Sammendrag
There is much invested in safety rule development, implementation and control of compliance, but the scientific knowledge about how to modify them is limited. This paper presents results from a case study of four safety rule modification processes in the Norwegian railway system. The cases modified rules for traffic operation and infrastructure maintenance.The study reveals that the cases applied a strategy given the name “reverse invention”. This strategy diverged from the intention of the cases to apply so called hierarchical and risk based approaches, and took more advantage of existing railway knowledge than these. The cases demonstrated four different ways of using risk analyses in the modification work. Also, they provided arguments for and against different rule principles in different contexts. The processes contributed to a revival of railway knowledge. However, as only written elements are systematically stored in organizational memory this knowledge might be in danger.