Risk assessment in railroad signaling: experience gained and lessons learned

A generic framework for risk analysis is presented, comprising the following tasks: system definition, hazard identification, definition of risk tolerability criteria, consequence and loss analysis, and risk assessment. The object of this approach is to derive qualitative and quantitative safety integrity requirements for technological systems. The framework is holistic and covers technological as well as human and operational factors. The framework is compared to other approaches. Three different railroad signaling case studies, that use the same process, but under different circumstances, are presented. The lessons learned from these case studies, which, like the process itself have applications beyond railroad signaling, are reported and discussed.