The graphical representation of the expert system in the form of a valuation-based system enables an easy use of variables and their relationships, and consequently simplifies their use for analysts and non-experts. This chapter begins with an overview of the Performance shaping factor based human Reliability assEssment using vaLUation-baseD systEms (PRELUDE) methodology. PRELUDE is a human reliability analysis methodology. The chapter introduces a case study where the suggested methodology is used for the retrospective analysis of a real railway accident scenario. The complete methodology is made up of a qualitative section that considers human factors specifically related to one type of field or application, as well as a quantitative section that builds an expert system, formalizing expert knowledge and providing a frame for formal decision-making. Human reliability analysis provides decision-making skills by presenting quantitative results as probability intervals – the estimation of the probability of human failure error.