Assessing a Safety Case: Bottom-up Guidance for Claims and Evidence Evaluation

As Automated Driving Systems (ADS) technology advances, ensuring safety and public trust requires robust assurance frameworks, with safety cases emerging as a critical tool toward such a goal. This paper explores an approach to assess how a safety case is supported by its claims and evidence, toward establishing credibility for the overall case. Starting from a description of the building blocks of a safety case (claims, evidence, and optional format-dependent entries), this paper delves into the assessment of support of each claim through the provided evidence. Two domains of assessment are outlined for each claim: procedural support (formalizing process specification) and implementation support (demonstrating process application). Additionally, an assessment of evidence status is also undertaken, independently from the claims support. Scoring strategies and evaluation guidelines are provided, including detailed scoring tables for claim support and evidence status assessment. The paper further discusses governance, continual improvement, and timing considerations for safety case assessments. Reporting of results and findings is contextualized within its primary use for internal decision-making on continual improvement efforts. The presented approach builds on state of the art auditing practices, but specifically tackles the question of judging the credibility of a safety case. While not conclusive on its own, it provides a starting point toward a comprehensive "Case Credibility Assessment" (CCA), starting from the evaluation of the support for each claim (individually and in aggregate), as well as every piece of evidence provided. By delving into the technical intricacies of ADS safety cases, this work contributes to the ongoing discourse on safety assurance and aims to facilitate the responsible integration of ADS technology into society.