Writing Accessible and Correct Test Scenarios for Automated Driving Systems

For Automated Driving Systems (ADSs), vehicle safety and functional correctness are assessed against scenarios the ADS would encounter - within or outside its operational design domain (ODD). A scenario specifies conditions and events that an ADS is expected to respond to when deployed. Scenario specifications underpin the verification and validation (V&V) life-cycle, and are used by a diverse set of stakeholders - from engineers to regulators. Due to the diversity in stakeholder expertise, scenarios must be available at different levels of detail. Further, the chance of writing syntactically or semantically incorrect scenarios is high. Due to the high reliance of V&V on scenarios, their correctness is crucial. Therefore, present-day scenario-description languages (SDLs) need to be supported by technologies to help authors compose scenarios and provide a mechanism for easy translation into executable forms for virtual or real-life testing. This paper addresses these issues by building on the existing two-level abstraction WMG-SDL in the following ways, (1) introducing a human-readable, natural language SDL, replacing the former Level-1 SDL, and complementing the more detailed Level-2 SDL, which is now syntax aligned with the ODD Taxonomy defined in ISO 34503, and (2) providing a tool consisting of a parser and a validator to assist writing syntactically and semantically correct scenarios. Our tool may be used within a graphical scenario editing interface or on the command-line. Further, for developers, an object-oriented interface for parsed scenarios enables further development and integration with off-the-shelf ADS simulation and language tools. The tools and technologies described in this paper are to be made open-source.