The Dockland light Railway is one of Britain’s great high-tech Automatic Train Control (ATC) system, now carrying over 60 million passengers. This highly developed train control system has expended more rapidly than any UK railways. DLR officially launched in 1987 to serve the existing Docklands population and helps to regenerate the Isle of Dogs area, with 11vehicles convoy and 15 stations. Since then the DLR network has extended to Bank, Beckton, Lewisham, London City Airport and King George V. It has 31 km of railway and 38 station with 94 vehicles [DLR Light News 2007]. DLR now carries more passenger than ever before, with additional increases in demand predicted over the coming years. The system’s current 6o million passengers a year is expected to rise up to 80 million by 2009, when a further 55 cars will be added to the fleet [DLR Light News 2008].Passenger numbers will rise further when the DLR assumes a major role in transporting passengers to and from the London 2012 Olympic and Paralympics Games, serving five Olympic venues. [Olympic Delivery Authority (ODA)]
For twenty years, passengers travelling on DLR have been intrigued and puzzled by the unique trait of this network, the absence of train drivers. The entire railway operates as a driverless system, carrying more than 200,000 people across East London every weekday. As the trains appear to stop and start with its own harmony, the operation of the network managed and monitored 24 hour a day, 365 days a year, from the DLR Control Centre. For passenger safety, security and assistance there is a Passenger service Agent (PSA) on every DLR train.
The DLR is operated through a computerised Automatic control system. Control Room staff has access to a visual overview of the entire DLR network showing exactly where each train is along the railway at any given time. The benefit of operating a network in this way is incredible. As the system is controlled automatically it allows DLR to run many more trains. [DLR Light News 2007]
In the field of Automated Train Control System it is imperative to know all trains position on the system for swift and safe operation. On of the common train operating system was ‘fixed block’ system, where railway track are divided in to number of blocks. These blocks only allowed one train to occupy that block. Until that block is clear, it does not permit other train to get in to that part or track and big gap used to generated between two trains. To operate a numerous train service like DLR, the railway track has to be divided into many short blocks, requiring setting up and maintenance numerous number of signalling equipment, side track and head shunt. Previously DLR operating system was run by fixed-blocks system due to short rail way tracks, lack of side tracks and head shunts and more frequent service demand this system was later replaced by SELTRAC a Transmission-Based Automatic Train Control (TBAC) system based on the Moving Block Principle. SELTRAC is a registered trademark of Alcatel SEL. [Alcatel Canada Transport Automation]
The sole purpose of this comprehensive study is to go behind the scene of the infrastructure of the Docklands Light Railway operating system and how this transport service has harness the Advanced Train Control System technology to operate and transporting thousands of people around its network in a diversely populated city with great magnitude of fast growing economy.
2. Comprehensive Literature on Advanced Train Control System
(ATCS), Latest System Technology on Train Operation and
Top-Level Description of the Docklands Light Railway (DLR)
Automatic Train Control (ATC) System
The First International conference on Advanced Train Control, which was held in 1991 in Denver, suppliers from different countries of the world attended and demonstrated their technology, products and operating system. Burlington Northern (BN) in conjunction with Rockwell produced the first version of ATCS, known as ARES (Advanced Railroad Electronic System), where they developed satellite navigation system for locating trains on the system. They tested this ARES on BN’s Iron Range lines in Northern Minnesota with the purpose to integrate trains information system with central commands and control functions. During year1987 to1993, Canadian National Railways (CN) and Canadian Pacific Rail (CP) made momentous improvements in the development and testing of ATCS. A key component in recuperating safety and productivity of train operations is ATCS technology; it provides better communication, more accurate information on train movement, train location, wayside interfaces and locomotive’s condition. Railways are part of a technological rebellion where sophisticated communications equipment and computer systems are in use to control the movement of train. A main new expansion in train operation is data transmission, which help the train driver and the control centre staff to transmit information directly, by radio and on-board computer. [Edward Furman, ‘Network Management for ATCS Communication System’ 1991]
2.1 Current Technological Expansions
2.2 Advanced Train Control Systems (ATCS)
Bombardier in Europe, Railway Association of Canada (RAC) and American Association of Railroads (AAR) began to explore the viability of a radio-based control system that would get rid of human error in the field of train operations [RAC, AAR, 1984].This development was co funded equally by these companies and several other railway companies, suppliers and consultants from Europe, Canada and the U.S. The main purpose of the project was to develop a modular computer-based train control system that will provide safe and more proficient railway operation. ATCS is state-of-art technology, where it ensures a safe train operation service, train separation, train verifying, the safety and the reliability of all movement establishment issued to train and maintenance staff, and also monitoring all equipment status.[U.S Department of Transport, ‘An Aid to positive Train Control’, June, 1995]
The main goals of the ATC system are to provide:
- Ability to implement a system with mechanism from different suppliers, which will reduce problems related to interconnecting and interfacing components from different manufacturers.
