Railway signalling is the fundamental safety system that regulates train movements. It is a vital safety component of the railway’s train control function. It is responsible for setting up non-conflicting and safe routes for trains, defining movement limitations, and communicating instructions or directives to train drivers once instructed by a signaller or an automation system. A train protection system consists of two major components: train detection (knowing where the train is) and movement authority (telling the train how far it can travel). These two components are used by the train protection system to ensure the safe functioning of a train.
Traditionally, signalling systems in Europe, Britain, and many other nations relied on train drivers reacting to indications displayed by line-side semaphore or colour light signals and adjusting the train’s speed accordingly. Over the 150-year history of railway signalling, failures by drivers to respond to directives communicated by signal elements of any type have resulted in a number of accidents, some resulting in a substantial number of fatalities. Various types of driver warning devices and signal command enforcement systems have been developed in response to the ongoing need to mitigate risks caused by train drivers failing to comply with signal commands. These are referred to as Train Protection Systems. Automatic Train Protection (ATP) systems are those that continuously monitor actual train speed and enforce conformity to a specified speed pattern.
Types of Train Protection Systems
The goal and objective of almost all train protection systems is to reduce or avoid and eliminate the likelihood of driver mistakes resulting in a train movement-related accident by failing to heed a visibly displayed line-side or in-cab signal instruction. Train protection on main line railways began with introducing and setting up warning systems and progressed to the execution and enforcement of the directives issued by these systems.
Originally, warning systems notified and warned the drivers when they approached an unfavourable or restrictive line-side signal aspect and required the drivers to recognise and acknowledge the indication issued by the warning systems. Otherwise, the systems would apply the brakes after a short delay or brief period of inactivity. Later advancements by national railway administrations included varied levels of speed limitation and enforcement. In addition, certain systems have been expanded to accommodate speed limits for permanent or temporary speed restrictions. Combinations of permanent magnets and electro-magnets, inductive polarity-changing responders, coded beacons, and simple coded track circuits are among the technologies used in such warning and train control systems.
Recently, fully Automatic Train Protection (ATP) systems have been designed and developed to enforce speed limits and movement authorities at the complete range of restrictive signals, including permanent and temporary line speed limitations, with and without line-side signals. Driving is still done manually, although speed limits are strictly enforced most of the times. However, degraded modes typically include low-speed driving on sight.
Two-Channel Safety Systems
Many older railway safety systems were built with the statistical nature of driver and equipment failure in mind. By carefully designing the systems, it is fair to presume that driver mistakes and equipment failures will not occur concurrently. A significant feature of such systems is that the driver is not informed whether the train protection system is operational or not, and is thus encouraged to drive with full responsibility for the train’s movement. The technical subsystem will only interfere if the driver attempts to pass a signal or drives too quickly. TPWS, train controls, and Indusi are typical instances of this type of setup.
Automatic Train Protection Systems
ATP systems are generally divided into two types: intermittent and continuous. Intermittent systems use electronic beacons (inductive or radio frequency) or brief electrical loops placed within a four-foot radius. These short-range gadgets are commonly known as ‘balises’ (from the French word for ‘marker’). Continuous systems feature a permanently active data transmission and monitoring system, either through electrical inductive coupling using track loops or coded track circuits or by means of radio communication of limit of movement authorities.
Fully working ATP systems were originally installed on metros in the late 1960s and are now widely used on such systems around the world. The majority of metro applications feature continuous systems in tandem with autonomous train operations. ATP was also introduced on the Japanese Shinkansen high-speed route in 1964, and it has since then been used and introduced in various forms on a number of main-line railways, frequently in conjunction with high-speed train operations.
The fundamental defining premise of ATP is that train speed is measured and monitored in context to currently approved speed limitations. The speed may be regulated by the line profile or signal indication, i.e., the requirement to safeguard other trains’ routes and track-related limits. If the permitted speed is exceeded, the brakes are applied until the speed is reduced to the acceptable limit or the train is halted. Most ATP systems rely on typical block signalling, which can be relatively short. A fixed dataset describes each block’s location, length, gradient, and maximum civil speed limits. Each block will also have a variable data set derived and generated from the signal aspects ahead and their impact on the resulting speed limits for that block and the blocks following it.
