# A Formal Model of the Exploitation Process for Railway Signalling Devices
## 2 Railway Signalling Systems Operating  
Railway traffic control is an area of technical science dealing with issues related to the movement of rolling stock in accordance with safety rules and ensuring the smooth running of rail vehicles. The organisation of railway traffic control is carried out using railway signalling systems, consisting of control systems and external devices. When organising the movement of rail vehicles, a fundamental aspect is to systematise the actions and activities performed, which we call the traffic control process. This process consists of acquiring signals from external devices, which are sent as commands to executive devices. Trackside railway signalling devices include the following elements [9; 29; 30]:  
* Railway signals;
* Track occupation control systems;
* Interfaces between railway station and line devices and level crossing protection devices;
* Switches and railway drives.  
The first methods of controlling railway traffic were based mainly on manual operations carried out by traffic dispatchers manually adjusting railway switches. In subsequent years, mechanisms such as switch levers were introduced, which allowed switches to be controlled from the railway signal control room. With the development of electronics as well as information and communication technologies, railway signalling devices began to rely on computers and automation. Nowadays, modern railway signalling systems make it possible to monitor and control train traffic while ensuring the highest level of safety [31].  
The concept of the system is generally understood as a collection of interrelated elements that form a functional whole. The system's elements must be selected in such a way that there is a relationship between them so that they will fulfil the functions assigned to them. A hierarchical view of the objects that make up the railway signalling system and illustrating their complexity is shown in Figure 3.  
Due to the functions performed in the control process, signalling systems are divided as follows [9; 10; 31; 32]:  
* At train stations, which are responsible for the realisation of railway traffic control functions within the traffic station: at interchange, branch or siding stations, and in the station setting and control districts;
* On railway lines that are responsible for implementing the function of controlling railway traffic on railway routes; an example of railway linear devices is automatic block signalling;  
Figure 2: Example of exploitation of the railway signalling devices in spatial terms, where (1)—set of device usage positions (e.g., onboard vehicle systems, interlocking systems, and level crossing systems); (2)—set of device service positions (e.g., detection systems and railway maintenance services).  
* On board (in the train drivers' cabs), which are responsible for the implementation of the control function of the rail vehicle in a fully or partially automatic way, using wireless transmission to communicate with external devices;
* On railway crossings responsible for carrying out the safety function of the single-level crossings of road and railway lines.