need for platform-to-track intrusion detection systems in automated metro linesby Antoine STEPHAN and Virginie RAOUL, CBTC Experts, SYSTRA

www.systra.com

COVER: © RATP (DENIS SUTTON), © SYSTRA (PAUL PRESCOTT)

Trending signaling system for urban railway applications, the Communications-Based Train Control (CBTC) system can manage various levels of automation, providing ope-ration flexibility, for which the system is required to fulfil specific functions of train operation and protection.

The Grade of Automation (GoA) of a line defined by the IEC 62290-1 standard characterizes five levels of automation from 0 to 4. GoA0 corresponds to a full manual mode with-out any automatic protection, and GoA4 represents the Unattended Train Operation (UTO), i.e. no staff is required on-board.

Automated systems, particularly without driver, imply a change in the way of operating the line. As safety always comes first, it is mandatory to protect passengers on platforms by means of protection systems so that any potential intrusion to the automated territory is detected, or even prevented.

Protection needs in a CBTC contextFollowing the IEC 62290-2 standard for urban guided trans-port management and command/control systems:

• In GoA0/1/2 modes, the guideway supervision is performed by the driver.

• In GoA3/4 modes (driverless and unattended, respec-tively), the system is required to manage the guideway supervision, i.e. to prevent collision with obstacles and persons on tracks. For collision with obstacles along the track, on-board obstacle detection systems are installed

under the trains and trigger a train emergency brake as soon as an obstacle is detected. For collision with passengers, as the station platforms are the main loca-tions for passengers’ access to the train and the track, these platforms should be equipped with a protection system.

The purpose of the platform protection system is to pre-vent any incident in station between trains moving along the platforms and passengers waiting on the platforms, and isolate tracks from any passenger’s intrusion. The protection system is connected to the signaling system, through vital control/monitoring interfaces, allowing the following functions:

• When no train is in the station, the system will either detect or prevent any intrusion on the track. In case of any intrusion detection (e.g., passenger falling on the track) or failure leading to a risk of intrusion (e.g., plat-form doors open), the train run authorization in this area will be inhibited by the signaling system.

• When the train is entering the station, in case of any intrusion detection or failure leading to a risk of intrusion, the protection system will trigger through the signaling system an emergency brake of the entering train.

• When the train is correctly berthed in the station, if plat-form screen doors are installed, the signaling system will authorize the opening of the platform doors facing the train doors, then control the closing of the doors. The train departure will only be authorized if the platform and train doors are detected closed and locked, and the protection system is not triggering any detection alarm.

Different types of platform protection systems can be proposed today for metro stations. In order to select the most adapted solution for a given metro project, various

the “communications-based train control” is defined by the ieee 1474 standard as a continuous automatic train control system whose intelligence goes far beyond the basic train driving. cbtc has become the heart of the metro system and, used for services with high added value, can improve availability and safety, which are the main concerns of the operators. to keep stations platforms a safe place while the grade of automation is growing, protection systems are needed. even if platform screen doors seem to be the ultimate solution, in some cases other detection systems can be more suitable mainly due to cost considerations or complexity of migration and infrastructures adaptation.

need for platform-to-track intrusion detection systems in automated metro linesby Antoine STEPHAN and Virginie RAOUL, CBTC Experts, SYSTRA

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criteria must be analyzed, including product cost, operation and maintenance cost, installation complexity, migration strate gy in case of brownfield project, platform infrastruc-ture constraints, life cycle duration, target safety level, environ mental conditions (including temperature, wind, light/sun, which could increase the risk of false detection).

Background on platform protection technologiesTwo main families of platform protection solutions are currently used for automated metro lines: platform screen doors (PSD) and intrusion detection systems.

The installation of PSD is the dominant solution over in-trusion detection systems for fully automated metro lines. The following figure provides the current total number of stations equipped with PSD vs. the ones with intrusion detection systems for fully automated metro lines world-wide, with the percentage of growth since 2006 (Ref. UITP, July 2016).

