Reclined Seating Postures on Passive Safety Performance in Automotive Seats: A Review

The increasing adoption of reclined seating postures in modern vehicle interiors challenges the assumptions underpinning current passive safety systems and occupant protection assessment frameworks. While restraint technologies and certification protocols have historically been developed for upright configurations, emerging trends in autonomous driving and comfort-oriented designs promote relaxed postures that fundamentally alter occupant kinematics, loading path, and consequently the injury mechanisms. This review critically synthesizes experimental and numerical studies addressing occupant biomechanics, restraint system performance, and injury risk in reclined seating. Evidence from crash tests using Anthropomorphic Test Devices and Post-Mortem Human Surrogates, alongside high-fidelity numerical Human Body Models, is analyzed to identify consistent trends and methodological limitations. The results highlight increased forward excursion, elevated submarining propensity, and posture-dependent abdominal and lumbar loading as critical consequences of increased seatback recline. Furthermore, this review discusses the effectiveness of adaptive restraint strategies, including active repositioning and modified airbag–belt integration. By identifying existing research gaps and regulatory limitations, this work aims to provide a roadmap for the development of future safety systems that ensure robust protection for all occupants in the era of automated mobility.