On the approach to a restricted signal, the speed limit creates a gradually decreasing curve that follows the braking profile required to reach the target speed at the signal. If the signal indicates a stop, the desired speed will be zero. The on-board monitoring technology will constantly compare the train speed to the curve required to attain the desired speed and shall initiate and issue a warning, which is usually both audible and can be seen. If no action is taken, the system will apply the brakes.
Automatic Warning System (AWS)
Following the death of 112 people in a Signal Passed at Danger (SPAD) accident in poor visibility at Harrow and Wealdstone in 1952, British Railways decided to deploy their Automatic Warning System (AWS) across the entire network to provide train drivers with an in-cab warning of the indication of the next signal. This was a non-contact variant of a system which was originally used and deployed on the Great Western Railway. After a lengthy development and certification process, widespread installation began in 1956. This system is still operational today.
The AWS ramp is installed between the rails so that a detector on the train may detect it and send a signal. As a result, the ramp alerts the driver about the signal’s state. The French railways use a similar system known as ‘the Crocodile,’ and the Germans’ Indusi.’
The AWS ramp has two magnets, one permanent and one electro-magnet, coupled to the signal, which provides an indication of the aspect.
The ramp is placed between the rails so that the indication data can be received by a detector on the train. The ramps between the rails are often visible to the more observant passenger on a station platform. The AWS ramp has two magnets, one permanent and one electro-magnet, coupled to the signal, which provides an indication of the aspect. The ramp is placed between the rails so that the indication data can be received by a detector on the train. The ramps between the rails are often visible to the more observant passenger on a station platform.
Driver’s Reminder Appliance (DRA)
The Driver’s Reminder Appliance (DRA) was launched in 1998 to help with SPAD prevention, especially at station launching signals. In the strictest definition of the phrase, it is not a train protection device. The usefulness of this technique is debatable because it may be ‘automated’ as part of the train starting route and sequence.
Train Protection and Warning System (TPWS)
To counter the limitations of AWS, the British railway system designed and developed an enforcement system known as TPWS (Train Protection and Warning System). It has been developed to enforce conformity and observance to restricted speed regulations and signal stops by prompting full brake application when overspeed is detected, or a train drives past a stop signal. TPWS was tested on a segment of the Thameslink line in 1996 before being implemented over the majority of the UK network between March 2000 and December 2003.
The theory behind TPWS is that if a train approaches a stop signal with a danger aspect at too high speed to stop at the signal, it will be compelled to stop regardless of the driver’s action or inaction.
Radio Electronic Token Block (RETB)
In some rural parts of the United Kingdom, where long portions of single-line require token block operation, a centralised control system based on current computer technology was implemented. It is referred to as a Radio Electronic Token Block (RETB).
A computer system is provided to the signaller, which assigns the coded tokens to each section and prohibits more than one token from being issued for an occupied section. It also accepts the tokens that each train sends back as it reaches the end of the single-line portion.
This system has been superseded by ERTMS test installation on designated routes. It was decommissioned in October 2012. RETB is still used on some of Scotland’s most isolated routes.
PZB Indusi (Israel, Serbia and others)
PZB or Indusi is a train protection and intermittent cab signalling system used in Germany, Austria, Slovenia, Croatia, Romania, Israel, Serbia, on two lines in Hungary, the Tyne and Wear Metro in the United Kingdom, and formerly on the Trillium Line in Canada. The historical and ancient short-term Indusi was taken from German Induktive Zugsicherung (inductive train protection) and was developed in Germany. Later, different versions of the system were named PZB, which stands for Intermittent Automatic Train Running Control, underlining that the PZB/Indusi system is part of a family of intermittent train control systems. Later, PZB systems, which rely on a train computer, give stronger enforcement. Germany, Indonesia, Austria, Romania, Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, and Israel all use the system.
