The functional safety calculation of a real interlocking system in Turkey

In this paper the safety integrity level (SIL) of a railway station in Turkey is considered. The paper is one of the results of a project which is sponsored by the Turkish State Railways (TCDD) where an xo03 architecture is required. The calculations of the failure rates of railway components' are carried out not only for the implemented 2003 interlocking system architecture but also for 1003 and 3003 architectures. Moreover the undetected dangerous failures of the interlocking system such as regulation, signalling, track circuit and point failures are given in terms of interlocking system components' failure types and algorithm failures. This relationship is shown with the help of Fault Tree Analysis (FTA). Finally the safety integrity level and mean time to failure (MTTF) are calculated with the help of the Markov Graph.