Railway Signaling and Control Systems Notes PDF

RAILWAY SIGNALING AND CONTROL SYSTEMS NOTES Signals have to meet the following general requirements: Signaling System The driver must be able to easily recognize the signal for what it is....

RAILWAY SIGNALING AND CONTROL SYSTEMS NOTES Signals have to meet the following general requirements: Signaling System The driver must be able to easily recognize the signal for what it is. The driver must be able to understand the signal indication The railroad is a very efficient transportation system. The use of steel wheels quickly. on steel rails yields a very low rolling resistance, and the capability of The information given by the signal must be unambiguous. carrying very heavy loads. But railroad have several disadvantages: The same information should always be given in the same way. Trains cannot steer around obstacles. The same signal aspects should be applicable for different cases. Multiple trains must share the track. The driver must be able to memorize the information easily. Braking distances are generally much longer than the distance The information shall be given in good and proper time, which the train operator can see. means not too late, but also not too early, to prevent the driver The purpose of signaling systems is primarily to control and regulate the from forgetting. movement of trains safely and efficiently. It ensures safe movements of Fail safe design. In case of technical defect, the signal must never trains on a railway infrastructure by locking movable track elements in a give a dangerous or misleading indication. It can, however, show proper position, checking the clearance of track sections, locking out a more restrictive indication. conflicting moves, and controlling train movements in a way to keep them Reliability: Technical defects should be rare. safely apart. Economic efficiency which, for example, requires relatively few signal lamps. Braking Distance In a steel wheel on steel rail system, the coefficient of adhesion is on According to (UIC code 734), railway lines can be divided into three classes average eight times less than in road traffic. As a result, the maximum according to speed and the related form of signalization: braking force that can be transmitted between wheel and rail for a given 1. Conventional lines: up to ca. 160 km/h; signaling by trackside weight is also eight times less. That leads to braking distances for railway signals possible. vehicles that may exceed the viewing range of the driver significantly. 2. Lines with speed: up to ca. 200 (220) km/h; trackside signals still Thus, train separation by the sight of the driver is only possible when running possible at a restricted speed. Usually, speed limits between 15 and 30 km/h are 3. High speed lines: over 200 (220) km/h; only cab signaling applied. This is only acceptable for shunting movements and for train possible. movements in non-regular operation. The speed restriction connected with movements on sight. Objective of Signaling KIND OF SIGNALS The objectives of signaling are as follows: Optical signals are suitable to give detailed information a. To regulate the movement of trains so that they run safely at including the location of the signal. maximum permissible speeds. Audible signals are suitable to attract a person's attention b. To maintain a safe distance between trains that are running on independently, so they are suitable to warn of potentially the same line in the same direction. dangerous situations. c. To ensure the safety of two or more trains that have to cross or approach each other. Trackside signals are given from a position along the track. d. To provide facilities for safe and efficient shunting. Vehicle signals are given from vehicles to persons outside the e. To regulate the arrival and departure of trains from the station vehicles. yard. Cab signals are given in the driver's cab to the driver. f. To ensure the safety of the train at level crossings when the train Hand signals, given manually by a person. is required to cross the path of road vehicles. Mechanical signals, given by different positions of objects. Signaling Safety Functions Light signals, given by different light arrangements and use of Fail-safe - is a concept where a signaling system component different colors. being in safety critical fault condition will fail to the safe side, not Positive signals give the information by the presence of an causing any dangerous situation for train movements. “Fail-safe” indication. This is the usual case today. means a design feature or practice that, in the event of failure, Negative signals give the information by absence of an inherently responds in a way that will cause no or minimal harm indication. Examples are an unlit light signal and mechanical to other equipment, the environment, or people. Foolproof - is a product or system design concept that is signals standing edgewise. designed so that humans do not fail or that failure does not lead Fixed signals (e. g. signal boards) always show the same to a major accident. For instance, washing machines do not start indication. washing unless the lid is closed. Even in a railway signal system, Switchable (multiple aspect) signals can switch between there is an operation panel that cannot be controlled by an different aspects. incorrect method, a system that prevents train overrun, and parts Colour light signals with aspects identified by different colours. that cannot be inserted in an incorrect direction. Position light signals with aspects distinguished using different Types of Signaling System light formations of the same color. Block – is a section of the rail track used for determining how far a train has Colour position light signals where aspects are shown by using traveled between signals. Track circuits, which conduct electricity, and different light formations of different colours. insulated joints act as bookends to the bricks (also known as block boundaries). When a train is parked in a block, it is considered to be Structure of a Light Signal “occupied” before the train departs, at which point it is said to be Light signals can be mounted differently. Most common is a high “vacant”. signal post directly beside the relevant track. The position of right Fixed Block System – the track is divided into fixed parts. A train or left usually reflects the normal direction of traffic entering a block could not reach the block until it was verified If there is insufficient space, signal heads may also be mounted that no other train was present. on signal cantilevers or signal bridges. On some railways, signals may be constructed as dwarf signals. Moving Block System – allows the stopping point to be inside a Typical structure of a light signal with a high signal post. Either track detection device, minimizing the gap between two several signal units can be placed in front of the same subsequent trains while preserving protection. The train’s Limit of background (practice in most European countries, figure 7.5 Travel Authority is continually modified depending on the exact left), or each signal unit has its own background (dominating position reported from the train, along with the requisite safety practice in North A margins and continuous two-way wireless contact between each train and the wayside system. Signal Units Light signals today are designed with a filament lamp or with Sign – is a tool that shows through the form, color, sound emitted, and other light emitting diodes (LED). To generate switchable signals in characteristics of a sign what the individual giving it wants to convey to different colours, signals with a filament lamp other people. Sign Marker – is a system that uses its own shape, color, and other Multi-unit signals: A separate lamp is used for each color. characteristics to signify a position, direction, or condition. Searchlight signals: Apertures are switched mechanically in front of a lamp, which is always lit. SIGNALS – positioned along the track, pass information to the train operators of passing trains. The signals might be mechanical, where the In an intermediate form (e. g. as used in Italy), several lamps are different physical positions of an arm give different indications, or light mounted in the same signal unit and the light from all lamps signals where different lights give different indications. directed to the same exit by a lens, mirror and filter system.  