Causes of severe injuries in wheelchair user motor vehicle passengers: pilot study for future safety restraint system.

Hitosugi, M; Kuwahara, A; Kitaguchi, Y; Yoshii, K; Inoue, M; Takaso, M; Nakamura, M; Nick, B · 2026 · PubMed Central

DOI: 10.1265/ehpm.26-00037

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Summary

This study addresses the rising risk of severe injuries and fatalities among older wheelchair users traveling in the rear spaces of motor vehicles in Japan. Motivated by demographic aging and data indicating that poor seatbelt fit is a primary cause of injury, the research aims to elucidate injury mechanisms in frontal collisions and propose design improvements for future safety restraint systems. The authors combined retrospective analysis of national accident statistics with biomechanical sled testing to identify specific failure modes of current restraint configurations. The methodology involved two main components. First, the researchers analyzed data from the Institute for Traffic Accident Research and Data Analysis (ITARDA) database, covering motor vehicle collisions in Japan from 2017 to 2022. They categorized injuries as death, severe, or mild and recorded seatbelt usage. Second, they conducted sled tests simulating a 48 km/h frontal collision using a Hybrid III AF05 dummy, which represents an average older Japanese female. Three test conditions were evaluated: (1) a standard wheelchair with a generally used seatbelt path; (2) a standard wheelchair with a closer seatbelt path; and (3) a sturdy wheelchair with a close seatbelt path. The tests measured kinematics, accelerations, and injury criteria, including Head Injury Criterion (HIC), Neck Injury Criterion (Nij), and chest deflection. The statistical analysis revealed that seatbelts were worn in the majority of cases across all injury severities, including 86.7% to 100% of fatalities, indicating that seatbelt use alone does not prevent severe injury if fit is inadequate. In the sled tests, Condition 1 resulted in the "submarine phenomenon," where the lap belt compressed the abdomen, leading to high HIC (1,274) and Nij (1.05) values due to severe neck flexion and head contact. Condition 2 caused the dummy to fall from the seat because the standard wheelchair collapsed. Condition 3, using a sturdy wheelchair, restricted pelvic displacement more effectively but still resulted in high chest deflections (51.3–53.8 mm) driven by excessive shoulder belt loads (8,217–8,660 N). The study concludes that current restraint systems are insufficient for wheelchair users due to improper belt positioning and lack of force management. The authors propose specific design indications for future safety systems: shoulder and lap belts must be correctly positioned across the bony structures of the shoulder and pelvis, respectively; a force limiter should be installed to reduce shoulder belt loads; and sturdy wheelchairs with adequate tie-down systems capable of resisting high applied forces are necessary. These findings highlight that simply wearing a seatbelt is not enough; proper biomechanical fit and structural integrity of the wheelchair are critical to preventing severe injuries in this vulnerable population.

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Topics

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• child passenger safety