The safety case (SC) is one of the railway industry's most important deliverables for creating
confidence in their systems. This is the first book on how to write an SC based on the
standard EN 50129:2003. Experience has shown that preparing and understanding an SC is
difficult and time consuming and as such the book provides insights that enhance the training
for writing an SC. The book discusses both regular safety cases and agile safety cases which
avoid too much documentation improve communication between the stakeholders allow quicker
approval of the system and which are important in the light of rapidly changing technology. In
addition it discusses the necessity of frequently updating software due to market requirements
changes in requirements and increased cyber-security threats. After a general introduction to
SCs and agile thinking in chapter 1 chapter 2 describes the majority of the roles that are
relevant when developing railway-signaling systems. Next chapter 3 provides information
related to the assessment of signaling systems to certifications based on IEC 61508 and to the
authorization of signaling systems. Chapter 4 then explains how an agile safety plan satisfying
the requirements given in EN 50126-1:1999 can be developed while chapter 5 provides a brief
introduction to safety case patterns and notations. Lastly chapter 6 combines all this and
describes how an (agile) SC can be developed and what it should include. To ensure that
infrastructure managers suppliers consultants and others can take full advantage of the agile
mind-set the book includes concrete examples and presents relevant agile practices. Although
the scope of the book is limited to signaling systems the basic foundations for (agile) SCs
are clearly described so that they can also be applied in other cases.
