Supplementary material for "How should drivers’ use of Automated Lane Keeping Systems (ALKS) be assessed?"

Supplementary material for the paper: Bazilinskyy, P., Heikoop, D., Verstegen, R., Martens, M. H., &amp; De Winter, J. C. F. (2026). How should drivers’ use of Automated Lane Keeping Systems (ALKS) be assessed? A study with experienced driving assessors in a Wizard of Oz vehicle. Accident Analysis and Prevention.<br>This study aims to contribute to guidelines for driver licensing organisations on assessing driver competence in using Level 3 Automated Lane Keeping Systems (ALKS), based on an on-road experiment with eight professional driving assessors (i.e., expert driving examiners who train experienced drivers to become driving examiners of their own) in a Wizard of Oz vehicle. Using a think-aloud protocol, we captured cognitive processes during system supervision and take-over requests (TORs) in real-world traffic jams. An LLM-based thematic analysis of transcripts revealed four themes: (1) Continuous situational awareness as a prerequisite for trust and action, (2) The need for system transparency and predictability, (3) Proactive manual control to ensure safety and traffic flow, and (4) The take-over action as an immediate, reflexive response. These results suggest that safe ALKS operation requires active monitoring and anticipatory skills. This blurs the distinction between Level 2 and Level 3 automation, as the expert participants in our study generally remained attentive rather than adopting the ‘mind-off’ state that Level 3 theoretically allows. In conclusion, assessing ALKS usage involves not only evaluating a driver’s reaction to a TOR but also judging their performance as a systems manager responsible for anticipating conflicts and smoothly executing control transitions.<br>Structure:* /walks-unity: Unity project used for the interface.<br>Notes:* The Unity project was developed using Unity 2023.2.20f1.