In Germany, the system is used for lines with maximum speeds up to 160 km/hr, and in Austria, used for lines with top speeds up to 120 km/hr. It incorporates speed supervision to a braking curve in the more recent computerised version. It is not fully developed to meet essential standards.
Continuous Automatic Warning System (CAWS, Ireland)
Some sections of the Republic of Ireland’s mainline routes, as well as the entire line between Dublin and Cork, are equipped with coded track circuits that provide in-cab signal indicators. The system is referred to as the CAWS (Continuous Automatic Warning System). When there is a change to a more restrictive aspect, the in-cab signal communications repeat line-side indications and are accompanied by an alarm siren. The driver must acknowledge the alarm within 8 seconds to avoid an irreversible automated emergency brake application. After emergency brakes being activated, there is a two-minute delay before the system can be reset and the train can proceed. However, the technology does not seem to be vital and important because the driver may recognise a restriction signal warning and let the train proceed without slowing down.
Train Stops (Trip-Cocks, London Underground)
On most of its lines, LUL (London Underground Limited) uses mechanical train stops in conjunction with fixed blocks and individually computed signal overlaps to offer train protection. The system avoids crashes by giving an individually computed full-speed braking distance beyond each stop signal, ensuring that a train ‘tripped’ by the train stop comes to a stop without violating a restricted block. Trains are limited to 10 mph after being tripped for three minutes to enforce driving on sight at a cautious speed. This is referred to as SCAT (Speed Control After Tripping).
ALSN (Russian Federation/Ex-Soviet Union States)
ALSN, which stands for Continuous Automatic Train Signalling in Latin, is a train control system that is widely used on the main lines of the ex-Soviet states (Russian Federation, Ukraine, Belarus, Latvia, Lithuania, and Estonia). Similar to the Italian RS4 Codici and American Pulse Code Cab Signalling, it involves modulated pulses injected into rails. On high-speed lines, the ALS-EN (-H) variation is used, which takes advantage and utilises a twofold phase difference modulation of the carrier wave.
CBTC (Multi Nation)
Communications-based train control (CBTC) is a railway signalling system that uses telecommunications between the train and track equipment to manage traffic and control infrastructure. CBTC enables more precise tracking of trains than standard signalling systems. This improves the safety and efficiency of railway traffic management. Metros (and other train systems) can minimise travel times while preserving or even improving safety using this system.
According to the IEEE 1474 standard, a CBTC system is a ‘continuous, automatic train control system using high-resolution train location determination independent of track circuits; continuous, high-capacity, bidirectional train-to-wayside data communications; 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.’ Brazil, the United States of America, Canada, Singapore, Spain, Gabon, Hong Kong, Indonesia, Denmark, the United Kingdom, and India all employ this train security system.
Fully Automatic Train Protection Systems
BR-ATP (Two Versions)
In the early 1990s, British Rail trialled two Automatic Train Protection systems with full-speed supervision, one on the Great Western Main Line (by ACEC Belgium – now Alstom) and one on Chiltern Railways (Selcab by Alcatel) between Marylebone and Aynho Junction. Both are intermittent systems with infill loops that allow for the early release of brake demand and its supervision when signal aspects change. Despite the fact that the systems were presented as an experiment, they are still working.
Tilt Authorisation and Speed Supervision (TASS)
The primary goal of TASS is to keep trains from tilting when clearances between trains or between trains and infrastructure are restricted. In addition, depending on whether or not the tilting mechanism is active, TASS imposes line speed limits for equipped trains. The TASS system, which is designed to European Rail Traffic Management System (ERTMS) demand and specifications, is installed on the Virgin Pendolino Class 390 and Super Voyager Class 221 fleets.
