This article presents a generic methodology for SIL allocation to railway rolling stock safety-related func-tions to solve the SIL concept application issues. This methodology is based on the flowchart formalism al-ready used in CSM European regulation. It starts with the use of quantitative safety requirements, particu-larly the Tolerable Hazard Rate (THR). The THR apportioning rules are applied. On the one hand, the rules are related to logical combinations of safety-related functions preventing hazard occurrence. On the other hand, to take into account technical conditions (last safety weak link, functional dependencies, technological complexity, etc.), specific rules implicitly used in existing practices, are defined for readjusting some THR values. SIL allocation process based on apportioned and validated THR values is finally established. Generic "Passengers doors" and "Emergency brake" sub-systems are examined in terms of SIL allocation to the safe-ty-related functions and the methodology is validated by compliance with the safety requirement objectives.