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All functional safety standards have some definition of “risk” and the automotive standard ISO 26262 is no exception. Risk is related to the exposure, the severity of the outcome, and in the case of ISO 26262, the controllability in relation to a specific vehicle hazard or hazards associated with the behavior of the vehicle or part of the vehicle. Thus hazards are central to understanding the risk associated with systems. When considering traditional power train systems, based on internal combustion engines or centralized electric motors, hazards are most usually limited to unintended acceleration and deceleration. The situation is complicated somewhat with the introduction of electronically controlled differentials, which can induce limited amounts of induced yaw, as can ABS and ESC. In a similar manner, replacing the centralized driveline system with in-wheel electric motors brings with it a similar set of issues.

Systems-Theoretic Process Analysis (STPA) is being used as a hazard analysis technique within automotive, due in part to its systems engineering viewpoint making it suitable to automated driving feature analysis and with several new and emerging standards and guidelines suggesting its use as one option its familiarity is increasing. Approaches incorporating the human into the STPA Control Structure Diagram (CSD) have been proposed, such as Engineering for Humans: A New Extension to STPA [1]. Such approaches position the human as the top controller in the CSD hierarchy. While placing the human at the top of the CSD is suited to reasoning about supervisory human machine interactions, perhaps in an industrial control setting, we argue that a different approach is needed to address automotive shared control. In an automotive context the driver is integral to vehicle control.