Reliability, Availability, Maintainability & Safety (RAMS) PDF

Page 496 of 530  Annexure: G1 Reliability, Availability, Maintainability & Safety (RAMS) 1.0 Introduction 1.1 (a) In any system output depends on input. In Railways, punctuality is an output...

Page 496 of 530  Annexure: G1 Reliability, Availability, Maintainability & Safety (RAMS) 1.0 Introduction 1.1 (a) In any system output depends on input. In Railways, punctuality is an output. It depends on how subsystems are available for service. Availability depends on Reliability and how good/fast the maintenance (maintainability). Hence R, A, M, S parameters are important. Punctuality is also related to equipment, failures and Reliability in the science of failures. (b) RAMS Assurance can help stakeholders in balancing performance requirements and Life Cycle Cost (LCC) to improve customer satisfaction along with compliance of National/International regulatory requirements. Many standards have suggested that RAMS characteristics can be visualized as the Key Performance Indicator (KPI) at System Level. (c) RAMS concept is relatively new to the Railways as compared to other industries such as nuclear, power, chemical, avionics, etc. 1.2 The key objective of a railway system is to achieve a defined level of rail traffic in a given time safely. The objective can be fulfilled by implementing RAMS principle and process as suggested by EN50126/128/129 or equivalent. 1.3 If there is lack of RAMS Assurance, the following may happen- (a) Loss of KPI (b) Customers satisfaction, project credibility will be on doubt (c) Global Certification may not be possible (d) Development as well as operational cost will be more. 2.0 Terms and Definitions 2.1 Please refer to Glossary of terms 2.2 Safety Assurance Acts & Standards: a) Indian Railways Act b) Metro Railway Act c) International Standards (EN50126, 50128, 50129 or equivalent) d) ROGS Legislation 2006 (Railway and other Guided Transport Systems) Annexure:G1: Reliability, Availability, Maintainability & Safety (RAMS) Page 497 of 530 3.0 Examples of RAMS Parameters for Railways 3.1 Reliability Parameters: Failure Rate λ(t ) Mean Up Time MUT Mean Operating Time To Failure (for non-repairable items) MTTF Mean Operating Time Between Failures(for repairable items) MTBF Reliability R(t) Failure probabilityR(t) F(t) 3.2 Maintainability Parameters: Mean Down Time MDT Mean Operating Time Between Maintenance MTBM MTBM (Corrective or Preventive) MTBM(C), MTBM(P) Mean Time To Maintain MTTM MTTM (Corrective or Preventive) MTTM(C), MTTM(P) Mean Time to Restore MTTR 3.3 Availability Parameters: Availability A Inherent Ai Operational Ao Ai = MTTF/(MTTF+MTTR) for non-repairable items Ai = MTBF/(MTBF+MTTR) for repairable items Ao = MUT/(MUT+MDT) 3.4 Safety Parameters: Hazard Rate h(t) Probability of Wrong Side Failure PWSF Tolerable Hazard Rate THR Annexure:G1: Reliability, Availability, Maintainability & Safety (RAMS) Page 498 of 530 3.5 Failure Rate and Mean Time Between Failures (MTBF) Consider a batch of N items and that, at any time to, a number to have failed. The cumulative time T is given by Repairable Case: T = Nt, if it's assured that each failure is replaced when it occurs. Non-Repairable Case T = [ t +t +t …...+t +(N-k) t ] Where, t is the occurrence of first failure, etc. Failed items are not replaced. The observed failure rate is given by Gama = k/T The observed MTBF of the N items MTBF = T/k ______(for repairable items) MTTF = T/k ______(for non-repairable items) The only difference between MTBF & MTTF is that the value of T will be calculated as indicated above. Reliability equation is as under R(t) = e-λt (for constant λ) 4.0 Safety Integrity Level (SIL) 4.1 Functional Safety: Functional Safety is part of the overall safety which depends on the correct functioning of a safety related system. 4.2 Safety Related System: A system is safety related if its failure can cause harm to life and property. A safety related system performs one or more safety functions. 4.3 Safety Function: Function which is intended to achieve or maintain a safe state of the Equipment Under Control (EUC). 4.4 Equipment Under Control (EUC): Equipment, Machinery, Apparatus or Plant used for manufacturing, process, transportation, medical or other activities, eg: Railway station points & signals, train, etc. 4.5 Equipment Under Control Control System (EUCCS): System which responds to input signals from the process and or from an operator and generates output signals causing the EUC to operate in the designed manner, eg. Interlocking system, train driver. 