Safety Case Variation using Goal Structuring Notation
Conference
New Zealand Systems Engineering Conference 2025
Title
Safety Case Variation using Goal Structuring Notation
Summary
This presentation explains how KiwiRail approached the challenge of preparing to operate and maintain the City Rail Link (CRL) safely while meeting regulatory requirements. To act as the Network Access Provider and Rail Operator, KiwiRail must submit a Safety Case Variation (SCV) to NZTA (Waka Kotahi) and have it approved. The SCV is complex, involving multiple stakeholders and extensive evidence to demonstrate safety risk reduction to a level that is So Far As Is Reasonably Practicable (SFAIRP).
To manage this complexity and avoid misalignment, KiwiRail adopted Goal Structuring Notation (GSN). GSN provides a structured, visual way to define and communicate the safety argument and the evidence required for the SCV. The presentation explored how this was done and the benefits achieved in its application.
Key takeaways:
- GSN provides a clear, visual structure that makes reasoning and evidence traceable and easy to understand, simplifying complex safety cases.
- GSN improved stakeholder alignment, as it became the central tool for workshops and regulator engagement, helping identify gaps early and avoid surprises.
- GSN adds value, but it’s only a model. Overcomplication can reduce benefits, so manage complexity carefully.
Authors
Christian Parra-John CEng, Principal Engineer, Fisgard Ltd
Steve Wallace CSEP CPEng, Principal Systems Engineer, Shoal Group
Date
Tuesday 11 November 2025
Learn more
Safety Case Variation using Goal Structuring Notation
About Shoal
Shoal is complex systems design company. We use Systems Engineering combined with Modelling, Simulation and Analysis to help our clients define, analyse, decide, optimise, and deliver technology-intensive projects in complex environments across Defence, Space, Transport, Energy and Infrastructure.
More: shoalgroup.com
Contact
Matthew Wylie
Chief Engineer, Shoal Group
[email protected]
