Electronic signalling systems as a part of conventional tracks modernisation

Within the context of railway lines modernization and ETCS building on Slovak railways, interlocking and track blocking systems are being modernized too. Old control systems based on mechanical or relay logic are replaced by electronic systems. Safety of electronic systems is based on different principles in comparison with relay or mechanical systems. It means that it is necessary to change approach to safety requirements definition and safety evaluation of electronic systems. Due to requirements for high safety integrity level (SIL) of a signalling system, it is impossible to prove its safety by tests only, but there must be appropriate theoretical methods for quantitative safety analysis applied. Safety related functions of interlocking system and the associated tolerable hazard rate (THR) are defined on the base of risk analysis.