• Improve the overall quality of service of the line opera-tion thanks to an efficient management of passengers’ exchange.

An alternative to PSD for protecting platforms is the use of intrusion detection systems to detect passengers’ intru-sion and fall on the track. This detection system is vitally interfaced with the signaling system. When an object is detected, it raises an alarm to the signaling system in order to automatically set a restrictive run authorization in the platform area, and switch traction power off when a third rail is present. For degraded operation, a bypass device must be implemented which allows trains to be operated, even when the intrusion detection system has failed.

Different technologies can be used for the intrusion detec-tion systems, including:

• Infrared/laser, based on light interception,

• Radar, based on forms and materials identification,

• Weight/sensor panels on the track,

• Video, based on image processing.

Advantages & drawbacksThe PSD system is the dominant solution for platform protec tion as it offers the best isolation between passen-gers on the platform and both tracks and running trains, which reduces risks of accidents and disruption of the daily operation. Thus, this system is highly recommended for all automated metro projects, and particularly for greenfield projects where its implementation could be easier than for brownfield projects.

On the other hand, intrusion detection systems are subject to several challenges that make them difficult to use. These systems can barely reach a safety integrity level of SIL2 according to CENELEC standards, whereas a PSD system can achieve higher levels (mainly SIL3, with some functions achieving SIL4, such as the PSD/CBTC interfacing functions for the train run authorization at the station). In addition, these systems should be designed to avoid false detec-tions due to objects (papers, plastic bags…), animals (birds, cats, rats…), interference, which could directly impact the operation performance following repetitive useless trains stops. Furthermore, they require more maintenance com-pared to PSD systems, and their life cycle duration is rela-tively lower.

Nevertheless, the use of PSD systems is sometimes challen ging, especially for brownfield projects, due to:

• Necessity to reinforce the infrastructure of existing station platforms to withstand the PSD weight,

• Reluctance to modify the architecture of existing stations for esthetic reasons,

• Significant disruption of the daily operation during the PSD deployment on existing lines,

• Necessity for legacy trains to stop in stations with high stopping accuracy,

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The PSD system is a component of the transportation infrastructure, installed on station platforms, physically protecting passengers against falls on the tracks or collision with a train running in the station. It can be composed of full-height doors with complete barriers between the station’s floor and ceiling, or mid-height doors that do not reach the platform ceiling. The PSD system helps to:

• Prevent accidental falls off the platform onto the lower track area, suicide attempts and homicides by pushing on the platform,

• Reduce the risk of accidents, especially from service trains passing through the station at high speeds,

• Improve climate control within the station, since heating, ventilation, and air conditioning are more effective when the station is physically isolated from the tunnel,

• Improve security, as access to the tracks and tunnels is restricted,

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installation. The intrusion detection systems could also be used for a temporary installation on a metro line, in order to facilitate the implementation and testing of other sys-tems under migration, such as the signaling system, before installing the PSD.

The following table compares the main platform protection technologies vs. typical analysis criteria. It was generated from UITP data and feedbacks from different automated metro projects.

• PSD/train doors mismatch for lines using mixed fleet with varying door divisions,

• PSD high cost,

• Potential need to add detection systems for passengers’ entrapment between train and PSD due to rolling-stock gauge or curves in stations.

In all these cases, the intrusion detection systems could be a good alternative to PSD thanks to their low cost and easy

Protection System

Laser/Infrared Radar

Weight/sensorPanel

VideoPlatform Screen Door

Full-height Mid-height

Projects Examples Lyon Metro Line D Budapest Metro Kuala Lumpur

Kelana Jaya LinePrograms under development Dubai Metro Paris Metro Line 1

Interferences Snow, Rain, Sun RF interference Heavy Snow, Sand Light/Sun Wind Wind

