This communication addresses the “Safety, Reliability & Quality Assurance” topic. It is located very clearly in the field of land guided transport (interurban train, HST, subway, tram). The land guided transport systems are mainly composed of four material classes: the infrastructure, the rolling stock, the energy supply chain and all of the signaling and control systems. This paper deals with different methodologies used to analyze and demonstrate the safety of a control system, but it more especially deals with the Preliminary Hazard Analysis (PHA), which is usually used first and very early in the Safety Management System.