# Methodology for Studying the Reliability of Interlocking Devices in Bulgarian Railways
###### Abstract
In [12], a comprehensive solution utilising LoRa (long-range) communication modules, infrared (IR) sensors, and ultrasonic sensors to develop an advanced train tracking and railway gate safety system is proposed. An Enhanced Safety System for Unprotected Level Crossings is also examined in [13]--the proposed solution is a combination of devices based on advanced technologies and is designed to significantly reduce accidents at railway crossings. In [14], it is proposed to use the development of information technologies to support the labour safety system in the field of railway transport--implementation of risk management and quality management tools. To analyse the accidents and use the technology of such AI methods to enhance safety, the authors in [15] propose using unsupervised topic modelling to better understand the causes of extreme accidents. The use of the thematic machine learning method for systematic characterisation of on-site incidents to improve safety and risk management in stations is described and advanced analysis is provided. An AI-driven warning device to ensure the safety of railway track workers is proposed in [16]--a low-cost portable smart gadget detects the sounds of the approaching trains and provides a warning signal to track workers via a phone call. The introduction of the Artificial Intelligence in the railway operations is discussed in [17]--the paper presents an operation, administration, and maintenance (OAM) architecture that provides management services for both virtualized and physical railway functions. The important role of artificial intelligence technologies in the digitalization of the railway industry is also discussed in [18]. The paper considersInternet of Things and Digital twin technologies as key enablers for deployment of AI in the railway sector. A paper [19] proposes another application of artificial intelligence (AI) in the Intelligent Transport Systems (ITS)--an object detection (OD) and activity recognition (AR) model for railway lines is presented with the goal of reducing accidents, fatalities, and improving safety. One of the most significant components of the railway infrastructure are the interlocking devices and high requirements are placed on them for reliability in operation. The increasing rail traffic requires fast-response interlocking systems--in addition to rich functionality, such systems should be based on a single and simple safety principle that ensures high availability and safety at the same time [20]. The generic safety principles for designing a highly safe generic product for railway interlocking tasks are introduced, and the design of such a product based on a new microarchitecture concept is also shown. The important role of safety computer platforms in railway signalling systems is discussed in [21]--the TYJL-III computer interlocking system has been developed and implemented in China. It has been proven that such a safety computer platform with reasonable structure, comprehensive function, unified interface, and strong compatibility can play an important role in the process of comprehensive upgrading of railway signalling equipment. Another railway signal safety control platform based on the functions and safety requirements of the railway signal is designed in [22] and is also studied from three aspects: design principle, hardware structure, and software structure. A computer interlocking system is discussed as an example of this platform, ensuring real-time communication and data transmission reliability. The problems of building a unified information system for ensuring the reliability and safety of transport systems based on system analysis, risk management, process approach, and reliability theory are discussed in [23]. Software and hardware are proposed that increase the reliability and safety of work at the railway station.