- The ability for each railway to select the capabilities and character it needs to implement. interoperability.
- System compatibility across the railway to ensure faultless operation and interoperability between different railways.
[Federal Rail road Administration, 1995]
The Advanced Train Control System’s 5 major systems
i) Central Dispatch System (CDS): CDS manage the movement of trains all over the railway networks and ensure safe operation without train delays and it also provides automatic train tracking and monitoring, status and control of the train and the field system.
ii) The On-Board Locomotive System with two major sub-systems:
On-Board Computer (OBC): OBC provides automatic location tracking and automatic transmission of train movement via the data communication system.
On-Board Display Terminal (OBT): On-Board Display Terminal display and provides all the necessary information for example; actual train speed, speed limits and restrictions, train location, milepost, track geometry, type of authority, track work protection, and status of switches. The display of the information can be presented in text form or in graphical form depending on type of terminals.
iii) On-Board Work Vehicle System: The on-board terminal allows communication between track maintenance staff, central dispatch and vehicles operator via data communications system.
iv) Field System: Wayside Interface Units (WIU) are essential equipments in the field system, which provide monitoring and control of wayside devices for example; switches, interlocking, hot-bearing detector and train defect detectors.
v) Data Communication System: DCS gather the various information processing systems collectively and considerably reduce voice communications.
[George Achakji, March, 1992]
2.3 Data Communication System
Data Communications System is based on 5 levels of information dispensation:
i) Continental level: Continental level provides the functions that are obligatory for inter-railway operations. For example, transferring waybill.
ii) Railway level: Railway level provides the functions which are compulsory for train operations and also for non vital management of train operations.
iii) Regional level: Regional level provides operations across dispatch regions, from one dispatch centre to another.
iv) Dispatch level: Dispatch level is a central control function for train control. It can communicate with vital or non-vital information and it is also necessitate for this level to communicating of vital information to and from trains, track forces, switches, and other wayside equipments.
v) Wayside/mobile level: Wayside/mobile level provides both vital and non-vital processing of locomotive data, track units, and wayside devices; and communications information between trains, wayside and track forces.
[George Achakji, ‘Advanced railroad Electronic system’, January, 1991]
2.4 Advanced Railroad Electronics System (ARES)
The exertion on ARES began in 1984, when The Rockwell International and The Burlington Northern (BN) began to study new technologies that provide automatic identification of train speed and position. Initial tests conducted by The Rockwell International and they demonstrated that GPS could successfully track moving trains. ARES is an integrated command, control, communications, and information system which applies modern avionics technology to railway operations. Its design objectives were similar to those of ATCS, for example, safety and the efficiency of railway operations. In year of 1985, these two companies started to develop a prototype system to determine the production feasibility of this conception. In the year of 1987, Burlington Northern starts their expedition with 17 locomotives, 8 switchers with ARES hardware and GPS receivers, 50 WIU (wayside interface units), two high-rail trains with GPS system on the Mesabi Iron Range [230 mile test track] in Northern Minnesota. Their prototypes testing began in parallel with the existing control system in 1988 and lasted for four year and the company (BN) reported that good results were obtained. [George Achakji, Advance Railroad Electronic System’ January 1991]
Advanced Railroad Electronics Systems are consists of the following integrated sub-systems: I) data management ii) rail operations control iii) locomotive analysis and reporting IV) on-board display v) energy management and VI) wayside interface. The ARES also has the capabilities for advanced traffic arrangement. The system provides direct dispatcher intervention in hazardous traffic situations, i.e., stopping the train by remote intervention [switch] which can be easily activated from the central dispatch office.