Docklands Light Railway
The Docklands Light Railway (DLR) features Seltrac, an ATP system with complete continuous speed supervision supplied by Alcatel of Canada and now part of the Thales empire. Seltrac is a transmission-based ATC system combining automatic train protection (ATP) and automatic train operation (ATO) technologies. This system is only suitable for metro-type operations with a high service frequency.
Transmission Voie-Machine 430 (TVM 430)
TVM is a safe, dependable, and well-proven system, but it is expensive to install and maintain because it is based on track circuit technology.
The Channel Tunnel Rail Link (CTRL) Phase I has been equipped with the French TVM 430 continuous transmission ATP system. This is the same technique that is used in the Channel Tunnel and will be used in Phase 2. TVM 430 is a cab signalling system used on more current TGV lines that was developed by the French company CSEE from the preceding TVM 300 system.
Automatische Trein Beïnvloeding (ATB NG, Netherlands)
The ATB NG system was introduced to the NS (Netherlands) in the mid-1990s in order to implement full ATP and replace the costly and time-consuming coded track circuits. It comprises track-mounted balise and onboard computing hardware. The original ATB EG trackside equipment is fully compatible with the ATB NG onboard equipment.
Ebicab (Sweden, Norway and others)
In Sweden, Norway, Portugal, and Bulgaria, Ebicab is the standard ATP system. Despite variations in signalling systems and rules, identical software in Sweden and Norway enables cross-border train movement and operations without changing drivers or locomotives. The systems in Portugal and Bulgaria use different software. The system is available in two versions: Ebicab 700 and Ebicab 900, both of which provide identical safety functions.
Contrôle de Vitesse par Balises, abbreviated KVB, is a train protection mechanism used in France and at London’s St. Pancras International Station. It monitors and regulates the speed of moving trains. Based on the signals received from the balises, the onboard computer generates two-speed thresholds. If the train exceeds the speed limit, passing the first speed threshold, an audible alarm begins, and the control panel instructs the driver to lower the train speed as soon as possible. If the second speed threshold is exceeded, the KVB automatically applies the train’s emergency brakes.
Except for locomotives that operate in conjunction with other locomotives, every locomotive unit on the French national railway network must be fitted with this technology. More than 5,000 engines are equipped, including foreign locomotives that move within France. This system is installed on all TGV routes that use conventional rail lines. ETCS, a European railway control system, will replace this and many other different systems in the European Union’s various member states. KVB is comparable to ETCS Level 1 Limited Supervision because it provides beacon-based speed regulation with no driver indication.
TBL 2 (Belgium)
TBL 2 is used on all Belgian lines where the allowable line speed exceeds 160 km/h. TBL 2 is a cab signal system similar to the UK GWML ATP system that uses and features a powered balise in the form of a steel loop with additional, long, and extended infill cable loops to provide early warning of signal indication changes. TBL 2 is sensitive to direction. This capability is achieved through mounting the balises between the rails at a slight offset from the centre.
LZB (Germany, Australia, Spain)
Linienzugbeeinflussung (LZB) is a cab signalling and train protection system that is used on certain German and Austrian railway lines, as well as the AVE and several commuter rail lines in Spain. The system was mandatory in Germany and Spain, where trains were allowed to exceed speeds of 160 km/hr. It is also used to boost capacity on some slower railway and urban rapid transit lines.
LZB has been planned to be phased down in favour of the European Train Control System (ETCS) between 2023 and 2030. The European Union Agency for Railways (ERA) refers to it as a Class B train protection system in National Train Control (NTC). Most driving cars must replace traditional control logic with ETCS Onboard Units (OBU) with a standardised Driver Machine Interface (DMI). Because high-performance trains are frequently not discarded or reused on second-order lines, special Specific Transmission Modules (STM) for LZB have been developed to help further and support the installation of LZB.
