# System for the Acquisition and Analysis of Maintenance Data of Railway Traffic Control Devices
## 4 Decision Support Method for Operational Decisions of Railway Traffic Control Devices  
The adopted maintenance strategy for railway traffic control devices is a key element that influences the course of the management process and, consequently, the exploitation process itself. Since the renewal of devices can be carried out according to various maintenance strategies, it is extremely important to determine how to properly select the appropriate renewal method. Strategies regarding maintenance (what and when?) for railway traffic control devices (whose technical condition is restorable) should be formulated based on the reliability and durability characteristics of the individual components of the device, taking into account reliability and technical criteria (Figure 2) [16]. Among the various maintenance strategies for railway traffic control systems, the most commonly used is the service-life-based strategy (also known as the main overhaul cycle principle). This approach involves performing maintenance and repair tasks at predefined intervals, regardless of the actual wear of components and subsystems [17; 18]. A significantly more advantageous method is the technical condition-based strategy [19; 20; 21]. The renewal strategy based on technical condition involves periodic or continuous monitoring of the technical condition of railway traffic control devices (referred to as a monitoring-based strategy) and developing diagnostic information from this monitoring to support rational decision-making [11; 22; 23]. In this strategy, fixed service intervals are not defined. Decisions regarding maintenance are made based on available diagnostic information. The operation is thus based on the current condition of the traffic control device [24]. The drawback of this strategy lies in the relatively high costs of designing and building diagnostic subsystems with high reliability, as well as information and decision-support systems [25; 26]. The condition-based renewal strategy for railway traffic control systems is based on the forecast of the system's remaining operating hours until failure. Predicting this remaining lifespan is one of the most critical exploitation challenges due to the continuous variation in the system's technical parameters, driven by variable loads during use--especially under harsh environmental conditions [27]. The problem of predicting the number of operating hours until failure can be illustrated using the classical wear curve (2), which includes the following phases:  
* Break-in wear period--initial phase where components are adjusting. * Stable (normal) wear period--the main operational phase with consistent wear. * Accelerated (catastrophic) wear period--aging and degradation of components and elements. The wear and tear of the railway infrastructure, on the existence of which the correct operation of the railway traffic control system depends, may vary from zero to a critical wear value \(z^{*}\), after which, at time \(t^{*}\), a failure occurs. The critical value \(z^{*}\) and therefore also the instant \(t^{*}\) depends not only on the type of wear but also on the properties of the dependency systems present in the devices and the external conditions or disturbances implying the operation of these systems. It is obvious that the time \(t^{*}\), after which the failure occurs, is a random realization of the time of correct operation, which is a random variable with the corresponding distribution \(F_{1}(t)\). Assuming a priori the required value of the confidence level \(\beta\), it is possible to estimate the resource of operating hours \(t^{*}\) of the selected components of the railway traffic control systems using the following relation:  
\[F_{1}(t^{*})=\beta=\int\limits_{0}^{t^{*}}f_{1}(t)dt \tag{1}\]  
Figure 2: Selection of maintenance strategy for railway traffic control devices.