Effects of non-driving related tasks on mental workload and take-over times during conditional automated driving

Müller, Andreas; Fernandes-Estrela, Natacha; Hetfleisch, Ruben Helmut; Zecha, Lukas; Abendroth, Bettina · 2021 · OpenAlex-citations

DOI: 10.1186/s12544-021-00475-5

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Summary

This study investigates the impact of Non-Driving Related Tasks (NDRT) on mental workload and take-over times during conditional automated driving (SAE Level 3). In this automation level, users are released from continuous monitoring and may engage in NDRTs until a Take-Over Request (TOR) requires them to resume control. The research addresses the critical safety concern that high workload from NDRTs may impair a user’s ability to safely and quickly regain vehicle control. Specifically, the authors examine how different naturalistic NDRTs affect mental workload and whether this workload correlates with take-over performance. The experiment utilized a static driving simulator at the Technical University of Darmstadt with 56 participants. Five NDRTs were tested: reading text, listening to a radio report, watching a video, texting, and monitoring the ride (baseline). Mental workload was measured using three methods: subjective assessment via the NASA-TLX questionnaire, psychophysiological data (Heart Rate Variability via ECG), and performance-based metrics using a Detection Response Task (DRT) as a secondary task. Take-over time was defined as the interval between the TOR and the first steering or braking intervention. Participants performed each NDRT in a randomized order during simulated urban driving scenarios, followed by a TOR requiring them to avoid a collision. The results demonstrated significant differences in mental workload across the tested NDRTs. Reading and texting imposed the highest subjective workload, with reading scoring 52.47 on the NASA-TLX scale, significantly higher than the baseline monitoring condition (23.24). Psychophysiological and performance-based measures corroborated these findings, showing that tasks with higher cognitive and visual demands reduced spare capacity. Crucially, the study found a direct correlation between mental workload and take-over time. NDRTs associated with high workload, particularly reading and texting, resulted in significantly longer reaction times compared to lower-workload tasks like listening or the baseline condition. The findings imply that not all NDRTs are equivalent in their impact on driver readiness. High-workload tasks significantly delay the ability to take over control, posing a safety risk in conditional automated driving. The study concludes that mental workload is a key explanatory factor for variations in take-over times. This suggests that future automated driving systems and regulations should consider the specific type and complexity of NDRTs permitted, rather than treating all non-driving activities as equally safe. The results highlight the need for strategies to manage workload and ensure rapid fallback capability in Level 3 automation.

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-25; verification: verified.

Topics

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• takeover transitions
• manual
• mental demand
• workload measurement
• temporal
• visual manual

Information type

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• Empirical Findings: behavioral performance data
• Theoretical Contribution: conceptual framework, theory or model