4.6 Safety System Diagram: Annexure:G1: Reliability, Availability, Maintainability & Safety (RAMS) Page 499 of 530 4.7 Requirement of Safety Related System: a) Safety function requirements i.e., what is function supposed to do b) Safety integrity requirements i.e., what is the likelihood of the correct operation of the safety function 4.8 Safety Integrity: The ability of a safety related system is to achieve its required safety function under all stated conditions within stated operational environment and within a stated period of time. If you introduce a protection system to reduce risk you are now “Trusting” it, to do the job. Safety Integrity is a measure of that Trust. 4.9 Safety Functions in Railway Signalling:- Important elements of Signalling System: (a) Interlocking System (b) Train Detection System (c) Point Operation (d) Signal (e) ATP and/or ATC Infrastructure The functions performed by the above systems can be considered safety functions. SIL is associated with these safety functions and not the equipment. 4.10 SIL is used for two purposes: a) SIL is used to give an interval for the rate of safety critical failures. Applies to random faults mostly due to intrinsic physical processes such as aging. b) SIL defines measures to be applied in the design and during the manufacturing process to keep systematic failures low. 4.11 SIL Integrity Level (SIL) Table: Tolerable Hazard Rate Safety Integrity Level (THR) (SIL) 10-9 THR 10-8 SIL 4 10-8 THR 10-7 SIL 3 10-7 THR 10-6 SIL 2 10-6 THR 10-5 SIL 1 Annexure:G1: Reliability, Availability, Maintainability & Safety (RAMS) Page 500 of 530  Annexure: G2 Brief of High-Speed Rail Signalling Ahmedabad-Mumbai Route 1.1 General 1.2 Objective: Objectives of the Signaling for high speed are The Automatic Train Control System (ATC) with the subsystems, their requirements, Interfaces with Rolling Stock, Telecom and other Infrastructure. 1.3 Requirement of High-Speed Train Control System: High Speed System operation requires ATC in compliance to UIC mandated requirements as well as to meet the following; a. Safe train operations b. Prevention of overspeed, derailments and collisions c. Fail safe train detection d. Interlocking enforcement e. Hazard protection f. Work Zone protection g. Headway requirements h. Quality of Service 2 Functional Sub-Systems of ATC: ATC comprises of the following functionalities a. Automatic Train Protection (ATP) b. Automatic Train Operation (ATO) c. Automatic Train Supervision (ATS) 2.1.1 Automatic Train Protection (ATP): This sub-system is responsible for the safety of train operations. Few of the safety features enforced by ATP are; a. Overspeed protection through speed control b. Rollback protection c. Maintaining inter train safe spacing d. Ensuring correct docking/stopping of the train e. Ensuring correct side door opening f. Train detection, etc. 2.1.2 Automatic Train Operation (ATO): This sub-system is responsible for the automatic operation of trains through throttle and braking control 2.1.3 Automatic Train Supervision (ATS): This function is responsible for centralized supervision and control of the train movements. The main functions are; a. Supervision b. Automatic and Manual Route setting c. Train Control and Regulation d. Passenger Announcements and Display System management e. Quality of Service, etc. 2.2 ATC System and sub-systems a. Equipment and Software on-board b. Equipment and Software along the track and wayside c. Equipment and Software in Central Control Room Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 501 of 530 2.2.1 Equipment and Software On-Board: It includes processors, firmware, software and electronics, operator displays, operator panel, data radios, antennas, transponder/ballise antennas, code pickup antennas, network components, GPS receiver and antennas, tachometer and other sensors, connections between train control elements and interfaces. 2.2.2 Equipment and software along the track and wayside: Vital equipment located in housings/location box/Relay huts along the Right of Way (track) including station equipment rooms, train control equipment houses and signal equipment cases and cabinets. The equipment includes track circuits, point machines, wayside signals, interlocking equipment and transponders. 2.2.3 Equipment and Software in Central Control Room: ATS Servers, Man Machine Interfaces, Large Video Screen along with Controllers, Firmware and Software, Fibre Distribution Systems, etc. 3.1.1 Temporary Speed Restriction Function: A temporary speed restriction function (a function to change control information indicated for Running Line outside of a Station to another control information which indicates a running speed lower than one of said control information) shall be provided. 3.1.2 Alarm Sound of Cab Signal: Cab Signal shall sound an alarm in a driving cab for the following item: a. In the case of the ATC and the fallback ATC (WHERE PROVIDED ) when control by the control pattern is received and when the control pattern is updated. 