Rolling-stock No specific interface

No specific interface

No specific interface

No specific interface

Doors synchronization

Doors synchronization

Inst

alla

tion

Duration Short Short Short Very short Long Medium

LocationOn top or along

the tracks or platform

Along the platform and

between double tracks

On the tracksDifferent

spots on top of the tracks

On the platform On the platform

Impact on Operations No No No No Yes Yes

Curved stations fitting N/A N/A N/A N/A Gap between

train and PSDGap between train and PSD

False and non-detection

High, mitigated using optimization algorithms

Medium Low To be assessed Null Null

SIL currently achieved SIL2 SIL1/SIL2 SIL2 SIL0 SIL3 SIL3

Overall cost Low Low Low Lowest High Medium

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the signaling system to prevent automated trains from entering this area. Taking into account that this system will only be activated at night at the end of the revenue service, and that the probability of having a passenger remaining on the platform at that time is low, the low impact on the operation (e.g., false detection rate) and the protection safety level are acceptable.

• Phase 2: As trains with GoA3 mode will be running with passengers on the whole line, the PSD system will be installed in all the stations, and the intrusion detection system of Phase 1 will be moved to another line.

The rail network of Buenos Aires city consists of 6 metro lines (A, B, C, D, E and H) in service with a total of 54km of route serving 86  stations, and 1 tram line of 7.4km, known as “Premetro”, serving 18 stations. SBASE, the local owner, is leading a series of improvement projects on the whole network, including upgrades and extensions of existing metro lines, and construction of new automated metro lines (F and G). One of the main projects is the modernization of Line D for which SYSTRA is supporting SBASE in the systems and operations preliminary design as the main Consultant. This project mainly consists in imple menting a new CBTC system and commissioning new automated trains.

The CBTC system on Line D is expected to be put in service in 2 phases:• Phase 1: All trains with passengers will be operated in

CBTC GoA2 mode, with a driver. Some operations with-out passengers will be performed in GoA4 mode. These automated operations include turnbacks at both ends of the line, parking and unparking the trains from/to some main line stations to/from the depots, and stabling and unstabling the trains on specific track positions on the main line at the end of the daily service due to a lack of available depot stablings for the additional trains.

• Phase 2: All trains with and without passengers shall operate in GoA3 mode.

In order to define the optimal platform protection for Line D, all the advantages and drawbacks of protection sys-tems listed in the previous section were analyzed, taking into account the characteristics and constraints of Line D project. The selected protection strategy, detailed below, consists in judiciously using both PSD and intrusion detec-tion systems, in order to benefit from the advantages of each of these systems, and particularly to provide good flexibility for the CBTC migration process.

• Phase 1: In order to ensure full protection, reduce any risk of operation disruption, and guarantee the performances of the defined operational model, the PSD system will be deployed in 8 stations where automated trains will be running while passengers are waiting on platforms, from Congreso de Tucuman to Olleros stations, in Scalabrini Ortiz station, and from Tribunales to Catedral stations.

In the other stations where trains will be running in GoA2 mode with a driver’s guideway supervision, the PSD system will not be deployed at the current stage, in order to respect the tight planning of this phase. Nevertheless, these stations will be equipped with an intrusion detection system (see figure hereafter), that will protect the platforms’ passengers during the automated stabling and unstabling of some trains on the main line at the end of the daily service. This intrusion detection system would detect any remaining passenger trying to pass the edge of the platform towards the track at the end of the revenue service, and consequently request

case study Automation of Buenos Aires Metro Line D

ConclusionWith the full automation of metro lines without drivers on-board, passengers’ protection on station platforms becomes mandatory. For greenfield metro projects with fully auto-mated trains, it is highly recommended to install PSD systems in order to achieve opti-mized safety and operational performances. In case of brownfield projects, PSD systems remain highly recommended. Nevertheless, intrusion detection systems can be a fair com-promise simplifying the migration process and optimizing the overall cost when PSD deployment is complex.

In the coming years, brownfield projects are more likely to become a major factor in the transpor tation market. Thus, it would be worth investigating the improvement of current in-trusion detection systems by the industrial providers, particularly in terms of achieved safety level and false detection rate.