Advanced train control system - concepts and applications G. Pedroso & A.C. Merlo

Transcription

1 Advanced train control system - concepts and applications G. Pedroso & A.C. Merlo Sao Paulo, Brasil Abstract Among several definitions of Advanced Train Control System recent published, the statement: "Advanced Train Control means the use of microprocessors and digital data communication to provide enhanced and cost effective new tools for supervision, control, and communications to improve mass transit and railroad operations" is the most discussed by signalling engineers. Microprocessor based signalling systems have been designed and applied with different architectures, such as dual checked redundant, triple modular with vital voter and single channel. Applications are achieving high levels of safety and reliability, as well as improving functionality at the control center, station and on board the vehicles. In the digital communications field, advances such as spread spectrum radios are improving the reliability of data transactions. For vital data transmission, protection techniques such as CRC have been analyzed and proved to be proper for failsafe applications. This paper describes an advanced train control system which uses the above concepts, combining distributed data communication network and microprocessed strutures located on board, at the station, along the wayside and at the control center. The system is capable of performing traditional fixed block and moving block modes of operation and due to its modularity, cost-effetive applications can be done for railroad and mass transit. Wayside

2 282 Railway Operations equipment is drastically reduced by combining radios and distributed "intelligent" modules. 1 Introduction Involved with design, manufacturing, installation and commissioning of signalling systems, CMW Equipamentos SA has developed a set of equipment addressed to the train control field, from the control center to wayside and on board levels. These products are designed as building blocks, with each of them maintaining their classic signalling nomenclature and functions: Centralized Traffic Control (CTC), Automatic Train Protection (ATP), Automatic Train Control (ATC) and Automatic Train Operation (ATO) are well known and accepted used structures. The approach of design is to apply modern techniques of Distributed Digital Control Systems to the Railway Traffic Control field, adapting proper requirements of reliability, functionality and safety. Microprocessors, associated with digital data communication networks and open software and hardware philosophy are extensively used. Proprietary concepts are restricted to the failsafe logic level, which is treated within rigorous requirements of design and validation. The system being presented throughout this paper is organized according to the architecture shown in Figure 1, with equipment is distributed at the Control Center Station Wayside, and at On Board levels.digital Data Communication takes place over several Data Networks. Smaller levels of data networks, Train Data Network and Car Data Network are implemented each one with its own dedicated lines or buses, for different functions like signalling, propulsion, brake control and passenger information. 2 Centralized Traffic Control - CTC The latest CTCs designed by CMW are based on a SCADA-(Supervisory Control And Data Acquisition)- like System, designed to run in PCs or RISC platforms, under open Operating Systems, as UNIX, for the case here presented. The Supervisory and Control Center with distributed Architecture - PRODIX - was conceived in order to make use of new Open Network Computing environments, allowing the im plementation of truly distributed applications. A highly modular software structure, associated to powerful platform

3 Railway Operations 283 capabilities, allows the designer to choose suitable blocks according to each system requirements. 3 Automatic Train Protection - ATP ATP protects trains against conflicting route alignments. Its related equipment is installed at the stations and along the track. The ATP's inteligence is in the Interlocking, which performs functions like the safe interlocking of route alignements, management of manual or automatic route requesting, monitoring and controlling track devices, data interchange with the controlling center, local control facilities and interface with adjacent Intelockings. Solid State Interlockings (SSI) are now being applied at yards and main lines for subway and commuter systems [4]. 4 Automatic Train Control - ATC ATC is responsible for maintaining the train under a safe speed profile, by supervising the maximum allowed train speed limit along the track. It has two basic subsystems, one at the wayside and another on board the train. The wayside ATC generates speed codes to be sent to the trains. It can be implemented as a sub-system of the SSI or as a separate subsystem, when used with conventional relay Interlockings. The on board ATC safely commands the application of service or emergency brakes, always supervising the maximum allowed train speed. Several Control algorithms are provided, such as the Brake Profile Monitor, which executes continuous supervision of the actual train deceleration rates when the brakes are applied; restrictive actions and alarms are taken when abnormal effective brake rates are detected. 5 Automatic Train Operation - ATO At each station, the ATO controls train schedules, from the moment of departure to the next programmed stopping point. This operation is performed under the ATP supervision and is coordinated by the CTC. The ATO has its own control capability and may act independently of the CTC, in the case of a local mode of Operation. The on Board Automatic Train Operation equipment performs automatic speed control,

