LGV signalling
Encyclopedia
Cab signalling
Cab signalling is a railway safety system that communicates track status information to the cab, crew compartment or driver's compartment of a locomotive, railcar or multiple unit, where the train driver or engine driver can see the information....
originally deployed in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and used on high-speed rail
High-speed rail
High-speed rail is a type of passenger rail transport that operates significantly faster than the normal speed of rail traffic. Specific definitions by the European Union include for upgraded track and or faster for new track, whilst in the United States, the U.S...
way lines. TVM-300 was the first version, followed by TVM-430.
TVM-300 was developed in the 1970s as part of the TGV
TGV
The TGV is France's high-speed rail service, currently operated by SNCF Voyages, the long-distance rail branch of SNCF, the French national rail operator....
project. At speeds of above 220 kilometres per hour, TGV trains run only on dedicated tracks designated as (LGV). At high-speeds it is not possible for a driver to accurately see colour-light based railway signal
Railway signal
A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...
s along the track-side. Signalling information is instead transmitted to the train and displayed as part of the train controls. The driver is shown the safe operating speed, displayed in kilometres per hour.
The 1980s-developed TVM-430 system transmits more information than traditional signalling would allow, including gradient profiles and information about the state of signalling blocks further ahead. This high degree of automation does not remove the train from driver control, although there are safeguards that can safely bring the train to a stop in the event of driver error.
History
The TVM system was developed by the French group Compagnie de Signaux et d'Entreprises Electriques (CSEE), now part of Ansaldo STSAnsaldo STS
Ansaldo STS S.p.A. is a multinational technology company which produces signalling and automation systems for use by rail and rapid transit operators. The firm also acts as lead contractor and turnkey provider on new rail developments...
.
Two versions of TVM signalling, TVM-430 and TVM-300, are in use on the LGV. TVM-430, a newer system, was first installed on the LGV Nord
LGV Nord
The LGV Nord is a French 333-kilometre long high speed rail line, opened in 1993, that connects Paris to the Belgian border and the Channel Tunnel via Lille....
to the Channel Tunnel
Channel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...
and Belgium, and supplies trains with more information than TVM-300. Amongst other benefits, TVM-430 allows a train's onboard computer system to generate a continuous speed control curve in the event of an emergency brake activation, effectively forcing the driver to reduce speed safely without releasing the brake.
TVM-430 was presented from an intended "modular and flexible" range of signalling system levels from TVM-400 up to TVM-440 (optional automatic train control) and TVM-450 (full driverless control).
Implementation
The line is divided into signal blocks of about 1,500 metres (~1 mi), the boundaries of which are marked by blue boards printed with a yellow triangle. Dashboard instruments show the maximum permitted speed for a train's current block, as well as a target speed based on the profile of the line ahead. The maximum permitted speed is based on factors such as the proximity of trains ahead (with steadily decreasing maximum permitted speeds in blocks closer to the rear of the next train), junctionJunction (rail)
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge.This implies a physical connection between the tracks of the two routes , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...
placement, speed restrictions, the top speed of the train and distance from the end of LGV route. Trains at high-speed take several kilometres to stop. Since trains will require more than one signal block to slow down, drivers are alerted to reduce speed gradually, several blocks before any required stop.
The signalling system is permissive; the driver of a train is permitted to proceed into an occupied block section without first obtaining authorisation. Speed in this situation is limited to 30 kilometres per hour (19 mph) and if speed exceeds 35 km/h (22 mph), the emergency brake is applied and the train stops. If the board marking the entrance to the block section is accompanied by a sign marked Nf, the block section is not permissive, and the driver must obtain authorisation from the Signalling and Control Centre () before entering the block. Once a route is set, or the signalling centre has provided authorisation, a white lamp below the marker board is lit to inform the driver. The driver then acknowledges the authorization using a button on the train's control panel. This temporarily overrides the emergency braking system, which would otherwise stop the train when proceeding past the non-permissive marker's ground loop.
When trains enter or leave the LGV from , they pass over a ground loop which automatically switches the driver's dashboard indicators to the appropriate signalling system. For example, a train leaving the LGV onto a French ligne classique would have its TVM signalling system deactivated and its traditional KVB system enabled.
