017 (18 Jun): Opening of the EWL’s Tuas West Extension and partial CBTC implementation 
  • 2017 (Jul): Trial runs commence on the EWL during off-service hours, EWL live testing announced for December 2017
  • 2018 (Mar): Projected full commissioning on the NSL

Gallery:


Gallery (LTA):

Diagrams produced by the LTA, re-published by Mothership.

CBTC signalling equipment installed on trains:

  • Radio and Antenna – For radio communication with lineside antennas
  • Train Operator Display – Signalling system interface, Replaces older dials
  • Speed sensor, transponder reader, proximity sensor, accelerometer – Used to calculate the position of the train in real time

CBTC signalling equipment installed on tracks (viaducts and tunnels):

  • Radio and antenna – For radio communication with trains
  • Fibre-optic cables – Links radio antennas to wayside controllers for two-way communication 
  • Transponder -For trains to determine their location on the track
  • Proximity plate – Determines if trains have aligned correctly with platform
  • Signals -Upgraded signals reflect new CBTC zoning

CBTC wayside signalling equipment:

  • Relay Interlocking: Racks of electro-mechanical relays offer interlocking protection and is a key part of the legacy Westinghouse signalling system (Photo: LTA)
  • Computer-based Interlocking: A signalling cabinet containing multiple modules, offering interlocking protection as part of the Thales CBTC signalling system (Photo: LTA)

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One thought on “CBTC Implementation: A review

  • 17 July 2017 at 5:10 PM
    Permalink

    Thnx guys! Great article…from an engineering and neutral perspective.

    Reply

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