LED Signals OSZD Signals – system is the result of efforts in the 1950s to provide a The overall advantage of the LED (Light Emitting Diode) is the standard European signal system. In the former socialist countries in Central very long life compared with the filament lamp. and Eastern Europe and Asia (member states of the OSŽD organization) Distributed Light Source - LED units with a distributed light source The signal aspect can be divided into the upper and the lower part (figure consist of several LEDs. 7.33). The lower part gives orders about the section beginning at the signal Concentrated Light Source - consists of at least one LED. This (main signal function). The upper part gives information on the next section single LED provides the whole luminous intensity of the LED unit. (distant signal function) or the speed which is permitted after passing the Multicolour LED - each of these units provides the colours red, points area. yellow and green. Without multicolour units, a signal design with six units would be necessary, and the dimension of the signal Modern Dutch Signal System - the signal aspects are designed as inherently would increase significantly. fail-safe. That means, if the driver fails to perceive a part of the signal aspect or a part of the aspect extinguishes, always a more restrictive or an Principles of Signaling by Light Signals undefined signal aspect is perceived. The 'Expect Stop' aspect got the Historically, most railways used the following colours for signal flags and the meaning 'Apply the brakes, beginning at the signal, until you reach the night signals of mechanical signals: speed 40 km/h. Then continue at 40 km/h until you see the next signal red for 'Stop' ahead'. green for 'Caution'. The meaning of this signal aspect was something between 'expect to Stop at the next signal' and The most important signal aspects are: 'proceed slowly' red: Stop white for 'Clear' yellow: Caution (Reduce speed to 40 km/h, then continue at 40 km/h and be prepared to stop at a stop signal.) (UIC code 732) defines the following colours: yellow+number: Speed Restriction Warning red for 'Stop' o (Reduce speed to the indicated value.) yellow (orange) for 'Caution' (USA: 'Approach') flashing green: Speed Restriction (Proceed at 40 km/h.) green for 'Clear' flashing green + number: Speed Restriction o (Proceed at the indicated speed.) The shades for these colours, which are in wide use, are defined exactly. green: Clear White is often used to permit shunting movements and blue or violet to German System 'Ks' (Kombinationssignal, combination signal) - The basic forbid them. idea of the signal system is to separate the signaling of movement authorities and signaling of speed restrictions into two partial aspects. Movement authorities are signalized by the following three aspects: red = Stop yellow = Caution (one section free, expect to stop at the next signal) green = Clear (two or more sections free) The signals are equipped with two speed indicators, one for the restriction warning and one for the restriction aspect. If a speed restriction warning is indicated, the green light flashes to attract the driver's attention to the speed indicator. Signal System on Japanese Commuter Lines - On several Japanese suburban lines (narrow gauge) with high capacity requirements, signals are Main and Distant Signals situated very close together. No distant signals are used, but speed is These signals indicate if the train has to stop or is allowed to continue until reduced in small steps between two consecutive signals and the sighting the next main signal or similar block limiting point. distance is sufficient to reduce the speed. With railways, in contrast to road traffic, the stopping distance is typically NORAC (Northeast Operating Rules Advisory Committee) Signals longer than the sighting distance of the signal. In most cases, the main signal NORAC operational regulations define the following speeds and kinds of has to be preceded by a distant signal (USA: 'Approach Signal') to enable movement (1 mile = 1.609 km and mph = miles per hour): the driver to decelerate in time. Distant signals are not necessary if the train Normal speed: maximum speed of the line approaches the main signal at low speed. Limited speed: 45 mph for passenger and 40 mph for freight trains Shunting Signals Medium speed: 30 mph Shunting movements are movements for making up trains, moving cars Slow speed: 15 mph from one track to another. Shunting movements are accomplished under Restricted speed: Move on sight at a speed which permits simplified requirements at a very low speed that allows stopping short of stopping within half the sighting distance short of other rail any vehicle or obstruction. Block rules are not in effect. Shunting units may vehicles, obstacles, movable track elements in the wrong enter occupied tracks. position and signals. The speed is limited to 15 mph within and 20 mph outside interlocking limits. This is also the indication used for These signals can either stand alone or be attached to a main signal as a shunting. subsidiary signal. Stand-alone shunting signals often have to be cleared or Permissive stop (stop and proceed at restricted speed) unlit if a train passes this signal to avoid confusion of the train driver. Stop Basically, the range of signal aspects for shunting movements has to include at least one 'Stop' and one 'Proceed' aspect. NORAC (Northeast Operating Rules Advisory Committee) Based on these speed levels, the following signal aspects are defined: Signal System Examples Clear: Proceed at normal speed. Stop German Mechanical and 'H/V' (Hauptsignal/ Vorsignal) Light Signals – The Stop and Proceed signals are separate main and distant signals. The mechanical main signals Restricting: Move at restricted speed, in interlocking areas until are designed as semaphores with the upper arm to open and close the clearing all points. signal and the lower arm to restrict the speed. Approach: Caution; Prepare to stop at the next signal. Advanced Approach: Preliminary Caution; Prepare to stop at Belgian Mechanical Signals – The Belgian signal system from 1919 is a good the second signal in advance. example of three-aspect- signaling. The signals consist of a maximum two Limited/Medium/Slow Clear: Speed Restriction; Proceed at semaphore arms, with the upper in red and the lower in yellow colour, also limited/medium/slow speed until the train has cleared all points; different in their geometrical shape. Four basic signal indications are then proceed at normal speed. defined: 'Stop', 'Caution', 'Expect slow movement' or 'Preliminary Caution' Medium Approach Medium: Speed Restriction; Proceed at and 'Clear'. medium speed until the next signal. British Light Signals – The modern British signal system is a typical example of Approach Limited/Medium/Slow: Speed Restriction Warning; route signaling by light signals. It is also widely used in Commonwealth Prepare to approach the next signal at limited/medium/slow countries. speed. Medium/Slow Approach: Speed Restriction + Caution; Drive at The movement authorities are signalized either by three-aspect- signaling limited/medium/slow speed; expect Stop at the next signal. with the aspect sequence green -> yellow -> red or by four-aspect-signaling with the sequence green -> double yellow- > yellow -> red. DETECTION The general purpose of detection is to gain