During the testing period [ARES] BN and Rockwell had some problem using GPS to achieve high accuracy of train position on parallel track. In an effort to correct the problem of parallel track, BN and Rockwell explored the possible use of real-time differential GPS in terminals and also used others methods to provide more accurate positioning inputs, for example, using transponders for trains approaching switches and sidings.
[George Achakji, ‘Advanced railroad Electronic system, ARES’, January, 1991]
2.5 Incremental Train Control System (ITCS)
On of the vital communications-based train control system is Incremental Train Control System (ITCS) where the system utilize digital data link between the wayside and on-board train location system and it also perform the requirement for traffic control functions. The ITCS provides enforcement of signal indications, speed limits, temporary speed restrictions, and advanced start of crossing signals. This system is developed by Harmon Industry for Amtrak in Michigan. [Peter Winter, ETCS system, 1995]
The Incremental Train Control System consists of 3 main sections:
i) The locomotive equipment: This locomotive equipment consists of On-Board Computer (OBC), display screen, GPS receiver and mobile communication package.
ii) The wayside equipment: This wayside equipment consists of Wayside Interface Units (WIU) and Wayside Interface Unit-servers (WIU-S) (WIU-S are the interface with the signal system), crossing signals and defect detectors.
iii) The communications network: This network consists of wayside local area networks (WLAN). This also use spread range radio, so it can link WIU with WIU-servers and radio frequency (RF) networks in the UHF range to link WIU-s with On-Board Computer.
Incremental Train Control System is supplemented by ATC or automatic train stop systems. During its normal train operation, the train driver are accountable for observing each signal feature and control the train accordingly the speed limits and restrictions and also stop the train where a stop is necessary. ITCS is responsible for monitoring the signal system and ensure that the train is properly controlled with the speed limits, speed restrictions, and stopping, not maintain these parameters in that case ITCS will automatically apply the breaks to stop the train.[Christian Tietze, ‘ICE’s On-Board Train Control and Diagnostics System’, 1994]
Incremental Train Control System is also known as a distributed control system, not like the ATCS architecture which is a central control system. The On-Board Computer (OBC) store the data from signal indications, track curvature, speed limits, mileposts, speed restrictions, and the locations of all the devices which are needed to communicate with the train. The OBC is also works on the train status report with the help of wayside devices. If three status reports are missed, the OBC will automatically apply the train brakes.
The OBC monitors the location of the train with the help of GPS data and compared the track data base. After receiving a signal indicator it determines the appropriate speed of that track. The OBC also calculates a braking outline for the train and display the necessary information on the display screen. In the events of track crossing the OBC will calculate and issue a time to crossing (TTC) to the wayside interface units (WIU). The WIU will synchronize train start timer with the OBC and will confirm that start time.
If the train speed exceeds the initial speed, the OBC will calculate and issue a new TTC to the WIU. If the OBC still cannot receive any confirmation that the crossing timer has been began with the correct value, in that case it will demand that train speed to be reduced. In the event of private crossings, the OBC will observe the status and warning system through update messages from the Wayside Interface Units-Server (WIU-S). If the OBC does not receive a message indicating the warning sign is active, in that case train speed will be reduced. Most of the operation manual of ITCS is very close to a conventional ATC. [Christian Tietze, ‘ICE’s On-Board Train Control and Diagnostics System’, 1994]
2.6 Positive Train Separation (PTS) System
The Positive Train Separation (PTS) System is a non-vital safety overlay system. PTS functions in combination with the active operation methods, signal and train control system. This PTS system was first designed for the Union Pacific/Burlington Northern Santa Fe (UP/BNSF) Railroads and state of Washington to Portland Oregon railroads. The PTS system is measured as an add-on system that enhances safety by protecting against all human errors.