The Chinese Train Control System (CTCS) is a train control system used on Chinese railway lines. CTCS is a train control system similar to the European Train Control System (ETCS). It is divided into two subsystems: the ground subsystem and the onboard subsystem. Balise, track circuit, radio communication network (GSM-R), and Radio Block Centre (RBC) may be used in the ground subsystem. The onboard subsystem consists of the onboard computer and the communication module. CTCS is divided into five levels (Levels 0 to 5). Levels 2–4 are backwards compatible with earlier ones.
PTC (ITCS, USA)
Positive train control (PTC) is a type of automatic train protection system that is widely used in the United States. PTC is used on the majority of the United States’ national rail network lines. These systems usually serve the purpose to ensure that trains move safely and to stop them if they do not.
Negative train control is a simplified form of train traffic governance in which trains must halt when issued a stop order and can move otherwise. Indusi is an example of negative train control. Positive train control, on the other hand, restricts and limits train movement to a stated permit; movement is terminated upon invalidation. A PTC-enabled train receives a movement authority with information about its location and where it is safe to travel. According to the American Association of Railways (AAR), the nation’s leading freight railways has been using PTC on 83.2 percent of the mandated route miles as of 2019. The ITCS (Incremental Train Control System) is a positive train control application.
The modern Russian train control systems are known as KLUB. The KLUB-U systems can handle high-speed tracks as the Velaro RUS (Sapsan). The KLUB-P type is limited to cab signalling and lacks track safety equipment. Only category II trains (including special cars and shunting actions) use it. The KLUB-UP variation is permitted for category-I trains (including passenger transport), where it substitutes the ALSN cab signalling.
KLUB-U is the most prevalent version, with U indicating for unified. KLUB-U in-cab signalling systems can decode trackside ALSN codes (Continuous Automatic Train Signallisation), which are akin to RS4 Codici (Pulse Code Cab Signalling in the United States). The KLUB-U systems in the latest ABTC-M block control decode signals through TETRA digital radio, including remote activation of a train stop. A satellite navigation system (GPS or GLONASS) determines the train’s position in certain areas. The ITARUS-ATC connects the KLUB-U in-cab system to the ERMTS Level 2 RBC block control via GSM-R digital radio.
European Rail Traffic Management System
The European Rail Traffic Management System (ERTMS) is an essential component and fundamental building block in the TEN’s interoperability implementation. The European Train Control System (ETCS) handles ERTMS’s physical signalling and train control section of the ERTMS. ERTMS has been developed and established to assist with the execution of two European ‘interoperability’ directives: 96/48/EC for high-speed lines and 2001/16/EC for conventional services. The European Rail Traffic Management System (ERTMS) includes the requirements for European interoperability.
The ETCS design has three significantly different ATP functioning levels that enable for a stepwise transition from traditional line-side signalling to a full moving block concept with certain incremental modifications. Throughout a train’s journey, the levels give complete speed supervision and varied amounts of in-cab information, and can be summarised as follows:
- Level 1 – No Infill (System A)Level 1 – With Infill (System B)
- Level 2
- Level 3
Global System for Mobile Communications (GSM-R)
GSM-R or satellite-based train control systems require some ground-based validation (passive Eurobalises) and train detection through track circuits most likely required for turnout locking and in complex junction areas. The installation of GSM-R as the data and speech carrier is required to implement ETCS Levels 2/3.
Conventional (Community) Railways
The ETCS technical specifications for conventional rail systems are yet to be released and made public. However, the equipment is expected to be identical to and compatible with that required for high-speed lines. This will allow trains to travel freely between ETCS-equipped high-speed lines and community railways without the need for dual system installation.
Kavach Automatic Train Protection System, India
Kavach is a train collision prevention system developed in India. This anti-collision technique reduces the likelihood of an error to one error in ten thousand years. Kavach technology is also known as the Train Collision Avoidance System (TCAS) or the Automatic Train Protection System (ATP) system. The primary objective is to eliminate all rail accidents. The technology has also received SIL4 certification, indicating that it can minimise errors to one in several hundred decades.