3.1.3 Function of Interlocking: Interlocking shall have functions set forth in the following: a. Track Lock b. Route Lock c. Sectional Route Lock d. Approach Lock e. Stick Lock f. Signal control 3.2 Centralised Traffic Control System 3.2.1 Function of Centralised Traffic Control System: Centralised traffic control system shall indicate the following items and shall allow setting of a Route of a Train which enter/leave a Station or a Route of a shunting Vehicle on Running Line: a. The position of a Train (including Vehicle) on Running Line and Depot Line which has ATC route b. Route clear situation on Running Line and Depot Line which has ATC route c. Train number of a Train on Running Line and Depot Line which has ATC route. 3.3 Train Detection Devices 3.3.1 Function of Train Detection Devices: Train detection device which is used for Signalling Equipment including ATC for Safety of Train Operation shall make sure to detect a Train (including Vehicle) on the track. Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 502 of 530 3.4 Maintenance and Action in the Event of Accidents, etc. 3.4.1 Maintenance Type: The Maintenance types shall be as follows: a. Preventive Maintenance: Preventive Maintenance shall be performed to detect, in an effective method, a risk that functions of equipment are lost and to perform necessary treatment to avoid such situation. It shall cover equipment of which breakdown can directly affect train operation or seriously affect customer service. b. Corrective Maintenance: Corrective Maintenance shall be performed basically for the treatment after breakdown of equipment. On-Board Display: The meaning of terms in this Implementation Standard shall be defined as below: 1. "○ × Signal" means a kind of stop signal indicated when the Train (including Vehicle) is required to stop immediately. 2. "0 Signal" means a kind of stop signal indicated when the Train (including Vehicle) is required to stop normally before the end of the Route which is indicated by ATC. 3. "02 Signal" means a kind of ○×Signal indicated when ATC Control Information is not received, or when such ATC Control Information is received like in case PESB is pushed. 4. "03 Signal" means a kind of ○ ×Signal indicated when the Train (including Vehicle) over runs the stopping limit without proper authority. 5. "Approach Lock" means a kind of lock function of interlocking system. Approach Lock shall lock the Turnouts on the set Route when the Train (including Vehicle) enters approach section. 6. "ATC Control Information" means control information transmitted to a Train (including Vehicle) within an ATC Route. Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 503 of 530 7. "ATC Route" means a portion of track where a Train (including Vehicle) can travel according to the Cab Signal displayed by ATC. There are two types of ATC Routes. a) Automatic Route – It is applicable for Block Route where ATC Route control information is automatically controlled and the operator cannot intervene except for temporary speed restriction. b) Semi Automatic Route – It is applicable for Station (including Rolling Stock Depot) Routes (Home Route, Departure Route, Fallback Home Route, Fallback Departure Route, Yard Route) where the ATC Route control information is automatically controlled based on Route setting by the operator. c) "Automatic Train Control (hereinafter "ATC")"is as defined in "General Guidelines for Management of Implementation Standards". 8. "Automatic Train Supervision (hereinafter "ATS")"means the real time Train control supervision system which regulates performance levels, monitors and controls the Trains services and provides data to Controllers to adjust Train services to minimise the inconveniences caused by Train operation disruptions. 9. "Base Station" means the radio device to communicate with on-board radio device, as well as with Train Radio network on the ground. 10. "Block Route" is as defined in "General Guidelines for Management of Implementation Standards". 11. "Cab Signal" is as defined in "General Guidelines for Management of Implementation Standards". 12. "Cable Gas Pressure Monitoring System" means the system which supplies dry air into the cable and monitors the gas pressure in order to detect breakage or cut of the cable. 13. "Call Recording System (hereinafter "CRS")" means the system which is installed in OCC having the function of recording designated incoming/outgoing calls to/from the OCC such as through a Despatcher Telephone or Train Radio System. 