Effects of body characteristics on lap belt fit and comfort

Sammanfattning

Proper seat belt fit is crucial for occupant safety and comfort, as incorrect positioningmay reduce injury protection and increase discomfort, potentially leadingto misuse. This study investigates how individual body characteristics influence lapbelt fit and perceived comfort, with particular focus on anthropometry and seatingposture, determined by the seatback recline angle. A controlled laboratory study wasconducted using a test rig representing a vehicle seating environment. Thirty adultparticipants, balanced by sex and distributed across Body Mass Index (BMI) categories,were evaluated in two seatback configurations (upright and semi-reclined).Three lap belt anchorage conditions were assessed: a manufacturer-defined position(P1), a forward-shifted position (P2), and a user-selected position.Objective measurements (anthropometry, belt geometry relative to the anterior superioriliac spine, and buckle position) and subjective assessments (perceived comfort,perceived safety, and usability) was used. Statistical analyses were used toidentify relationships between body characteristics and belt fit. The results showthat seatback recline angle has the strongest influence on lap belt fit, followed byBMI and anthropometric measures. Higher BMI is consistently associated with amore superior lap belt position relative to the pelvis, reflected as an upward displacementof both belt segments. However, the belt position relative to the pelvis inthe anterior–posterior direction is strongly affected by seating posture, with reducedanthropometric predictability in the semi-reclined condition.P2 generally reduced perceived abdominal pressure and improved usability, particularlyin terms of buckle accessibility and ease of buckling, but introduced tradeoffssuch as increased perceived thigh loading and shoulder belt interference. Despitethese improvements in local comfort, P2 was perceived as less safe than P1,however, perceived safety does not necessarily reflect actual restraint performance.User-selected positions minimized discomfort in most cases but were typically locatedoutside regulatory acceptance regions, indicating a mismatch between userpreference and standards.The findings highlight the combined influence of anthropometry, seatback reclineangle, and restraint geometry on lap belt fit, showing that no single factor explainsoccupant variability. This study contributes empirical evidence supporting the needto consider occupant diversity and seatback recline angle in future restraint systemdesign, particularly in the development of more adaptive anchorage positions.