Kavach, designed and developed in collaboration with the Indian industry by the Research Design and Standards Organisation (RDSO), can assist locomotive pilots in avoiding Signal Passing At Danger (SPAD) and overspeeding. Additionally, it facilitates train operations in adverse weather situations such as heavy fog. The device promotes train speed management and minimises potential accidents by automatically deploying brakes when necessary.
Other popular warning and train control systems
This is a French-designed AWS system that is conceptually very similar to the UK AWS. The term is derived from the track-mounted equipment’s corrugated appearance. It is officially referred to and described as the Brosse Repetition Signal (BRS). BRS is installed on all main lines of SNCF, SNCB, and CFL. Crocodile basically is a vigilance system. Crocodile tends to be lesser protective than AWS since voltage absence cannot be detected. The device usually fails to provide the driver with any indication if the system becomes problematic or faulty. The crocodile system may now be considered obsolete and outdated.
ASFA is a popular cab signalling and train protection system in Spain. Intermittent track-to-train communication is based on magnetically coupled resonant circuits and can communicate nine different sets of data. A trackside resonant circuit is tuned to a frequency representing the signal aspect. The device is not fail-safe, but it does remind the driver of the signalling conditions and requires him to recognise limiting characteristics within 3 seconds. The driver is given a lamp and bell warnings.
Automatische Trein Beïnvloeding (ATB EG, Netherlands)
On Dutch railway lines, the ATB system is available in two basic configurations: ATB EG and ATB NG. The original continuous system is the ATB-EG, while the new intermittent system, ATB-NG, is suited for speeds up to 360 km/hr.
ATB EG is a fail-safe system that uses coded track circuits of traditional design and two variants of on-board equipment, ACEC (computerised) or GRS (electronic) and is deployed on the vast majority of ProRail (the new Dutch infrastructure authority) lines. Vehicle-mounted induction pickup coils suspended above the rails transmit data between coded track circuits and onboard equipments.
Transmission Balise Locomotive – (TBL, Belgium)
TBL is available in two versions: TBL1 and TBL2. TBL1 indicates the signal aspect in advance, followed by an emergency brake application and a train trip function for signals passed at risk. Data is delivered by track-mounted loops. Unlike most other balise systems, the TBL loops require an external power supply.
BACC-RS4 Codici /-SCMT (Italy)
BACC or BAcc (automatic block with codified currents) is a signalling block system used on 3 kV DC electrified railway lines in Italy. The track circuits that detect the presence of a train also provide coded signals to the trains for train protection and cab signalling. RS4 Codici, RS9 Codici, and SCMT are train protection systems that use BAcc.
BACC is used in two variants on the majority of RFI (Rete Ferroviaria Italiana) infrastructure, both of which operate in a similar fashion. Conventional coded track circuits operate at one of two carrier frequencies to handle two train classes that travel at speeds higher than 180 km/hr or lesser. Induction pickup coils suspended above the rails transmit data between coded track circuits and onboard equipments.
Train Protection and Warning Systems in various countries
|ACSES||United States of America|
|ALSN||Russian Federation, Belarus, Estonia, Latvia, Lithuania, Ukraine|
|ATC||Sweden, Denmark, Norway, Brazil, South Korea, Japan, Australia (Queensland), United Kingdom|
|ATCS||United States of America|
|ATP||United Kingdom, United States of America, Brazil, Australia (Queensland), Hong Kong, Indonesia, Ireland, Dominican Republic, Denmark|
|AWS||United Kingdom, Queensland, South Australia|
|BACC-RS4 Codici /-SCMT||Italy|
|CBTC||Brazil, United States of America, Canada, Singapore, Spain, Gabon, Hong Kong, Indonesia, Denmark, United Kingdom|
|EBICAB||Bulgaria, Finland, Norway, Portugal, Spain, Sweden|
|I-ETMS||United States of America|
|ITCS||United States of America|
|LZB||Germany, Austria, Spain|
|LS||Czech republic, Slovakia|
|LKJ 2000||China, Ethiopia|
|PZB Indusi||Germany, Indonesia, Austria, Romania, Slovenia, Croatia, Bosnia-Herzegovina, Serbia, Montenegro, Macedonia, Israel|
|SACEM||France, Hong Kong|
|TBL||Belgium, Hong Kong|
|TPWS||United Kingdom, Victoria|
|TVM||High speed lines in: France, Belgium, United Kingdom, Channel Tunnel, South Korea|
Metros and Light Railways
Although most metro systems around the world already have more or less advanced train protection systems available, and risks are generally low, the European Union is working to standardise a single European Urban ATP system for better train security and enhanced operations. Since most operators have their own standards, implementation is likely to be a long-term and extended objective. The benefits of unified metro train protection may appear limited at first glance, but they could result in significant cost savings in the long run.