information about the positions of movable objects and obstacles on the railway network. Detection systems include the reception of that information, its transmission and its evaluation. The following groups of objects can be identified: Railway vehicles of all types. Rail guidance facilitates their detection. Road users on crossings are people or objects not associated Magnetic Detectors – contain a magnetic circuit formed by a permanent with the railway but temporarily occupying jointly used areas. magnet with a gap at the rail. This magnetic circuit is adjusted that way so This refers mainly to persons, vehicles and animals on level that if no wheel is present there is no magnetic flux at the electric contact. crossings. This is therefore open. When a wheel enters the gap, the magnetic field is Obstacles are all other objects, including persons and road deformed and thus switches the electric contact by magnetic force. vehicles, on railway property which are not assigned for Inductive Detectors – Most detectors for rail vehicles in new installations are common use. based on electromagnetic induction. Inductive detectors use an When considering the detection of rail vehicles, the following information electromagnetic field around the rail. The sender emits a magnetic field can be relevant: continuously. The presence of a wheel with its steel mass changes the lines of magnetic force. The point where that voltage is zero is at a distance of 1. A railway vehicle (train or shunting movement) has reached a about 20 cm between the wheel and the sender-receiver-pair. certain point with its front end. Lrt 1 uses this 2. A railway vehicle has passed a certain point with its current rear For axle counting end. This does not necessarily imply the detection of train integrity, so any 'lost' wagons will not be detected. Fiber-Optical Detectors – A recent detection principle for spot wheel 3. A particular track section is clear of railway vehicles detectors is based on optical sensor technology that is in use for monitoring strain inside large structures. Instead of induction coils, an optical laser is needed to send the signal through the sensors. This signal is permanently on and modulated in intensity. Besides axle counting and detection of direction, this sensor technology allows measurement of train speeds and axle loads as well as detection of wheel flats. Linear Wheel and Axle Detectors Mechanical Detection Bars – In mechanical signaling, mechanical detection bars are used by different railways. The bar is normally in the low position. It must rise in order to release The following special cases are relevant to specific signaling systems: the interlocked function, which is prevented if a wheel is present. A train has a particular length. Galvanic Detector (Track Circuit) – Today, the most used linear There is a particular distance between a train and a certain detector is the track circuit. Caused by an electric shunt object (e. g. CBTC systems or ETCS Level 3). between the rails formed by wheels and axle, the presence of vehicles in an isolated track section can be detected. The isolation can be solved either by cutting the rail and fitting an isolating material, or by electrical means without physical disruption of the rails, the so-called jointless track circuit. Lrt 2 - jointless track circuit Area Detectors for Vehicles and External Objects Area detectors detect objects which are present in or move through this area. In contrast to the wheel and axle detectors described above, area detectors can detect not only railway vehicles, but also external objects. Active Electromagnetic Wave Systems – Systems of this group Means of Detection actively send electromagnetic waves in the form of microwave Detection systems can be classified according to different criteria. For radar, laser, infrared or others and use the reflection or detectors of railway vehicles, one important criterion is the specific object absorption by objects to detect objects with a certain minimum of detection. size. Each ray has a transmitter on one and a detector on the Wheels of the rail vehicle. other side. Objects are detected by one or more rays being Electrical connection between the rails via wheels, axles, bogies disrupted. and/or others. Mechanical Technologies – Mechanical supervision of the The body of the rail vehicle. limiting areas of the clearance profile is applied by some Other passive parts of the railway vehicle. Examples are the railways. A net of wires or a single horizontal wire stretches pantograph of a tram or bogies of vehicles. outside the limits of the clearance profile and carries a low Acoustic waves or vibrations emerging from moving railway voltage current. vehicles. Fiber Optic Sensing (FOS) – The principle of FOS is based on the Particular active communication devices on the train. Systems ability to detect changes in intensity of light reflections caused using these can be further divided into systems which know an by vibrations or sound waves radiating against a single-mode ID number or other individual identification of the train, and fiber optic cable. Tests have shown that a single FOS/DAS unit systems where the trains move anonymously in the network. (Frauscher) can cover up to 40 kilometers of glass fiber, resulting in 80 kilometers in total when using two units at a certain location. Different Types of Spot Wheel Detectors At that length, 2500 laser pulses are sent into the fiber per second. Spot Rail Contacts are a suitable solution when the passage of a railway vehicle at a certain location is to be detected, but also for axle counting. Three-dimensional Detection They use the guidance function in rail transport and are only capable of detecting railway vehicles, not external objects. Visual Observation – The simplest and historically oldest form of detection is visual observation of the respective track by staff. An Mechanical Detectors – Historically, mechanical detectors are the oldest alternative is remote visual observation via camera and monitor form. Usually, an arm is mounted on the rail on the inner or outer side. When (closed-circuit television - CCTV). The number of staff required a wheel passes the detector, the arm is depressed and therefore the wheel for observation purposes can be significantly reduced by this is detected. As each wheel depresses the arm, this form of mechanical method. detectors is capable of axle counting. Automatic Image Processing – The most common evaluation Hydraulic and Pneumatic detectors – are installed below the rails and method is differential image processing, evaluating the detect the slight bending of the rail caused by the presence of a large difference of the current image with a fixed reference image or mass. This force is amplified by a liquid or gas, which finally switches an with an image taken a short time before, giving an alarm or electrical contact in the evaluation installation. automatically stopping trains in the case of critical results. INTERLOCKING SYSTEM Interlocking is the central function to ensure that trains move safely in towards the parallel tracks. Ladders are mainly used for the technical terms. To achieve this, the interlocking obtains information about points in the station throat and yard necks. track occupation (by rail vehicles and other objects) and the position of movable track elements. It then evaluates this information and permits movements via the signals. Amongst others, two basic principles are enforced technically by interlocking functions: A signal can only permit a train movement if all movable track elements are in proper position and locked (dependence between points and signals), and the elements must remain locked as long as they are being used by the train. Other Solutions for Connection of Tracks With train spacing by fixed block, a train can only be permitted A diamond crossing is used for the crossing of two tracks