# A Review of Seatbelt Technologies and Their Role in Vehicle Safety
## 3 Results
### Autonomous Vehicles and Adaptive Seatbeltls
These findings provide a strong foundation for an intelligent seatbelt system that not only reacts to external threats but also tailors its response to the occupant's condition and posture. The growing significance of multi-sensory human detection systems in autonomous vehicles was emphasized by ref. [68], highlighting the role of visual, auditory, and tactile data streams in enabling real-time occupant state monitoring. This interdisciplinary perspective reinforces the need to design seatbelt systems that function as integral components of a broader human-machine interface. By embedding AI models trained on diverse sensor inputs into seatbelt control architectures, anticipatory safety mechanisms--such as dynamic belt pretensioning and personalized load adjustment--can be implemented in response to occupant biometrics and predicted impact scenarios. The paper by [69] examines the effectiveness of various restraint systems in self-driving cars, highlighting the need for smart restraint systems adaptable to different occupant postures. Also, the study by [70] investigates how occupant positioning during pre-crash scenarios affects injury metrics. It proposes a crisscross seatbelt design to enhance protection for occupants in non-ideal seating positions. While reversible pretensioners and AEB systems offer promising synergistic potential, their effectiveness has largely been evaluated under conventional seating postures. In Level 5 autonomous vehicle contexts, where occupants may adopt fully reclined or rotated positions, these systems face significant limitations--most notably increased submarining risks and reduced engagement of load paths. To contextualize these challenges, future research should incorporate data from OEM testing initiatives or assess restraint system compliance with emerging standards like SAE J3027 [71], which addresses safety protocols for alternative seating orientations. The primary objective of SAE J3027 is to provide manufacturers, ambulance builders, and end-users with standardized testing procedures and, where appropriate, acceptance criteria. This ensures that patient litters and their associated systems utilize dynamic performance test methodologies similar to those applied to other vehicle seating and occupant restraint systems. Impact simulations associated with the concept of \"couch mode\"--a term informally used to describe relaxed or reclined seating positions--aim to assess the elevated safety risks posed by non-standard occupant postures. Key concerns include submarining, where the pelvis slides under the seatbelt during reclined positioning, thereby compromising restraint effectiveness; inefficient distribution of impact forces, resulting from shifted contact points between the seatbelt and airbag; and the diminished performance of pre-tensioners and load limiters, which are typically optimized for conventional seating postures. Although comprehensive official data from these simulations remain limited, such scenarios are increasingly being explored in collaborative research, automotive safety conferences, and development projects by various OEMs seeking to adapt occupant protection strategies to the evolving demands of autonomous mobility. Yanfeng has developed the SafeUnit, an advanced seat-integrated safety system designed to protect occupants in both upright and reclined positions during various types of crashes. This system is built for both current and future vehicles [72]. A simulation-based study using the Active SAFER human body model (SHBM) examined how seatbelt geometry and load-limiting configurations affect the kinematics and injury risks of a reclined (50\({}^{\circ}\)) occupant during a full-sequence frontal crash. The comparison of B-pillar-integrated (BPI) and Belt-in-Seat (BIS) configurations revealed that BIS reduced the risks of mild traumatic brain injury (mTBI) and rib fractures, whereas BPI seatblets were associated with lower lumbar spine fracture risk. Variations in belt force distribution were found to be critical during the in-crash phase.