PTS system is centrally controlled communications-based system, which takes control of movement ability and speed limits of the equipped trains. It is also translucent to the train driver as long as the train is operated according to its movement ability and speed requirement. It will become apparent if the train attempt to exceed its speed limit and movement authority, PTS will issue a warning sound alarm to the train driver and the brakes will be applied if the train driver does not brought the train under control immediately.
[Ted Giros, ‘Amtrak Tests Cab Signalling, July 1996]
The PTS system consists of 3 following segments:
I) The server: This segment confirm the enforceable movement authority and speed limit, train’s identification, destination for each train under the PTS control and digitally transmit this information with the help of communication network to the locomotive segment of each equipped train. It also monitors all train movements to prevent conflict.
ii) Locomotive: This segment is consists of an On-Board Computer (OBC) and a location determination System (LDS), a mobile radio and a display unit, where train staff can receive textual information. The OBC calculates and constantly updates information about authority limits and speed limits and applies breaks if the authority limits are exceeded. It also calculates the distance required to stop the train.
iii) The Communication Segment: Communication segment gather and transmit all information with high reliability between the server and locomotive during the train operations.
[Railway Age, May 1997]
2.6.1 Positive Train Control (PTC) System
PTS is also a centrally controlled communications-based system. Its software is written in conformance with ATCS stipulation. The purpose of the PTC design is the removal of wayside block signal systems and the management train movements, for example; speed enforcement, enforcement of limits of the authority, protection of maintenance-of-way employees and work vehicles and also monitoring of highway-rail grade crossing.[W Moore Ede, ‘Communications-Based Train Control, May 1997]
The Positive Train Control system has 3 main sections:
I) Office Equipment: The office equipments are consists of Computer-Aided Dispatching System (CAD), PTC Interface Computer (IC) and a protocol converter to interface with CAD, IC and data communication system.
ii) The Data Communications System: This system is consists of 3 interconnected networks: a) Ground Network b) Radio Frequency link Network c) User Network
- The ground network is consist of cluster controller(CC), base communications package(BCP), message processing nodes, microwave channels, telephone circuits, fibre-optic links and modem to connect the nodes.
- The Radio Frequency (RF) link is consists of base, mobile radio and radio communication channels.
- The User Network is consists of all application software within each field device.
iii) The Field Equipments: The field equipment is consists of mobile communication packages (MCPS), locomotives and wayside interface units (WIU). During an emergency brake application in normal routing operations, the system automatically transmits an emergency message that will invalidate the limits of authority of the other trains in the surrounding area. The PTC system carries out safety critical data through digital data communication system between Interface Computer (IC) and it self for the train locations, trains preset time and devices for highway-rail grade crossing. In PTC the higher priority data message is an emergency message which occurs due to train’s emergency brake application. The PTC system has designed in such a way where failure of an emergency data message will not create any unsafe condition. [Railway Age, Washington may 1997]
PTC also uses transponders in the following critical areas: a) during approaching to PTC-equipped territory, b) during the entrance of PTC territory and c) during approach to a controlled point within PTC territory. This transponder provides exact train location and routing determination. When an equipped train passes the transponders to move towards PTC-equipped territory, the system initialize the On-Board Computer (OBC) and set the tachometer to zero for location determination. The equipped train does not enter in to the PTC territory if the OBC cannot be initialized. [R Lindsey, ‘Communication- Based train Management’, May 1997]
2.7 European Train Control System (ETCS)
The European Union (EU) has adapted a railway network system to overcome the major problems in the field of technical operating system, multiplicity of signalling and train control systems. In 1991 nine foremost European railway companies of the signalling industry reached an agreement with EU to develop a new train control system, which is now known as European train Control System (ETCS). ETCS has the ability to perform in combination with all the existing tracks and wayside equipment under the train protection and train control systems. [R. Ford, 1996]
The ETCS is designed to congregate wide series of operational requirements. The capability of ETCS are provided in three levels
a) Level 1: The new ETCS interfaces can meet the terms with the existing system. ETCS can also provide a basic Automatic Train Protection (ATP) capability combination with the conventional wayside signals.