and represents a to enter a section which is clear of other rolling stock; and no construction consisting of two sharp and two blunt crossing frogs. Diamond other train may be permitted to enter that section. crossings can have movable frogs or not, mainly depending on the crossing angle and the required speed. In both cases, diamond crossings have to Movable Track Elements be route interlocked to prevent train collisions. The purpose of points is to split a single track into two or more different tracks, or to provide connections between crossing tracks. Fouling point – is the intersection of the outer limits of the clearance profiles of both tracks, which means that location up to which a vehicle can stand on the one track without endangering a movement on the other track of the points. A slip crossing combines the functions of a diamond crossing and points. There are single slip crossings as well as double ones. A double slip crossing has eight blades, two sharp and two blunt frogs and four guard rails. The two pairs of blades at the same end of the slip crossing are switched together by one point machine. Double points, also called three-way-points, permit the branching of a single track into three. It contains the two pairs of blades, five guidance rails and three frogs. Where different gauges (e. g. standard and narrow gauge) meet, points with different gauges can be required. Points can be positioned in three ways: two of them are called end positions, the other one the intermediate position. Traditionally, on most railways one of the two end positions is referred to as normal (plus) position, the other one as reverse (minus) position, usually according to the position in which the points are used more frequently and to the position of the point lever in mechanical interlocking. It is thus incorrect to identify a point's plus Interlacing of tracks provides the transition to single-track movement position always with the straight position. without the laying of points on short sections of the double line. Interlacing of tracks can also be used to combine standard and narrow gauge. At the intersection of the rail threads, the frogs are laid, the internal rail threads intersect with each other, and the rail threads along the length of the interlacing are placed on common sleepers. Coupled Elements Coupled elements — are operated by the same operational element and can only be switched together in regular operation. Often both coupled sets of points have the same identification number, possibly distinguished by the suffixes A and B. Arrangements of Several Movable Track Elements 1. Crossover represents an arrangement of two simple sets of points. It is the standard solution to connect two parallel tracks. Unidirectional Locking In unidirectional locking with two interlocked elements, one independent and one dependent element exist. The independent element can be moved freely (unless locked by other functions). The dependent element can only be set to a certain position if the independent element is also in a certain position and leaves this immediately when the independent 2. Double crossover, also known as a scissors crossing, emerges element leaves its position. when two crossovers meet together. It is a more compact solution than two crossovers but requires an additional diamond crossing. As with the simple crossover, it enables independent movements along the straight tracks, but transfers from each side of those tracks to the parallel track exclude other movements. Simple Bidirectional Locking In bidirectional locking, two or more elements are interlocked that way so that one combination of positions is impossible and each element is locked if the others are in these respective position(s). A typical example here is the most frequently used form of dependence between points and Signals. The signal is locked in the Stop position if the 3. Ladder is an arrangement of different sets of points with the same points are diverging, and the points are locked in the straight position if the point angle to split up one track into three or more parallel tracks. signal shows a proceed aspect. Thus, this kind of locking is also named The points are placed in a line which is inclined by point angle 'sequential locking'.  Normally, train protection systems protect only against errors, not willful misconduct. ATP is in charge of ensuring that a signaling system operates safely. It sets Conditional bidirectional locking is similar to the simple, but for three or speed limits for trains in order to ensure a safe operating distance between (rarely) more interlocked elements. Signal 1 can only be cleared if there is them as well as to meet safety and speed standards. It monitors the train's a safe path ahead. One condition (not considered further here) is that position, regulates the train's speed, and, if necessary, applies the brakes to points 2 must be locked in either end position, which is in fact an OR- prevent a collision. combination of two simple locks, one for each end position. However, if The functions of train protection/control systems can be classified into the points 2 are straight, there is another safety condition: points 3 must also be three groups of: locked straight. Cab signaling functions Supervision functions Intervention functions ATP panel - makikita ang speed restriction Cab Signaling Functions Generations of Interlocking Systems Non-selective warning signals (mainly audible). Whenever the Mechanical and Electro-mechanical Interlocking Systems – are train passes a certain position, e. g. the location of a distant controlled by lever frame machines, in which the levers of points signal, a warning tone sounds to direct the driver's attention to and signals are mechanically interlocked. The development of the trackside signals, independently from the signal aspect. No mechanical interlocking systems dates back to the late 19th information connection between the trackside signal and the century. In mechanical interlocking, points and signals are train protection system needs to be provided for this function operated by the muscle-power of the local operator. The levers which is applied in old train protection systems. are connected to the controlled track elements by mechanical Selective warning signals (again mainly audible). The audible wire or rod transmission. signal is applied selectively in cases which imply restrictions for Relay interlocking systems – the control logic is realized by relay the driver. Usually, the cab signal is connected to signal aspects circuitry without any mechanical elements. The circuitry may be which require the start of a braking process, such as Caution and based either on tabular interlocking with a free-wired logic, or on Speed Restriction Warning. geographical interlocking. Points and signals are no longer Visual repetition of trackside signals. The aspect of the trackside operated by levers but by simple push buttons usually located in signal in advance (in some cases in rear), is repeated in the cab an illuminated geographical track diagram. during the train's passage between two signals (the signal Electronics interlocking system – section), or while the train is within a defined partial section in the vicinity of the trackside signal. Tabular Interlocking Model Continuous static speed information. Not only are indications of In tabular interlocking, the interlocking conditions are described by a route trackside signals repeated, but the permitted speed after control table (also known as a locking sheet, locking chart, or interlocking consideration of all restrictions is always displayed. In addition, table). In that table, the rows represent the routes and the columns speed restriction warning information can also be displayed, but represent the interlocking conditions relevant for these routes. the driver is still responsible for estimating the braking curve. Dynamic