© 2018

The Agile Safety Case


Table of contents

  1. Front Matter
    Pages i-xii
  2. Thor Myklebust, Tor Stålhane
    Pages 1-18
  3. Thor Myklebust, Tor Stålhane
    Pages 19-46
  4. Thor Myklebust, Tor Stålhane
    Pages 47-65
  5. Thor Myklebust, Tor Stålhane
    Pages 67-86
  6. Thor Myklebust, Tor Stålhane
    Pages 87-99
  7. Thor Myklebust, Tor Stålhane
    Pages 101-110
  8. Thor Myklebust, Tor Stålhane
    Pages 111-135
  9. Thor Myklebust, Tor Stålhane
    Pages 137-164
  10. Thor Myklebust, Tor Stålhane
    Pages 165-200
  11. Thor Myklebust, Tor Stålhane
    Pages 201-213
  12. Back Matter
    Pages 215-235

About this book


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.


Safety critical systems Software safety Software verification and validation Agile software development Empirical software engineering

Authors and affiliations

  1. 1.Software Engineering, Safety and SecuritySINTEF ICTTrondheimNorway
  2. 2.NTNUTrondheimNorway

About the authors

Thor Myklebust is a senior safety assessor, business developer and researcher at SINTEF Digital in Norway, where he is involved in mainly international but also national development and research projects. He has participated in several international committees since 1988, been a member of safety IEC 65, the IEC 61508 international committee, railway CENELEC/TC 9 and NB-rail (notified bodies) since 2007. In addition he was vice chair of NB-Rail in 2014 and chairman of NB-Rail in 2015. He is also one of the founders of SafeScrum.

Tor Stålhane is professor emeritus at the Norwegian University of Science and Technology in Trondheim. He holds a PhD in statistics and is currently doing research in software engineering and system safety analysis. He is one of the founders of SafeScrum.

Bibliographic information