4 284 Railway Operations automatic opening and closing of vehicle doors and reports train identification, length and train speed profiles. Main functions of the ATO are the Station Dwell Time Control, Automatic Train Dispatching, Speed Maintaining Programmed Stop, Train Identification, Doors Control and Data Transactions between train and CTC. 6 Application The increasing growth of passanger transportation demand at the East/West line of the Sao Paulo Metro is imposing imediate actions regarding technical solutions for the system to cope with that demand. The line operates today with 40 six car trains, transporting about passengers/hour in either direction, with a critical situation, during peak periods, of aproximately 8 passengers per 40 square inchs (1,0 m2) on board the trains. Several possibilities have been considered to improve the transportation capacity of the line, such as: Construction of a new parallel metro line; Constrution of a new parallel LRT line; Modernization of an existing parallel commuter line; Trains operating with more cars; Reduction of Headway, by improving or revamping the Signalling and Train Control system. Among these technical solutions, Headway Reduction was taken as the most feasible one, in terms of amount of investment and feasibility to be implemented without stoping the operation of the line. Studing the problem, CMW had done a detailed review over the entire signalling and Train Control System, designing two solutions to solve the problem. One of them, by improving the existing signaling technology, is able to reduce the headway from the current 110 seconds, down to 66 seconds. The second one, using communication based signaling technology is able to reduce the headway down to 60 seconds. The existing technology, composed of: Automatic Train Supervision (ATS), Automatic Train Protection (ATP), Automatic Train Control (Wayside and Onboard ATC), and Automatic Train Operation (Wayside and Onboard ATO), is designed to operate trains under the traditional signaling concepts by means of Block Dispatching and by using Track Circuits for train detection. In order to optimize the headway, the modifications would mainly relocate and increase the number of

5 Railway Operations 285 track circuits, add modifications on the on board ATC, and optimize the data communication link between Central Control, wayside and vehicle. Although the installation plan for the necessary modifications was technically feasible, some critical tasks had shown, representing high risks for day to day recovery of the commercial operation of the line. Transporting 1,2 million people per day, it is just impossible to stop or disturb the flux of trains, mainly during peak periods. After several studies involving new technologies and a strategic program for equipment installation, the communication based signalling upgrade with moving block mode of operation, was the adopted solution. As the Signalling System already has a modular construction, basically its up grade will be accomplished by adding a new automatic train control module at the station and on board levels, connected through a proper radio based data communication link. The new module is named Communication Based Automatic Train Control CBATC. The CBATC was designed to support a heavy mass transit operation, with the following characteristics: Six car trains, 130 m (426 feet) long; Headway below 60 seconds; Station spaced at 800 m (2600 feet); Average operating speed around 40 Km/h (25mph); Train acceleration and brake rates of 1,0 m/s2 (2,24 mphps); Controlled Territory around 4,0 Km (2,50 miles); Maximum train speed of 100 Km/h (62,5 mph); 10 trains per Track, 20 trains on both tracks; All train locations and status updated every 1 second; Station dwell time from 20 to 30 seconds. Evolution was taken as a very important premise, since: Existing systems, operating and built around well known and well proved signalling concepts, could be easilly upgraded; Efforts regarding installation training and commissioning should be minimized; Migration should be done with the line operating, and without disturbing the transportation capacity. The Station CBATC, installed at each Train Control Room, manages a Controlled Territory (CT). Each CT has, at its boundaries, Interface Zones (IFZ). Trains move from one CT to another, through a transfer operation, done over the IFZ. Transfer operation has to provide safe train transitions: From Wayside Controlled Territories (WSCT) to CBATC Controlled Territories; From CBATC Controlled Territories to WSCT; Between

