This study investigates passenger postures in future Level 5 autonomous vehicles (AVs) where the absence of driving responsibilities allows for greater freedom in seating. Building on existing literature on AV development and posture analysis, the research explores how passengers might position themselves when free from the constraints of traditional car seats.

To examine these natural postures, participants were invited to construct a "Build-Your-Own" seat using foam blocks, enabling them to achieve their most comfortable positions during various non-driving-related activities (NDRAs) while also sitting in an existing car seat as a comparison. Thirty-six participants, with diverse anthropometric characteristics, were involved in the study. The research setup ensured ethical considerations were addressed, and a range of measurement methods were used to capture joint angles and subjective comfort levels.
Results indicated that participants rated the Build-Your-Own seat significantly higher in comfort compared to conventional car seats, especially for the upper body and limbs. Analysis of joint angles revealed key differences in the shoulders, thighs, knees, and ankles, suggesting that future vehicle seats might need to be designed with these areas in mind for enhanced comfort. The study also noted that the Build-Your-Own seat allowed for more diverse and less predictable postures, particularly during activities such as Rest and Relax or Sleep, where freedom of movement was highly valued.

Further analysis of posture support highlighted the importance of armrests for certain activities and the necessity of calf support for others. The study also found that crossed-leg postures were preferred by a significant portion of participants, suggesting that future vehicle designs should accommodate such variations.

Comparative analysis between the one-g NBP (Neutral Body Posture) derived from this study and existing zero-g NBP data, as well as recommended joint angles for SUVs, revealed challenges in directly applying these models to future car seat designs. The influence of gravity on posture was significant, indicating that optimal joint angles in a zero-g environment might not directly translate to one-g conditions.

The study concludes that future AV seating designs should consider the diverse and dynamic postures passengers may adopt, emphasizing the need for more adaptable and supportive seating solutions. Future research should focus on asymmetrical postures and longer-duration studies to better understand the long-term effects of different seating configurations, especially in the context of crossed-leg postures.

Overall, this research provides valuable insights into passenger comfort in Level 5 AVs and suggests directions for future vehicle seat design that prioritize natural and comfortable postures in a gravity-influenced environment.