High-Speed Line Requirements
In recognition of the difficulty in preventing driver perception overload, line-side signals are no longer considered suitable for trains travelling at speeds in excess of 125 miles per hour. Full ATP with cab signalling is expected to boost operating speeds to 140mph and above, and the deployment of ETCS-compatible equipment is expected to be an unambiguous approach to accomplish this. The current signalling systems need to be maintained for conventional trains and may be required for fall-back purposes, at least during the early years of operation of any stand-alone ETCS Level 2/3 system, until reliability and operational experience allow line-side signals to be removed.
When signalling renewals become essential, it will be a logical development for traditional railways to incorporate ATP using ETCS standards. Once the GSM-R network is built and developed and the omission of full line-side signalling has been approved, viable, and reasonable, this is expected to be demonstrated as a cost-effective alternative for renewals.
As per the analysis of various train protection systems around the world, it is possible to conclude that the majority of the systems require a positive action to issue a warning or restrictive data and that almost every signalling systems discussed are more or less used for continuous speed supervision and that all of them can be isolated in the cab and the train can be driven at normal speeds regardless of signal aspects. While the signalling technologies discussed above appear to give some protection against collisions and over-speed derailments, none seem to provide the complete and critical safety as provided by modern automatic train protection systems.
Given that the system is capable of recognising missing balises, TASS exhibits some of the behaviours of a legitimate ATP system. In the case of TPWS, the transmitters at a given location are linked to the signal in the rear so that in the event of TPWS failure at the next signal, this signal will show a red aspect. This is because passing trains are unable to notice track-mounted equipment failures. The indigenous Kavach train safety system, newly deployed by Indian Railways, is a SIL4 (Safety Integrity Level-4) certification technology, demonstrating that it can decrease errors to one in several hundred decades.
However, fully automatic railway protection systems have some drawbacks as well. First and foremost, it is crucial to approach the implementation of any new system from a life cycle perspective. Rapid technical change is not permitted in the railway industry. The high equipment cost and the requirement to design to tough specifications to guard against a severe operating environment necessitate a lengthy depreciation period before replacement. This limits the ability to adapt to technological progress and development. Shortages of skills will further limit the scope of change that can be handled through a life-cycle replacement task.
The benefits of deploying a fully ETCS-compliant ATP system may be difficult to sustain in many regions, with TPWS and TPWS+ train protection systems being deployed across most of the advanced and majority of the European rail networks. When maintenance is factored in, the situation becomes even more challenging and complicated. Infrastructure managers aim to reduce the amount of line-side or track-based hardware that needs to be maintained regularly. However, a balance needs to be established between the cost of providing complex technology and updating software with highly trained staff on one hand and ground-based hardware that requires regular but less expensive maintenance on the other. With modern, safe working practice regulations and the proliferation of electronic signalling systems and accompanying knowledge, this balance is likely to benefit ETCS systems.
However, the position regarding the provision of ETCS capabilities is obvious in the case of new trains – all new stock is provided with at least the physical capability of accommodating ETCS. It should also be a necessity that future rolling stock designs accommodate the needs and sensitivities of the new generation of electronic control and protection systems across all rail transport networks worldwide for increased and safe rail transit.