speed information. Based on the static speed information, braking patterns are calculated on the train and/or in the trackside equipment. The technical system displays a guidance speed continuously to the driver. This must not be exceeded momentarily in order to comply with the next target speed. Supervision Functions Check on driver ability. At regular intervals, independently from trackside information, the driver has to use an alertness device to guard against falling asleep or similarly, the so called 'dead- man's handle'. The interval between depressing a handle, pushing a button, or whatever is required, can be either time or distance measured. Check on driver attentiveness. In certain situations, e. g. after passing a signal showing Caution, the driver has to acknowledge his attentiveness, e. g. by pushing a special button. Thus, the danger from a driver failing to perceive a signal can be reduced significantly. Train Stop function. The passing of a red signal is detected, which results in an immediate emergency stop. As the above functions are not sufficient to bring the train to a halt before the point of conflict in most cases, modern systems provide braking supervision: When the train has to brake for a signal at danger or to comply with a speed restriction, the braking process is supervised continuously or at certain points. Compliance with speed limits. In addition to the supervision of the braking process, many systems provide for the checking of speed restrictions. These can be the maximum speed of the line, local speed restrictions, restrictions on the vehicles themselves and others. AUTOMATIC TRAIN CONTROL (Part 1) Intervention Functions Automatic Train Control (ATC) – is a system designed to automate the When the supervision functions detect a problem in the behavior of the operation and control of trains. The purpose of ATC is to increase safety, vehicle, intervention functions are activated. Most modern systems grade efficiency, and reduce operating costs. The system is responsible for these. Possible levels of intervention are: controlling the speed, acceleration, deceleration, and stopping of trains. It The weakest is to warn the driver of a problem, mostly by an comprises three sub-systems, which include onboard and wayside audible warning tone, and to demand correction. equipment: The next step applied on some railways is to switch off the Automatic Train Protection (ATP) traction power automatically. Automatic Train Operation (ATO) – pag accelerate and The next step is the service brake intervention. decelerate and stop ng trains The strongest intervention function is the emergency brake Automatic Train Supervision (ATS) – intervention. Automatic Train Protection (ATP) Automation of Train Operation (ATO) The human beings are perhaps the weakest element in railway safety. Train ATO operates non-essential on-board tasks usually performed by a train protection systems to guard against driver error developed rather later to driver, such as maintaining smooth acceleration to running speed, speed supervise the actions of the driver and, if necessary, to enforce safety. regulation, and seamlessly halting the train at the appropriate position at ETCS Level 1 train stations or in front of stopping signals. In Level 1, ETCS works as an advanced intermittent ATP system (the data is transmitted to the train at discrete points along the track). Train control For urban guided transport CENELEC standard (IEC 62290-1) defines grades information is transmitted by controlled transponders, which get their of automation, based on different responsibilities for the functions needed information from the traditional signaling system via a lineside electronic to fulfill the desired operation. unit. When approaching a stop signal, a transponder at the beginning of the braking distance will transmit data to calculate the brake supervision GRADES OF AUTOMATION curve in the on-board unit. If the driver passes a stop signal at release GoA0 Manual driving on sight without any automation. The driver is fully speed, the train will get an emergency brake intervention. responsible for driving. This is the case without train protection systems; a The balises are working as transponders and need no lineside energy supply typical application is trams running in street traffic. Nevertheless, points and to send information to the train. They are either fixed data balises without single-track lines might need to be protected. – PNR any informational connection to other trackside devices or switchable GoA1 Non-automated train operation. This is the case of a train protection balises with data connection, e. g. from signals, via a Lineside Electronic system supervising the driver and enforcing safety in the case of driver's Unit (LEU). error. Safe closing of the doors and setting the train in motion are tasks of the driver. – LRT 1 GoA2 Semi-automated train operation. This is the case when acceleration and the application of brakes are automated. Other tasks like the safe closing of doors and supervision of the track are assigned to the driver. LRT2 GoA3 Driverless train operation. Here the train is normally driven automatically. There is no driver permanently in the cab who would watch the track continuously. There is a train attendant, who could be in charge To improve capacity, a train approaching a stop signal may be released of other tasks (such as selling tickets) and who can take action in the case from the braking curve supervision after the signal has been cleared by of danger or technical failure. The closing of doors can be done by the staff transmitting infill information. Infill information may be provided by or automatically. additional transponders (spot infill), a loop antenna (loop infill), or by digital radio (radio infill). If the signal has been cleared in the meantime, the transponder at the signal will upgrade the on-board unit to the speed permitted in the section beyond the signal. Euroloops and Radio Infill Units are linear transmitters of limited extent for the transmission of infill information related to a position in advance, such as upgrades of signal aspects. Automatic Train Supervision (ATS) This is the most advanced level of control for an ATC subsystem that uses ATO and ATP to automatically control trains in accordance with the railway timetable. It guarantees that the train follows the required schedules while also allowing for schedule changes as needed and unplanned events such as breakdowns and track blockages. It is also responsible for scheduling, controlling, managing and supervising the running of trains. Below are the several function of ATS: 1. Automatically produce timetables for train services. 2. Obtain train positions and speeds from the ATP system. Fixed block 3. Obtain train arrivals and departures from the ATO system. 