Identification of Preferred Relaxation and Sleeping Postures in Highly Automated Vehicles

Abstract: The advancement of automated driving technologies to SAE-Level 4 introduces new opportunities for optimizing vehicle interiors for relaxation and sleep. As the driver is no longer required to permanently monitor the driving process, the in-vehicle time can be repurposed for rest and recovery, especially on long-distance journeys. Although the automated driving system in SAE-L4 independently carries out the driving task, manual driving will still be necessary. Therefore, the cockpit layout of these vehicles must still enable safe manual driving. Current vehicle interiors, and especially driver cockpits, are not designed for relaxation and sleeping. Adaptations of the vehicle interior creating an appropriate environment are needed to relax and to sleep in a small space such as a vehicle’s interior.In this contribution, preferred relaxing and sleeping postures in vehicles are identified to derive comprehensive ergonomic and safety-related requirements for the design of highly automated vehicles. The goal is to establish interior concepts that not only provide comfort but also meet safety standards and accommodate varied user needs. This includes a comprehensive literature review, expert interviews, observational studies conducted in a recliner within a vehicle environment, and the analysis of existing solutions for relaxation and sleep in transportation modes. Additionally, a biomechanical simulation of posture scenarios using RAMSIS simulation tool is employed to visualize sleeping postures within vehicle interiors. Particular attention is paid to the conflict between ergonomic comfort and safety requirements, especially in the context of take-over situations, where users may need to resume vehicle control under certain edge cases.The findings indicate that relaxation and sleep postures are significantly influenced by ergonomic design, seat configurations, and spatial constraints within the vehicle. Key ergonomic requirements for optimal comfort include support for the head, neck, lower back, and legs, as well as adjustable seating options to accommodate side, back, and reclining positions. Special emphasis is placed on leg support and adjustable footrests to maintain comfort and reduce fatigue during extended periods of relaxation or sleep. Furthermore, the study reveals significant discrepancies between perceived and actual ergonomic effectiveness of current seat designs, especially in reclining configurations.Based on the results, specific design recommendations are proposed to enhance sleeping comfort in SAE-Level 4 vehicles. These include optimized seat adjustability, improved head, neck, and leg support, modular seat configurations that support dynamic posture changes, as well as enhanced safety mechanisms. The contribution concludes that addressing these requirements is critical to making sleep a viable and comfortable option during automated driving, ultimately contributing to enhanced well-being and travel experience for passengers.Acknowledgements: This research was supported by Federal Ministry for Economic Affairs and Climate Action in the national research project SALSA.

Keywords: Automated Driving, Relaxation, Sleep, Occupant Postures, Seat, Ergonomic Design

DOI: 10.54941/ahfe1007113

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