Assessing Cognitive Workload and Driver Performance: A Comparative Study of Pneumatic and Vibrotactile Haptic Alerts for Takeover Requests in Autonomous Vehicles

Liu, Yang; Shangguan, Zhegong; Détienne, Françoise; Safin, Stéphane; Lecolinet, Eric · 2025 · Crossref

DOI: 10.54941/ahfe1006532

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Summary

This study addresses the critical challenge of optimizing Take-Over Requests (TOR) in Level 3 autonomous vehicles, where drivers must safely resume control from disengaged states. While haptic feedback on steering wheels is a promising solution to enhance situational awareness, existing research has largely prioritized technical metrics like reaction time over holistic human factors such as cognitive workload, stress, and ergonomic comfort. Specifically, there is a lack of empirical comparison between pneumatic feedback, which offers bio-inspired, naturalistic tactile sensations, and traditional vibrotactile feedback, which provides mechanical urgency. The authors aim to bridge this gap by evaluating how these two haptic modalities, both independently and combined with audio cues, impact driver performance, cognitive load, and well-being during TOR scenarios. The researchers conducted a within-subject experiment using the CARLA driving simulator and a custom-built dual-modality haptic steering wheel system. The device featured silicone pads with embedded air sacs for pneumatic feedback and vibration motors for vibrotactile stimuli, allowing dynamic switching between modalities. Twenty-seven licensed drivers participated in nine distinct TOR tasks, varying notification types: audio-only (baseline), haptic-only (pneumatic or vibrotactile), and multimodal combinations (audio plus haptic). Tasks included both non-directional alerts and directional cues for lane changes. Performance was measured via Time to Collision (TTC) and Reaction Time (RT), while cognitive workload and stress were assessed using the NASA Task Load Index (NASA-TLX) and post-task interviews. Results demonstrated that multimodal notifications (audio combined with either pneumatic or vibrotactile feedback) significantly outperformed audio-only alerts, yielding faster reaction times and longer time to collision, indicating safer transitions. Contrary to initial hypotheses, haptic-only notifications did not perform as poorly as expected; while they resulted in slower reaction times than multimodal conditions, they did not significantly differ from multimodal conditions in terms of mental demand or frustration. When comparing the two haptic modalities directly, no significant differences were found in general reaction times, TTC, or overall NASA-TLX scores. However, vibrotactile feedback induced higher post-TOR driving speeds, suggesting it may increase driver anxiety or urgency. Additionally, directional accuracy revealed a bias toward rightward lane changes, with participants occasionally misinterpreting unilateral vibrotactile cues as whole-wheel vibrations. The study concludes that while both pneumatic and vibrotactile systems effectively enhance driver response when paired with audio, they serve different ergonomic roles. Pneumatic feedback offers a gentler, more naturalistic interaction that may reduce stress and is suitable for prolonged or less urgent alerts. In contrast, vibrotactile feedback, though effective for capturing immediate attention, may induce higher anxiety and overcompensation in driving behavior. These findings advocate for adaptive, user-centered haptic systems that modulate feedback type and intensity based on contextual urgency and driver state, balancing safety performance with user comfort and well-being.

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Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• haptic feedback
• feedback modes
• hands on hands off engagement
• automation
• takeover transitions
• multimodal feedback

Information type

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• Applied Guidance: design guidelines
• Empirical Findings: behavioral performance data
• Theoretical Contribution: conceptual framework