14. "CCTV System for Train Operation" means the system which is installed at the platform and is used to facilitate the Station staff to monitor the areas at platform where visibility is not good enough and where the Station staff requires to have assurance in respect of opening/closing of Train doors. 15. "Centralised Information Control System (hereinafter "CIC" or "CIC System")" means the system which shall collect and monitor the information of Signalling & Telecommunication facilities and disaster information necessary for train operation etc. in real time, and also perform controlling operation for some of Signalling and Telecommunication equipment. 16. "Centralised Traffic Control (hereinafter "CTC")" is as defined in "General Guidelines for Management of Implementation Standards". 17. "Contact Detector" means a device mounted on the stock rail at the turnout to check whether tongue rail and stock rail contacts closely for safe passage of Train. 18. "Control Information Section" means a section where the control information for Cab Signal is transmitted. 19. "Controller" or "Despatcher" is as defined in "General Guidelines for Management of Implementation Standards". Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 504 of 530 20. "Corrective Maintenance" is as defined in "General Guidelines for Management of Implementation Standards". 21. "Data Transmission system (hereinafter "DTS")" means the system which is installed as communication backbone between OCC, Stations, Traction Substations, Depots and other locations and shall be highly reliable for usage of important, vital and critical system. 22. "Dead Section" means a section of track, either within a track circuit or between two track circuits, the rails of which are not part of a track circuit for detecting Trains. 23. "Departure Route" is as defined in "General Guidelines for Management of Implementation Standards". 24. "Departure Route (ATC) (hereinafter "Departure Route")" is as defined in "General Guidelines for Management of Implementation Standards". 25. "Despatcher FAX" means the system which transmits Fax simultaneously to designated groups such as Stations (including Rolling Stock Depots), train crew depots and maintenance depots. 26. "Despatcher Telephone" means the system which provides voice communication between Controllers and agencies involved in safety and/or train operation for carrying out tasks smoothly and quickly. 27. "Audio Frequency Track Circuit (hereinafter "AFTC")" means the track circuit which uses audio frequency to transmit MA to the on-board system for ATC. 28. "Direct Telephone between Adjacent Stations" means the system which ensure instant and uninterruptible voice communication between two adjacent Stations (including Rolling Stock Depots) for substitute safety operation or other operations as required. 29. "Disaster Prevention System" means the system which shall collect the information like the wind, rainfall and rail temperature and have the function of displaying the received information on the monitoring terminals and CIC Systems in OCC and at other locations as required. 30. "Interlocking" means an arrangement of Signals, Points and other appliances which are operated from a panel or lever frame and interconnected by mechanical locking, electrical locking or electronic locking so that their operation can take place in proper sequence to ensure safety. 31. "Leaky Coaxial Cable (hereinafter "LCX")" means the cable that radiates radio waves of a desired frequency along its length. 32. "Maintenance" is as defined in "General Guidelines for Management of Implementation Standards". 33. "Maintenance Work" is as defined in "General Guidelines for Management of Implementation Standards". 34. "Movement Authority (hereinafter "MA")" is as defined in "General Guidelines for Management of Implementation Standards". 35. "Passenger Station" is as defined in "General Guidelines for Management of Implementation Standards". Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 505 of 530 36. "Point Device" means various equipment including ground connections such as Point Machine and contact detector, which is used for changing, detecting and locking the setting of Turnout. 37. "Repeater" means the communications device that amplifies (analog) or regenerates (digital) the data signal in order to extend the transmission distance. 38. "Replacement" is as defined in "General Guidelines for Management of Implementation Standards". 39. "Rolling Stock Depot" is as defined in "General Guidelines for Management of Implementation Standards". 40. "Route" is as defined in "General Guidelines for Management of Implementation Standards". 41. "Route Lock" means a kind of lock function of interlocking system. Route Lock shall lock the Turnouts on the set Route until the Train (including Vehicle) pass through the Route. 