B) Level 2: This level has the option of speed data display for automatic train speed control. New Cab signalling system is also been added up to ATP capability. But still the train’s can be driven by wayside signals equipment and it can also determine the train location with help of tracks fixed equipments and track circuits.
c) Level 3: Train location and train integrity detection can be utilize with the help of transponders on the track (same as in ATCS). This system eliminates the need of track circuits and other detection techniques. In this level, the system incessantly provides an update of train location and also transmits the signalling information to all trains to ensure a safe separation. Level 3 ETCS is also capable of moving block signalling to maximize line capacity. One of the main goals behind the ETCS design is to develop common display units which can be easily understood by the all drivers across the boundaries of different European countries. The ETCS operates frequency range in 900 MHZ using data radio transmission called Euradio. This Euradio transmit encoded data in digital form with vital safety signalling standards. Each operational train does constant radio contact with a central computer. This central computer is responsible for controlling the trains movement and safe separation. [R.Ford, Railway Technology International, 1996]
2.7.1 Train a Grande Vitesse (TGV) Train Control System
TGV (train grande vitesse) is French high-speed train, which has no wayside signals. SNCF (French National Railways) has determined that for a safe train operation track side signals, cab signalling system and on- board equipment with reliable advance information (road status) are vital to the operator. These requirements led to the development of an ATC system. There are two generations of ATC systems are in use on the TGV network system. Both these systems are significant for continuous link between the train and the track. [George Achakji, ‘TGV System Development’, 1992]
TVM 300 is the first generation TVM. This TVM uses wired logic and has the following performance levels: at speed of 270 km/h with 5 min headway on the SE Line (in 1981) and at speed of 300 km/h with 4 min headway on the Atlantic Line (in 1989). [George Achakji, ‘TGV System Development’, 1992]
TVM 430 is the second generation TVM This TVM is a fully-digitized system and it also design to companionable with all versions ground equipment. The TVM 430 is designed to have the following performance levels: at speed of 320 km/h with 3 min headway on the North Line and a mixed traffic with 2.5 min headway in the Channel Link which connects Paris -London-Brussels operation route. The TVM 430 based on a real-time, fault-tolerant architecture. To establish the safety requirements and all other techniques are based either on the intrinsic features of certain components, or on hardware or functional dismissal. [George Achakji, ‘TGV System Development’, 1992]
The TGV has an on-board data transmission network called TORNAD. It has the facility to communicate between 18 computers (single-unit) and 36 multi-unit computers. The TORNAD has the following main functions: controlling, monitoring, and regulating of equipment; and carrying out the information exchanges for operation and maintenance. [George Achakji, ‘TGV System Development’, 1992]
TGV has built with an automatic braking system. It stops the train when the driver exceeds the speed limit. During operation period, the brakes are monitored in the region of once a minute, and their status is indicated to the train driver’s OBC screen. If the train driver exceeds the maximum speed limit which is permitted by the system, than the automatic train stop system instigate an emergency braking action [George Achakji, ‘TGV System Development’, 1992]
2.7.2 Advanced Control System
Advance control system for train communication is an incorporated command, control and communication system. It is also known as ASTREE system. It was developed by the Société National des Chemins de Fer (SNCF), for train operations and for the railway network management. The ASTREE system offers computerized real-time control of train movement, with the help of radio telephone communication between a central control and onboard microprocessors. This system provides train position and location modification, ground-train transmission (known as data and voice transmission), switch control, monitoring and interlocking, automatic vehicle identification, train consist acquisition, and train integrity checking.
ASTREE system does not put any strong command for safety requested from the communications mechanism because in this system every train is equipped with location and communication capability equipment. During the train operation the train’s location can be adjust with passive microwave tags (same as the ATCS track transponders, SNCF has new identification tags, capability to read train speed at 400km/h) through an on-board interrogator and the train constantly knows its own position and speed limit according to authority restrictions.
[George Achakji, ‘High-Speed Train, TGV system Development, March 1992].
