Quantification of the safety and security of the complete functionally isolated railway systems

There is no doubt, that railway has to be safe. More precisely safety, security and cybersecurity have to be ensured. However, it was always a question how safe railway system has to be to be accepted as safe. Paper starts from ‘failsafe’ principle and ‘safety integrity levels’ which were introduced respectively for traditional and electronic signalling equipment. It describes then three most representative explicit risk estimation methods, which are used for assessing influence on safety caused by significant changes being introduced or planned to be introduced in the railway system (not only for signalling). It also presents how overall railway related risk is calculated for individual countries in the European Union. All that however, does not support safety, security and cybersecurity related decisions, which have to be taken in case of planning, constructing and reconstructing of modern railway systems utilising control command and other communication based systems supporting safety and security. Paper proposes matrix based approach defined by author on the basis of the ‘communication based train control and management enhanced safety and security impact reference model’ (e-SSIRM model), which was defined by author and presented during Transport Systems Telematics TST’2018 conference.