# A Formal Model of the Exploitation Process for Railway Signalling Devices
## 1 Introduction  
Railway signalling systems are very important for ensuring railway traffic safety [1; 2; 3; 4; 5]. The estimated cost of rail accidents in Europe in 2022 was, respectively, millions of euros, corresponding to the cost of fatalities (2.592), the cost of serious injuries (270), material damage, the costs of delays, costs to the environment (868), and other costs (312) [6]. Proper traffic management provides the opportunity to minimise the risk of train collisions and accidents. Devices designed for controlling railway traffic often operate in harsh exploitation conditions and this can affect safety in railway transport [7; 8]. In turn, an increase in the safety of train movements causes increasing demands on the reliability of railway signalling devices. The use of complex railway signalling systems (technologically and functionally different) on railways creates the need to analyse and evaluate their operation and interaction and the forecasting of exploitation effects [9; 10; 11; 12; 13].  
Exploitation consists of the totality of all of the events, phenomena, and processes occurring in a given real-world facility from the moment its manufacture is completed to its decommissioning. It deals with the methods and ways of maintaining technical objects in such a condition that they can operate effectively, safely, and without harm to the environment. In the case of the maintenance and exploitation of railway signalling devices, it is important to refer to all of the activities to be carried out from their production onwards in order to keep them operational for as long as possible. These activities should lead to ensuring that these devices are as reliable as possible and that they are properly serviced [14; 15].  
Various processes take place during the exploitation phase of railway signalling devices, in particular, the use and wear and tear (ageing) of the devices and their components; diagnosis; forecasting of the signalling devices' states and operation; the processing, storage, and presentation of information; exploitation management, etc.  
During the usage of railway signalling devices, the physical and chemical properties of these devices and their components are altered, which causes, among other things, the devices to enter a non-usable state. The renewal of the exploitation potential and the restoration of the devices' usable states (technical readiness) of operability take place through the implementation of a servicing process (Figure 1) [11; 14; 15; 16; 17; 18; 19].  
In a complex approach, the exploitation of the signalling systems comprises a spatially shaped set of technical and organisational elements (Figure 2) controlling the railway traffic process for the safe and efficient transport of passengers and cargo, together with methods and means to ensure adequate technical readiness [20; 21]. Two basic states can be distinguished in the exploitation of the railway signalling system and its constituent equipment [21]:  
1. The state of usage determining its effects (and its components) on railway traffic processes using the organisational measures of the railway signalling system (the usage phase--Figure 1);
2. The state of renovation defining a set of technical methods and measures to maintain the technical readiness of railway signalling devices (the repair phase--Figure 1).  
The main goal of this paper's authors was to prepare a model for the exploitation of railway signalling systems that would allow for the prediction of the future exploitation states of these systems and their consequent service needs. As a result, a change in the signalling devices' exploitation strategies from a service-life-based strategy to a current-technical-state-based strategy while ensuring the required safety level should be made possible. A reduction in the maintenance costs of the above systems should also be expected [22; 23; 24; 25; 26; 27; 28].  
Figure 1: Diagram of the exploitation process for railway signalling devices.