2.7.3 German InterCity Express (ICE) System
The German InterCity Express (ICE) System is one of the state of-art train operation system set with locomotive at each train coaches. This system implements a sophisticated integrated data transmission system network, which imposes with traction control and also interacts with the each coaches control system. ICE System network uses fibre-optic cable to transmit data for train’s diagnostic systems, real-time processing, and block maintenance and also for on-board passenger information and amusement. Using of fibre-optic is the best method for train-bus communication, because it is technically more effective and much more economical. [Christian Tietze, ‘ICEs Onboard Train Control and Diagnostics System, 1994]
ICE’s electronic control and supervision devices are divided into 4 subsystem levels:
I) Train operation level: Train engineers inputs resolute command during train operation from Automatic Train Control (ATC) wayside and Automatic Train Protection ATP) devices.
ii) Train control level: This level handles trains automatic driving and braking and traction effort with the help of closed-loop control.
iii) Vehicle control level: The vehicle control level has resulting redundancy for the train bus fibre-optic interface and the train control, for example, power car (locomotive) and the train coach. Central diagnosis device on the locomotive called the David monitors and stores all functions and malfunctions. It also checks trains equipment at the beginning of operation. The train controller unit on the trailer coaches called the Zeus. Zeus controls diagnosis and co-ordinates functions for each car. After receiving data from the train levels, it distributes this information to the subsystem level.
iii) Subsystem level: The subsystem level includes propulsion control, brake control, auxiliary control, door control, and air conditioning control devices of the train.
[Christian Tietze, ‘ICEs Onboard Train Control and Diagnostics System, 1994]
2.8 Intermittent Cab Signalling (ICS)
Cab signalling technology has been available and in use for many years. In 1979 it was first established on the Swedish State Railway (SJ – X2000) for high-speed train operations. Its function has been proven both in European and North American railways. In the recent years, supplementary developments were undertaken by various railway companies. In U.S.A, Amtrak has tested an intermittent cab signalling system for the future advanced civil speed enforcement system (ACSES). In their signalling design, the system can operates independently and it can also be integrated with existing train control systems. It has the capabilities for enforcement of train speed limits and the automatic stop command by applying the train’s breaking system (calculates and compares by trains on-board computer). This system also uses separate passive radio frequency transponders to provide the required data to a passing train. [Ted Giras, ‘Amtrak Tests Cab Signalling’, July 1996]
2.9 Docklands Light Railway (DLR) System Overview
The Dockland light Railway (DLR) system outline is shown in Figure 1-1. The system comprises existing connection from Bank (BAN) to Canary Wharf (CAW), Tower Gateway (TOG), Stratford (STR) and Lewisham (LEW), Beckton (BEC), as well as a new line to the King George V (KGV) station. This automated system consists of approximately 27 km of double track, except between station Bowchurch (BOC) and Stratford, where section of single track exist. There are two manual deports, which are located at Poplar (POP) and Beckton (BEC).Alcatel Canada provided SELTRAC system, a transmission based signalling system for DLR.
Conventional signalling follows the ‘fixed block’ principle, where tracks are divided into section (blocks) of a prearranged length. A train is only authorized to carry on into a block when that block and the next are clear of traffic. To achieve the closer headway and system flexibility demanded by urban transit, shorter and more numerous blocks are needed in affixed block system.
An adaptation of the system known as SELTRAC was developed and implemented by SELC. The technology was expanded to permit fully driverless operation in high capacity (i.e. passenger) application for the cities of Vancouver, Toronto and Detroit for Light rapid transit systems. Over the years these systems have demonstrated high availability and superior operating flexibility. SELTRAC has provided several operation modes including fully automatic known as Automatic train Operation Function (driverless) and Automatic Train Protection function (ATP) Manual.
SELTRAC is based on the moving block principle, in which the safe separation behind the proceeding train is dynamically calculated based on the actual operating speeds, breaking curves and locations of the trains on guide way. This dynamic method allows shorter headways to be achieved without impinging on safety principles.
With the SELTRAC system, all DLR Automatic Train Operation (ATO), Automatic Train Protection (ATP), and Automatic Train Supervision (ATS) function are performed with a minimum of wayside hardware. Checked-redundant centralised computers are in continues cyclic two-way communication with vehicle-borne, checked-redundant microprocessor control component.
DLR major departure from conventional signalling is the centralisation of route
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