Railway systems have become increasingly complex and challenging. That makes it difficult for project owners to analyse and ensure system safety. The risks resulting from this increase in complexity can be mitigated by an Overall-Independent Safety Assessment (O-ISA). The O-ISA helps project owners, operators, suppliers and system integrators prevent failures and ensuring their system are compliant with the local and global safety requirements such as EN 50126, EN 50128, EN 50129, among others.