6 286 Railway Operations CBATC Controlled Territories and at Turn Back Zones (TBZ). The station CBATC is a microprocessed module, with the following main functions: Trace all trains moving in the CT; Transmit to all trains system parameters used by on board algorithms; Receive and release trains at the IFZ and TBZ zones. To perform these functions, it interfaces with the Interlocking ATO, Control Center, adjacent station CBATC and on board CBATC. The on board CBATC is also a microprocessed module that processes: Safe Distance to Travel and Safe Allowed Speed Limit; Train Location along the Controlled Territory; Train Consist. Interface is done with the existing on board ATC, with the rear end CBATC through train lines for train length integrity check and with the station CBATC. Data interchange between station and train CBATCs, is done through slotted cables inside the tunnels and uses spread-spectrum radios. The CBATC technology should begin field tests by the end of this year, and the East/West line of the Sao Paulo Metro should be fully operating applying this type of solution by the end of 1995, taking full advantage of moving block to optimize headway. Safety and reliability goals are achieved through the appropriate use of redundant architectures for critical equipment, and special techniques, such as voting, checking the redundant elements integrity, auto-dignosis and fail-safe principles. The information exchanged between train and station is protected by redundant check bits, which guarantee simple and multiple errors detection during each data transaction. A consistence analysis is also performed by the receiver to check data plausibility. A non receiving message is detected by timeout, resulting in a restrictive action of the receiving system. The station CBATC is based on a 1 out of 2 processing architeture implementation; each channel is built considering "Fail-Safe" principles; 2 processing channels are provided to guarantee availability; On board CBATC is based on a 1 out of 2 processors implementation, with possibility to operate with rear equipment (handback mode for availability purposes);

7 7 Final Comments Railway Operations 287 This general overview gives an idea about the signalling technology that CMW Equipamentos SA is constantly updating, following a pragmatic evolution, by combining state of the art components, open architecture philosophy and traditional signalling concepts. Applications have shown that this is a reasonable way of introducing computer technology in the train control field, which usually treats new technology in a very conservative way, due to the great responsibility in terms of safety and reliability constraints, inherent to transportation systems. Well proven theory has shown high levels of Mean Time Between Unsafe Failures (MTBUF), Mean Time Between Unsafe Transactions (MTBUT) and Reliability, with figures even better than those achieved by traditional systems. We foresee for the near future the consolidation of computer based technologies in the Train Control area, since various benefits are continually becoming more evident. 8 References 1. AAR - Signal Manual for Signalling and Telecommunications - rev Proceedings of the III International Conference on CAD Manufacture and Operation in the Railway and Other Advanced Mass Transit Systems - Washington DC-USA Aug/ A.P. Rangel, A. Yokomizo - Sistema Avancado de Sinalizacao e Controle - I Congresso Internacional de Transportes Metropolitanos Sobre Trilhos - Sao Paulo Nov/ G. Pedroso, A.P. Rangel, F.J.O. Dias - CMT: A Fault Tolerant And Fail Safe Microprocessed Interlocking System - COMPRAIL R.D. Pascoe, C. Rossi, S. Savio, G. Sciutto Comparisom Between Fixed and Moving Block Signalling Systems Performance by Digital Simulation - COMPRAIL S.R. McKay, V.I. John, G.E. Dawson - Rapid Transit Performance Studies with an Interactive Operations Simulator - COMPRAIL 92.

8 <D O Train Control Center - TCC Data Transmission System K) oo 00 Adjacent CBATC i CO 1 Local Console Adjacent Interlocking Route 1nterlocking Speed Code Code Generation and j. Select/ Occupancy Detection Occupancy ATC Traffic Light Control Switch Machine Control CZZhO i ATP RX Track Circuit Communication Based ATC CBATC ATP _+_ Aut< >m atic T rain Opeiratlon ~~A1"O ATO Ante 1 Identlflc*. Program Stop. Doors Station Platform Data Communication FIGURE 1 - COMMUNICATION BASED TRAIN CONTROL SYSTEM