Electronics
It is one of the more advanced railway signalling systems in the world, although the implementation itself is still based on relayRelay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
s rather than solid state electronics.
There are two components to the TVM-430 system: one ground-based, the other on board the train. Both run using Motorola 68020
Motorola 68020
The Motorola 68020 is a 32-bit microprocessor from Motorola, released in 1984. It is the successor to the Motorola 68010 and is succeeded by the Motorola 68030...
class processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
s, and are programmed in Ada, a computer language often used in safety critical systems
Life-critical system
A life-critical system or safety-critical system is a system whose failure ormalfunction may result in:* death or serious injury to people, or* loss or severe damage to equipment or* environmental harm....
. The system makes extensive use of redundancy
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
; the mean time between dangerous failures is estimated to be over 1 million years.
The ground-based segment of TVM-430 resides in trackside boxes, which control stretches of track about 15 km (9.3 mi) long. Each one is linked to the line's centralized traffic control centre, and directly controls about ten blocks of track, each with its own track circuit
Track circuit
A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...
. Signaling information is encoded in AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
signals which are fed into the rails of each block. There are four different carrier frequencies
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
available in TVM-430 and they are used alternately in pairs on both tracks of the TGV line. On one track, blocks use alternately 1,700 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
and 2,300 Hz, while on the other track blocks use alternately 2,000 Hz and 2,600 Hz. Upon these carrier frequencies can be modulated 27 separate audio frequencies, any combination of which can be present at one time; the earlier TVM-300 used eighteen separate frequencies, only one of which could be present at any time. Each block has a receiver at the opposite end to the transmitter, and the loss of the track circuit signal (owing to shorting by train wheels or due to a failure) is interpreted as an indication that the block is occupied. Signalling block boundaries are equipped with electrical separation joints that prevent adjacent blocks from interfering with each other, whilst still letting the traction return current (at 50 Hz) pass through. These tracks circuits are referred as a UM71 track circuit.
The signals which are present in the rail are detected by antennas mounted underneath the front airdam of TGV trains, approximately 1 metre (3 ft) forward of the front axle
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...
. These antennas work by inductively coupling to the AC signal shunted between the rails by the first axle. There are four redundant antennas per train, two at each end. Only the two at the "front" of the train (in the direction of travel) are used. The signal from the track circuit is filtered, conditioned, and decoded on board the train by two redundant digital signal processors.
Encoding
The decoded signal takes the form of a 27-bit digital word, with each bit corresponding to one of the 27 frequencies modulated onto the carrier frequency in the track circuits. The presence of a particular frequency indicates a "1" bit and lack of corresponds to a "0". The resulting word contains several fields, in the following order:- Speed Codes containing three pieces of information: the current maximum safe speed in the block, the target speed at the end of the block, and the target speed at the end of the next block. Each of these can take on six different values; in the case of a high speed line these are (in km/h) 300, 270, 230, 170, 80 and 0, roughly corresponding to a typical braking and deceleration profile.
- Gradient information, averaged over the length of the block. This allows the train's signalling computers to account for this in speed calculations.
- Block Length, which can vary quite a bit, and is also important in speed calculations. For example, on a flat stretch of high speed track, a block can be a full 1500 metres long, while in the terminal areas of the Channel TunnelChannel TunnelThe Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...
, blocks are one-tenth as long. - Network Code, a number which determines the interpretation of the speed codes which should be taken by the train's computer. For example, on high speed lines where the maximum allowable speed is 300 km/h (186 mph), a different network code is used from that in the Channel Tunnel, where the speed limit is 160 km/h (100 mph). Eurostar trainBritish Rail Class 373The British Rail Class 373 or TGV-TMST train is an electric multiple unit that operates Eurostar's high-speed rail service between Britain, France and Belgium via the Channel Tunnel...
s need this information since they operate both on high speed tracks and in the tunnel. - Error-Checking code, allowing the integrity of the entire 27-bit word to be checked if the information has been misread. This allows error correcting as well as error detection in most cases. The code takes the form of a 6-bit cyclic redundancy checkCyclic redundancy checkA cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
(CRC).
