Kavach (train protection system)
Kavach () is an automatic train protection (ATP) system indigenously developed by Indian Railways through Research Designs & Standards Organisation (RDSO). Initial development of Kavach started in 2012 under the name Train Collision Avoidance System (TCAS) and completed development in 2022. Kavach has been certified for compliance with safety integrity level 4 (SIL-4) operations. Kavach has been promoted as being the cheapest ATP system available in the world, costing roughly 50 lakh (five million) rupees per kilometre to operate compared to about two crore (20 million) rupees worldwide. The Union budget of India for the FY 2022-23 allocated funds for the rapid implementation of Kavach across 2,000 km of track, as well as sanctioning its implementation along 34,000 km track of the Golden Quadrilateral rail route, which is to be implemented by 2027-2028. Development

Origins 
During the early twenty-first century, Indian Railways became increasing interested at deploying automatic train protection (ATP) upon its existing mixed-traffic routes. An extensive evaluation of internationally available systems, such as the European Train Control System (ETCS), was conducted; it was ultimately concluded that there was no existing off the shelf ATP system that fulfilled its requirements. These requirements included the prevention of instances of signal passed at danger (SPAD), collision prevention, in-cab signalling, automatic whistling at level crossings, intelligent real-time health monitoring, and to facilitate substantial speed and capacity increases for both freight and passenger operations. A further key target to be pursued in part via the addition of ATP is the Indian Railways’ ambition to achieve a zero accident rate. Instead of procuring and installing an existing system, a project to domestically develop a suitable ATP system was pursued by Indian Railways instead. During 2011, work on what would become Kavach commenced; this project was originally titled as the Train Collision Avoidance System (TCAS). An early proof of concept was produced in 2012 while a development order for the design and manufacture of the system was issued during the following year. An explicit requirement was for it to be interoperable between multiple vendors. During 2014, the deployment of an initial trial system along a 265 km section of line commenced, upon with the first real world evaluations of Kavach were performed. Testing
Between 2015 and 2017, field trials of the system were carried out. Data and experiences gathered from these trials were used to refine the specification, which was formalised in March 2017. Final approval of the system was issued in 2019, permitting the training of railway employees on Kavach ahead of the formal rollout and commencement of operations. Kavach has been subjected to tests performed by an independent external assessor to validate its performance. The onboard equipment component has demonstrated a mean time between failures of 40,000 hours, and reportedly achieved an overall availability of 99.9 percent during testing. Accordingly, it has been certified for compliance with safety integrity level 4 (SIL-4) operations. On 4 March 2022, a high profile live demonstration of Kavach was conducted between Gullaguda and Chitgidda railway stations in Secunderabad Division. Indian Railway minister Ashwini Vaishnaw was travelling in one locomotive travelling in one direction, while Vinay Kumar Tripathi, chairman and CEO of Indian Railway was travelling in another locomotive on the opposite direction on the same track while Kavach was operational. It successfully  detected that both locomotives were on the same track and responded by automatically applying the brakes on both trains, thus averting an impending collision. Description
The system consists of a three core elements, these being trackside (radio-frequency identification (RFID) tags between the running rails), onboard locomotives (RFID readers, computer, brake interface equipment, and UHF and GSM radio links), and radio infrastructure (towers and modems). Multiple forms of data input are used to determine criteria such as location and direction; an odometer onboard each train measures these data points, being periodically reset when passing over an RFID tag, while time data is verified via a GPS satellite link. Drivers are presented with information primarily via a screen interface; an event recorder is present to retain a record of all interactions. Specific data exchanged includes speed, direction, location, and identifiers (individual to train and tracks). Some of the track-fitted RFID tags are used for additional purposes, such as to communicate an upcoming signal, level crossing , and that the train is leaving an area covered by Kavach. All messaging between trains and the trackside infrastructure is handled via radio communications. The radio infrastructure used by Kavach is installed alongside the tracks, often being aligned with lineside signalling equipment and railway stations, being deployed at a regular interval of 1 km. Kavach communicated with relevant signalling control stations, being interfaced with the interlocking to retrieve information on signal aspects, permitted speeds, movement authority, and any restrictions; these criteria are continuously and automatically checked against each train’s reported criteria and presented to the driver. The GSM radio link is also used to send data to a network management system to log all train movements, inputs, and fault messages; where appropriate, fault teams are automatically contacted to address issues that arise in real time. The initial implementation of the system harnesses UHF radio frequencies while the development of 4G LTE based version of Kavach is reportedly underway as of 2022. Kavach incorporates several key characteristics of the European Train Control System (ETCS) as well as the Indian Anti-collision device; however, it is a considerably cheaper system in comparison to ETCS. Furthermore, unlike ETCS, Kavach is not intended to function as a replacement to traditional lineside signalling. While ETCS requires a centralised trackside infrastructure, Kavach is distributed, permitting piece-meal deployments. Kavach is also not intended for have interoperability with other country’s systems, unlike ETCS’s rigorous cross-border interoperability requirements. To use Kavach, each train must be either built with compatible apparatus or to undergo a retrofit of such apparatus. Various operating and engineering departments across India Railways are expected to facilitate such retrofits on a mass scale throughout the 2020s. While not presently intended, it is believe that modifications could be made to Kavach to support automatic train operation (ATO) as well as its intended ATP function. As of 2023, work is underway to integrate Kavach with traffic management systems, electronic interlockings, and new radio communication technologies. Operationally, in a circumstance where a locomotive has gone through a stop signal (known as a signal passed at danger or SPAD), which is the leading cause of train collisions, Kavach automatically alerts its driver to the dangerous situation. Furthermore, the system is able to apply the locomotive’s brakes and automatically bring such a train to a halt when it is aware that another train is on the same line within a prescribed distance. Kavach continuously monitors train movement and transmits signals ahead to the locomotives; unlike traditional observation, this functionality is not impacted by visual obstructions, such as terrain, or adverse weather conditions like fog. Drivers are still expected to obey all trackside signals as if Kavach is not present. Deployment 
Kavach to be implemented on 65 locomotives, 1,445  km route and 134 stations in South Central Railway zone, while implementation on 1200 km is underway as of April 2022. Upgrades to Kavach will be made so that it can handle trains at speeds of up to 160 kmph prior to it being implemented across 3000 km of track, including the majority of the New Delhi–Mumbai main line and Howrah–Delhi main line. as part of the ‘’Mission Raftar’’ project being undertaken by Indian Railways. The Union budget of India for the FY 2022-23 allocated fund for the rapidly implementation of Kavach along 2000 km of track, while also sanctioning its later implementation across 34,000 km track of Golden Quadrilateral rail route. Indian commentators have claimed that had Kavach been deployed at the site of the 2023 Odisha train collision that the system would have prevented the accident from occurring. Newly built WAG-9HH locomotives will be equipped with Kavach apparatus; the system will be useable even at these locomotives’ maximum design speed of 120 kmph. By June 2023, two percent of all Indian trains had been outfitted with Kavach apparatus. References

External links
 Handbook on Train Collision Avoidance System (TCAS) - An Indigenous ATP System 
 Kavach - Ministry of Railways

Train protection systems
Indian Railways