Functional Safety of Railway Signaling Systems: Performance Requirements and Evaluation Methods

Abstract

Signaling is fundamental to the safe operation of the railway, ensuring that trains are spaced safely apart and conflicting movements are avoided. Railway signals are `traffic light' devices, which tell a train driver if it's safe to proceed along the track. A railway signaling system consists of several complex subsystems, e.g. trackside- and onboard signaling systems, which cooperate to ensure the safe operation of railway traffic. The failure of signaling system will weaken both capacity and safety of the railway. It is therefore important to keep the railway signaling system complying with the defined performance requirements. The purpose of this study starts with the summarization of railway RAMS, focusing on railway signaling systems. The tolerable hazard rate (THR) which is an indicator of signaling system performance in EN 50129 (2018) has been compared with the similar indictor PFH (probability of failure per hour) for safety-related systems in IEC 61508 (2010). Based on the commonly used methods for safety-related systems in IEC 61508 (2010), several reliability modeling and analysis methods have been listed and reviewed for the specific system. This paper aims to provide clues for the engineers and analysts in the performance evaluation for the railway signaling system.