These 27 bits of information are used as an input to the train's signalling computer, the onboard part of the TVM-430 system. In older versions of TVM, the target speed was updated only at every block boundary, resulting in a "staircase" style speed profile which is not representative of the continuous speed changes effected by the driver. However, with the additional information of block length and profile, TVM-430 is able to generate a continuously varying target speed through calculations performed in the onboard signalling computer, thus giving a much more realistic speed profile of continuous acceleration or deceleration for the driver to follow.
In addition to the continuous speed control afforded by TVM-430, single instructions can be passed to the train by inductive loops located between the rails, which couple to a corresponding sensor under the train. Using the same frequency encoding principle, 28 bits of information can be recovered from a beacon, at speeds up to 400 kilometres per hour (250 mph). They come in two lengths depending on the line speed, 7 metres and 4.5 metres. These are called BSP Intermittent Transmission Loops (ITL). They consist of two half loops, which together transmit the message via a 125 kHz frequency, phase shifted with a 62.5 kHz carrier frequency. The information passed along concerns a variety of events or actions required:
- Entry or exit from a high-speed line
- Arming or disarming the TVM-430 system
- Closing air conditioningAir conditioningAn air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
vents before entering a tunnel - Raising or lowering the pantographPantograph (rail)A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...
s - Switching to a different electrical supply voltage
Oversight
A "black box" similar to an aircraft flight data recorderFlight data recorder
A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...
, passively watches over the entire process, monitoring a variety of parameters and recording the events. In TVM-430-equipped trainsets, older paper-strip recording equipment has been replaced by the ATESS digital recording system. Every action taken by the driver (throttle, brakes, pantographs) as well as signalling aspects (for TVM-430, KVB, and conventional signals) are recorded on magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
for later analysis using a desktop computer.
Another system, known as VACMA oversees the driver's alertness. It consists of a foot pedal control that the driver needs to hold down for the TGV to move. This pedal must be released then re-pressed once every 60 seconds if no other activity takes place. There is one period of time before a buzzer sounds, and another period of time before the automatic emergency brakes come on. The control can be released for a very short period of time before a buzzer sounds, and another very short period of time before the automatic emergency brakes come on.
Overspeed
A small amount of over-speed allowance is made before the train's emergency brakes are applied. At speeds below 80 km/h, the allowance is five kilometres per hour. At nominal speeds of 80–160 km/h, the tolerance is ten kilometres per hour and at speeds in excess of 160 km/h, it is fifteen kilometres per hour.Cab display
In the centre of the driver's desk in a TGV cab, just below the windscreen, there is a double or triple row of square indicators. This is where target speeds for the current and subsequent blocks are displayed to the driver, in the form of numbers (in kilometres per hour) on a colour-coded background. Full line speed is indicated in black numerals on a green background, while slower aspects are indicated in white numerals on a black background and a full stop is indicated as "000" on a red background. Below this display is the speedometerSpeedometer
A speedometer is a gauge that measures and displays the instantaneous speed of a land vehicle. Now universally fitted to motor vehicles, they started to be available as options in the 1900s, and as standard equipment from about 1910 onwards. Speedometers for other vehicles have specific names...
, where the continuously varying target speed is indicated as well as the current speed. Speed is measured by the train's redundant tachometer
Tachometer
A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
s to a precision of +/-2%. The allowable variation between target speed and actual speed is dependent on speed.
All the in-cab signalling displays must be very reliable, since they are critical to safety. They have relay-based position sensors which feed back to the signalling computer the current aspect being displayed to the driver. If there is a failure in the display unit, appropriate action is taken to stop the train.
In order to reduce stress on the driver, speeds are displayed over several blocks ahead of the train. When a block is followed by a more restrictive (slower) block, the display for that block flashes so the driver can better anticipate the speed change without releasing the brake. Restrictive indications can only be updated at block boundaries, except in emergencies. They are accompanied by an audible in-cab horn signal. Restrictions can however be lifted at any time within a block.
