A Hazard Analysis Approach based on STPA and Finite State Machine for Autonomous Vehicles

Hazard analysis is a quite significant step to ensure vehicle safety in the early stage of vehicle development according to current standards. However, the complexity of the Advanced Driving Assistance System (ADAS) and Automated Driving Systems (ADS), which consist of various software and hardware components, makes it difficult to identify system hazards. Nowadays, System-Theoretic Process Analysis (STPA), a hazard analysis method for complex systems, is applied to ADAS, and simple ADS gradually and proved applicable. This paper introduced Finite State Machine (FSM) to complement the STPA for its weakness in analyzing high-level autonomous vehicles with multiple automated modes and functions. Firstly, previous applications of STPA to ADAS and ADS and their limitations are analyzed. Secondly, the hazardous event is defined. An extended method combining STPA and FSM is proposed to model the vehicle states and environmental conditions and analyze unexpected behaviors. Finally, a case study on an autonomous vehicle is given to compare the traditional STPA and the extended method. Comparing with the traditional STPA, the proposed method can identify more hazardous events and give more detailed information about hazardous events to generate testing scenarios.