42. "Safe Signal Failure" means the same as "Right Side Failure" in MSS. It means types of signal failure which will not cause danger to rail traffic and may only affect performance of train operation. 43. "Sectional Route Lock" means a kind of lock function of interlocking system. Sectional Route Lock shall lock the Turnouts on the set Route and progressively release the Turnouts as soon as the Train (including Vehicle) passes through the section. 44. "Signalling Equipment including ATC for Safety of Train Operation" means following devices to ensure safety of train operation and its management. a) All the devices/equipment including displays required to facilitate stop/proceed aspect on display devices in a safe manner. b) The on-board & ground devices which indicate the condition(s) of Route ahead and/or automatically decrease the speed of or stop the movement of a Train (including Vehicle) in a safe manner. For details of on-board device, refer to "Implementation Standard for MAHSR Rolling Stock Maintenance". c) The device which controls signal aspects and turnouts of stations and conducts the Train operation management from a control centre (CTC). 45. "Stick Lock" means a kind of lock function of interlocking system. Stick Lock shall lock the Turnouts on the set Route for specific time (release time). 46. "Supervisory Control and Data Acquisition System (hereinafter "SCADA")" means the system which can remotely monitor and control all traction substations, sectioning posts, sub-sectioning posts, auto-transformer post, distribution substations, disconnectors (motorised) in Depot, tunnel separation disconnector equipment, and other related facilities. 47. "Track Lock" means a kind of lock function of interlocking system. Track Lock shall lock the Turnouts when the Train (including Vehicle) is on the track circuit which includes these Turnouts. Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 506 of 530 48. "Train Protection Radio" means the system which shall be used by any staff or worker to alert the Train Operator to stop and protect a running Train in the event of an emergency. a) "Train Radio" or "Train Radio System" means the system for Controllers (specifically Traffic Controllers) and Train crew to communicate with each other, and exchange necessary data information between the wayside/ground devices and on-board devices. b) "Transponder" means a part of ATC Device installed between rails to send information to Trains for the position correction. c) "Yard Radio" or "Yard Radio System" means the system which is used for communication between Station (including Rolling Stock Depot) staff and On-board crew during shunting in yard. Annexure G2: Brief of High Speed Signalling – Mumbai-Ahmedabad Page 507 of 530  Annexure: G-3 Communication Based Train Control (CBTC) in Metro Railway Systems 1 A centralized control is inescapable to monitor and handle any emergencies. With closed doors to ensure passenger safety, there is a need for opening the train doors on the correct side for the platform which has to be again failsafe to prevent wrong side opening leading to passenger injury. 2 In order to achieve safety with a number of trains using the same line, it is essential to provide information to the driver by some sort of “signals” about where to stop or how fast the train can go etc. 3 To derive the information required to convey to the driver through “signals”, some form of train detection was essential, to know where exactly the train in question is with reference to other trains or other hurdles. 4 To provide means for more than one train to use the same line, it became necessary to divide the line into “blocks” and ensure there is only one train in each “block”. 5 To control the trains and allow precedence between slow and fast trains, it became necessary to have stations with turnouts and loops. 6 To ensure the points and crossings of a turnout were set within safety limits for prevention of derailment, it was necessary to ‘detect’ the point by the signalling system before allowing train movement i.e it was necessary to “interlock” the signal with the points. The interlocking may be achieved through Relay based or Microprocessor based. 7 Centralized Traffic control by a single operator controlling a line to avoid time delay for exchange of information between Station Masters for increasing the line capacity resulted in further advances such as block working, automatic Block signalling. 8 The rolling stock must have automatic train protection to eliminate driver errors. 9 The need for high frequency of train service necessitate automation of train supervision and route setting for quick turn round in terminal stations. 