4. Automatically issue train routing commands based on the ETCS LEVEL 2 schedule and train position. In Level 2, ETCS works as a continuous ATP system (transmit control data 5. Train timings can be adjusted by sending the dwell time at each continuously from track/wayside to train) in which the train control data is station and the maximum speed to the next station allowed by transmitted by digital radio. Non-controlled transponders are used as ATP to ATO (motoring and coasting data). reference points ('electronic mileposts') for the on- board train location 6. Train service at the control center can be operated remotely system. and centrally. Radio Block Centre (RBC) is the central trackside controlling unit in Levels 2 7. Train service regulation will be made easier during service and 3. It is, among others, responsible for storing static line data, for disruptions (centrally-controlled at control center). obtaining dynamic data from the interlocking systems and for generating 8. Information for passengers (schedules, arrivals and departures, the movement authorities (MA) and profiles. The RBC communicates with destination) trains by the Euroradio based on GSM-R 9. Data and events related to train services (faults, alarms, train delays, deviation reports ETCS (European Train Control System) – is a layer (i.e., a sub-project) of the European Rail Traffic Management System (ERTMS). Today, the ERTMS consists of the ETCS and the digital radio system Global System for Mobile Communications - Railway (GSM-R). While ETCS represents the train control part of ERTMS, the GSM-R provides the wireless communication system needed for the higher ETCS levels. The idea of ETCS is to gradually replace the existing ATP systems by an advanced train control system. In that system, train control information can be transmitted by transponders (so-called Eurobalises), short loop antennas (so-called Euroloops), or by digital radio. In specified intervals, trains automatically transmit their location data to a ETCS - LRT 1 NON ETCS - LRT 2 (ATO, ATP) Radio Block Centre (RBC) that issues the movement authorities to the trains. MRT 3 - ATP ATS However, positive train separation is still affected by fixed block sections equipped with traditional track clear detection technology (track circuits or axle counters). Balises are mainly needed for positioning the train, the Transponders (Tags) are used to provide absolute location references that error of the odometry rises with increased distance enable trains to become and remain localized. The data encoded in each Most railways prefer to replace controlled signals by ETCS stop markers that transponder represents line section, track segment and identifier within must not be passed without valid authority. Since these ETCS location each track segment. markers do not provide an absolute stop indication, the design differs from the ETCS stop markers CBTC Modes can generally be categorized into four categories: 1. Automatic CBTC modes that provide full ATP and full or partial ATO functionality (unattended or attended operation) 2. Manual CBTC modes that provide full ATP but no ATO functionality (train operator is responsible for ATO part) 3. Restricted CBTC modes that provide limited ATP functionality (Yard or Restricted Manual mode that provide only overspeed and/or end of track protection and train operator is responsible for safe train separation) 4. Non-CBTC mode (Bypass, CBTC is disabled) FIXED BLOCK CTCS (Chinese Train Control System) ETCS Level 3 The CTCS is based on ETCS technology with some modifications to meet the ETCS Level 3 finally adds train-borne checking of train integrity (i.e., train specific operational requirements of Chinese railways. Different from the completeness) to the system. This eliminates the need for fixed block ETCS approach, there is no separation between the computer-based sections for track clear detection. In contrast to Levels 1 and 2, ETCS Level interlocking system and the Radio Block Centre. Instead, there is one 3 is not only an ATP and cab signal system but provides also a radio-based integrated control system for inter-locking and train control. train separation replacing the traditional block system. For the use of coded track circuits, a separate level was defined that has no equivalent in the ETCS specification. CTCS level 2 may be used up to a speed of 250 km/h. Moving block PTC (Positive Train Control) "Positive train control" (PTC) describes technologies designed to automatically stop a train before certain accidents caused by human error occur. PTC is designed to prevent: Train-to-train collisions. Derailments caused by excessive speed. Unauthorized incursions by trains onto sections of track where maintenance activities are taking place. and the movement of a train through a track switch left in the wrong position PTC system combines GPS, wireless radio and computing technology to send up-to-date visual and audible information and notify train crew members when a train must be slowed or stopped. If an engineer does not respond to the PTC warning system, onboard computers will activate the CBTC (Communication Based Train Control) brakes and safely stop the train. CBTC is defined as a continuous Automatic Train Control (ATC) system LEVEL CROSSINGS utilizing high resolution train location determination, independent of track circuits; with continuous, high capacity, bidirectional train to wayside data Level Crossing is a place where a railway line and a road intersect each communications; and train-borne and wayside processors capable of other on the same level. It is also called a grade crossing, a railway crossing, implementing safety related functions (IEEE 1474). or a railroad crossing. The moving block concept is based on a continuous calculation of the safe It is also a place where serious accidents occur frequently. That is why level distance ahead of each train based on the target point, safe braking crossing equipment is installed as part of the railway signaling system. distance and safety margin. A basic classification of level crossings by the ERA (European Union Agency TRAIN-BORNE COMPONENTS: for Railways) is as follows: 1. Passive level crossings: These always appear to the road user in Train Operator Display (TOD) is a processor based device that provides the same way, irrespective of whether or not there is a train visual and audible indications for all data required for a driver including approaching. Therefore, the road user has to look for trains permissive speed, current speed and type of mode, train status and alarms. himself. It also accepts commands from the driver. TOD is interfaced with CC via 2. Active level crossings: These indicate to the road user whether a communication-based connection and is supplied with reserved power. train is approaching or not. Carborne Radio (CR) for communication-based interface with Zone Controller, Auxiliary Wayside System (if required) and Automatic Train Passive Level Crossings Supervision. It consists of a redundant set of equipment that includes In passive level crossings, the road user is responsible for observing the antennae, radios, network devices (i. e. Ethernet Switches) and railway line and recognizing an approaching train directly. The most widely interconnections between them. used sign to indicate the presence of a level crossing to road users is the distinctive St. Andrew’s cross. Odometry Devices that provide constant localization data to CC. Tachometers are used on the vast majority of CBTC systems. Tachometers In addition to the St. Andrew’s cross, in many cases other signals such as measure the rotation of a train's axle. To compensate for wheel wear and text boards are installed immediately in front of the level crossing to warn to accommodate slip/ slide effects several sensors are installed on a train the road users and give instructions, these are called Railroad Signages. or free axle is used for installation. The advance warning sign is placed to attract the driver's attention and warn that there is a railroad crossing ahead so the driver can slow down to WAYSIDE COMPONENTS: look and listen for a train. It's the driver's responsibility to be in control of the Zone Controller (ZC) is a fail-safe processor that is responsible for the issuing vehicle and stop if required. of Movement Authority Limits (MAL) to communicating trains. ZC has communication- based interfaces with every CBTC train located within its Pavement markings include the white RXR symbol on the roadway, usually zone. near the advance warning sign, to warn that a crossing is ahead. These markings alert drivers that the road crosses railroad tracks and identifies the Signal Blades - it physically moves into different positions to safe place to stop and look for an approaching train. display the aspect. Channelization is used to guide pedestrians, including bicycles, to cross the Types of Wayside Signals: tracks where active warning devices are in place. Channelization