TVM-430 has extensive redundancy built into it, and one might wonder why it is not used to control the train directly. However, in view of the lack of adaptability of the system to unexpected situations, it is considered desirable to retain a human
Human
Humans are the only living species in the Homo genus...
in the loop. Driving a TGV is therefore done entirely manually, but the signalling system keeps a very close watch to ensure maximum safety.
| Rouge (Stop, track section is occupied or end of line) |
(Nf or F marker) |
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| Zéro (Avertissement 0; stop at next signal) |
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| 080E (Exécution 80; do not exceed 80 km/h) |
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| 080A (Avertissement 80, speed change to 80 km/h ahead) |
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| 160E (Exécution 160, do not exceed 160 km/h) |
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| 160A (Avertissement 160; speed change to 160 km/h ahead) |
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| 220E (Exécution 220; do not exceed 220 km/h) |
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| 220A (Avertissement 220; speed change to 220 km/h ahead) |
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| 270V | ||||
| 270VL (Voie Libre 270 km/h; proceed at 270 km/h) |
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| 270A (Avertissement 270; speed change to 270 km/h ahead) |
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| 300V | ||||
| 300VL (Voie Libre 300 km/h; proceed at 300 km/h) |
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Other signalling systems
The TVM system is used only on high-speed lines and in the Channel TunnelChannel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...
. Outside of the high-speed lines, other signalling systems are used. Every TGV train is equipped with the KVB (, "Beacon Speed Control") which is used throughout the French network. In addition to TVM, the following systems are used in various combinations:
- KVB, the French signalling system (electro-mechanical with radio beacons)
- ATBAutomatische treinbeïnvloedingAutomatische TreinBeïnvloeding or ATB is a Dutch train protection system developed in the 1950s. Its installation was spurred by the Harmelen train disaster of 1962....
, the Dutch signalling system (induction based) - ATB-NGAutomatische treinbeïnvloedingAutomatische TreinBeïnvloeding or ATB is a Dutch train protection system developed in the 1950s. Its installation was spurred by the Harmelen train disaster of 1962....
a newer version of ATB (also induction based) - ATCAutomatic Train ControlAutomatic Train Control is a train protection system for railways, ensuring the safe and smooth operation of trains on ATC-enabled lines. Its main advantages include making possible the use of cab signalling instead of track-side signals and the use of smooth deceleration patterns in lieu of the...
the JapaneseJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
signalling system (induction based) - MEMORMemorMemor was a Roman usurper against Emperor Gallienus.Memor was a Northern African Roman official, responsible for the Egyptian grain supply to Rome. After the defeat of the Macriani usurpers, Emperor Gallienus sent his general Aurelius Theodotus to Egypt to secure his hold on the province....
, the BelgianBelgiumBelgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
signalling system (electro-mechanical) - TBL, a newer version of MEMOR (electro-mechanical with radio beacons)
- InduSiPunktförmige ZugbeeinflussungPZB or Indusi is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania, Israel and on one line in Canada....
the GermanGermanyGermany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
signalling system (induction based) - LZBLinienzugbeeinflussungLinienzugbeeinflussung is a cab signalling andtrain protection system used on selected German and Austrian railway linesas well as the AVE in Spain.In Germany, the system is mandatory on all lines where trains exceed speeds of...
, the German system for high-speed lines (also induction based) - AWSAutomatic Warning SystemThe Automatic Warning System is a form of limited cab signalling and train protection system introduced in 1956 in the United Kingdom to help train drivers observe and obey signals. It was based on a 1930 system developed by Alfred Ernest Hudd and marketed as the "Strowger-Hudd" system...
, the BritishUnited KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
signalling system (induction based) - TPWS, the warning system which supplements AWS
- ETCSEuropean Train Control SystemThe European Train Control System is a signalling, control andtrain protection system designed to replace the many incompatible safety systems currently used by European railways, especially on high-speed lines.- History :...
, the European Train Control System is a signalling and control system designed to replace the 14 incompatible safety systems currently used by European railways, especially on high-speed lines. - Integra-SignumIntegra-SignumIntegra-Signum is a Swiss train protection system introduced in 1933. Originally it was called Signum; the name Integra was added later. It transmits data inductively and is simple, robust and reliable also in snow.-How it works:...
the Swiss induction based signalling system.