10 In Communication Based Train Control (CBTC) signalling system, the primary train detection is purely based on failsafe communication link between the train and the control centre with the train communicating its position continuously and the control centre communicates the position to other trains for maintain the safety distance between two trains. Track circuits or axle counters if any are used only as a secondary detection in case the Metro operator desires a fall back system. 11 Train Spacing and its Impact on Safety and Line Capacity (Headway): Considering the need for higher order of safety, as well due to the presence of halts at frequent intervals of even less than a KM length, Primarily the train detection is done by communication, based on the train location, the movement of authority is to be updated which is known as a moving block, which include a safety envelope behind and in front of a train, always moving along with the train. Annexure G3: CBTC in Metro Railway Systems Page 508 of 530 12 Cab Signalling and Need for Track to Train Communication: CBTC uses Cab signalling in which the signal aspects were made available right inside the driver’s cab by way of displays. Information to be displayed had to be provided from track side to the equipment on-board the train. The information exchange between track to train is done through (a) by fixing coils on the track as well as underneath the cab and transferring information by magnetic induction. (b) By fixed Beacons or Balises mounted between rails transmitting the information electro magnetically through low frequency modulations to be picked up by antenna mounted below the engine of the trains. or (c) By the provision of Coded AFTC. (i) The rolling stock must have on-board electronic/computing equipment for cab signalling equipped with Automatic Train Protection (ATP) for eliminating accidents due to SPAD. (ii) Automatic Train Control Systems (ATC) for Metro Rail networks: (iii) The rolling stock must have on-board electronic/computing equipment for cab signalling equipped with Automatic Train Protection (ATP) 13 CBTC mainly comprises (a) Automatic Train Protection (ATP) comprises of the sub-systems which provide the basic safety by way of fail-safe detection of dangerous conditions and controlling and stopping the train when required independent of any action by the driver when the train is being driven manually. ATP also ensures similar fail safe protection even when train is being driven automatically. (b) Automatic Train Operation (ATO) which comprises of sub-systems which can enable automatic operation of the train without any intervention by the driver except for closing of the train doors. ATO obtains the safety instructions from ATP and other operational information from the ATS system automatically and runs the train as required. (c) Automatic Train Supervision (ATS) which comprises of various sub-systems which are used to regulate and control the operations of all the trains in the network by monitoring the positions of trains all over the network at every instant and implementing the pre defined operator commands for automatic route setting at interlocking and automatic turn backs at the terminal station etc. (d) ATS works with the driver if the train is manually driven to keep him informed about when to leave a station. In case of ATO operation, the ATS will work with ATO and control the movements of all trains in the network. The Traffic Controller can manually intervene and take over the functions any time as required, due to any emergencies or disruptions in the network. Annexure G3: CBTC in Metro Railway Systems Page 509 of 530 Communication-based train control (CBTC) is a railway signaling system that makes use of the telecommunication between the train and track side equipment for the traffic management and infrastructure control. By means of the CBTC systems, the exact position of a train is known more accurately than with the traditional signaling systems. This results in a more efficient and safe way to manage the railway traffic. Metros (and other railway systems) are able to improve headway while maintaining or even improving safety. IEEE 1474 standard defines CBTC as a "continuous, automatic train control system utilizing high-resolution train location determination, independent from track circuits; continuous, high-capacity, bidirectional train-to-wayside data communication; and trainborne and wayside processors capable of implementing automatic train protection (ATP) functions, as well as optional automatic train operation (ATO) and automatic train supervision (ATS) functions". CBTC applicability:  Mainly suitable for urban railway lines (either light or heavy) and APMs (Automated people mover)  Also deplorable on commuter lines/suburban lines.  