How Does it Feel and How is it measured? Assessing Sitting Comfort and Postures of Rear-Seated Car Passengers in Stationary and Driven Scenarios Over Time

Abstract: This licentiate thesis presents the results of an empirical study focused on examining the comparative effectiveness of short stationary studies versus long driving studies in evaluating sitting postures, belt fit, and sitting comfort in cars. The study employed a mixed-methods approach, in which 19 participants experienced two different test scenarios in the rear seat of a car: a stationary scenario within an indoor garage and a driven scenario on a predefined route in regular traffic, each lasting 45 minutes. The data collection methods used to capture objective and subjective data included video recordings, questionnaires, and interviews. The Wilcoxon’s signed-rank test was used to identify significant differences in sitting postures and seat belt positions estimated using a machine-learning based algorithm, as well as differences in discomfort ratings between the scenarios and over time, while interviews were analysed thematically.   The findings reveal that shorter, stationary studies of 3 minutes effectively capture the average sitting postures and belt fit, while more extended studies are necessary to capture posture variations, particularly for individuals with specific body shapes. The study emphasizes the importance of longer driving studies for comprehensively assessing variations in shoulder belt positions.   Additionally, the study emphasizes the influence of the type of study scenario and duration on the comfort experience. Discomfort changes become noticeable after 15 minutes in both scenarios, with further increases in discomfort, particularly in the back, buttocks, thighs, and feet, observed over time. Increased back discomfort is associated with participants adopting slumped postures. Furthermore, the type of scenario influences the participants' emotions and behaviors, with the stationary scenario leading to increased awareness, boredom, and tiredness due to the lack of visual and haptic stimuli. In contrast, the driven scenario results in more natural movements and engagement in window-gazing.   Lastly, the study underscores the complex relationship between posture data and comfort perception. It suggests that upper body movement ranges are not directly associated with discomfort; rather, the movements are influenced by various factors, such as individual behavior and strategies to mitigate discomfort. The results highlight the complementary role of video recordings, questionnaires, and interviews in providing a comprehensive understanding of comfort perception.   To conclude, this licentiate thesis contributes with valuable guidelines for efficient studies of sitting comfort and postures in cars, highlighting the influence of study scenario type and duration in the assessment of sitting comfort and postures in cars. It shows that shorter, stationary studies of 3 minutes capture the average posture and belt fit, while discomfort changes become notable after 15 minutes. Further, it emphasizes the need for extended driving studies to capture the full spectrum of variations in comfort, especially related to shoulder belt positions, and offers a nuanced view of how emotional states and behaviors are influenced by the study scenario. The study's holistic approach provides a deeper understanding of the interplay between posture data and comfort perception, underscoring the synergistic value of multiple data collection methods.