[Paper Review] Exploring the Relationship Between "Positive Risk Balance" and "Absence of Unreasonable Risk"

Francesca Favarò|arXiv (Cornell University)|Oct 20, 2021

Risk and Safety Analysis4 citations

TL;DR

This paper clarifies the conceptual relationship between 'positive risk balance' (PRB) and 'absence of unreasonable risk' (AUR) in automated driving safety. It identifies two distinct interpretations of PRB—risk trade-off justification and risk optimization—and argues they can coexist within non-prescriptive safety guidelines, resolving ambiguity in international regulatory discourse.

ABSTRACT

International discussions on the overarching topic of how to define and quantify what a "safe enough" Automated Driving System (ADS) is are currently hinged on the question of determining the relationship between "positive risk balance" (PRB) and "absence of unreasonable risk" (AUR). In order to advance the conversation on these important safety topics at the international level, it is first important to start from a shared common understanding, grounded in clear definitions and terminology. To that end, this paper will start with an overview of the notions of PRB and AUR; it will then summarize different positions of the present debate; finally, it will conclude that two possible interpretations exist for PRB, and that failure to distinguish them can lead to misunderstanding different parties' positions. The argumentation in this paper is aimed at showing that the two interpretations for PRB can actually complement each other, but can be considered independently, and can both be subsumed within non-prescriptive guidelines toward ADS safety assurance.

Motivation & Objective

• To establish a shared, terminology-grounded understanding of 'positive risk balance' (PRB) and 'absence of unreasonable risk' (AUR) in automated driving systems.
• To analyze the current international debate on defining a 'safe enough' Automated Driving System (ADS).
• To resolve conceptual confusion arising from ambiguous interpretations of PRB in regulatory and technical discussions.
• To demonstrate that two interpretations of PRB can coexist and complement each other within non-prescriptive safety assurance frameworks.
• To support international alignment on ADS safety by clarifying foundational concepts and terminology.

Proposed method

• Conducting a conceptual analysis of PRB and AUR using definitions from international regulatory and technical literature.
• Surveying and summarizing divergent positions in the current international debate on ADS safety thresholds.
• Distinguishing between two interpretations of PRB: (1) risk trade-off justification and (2) risk optimization.
• Analyzing how each interpretation of PRB relates to the AUR principle without prescribing specific safety metrics.
• Proposing that both interpretations can be integrated into non-prescriptive safety assurance guidelines.
• Using logical and conceptual reasoning to show complementarity rather than contradiction between the two PRB interpretations.

Experimental results

Research questions

• RQ1 What are the two distinct interpretations of 'positive risk balance' (PRB) in the context of automated driving safety?
• RQ2 How does the concept of 'absence of unreasonable risk' (AUR) relate to PRB in regulatory and technical discourse?
• RQ3 Why does failure to distinguish between the two interpretations of PRB lead to misunderstandings in international discussions?
• RQ4 Can both interpretations of PRB coexist within a unified safety assurance framework?
• RQ5 How can non-prescriptive guidelines incorporate both interpretations of PRB while supporting international regulatory alignment?

Key findings

• Two distinct interpretations of 'positive risk balance' (PRB) exist: one focused on justifying risk trade-offs and another on optimizing risk levels.
• The distinction between these two interpretations is critical to avoid miscommunication in international regulatory and technical discussions on automated driving safety.
• Failure to differentiate the interpretations can lead to misalignment in how stakeholders perceive safety thresholds for Automated Driving Systems (ADS).
• Both interpretations of PRB can be meaningfully subsumed within non-prescriptive safety assurance guidelines, enhancing flexibility and international coherence.
• The paper concludes that the two PRB interpretations are complementary rather than contradictory, supporting a more nuanced and robust safety framework.
• The analysis supports the development of non-prescriptive safety assurance approaches that accommodate diverse risk management philosophies across jurisdictions.