For main lines, a similar system of ERTMS (Level-3) exists, though it is not yet fully defined. CBTC systems in India Metro Make Kochi Metro Alstom Hyderabad Metro Thales Lucknow Metro Alstom Delhi Metro Line-7 Bombardier Delhi Metro Line-8 Nippon Noida Metro (operated by DMRC) Ansaldo Nagpur Metro Siemens Ahmedabad Metro Nippon CBTC Functions:  The trains continuously calculate and communicate their status via radio to the wayside equipment distributed along the line.  This status includes, among other parameters, the exact position, speed, travel direction and braking distance.  This information allows calculation of the area potentially occupied by the train on the track.  It also enables the wayside equipment to define the points on the line that must never be passed by the other trains on the same track. Annexure G3: CBTC in Metro Railway Systems Page 510 of 530  These points are communicated to make the trains automatically and continuously adjust their speed while maintaining the safety and comfort (jerk) requirements.  So, the trains continuously receive information regarding the distance to the preceding train and are then able to adjust their safety distance accordingly. Moving Block principle First, let us understand the conventional Fixed Block system as depicted in the first figure.  The figure shows the total occupancy of the leading train by including the whole blocks which the train is located on.  This is due to the fact that it is impossible for the system to know exactly where the train actually is within these blocks.  Therefore, the fixed block system only allows the following train to move up to the last unoccupied block's border. Now, the Moving block is a significant refinement over the Fixed Block system.  The train position and its braking curve is continuously calculated by the trains.  Train then communicates its train position via radio to the wayside equipment.  Thus, the wayside equipment is able to establish protected areas, each one called Limit of Movement Authority (LMA), up to the nearest obstacle (in the figure the tail of the train in front).  Movement Authority (MA) is the permission for a train to move to a specific location within the constraints of the infrastructure and with supervision of speed.  Occupancy calculated in these systems must include a safety margin for location uncertainty. o It is depicted by the yellow lines in front and rear of the trains. o It is called footprint. o This safety margin depends on the accuracy of the odometry system in the train. Annexure G3: CBTC in Metro Railway Systems Page 511 of 530  CBTC systems based on moving block allows the reduction of the safety distance between two consecutive trains.  This distance is varying according to the continuous updates of the train location and speed, maintaining the safety requirements.  This results in a reduced headway between consecutive trains and an increased transport capacity. Grades of Automation CBTC Architecture: Annexure G3: CBTC in Metro Railway Systems Page 512 of 530 The typical architecture of a modern CBTC system comprises the following main subsystems:  Wayside equipment. It includes o Interlocking - vital control of the trackside objects such as switches or signals, as well as other related functionality. o Trackside ATC - management of the communication with the trains in its area. Calculates the limits of movement authority that every train must respect while operating in the mentioned area. o Trackside ATS - Interface between the operator and the system, managing the traffic according to the specific regulation criteria.  On-board equipment. It includes o Onboard ATP - Ensures continuous control of the train speed according to the safety profile, and applying the brake if it is necessary. o Onboard ATO - Responsible for the automatic control of the traction and braking effort in order to keep the train under the threshold established by the ATP subsystem.  Data communication system. It includes o Wired part o Wireless part (set of Radio Access Points, distributed along the Trackside). Although, CBTC architectures are always dependent on the supplier and their technical approaches, the aforementioned logical components may be found generally in a typical CBTC architecture: Advantages of CBTC in brief  Continuous bi-directional communication based vs. unidirectional based.  Moving block vs. the hundred year old traditional fixed block principle.  Integrated SW based interlocking.  No secondary detection needed.  Driverless/Unattended operation possible.  Fully automated depots.  Auto coupling possible.  Less than 90 sec. headway Annexure G3: CBTC in Metro Railway Systems Page 513 of 530