may Semaphore Signals – revolutionized and standardized the include fencing, swing gates, median islands, and various passive traffic railroad signal industry during the time. These signals provided control devices. railway operations with an efficient method of transmitting track conditions. Semaphore signals use moving blades to interpret Active level crossings include all those which give different indications to information or instruction to the personnel. the road user depending on the approach of a train. This includes technical Color Light Signals safeguarding with light signals, barriers and others as well as manual Position Light Signals safeguarding by hand signals of a level crossing post. Color Position Lights Active Level Crossings REPORTING 2: TRACK CIRCUIT Road Light Signals – Level crossing light signals are mounted on a signal post. When the red lights are flashing, a train is Track Circuit – is an electrical device used to detect the absence of a train approaching. Stop and wait for the train to pass, then proceed on rail tracks to signalers and control relevant signals. Track circuits when it is clearly safe to do so. operational principle is based on an electrical signal impressed between Barriers – can be placed in the same location as level crossing the two running rails. The presence of a train is detected by the electrical light signals. When placed in different locations, the barrier is connection between the rails, provided by the wheels and the axles of the placed not further from the railway than the light signal. It is used train (wheel-to-rail shunting). to close the road when a train approaches. Additionally, it is Are used to control train speed and ensure safe operation illegal to go around the gates. Are designed to indicate the presence of a train when failure Automatic Road Blockers – In addition to light signals and occurs. barriers, the countries of the former Soviet Union use road Allow railway signaling systems to operate semi-automatically blockers to prevent the passage of a level crossing by road Help prevent dispatchers and operator from causing accidents vehicles. These devices for blocking of the level crossing consist of four covering lids which are placed in a bed. Types of Track Circuit Level Crossing Protection Devices 1. Alternating Current Track Circuits (AC Track Circuits) – AC track circuits are a type of train detection system that uses alternating Manually activated signals – are operated by level crossing staff, current to create an electromagnetic field around the tracks. on instructions transmitted remotely by telephone or radio signal 2. Direct Current Track Circuits (DC Track Circuits) – DC track from the nearest station. circuits are a widely used system for train detection. They work Automatic warning signals – need short track circuits or markers by creating a continuous electrical circuit along the rails. which detect trains and activate warning indications at level crossings. These warning indications are usually flashing lights, or Types of DC Track Circuits sounds emitted by bells or claxons (horns), or a combination of Occupied Track Circuit – An occupied track circuit these two. signal train presence, prompting the system to adjust Automatic crossing barriers – it is a physical barrier to prevent or signals. to dissuade motorists from entering a level crossing into the path Unoccupied Track Circuit – An unoccupied track of an oncoming train; it is also activated by detecting the circuit indicates that the section is free of trains, presence of the approaching train. ensuring safe train movement. Obstruction warning devices for level crossings – These types of 3. Audio Frequency Track Circuits – An Audio Frequency Track devices are usually only installed at unmanned level crossings. Circuit (AFTC) is a joint-less track circuit that uses audio Their function is to provide signal warnings to train drivers when frequencies transmitted through the track to detect the level crossings are blocked by motor vehicles or other presence or absence of a train. obstruction. 4. Single Rail Track Circuit – A single rail track circuit is used where one of the rails is reserved for the traction return current. This rail REPORTING 1: WAYSIDE SIGNALS is referred to as the uninsulated rail. Wayside Signals 5. Double Rail Track Circuit – Both the running rails are insulated Fixed signals positioned alongside railway tracks from adjoining sections by the insertion of block joints. Consist of signal heads mounted on masts or poles Components of Track Circuit Utilize visual indications such as colored lights or mechanical arms 1. Rails – The rails themselves form a part of the track circuit. They Strategically placed for clear visibility and guidance to train are typically made of steel or aluminum steel and serve as operators conductors for electrical currents. 2. Sleepers – are usually rectangular support structures placed Importance of Wayside Signals perpendicular to the rails in railway tracks. The track circuit 1. Safety: They provide vital information to train operators sleepers are required to be of the insulating type, such as regarding track conditions, speed limits, and permissions to concrete or wood sleepers. Sleepers made of steel or cast iron proceed or stop. cannot be utilized in track- circuited sections because they will 2. Regulation of Train Movements: They indicate when trains should cause the rails to short-circuit immediately. stop, proceed at reduced speeds, or continue at normal speeds. 3. Battery – Batteries (4V) are used to pass the current at one end 3. Communication: Through visual indications such as colored lights and the current is regulated by a resistance. However, batteries or mechanical arms, signals convey essential information about can also serve as backup power sources for critical signaling track occupancy, route permissions, and track conditions. equipment, such as signal lights, track relays, and occupancy Physical Components of Wayside Signals detection systems. Signal heads - is the housing that contains the colored lights or 4. Insulated Rail Joints – are provided at both ends of the section aspects that convey the signal indication. It can be mounted on to ensure that the flow of current is restricted to a particular one or both sides of the mast for better visibility depending on section. track configuration. a. Nylon Insulated Rail Joints - Nylon-insulated rail joints Mast or pole - is the vertical structure that supports the signal consist of nylon or plastic insulating material inserted head(s). It can be made of steel, concrete, or fiberglass. This between the ends of two adjacent rails at a rail joint. comes in various heights depending on location and the need b. Glued Joints – are fabricated in a workshop in 6.5 m for signal visibility over long distances or obstructions. Length and transported to the site for insertion in the Signal housing - it is the body of the wayside signal. This contains track. These have more mechanical strength to retain all the optics and wiring for the signal head. insulation and to withstand rail creep. Wiring and electrical components - it is crucial in transmitting 5. Bond Wires – are used to maintain electrical continuity between information and controlling the illuminated aspects displayed by sections of rails. the signal head. 6. Ballast Resistors - are used to limit the amount of current flowing Color Light Aspects - it is the combination of illuminated colors when the section is occupied. displayed by the signal head. Each aspect conveys specific 7. Track Relays – are electromagnetic devices used to amplify and instructions to the train operator. The most common colors used control electrical signals within the track circuit. The relay remains are red, yellow, and green. energized when the track is clear due to the current flowing through the relay.  