Brandon Fugger, Lina Bouakkaz, Jesse Rhoades, Enrique Alvarez Vazquez
These results identify D-ring anchor location as the primary identifiable moderator of the inconsistencies previously reported across studies, rather than platform setup (sled vs. vehicle) or pulse severity. Other factors, such as seat pan angle, anthropometry, and pulse characteristics could also contribute but could not be fully controlled for in this study. Because forward excursion depends on D-ring anchor location, kinematic data from one belt configuration should not be used to validate computational models designed for the other. The lack of impact-severity data for females, older adults, and high-BMI occupants represents a critical gap in the current volunteer dataset that should be addressed before computational models can be considered broadly validated. Future volunteer testing should include these populations to establish response corridors that ensure restraint systems in highly autonomous vehicles are designed and validated across the full range of real-world occupant anthropometry.
OBJECTIVES: The emergence of autonomous vehicles is expected to introduce nonstandard seating configurations, including reclined postures, that fall outside the design basis of current restraint systems. A growing body of research has investigated occupant kinematics in these configurations, but most of this work relies on anthropomorphic test devices or postmortem human subjects. Human volunteer data, which captures active musculoskeletal responses and demographic variability, remains limited and has not been synthesized across studies.
METHODS: This scoping review identified 10 human volunteer studies encompassing 127 volunteers and 1,327 trials that examined occupant kinematics in reclined seating during pre-impact braking, lane change, and low-severity impact events. Studies were included if they used human volunteers in reclined positions ≥40˚. Studies were excluded if they exclusively used ATDs, PMHS, or computational modeling. Studies were classified by B-pillar mounted or seat-integrated belt types. A weighted meta-regression was performed across 20 group-level observations from 6 studies to test whether D-ring type influences the relationship between seatback angle and forward head excursion while controlling for braking severity and sex composition.
RESULTS: The meta-regression identified a significant interaction between seatback angle and D-ring type (β = -9.49, p < 0.0001, R2 = 0.868). B-pillar belts produced increasing forward head excursion with recline (+7.20 mm/deg), while integrated belts showed the opposite trend (-2.29 mm/deg). This interaction remained significant after controlling for peak deceleration and percent male (p < 0.0001, R2 = 0.917), and after conducting a leave-one-study-out sensitivity analysis (p ≤ 0.015). The same pattern was observed at the torso. Males showed more excursion under B-pillar restraint at reclined angles, while females showed more excursion under integrated restraint. Belt forces decreased with recline regardless of D-ring type, indicating a load path shift from belt to seat structure.
CONCLUSIONS: These results identify D-ring anchor location as the primary identifiable moderator of the inconsistencies previously reported across studies, rather than platform setup (sled vs. vehicle) or pulse severity. Other factors, such as seat pan angle, anthropometry, and pulse characteristics could also contribute but could not be fully controlled for in this study. Because forward excursion depends on D-ring anchor location, kinematic data from one belt configuration should not be used to validate computational models designed for the other. The lack of impact-severity data for females, older adults, and high-BMI occupants represents a critical gap in the current volunteer dataset that should be addressed before computational models can be considered broadly validated. Future volunteer testing should include these populations to establish response corridors that ensure restraint systems in highly autonomous vehicles are designed and validated across the full range of real-world occupant anthropometry.