## 1 Introduction  
Occupants are no longer responsible for driving fully autonomous vehicles (levels 3 to 5, as described in a previous study [1]). This creates both significant safety benefits and new challenges [2]. Since most conventional vehicle accidents are attributed to human errors [3], autonomous vehicles can lower crash risks for both occupants and pedestrians [2, 4, 5]. Nevertheless, complex and dynamic environments in which autonomous vehicles operate pose significant challenges in realizing reliable autonomous driving technologies [2]. Although some may expect that accidents will cease entirely with autonomous vehicles, crashes are still likely to happen during the transitional period when autonomous and non-autonomous vehicles share the road [6; 7]. Therefore, evaluating vehicle crash safety remains essential as autonomous technologies advance. Common crash scenarios of autonomous vehicles can be different from established common crash modes of conventional vehicles because the former can automatically execute crash avoidance maneuvers such as automatic emergency braking (AEB) or evasive steering prior to a crash [8]. Previous studies using human models to analyze crash scenarios in autonomous vehicles have primarily focused on full frontal or side collisions, which were derived from the crash data with mostly non-autonomous vehicles. However, to evaluate the crash safety of autonomous vehicles, it is necessary to consider crash conditions that are specific to these vehicles. One computational study has examined three autonomous vehicle-relevant crash scenarios [9]. Although that study demonstrated that seating positions and lower limb postures had the greatest impact on whole-body responses, it did not account for pre-crash maneuvers or autonomous vehicle-specific occupant restraint conditions. Therefore, further investigation is needed to assess the effects of additional autonomous vehicle characteristics on occupant injury risks under relevant crash scenarios. At the same time, as driving becomes increasingly automated, the frequency of pre-crash maneuvers is expected to rise [10]. Such maneuvers can cause occupants to shift from their nominal positions into out-of-position states at the moment of collision. Experimental studies on occupant behavior during emergency braking have reported head excursions ranging from 115 mm to 200 mm [11; 12; 13]. These studies also indicate that, during hard braking, the standard deviation of head displacement is approximately 30% of the average excursion, suggesting substantial subject-to-subject variability. Therefore, the effects of occupant excursions on injury risk during autonomous vehicle-related crashes should be investigated under varying muscle lensing levels to support more generalizable conclusions. For autonomous vehicles, seating preferences are expected to differ from the conventional upright posture. Surveys on seating preferences of autonomous vehicles have revealed a strong preference for inclined seating, particularly during longer or leisure trips [14; 15; 16; 17]. However, in inclined postures, the effectiveness of conventional occupant restraint systems, including B-pillar-integrated (BPI) seatbelts, frontal airbags, and knee bolsters, might be reduced due to the increased distance between restraints and occupants at the onset of a crash. Epidemiological studies have indicated that occupants in reclined seating postures face higher injury risks [18] and increased mortality rates [19] than those in upright postures. Moreover, modeling studies using human body models have shown that reclined postures in frontal collisions can elevate the risk of lumbar injuries and submarining [20; 21]. Therefore, to comprehensively assess occupant crash safety in autonomous vehicles, reclined occupants should be considered.