8. Signaling Equipment - such as control panels, signal cabins, and The train then uses this information, together with data from other electronic control systems, processes and interprets the track sources (e.g., tachometer), to recalibrate its location and/or relay signals. The signaling equipment controls the data current speed. gathered from several track circuits along the railway and Active (Controlled) balises - provide variable information coordinates the safe movement of trains accordingly. regarding local speed limits and even control orders related to 9. Train Wheel and Axles – The metal wheels and axles allow the authority over train movement. The trackside signaling supply electrical current an alternative channel when a train enters a operates a track-based transponder, which continuously block covered by the track circuit. This causes a drop in current broadcasts data packets to passing trains. flow and activates the track relay, signaling the arrival of the Physical Components train. 1. Balise Transmission Module: The balise transmission module Functions of Track Circuit transmits a tele-powering signal to the balise, which transforms it A track circuit functions by utilizing the railway tracks as conductors in an to electrical energy and powers it. electrical circuit. When a train enters a track section monitored by the 2. Antenna – is where the balise transmission module is attached circuit, its wheels and axles complete the circuit, allowing current to flow. that passes directly over the balise, while a train communicates Train Detection & Occupancy Determination: These functions are with it. It detects magnetic fields produced from the balise. closely related as they both involve detecting whether a train is 3. Enclosure – covers the balise placed between the rails of a present on a specific section of track and determining the railway for protection from the train running through it. occupancy status of that section. Safety Enhancement & Interlocking Systems: These functions are REPORTING 5: POINT MACHINE interconnected, as safety enhancement through preventing conflicting train movements relies heavily on the proper Point machine – sometimes referred to as a switch machine or turnout functioning of interlocking systems, which use track occupancy machine, is a signaling tool used in railroading that regulates the movement information to control signals and points. of switches or points. It is the actuators that move trains from one track to Signal and Points Control & Real-time Monitoring: These functions another in railway switching and crossing systems. work together to ensure the effective control and monitoring of It consists of the following parts: train movements. Signal and point control rely on real-time 1. Housing – encloses the Point Machine and is made of Cast Iron occupancy information provided by track circuits, enabling the Base. automatic operation of signals and points. Real-time monitoring 2. Transmission Assembly – typically refers to the mechanism allows signalers to continuously track train locations for efficient management. responsible for converting the rotational motion generated by the motor or power source into linear movement. This linear REPORTING 3: AXLE COUNTER movement is essential for actuating the switch rails, which control the direction of train tracks at junctions or crossovers Axle Counter – is a device on a railway that detects the passing of a train 3. Contact Assembly – is to establish and maintain electrical between two points on a track. A counting head (or detection point) is connections between different parts or components within a installed at each end of the section, and as each train axle passes the system counting head at the start of the section, a counter increments. 4. Electric Motor – The motor is the primary power source of the Components point machine. It provides the rotational force needed to drive 1. Sensors: This detects the individual axles of a train by the transmission. mechanical, electrical, or even fiber optic methods. It's installed 5. Reduction Gear Box – Its primary role lies in reducing the speed at each end of a section of track that needs to be monitored. of the input shaft, typically driven by a motor or power source, to 2. Evaluator: This unit counts the axles passing into and out of a rail a level suitable for driving the switch mechanism. By slowing section. It may also convert the analog signal from the axle down the rotational speed, the reduction gearbox ensures that sensor into a digital signal for processing. 3. Counting Heads (Detection Points): Positioned at each end of the switch mechanism operates at an appropriate pace for the the section, it increments a counter as each train axle passes by. safe and efficient switching of railway tracks. 4. Safety-Critical Computer (Evaluators): Centrally located, these 6. Point Throw Slide – In a point machine, the point throw slide is a computers compare the counts at the beginning and end of the fundamental component responsible for translating the section to determine if the track is clear. rotational motion generated by the motor or power source into 5. Transmission System: The axle counter sensors can be linear movement. connected to the evaluator via a dedicated copper cable or a 7. Point Lock Slides – Lock slides are used to securely lock switch telecommunications transmission system, allowing significant rails in their intended positions. distance between the sensors and the evaluator. 8. Point Detector Slides – The detector slides are moved via Function/Application attached rods by the point tongues and check whether the Railway axle counters take center stage in modern railway operations. Their point tongues have followed the movement of the point ability to provide real-time data and enhance safety measures is machine and have reached the end position. unparalleled. Let’s dive into their primary applications. 9. Crank Handle Cut Out Switch – is a safety feature commonly 1. Train Detection and Occupancy Monitoring: This functionality is found in manual point machines used in railway signaling critical for the seamless flow of railway traffic. These systems systems. It serves to prevent accidental or unauthorized accurately count the axles as trains enter and leave a block operation of the point machine by disabling its functionality section, thereby determining if a track segment is occupied or when not in use. free. 10. Crank Handle – Manual operation with crank handle: During the 2. Level Crossing Safety: At level crossings, the safety of both train failure of motor, point etc. due to power supply or for passengers and road users depends on precise and reliable maintenance work, facility must be provided for locally detection of train movements. Railway axle counters play a crucial role here, providing the exact moment a train operating the points manually. approaches the crossing, ensuring that barriers are lowered in time to prevent any accidents. Functions of the Point Machine 3. Train Speed Measurement: By calculating the time, it takes for all While Point Machines come in various types and variations, they all share axles of a train to pass between two points, these systems can the same core components and perform the same function. accurately determine the speed of the train. The primary function of a point machine is to actuate a railway switch that directs trains from one track to another. REPORTING 4: BALISE It opens or closes the switch rails through the operating rods and Balise – is a sensitive electrical beacon or transponder that is installed on a switch motor. railway track and can transmit data to a train passing overhead. It is operated remotely from a control room to switch the track for a train. Its secondary functions are the following: locking the Types of Balise rail switch and detecting the position of the rail switch (Normal Passive (Fixed) balises - provi