Tailoring STPA for SOTIF: Terminology Mapping and Methodological Extension

Abstract

According to ISO 21448, it is essential to consider the Safety of the Intended Functionality (SOTIF) to ensure the safety of automated vehicles. A key objective for SOTIF is the identification and analysis of triggering conditions and functional insufficiencies. To support this objective, ISO 21448 suggests the System Theoretic Process Analysis (STPA) as a suitable analysis technique. Although STPA is a promising hazard analysis method, it was not specifically developed for SOTIF. Consequently, it is necessary to create a terminology mapping and methodological extension in order to adapt STPA for SOTIF. For example, STPA terms such as “loss” have more specific meanings than their ISO 21448 counterparts. At the same time, SOTIF requires a systematic analysis of scenarios to identify triggering conditions and functional insufficiencies. Although STPA is suitable for scenario-based analyses, it does not guide the scenario specification. To address the identified gaps, this article proposes the use of SOTIF-specific terminology mapping and an extension to the STPA method. These extensions include a behavior specification and hazard identification approach, building the foundation for a STPA tailored for SOTIF. With these changes, it becomes possible to trace the STPA artifacts to ISO 21448 objectives.