Historically, the rear seat has been considered safer compared to the front seat for all restrained occupants; however, studies have found that the front seat in newer vehicles might be safer for older adults than the rear seat. While adults make up only 19% of rear seat occupants in frontal crashes, they make up 48% of fatalities (Tatem and Gabler, 2019). The rate of rear-seat occupancy by adults is expected to increase due to the use of ride share services and the potential of autonomous vehicles. Minimal research has been done to assess rear-seat occupant protection for a mid-sized adult male. Submarining, in which the lap belt slips off of the pelvis and directly loads the abdomen, is of particular concern as a restraint-based injury mechanism of the abdomen. The objective of this study is to investigate submarining protection and abdominal injury risk for rear-seated mid-sized male occupants in frontal crashes and to assess the biofidelity of two anthropomorphic test devices (ATDs) with respect to submarining response when compared to post-mortem human surrogates (PMHS). Twenty-four frontal crash sled tests were conducted with the THOR-50M and Hybrid III 50th-percentile male ATDs in three crash conditions and seven modern vehicles. The vehicles included a minivan, an SUV, 3 compact SUVs, and 2 sedans from the US vehicle fleet (model years 2017-2018). Four vehicles had conventional restraints (ie. 3-point belt with retractor at the shoulder) in the rear seat and three vehicles had advanced restraints (ie. 3-point belts with a pretensioner and load limiter at the retractor). Two of the crash conditions were vehicle-specific pulses: NCAP85 (ΔV = 56 kph) and Scaled (ΔV = 32 kph). The final pulse was a Generic (ΔV = 32 kph) pulse, created by averaging all seven Scaled pulses. Matched PMHS tests were conducted on four of the vehicles in the NCAP85 condition. Two tests were conducted for each vehicle with 8 PMHS for a total of 8 sled tests. The occurrence of submarining was identified and assessed for severity by: symmetry of lap belt slip, degree of abdominal loading, and forward excursion of the pelvis. Pelvis and lap-belt kinematics were assessed for the matched NCAP85 tests to identify trends with respect to submarining. Damage to the abdomen, pelvis, and lumbar spine of the PMHS was identified during post-test autopsy. The Hybrid III did not submarine in any test, but the THOR submarined in 16/24 tests. Three PMHS underwent submarining in 2/4 vehicles, and the THOR submarined in 3/4 vehicles in the matched NCAP85 tests. Three PMHS did not undergo submarining but sustained pelvis fractures at lap belt loads of 7.4 kN and higher, and damage to the abdominal viscera occurred regardless of submarining occurrence. Pelvis and lap-belt kinematics revealed the complex nature of the interactions of the occupant and the restraints within each vehicle environment, but did not clearly differentiate between submarining and non-submarining tests. The Hybrid III was not able to predict submarining risk for the PMHS in the rear seat environment. While the THOR underwent submarining, it was not perfect in predicting submarining risk. Pelvis geometry, lap belt engagement, and other factors contributed to the differences in submarining between the two ATDs and the PMHS. Restraint type was not indicative of whether or not the THOR or PMHS would submarine. Many other factors in the rear seat environments of these vehicles likely contribute in combination to the effectiveness of submarining prevention and occupant protection in the rear seat. This study provides information regarding submarining and abdominal injury for three surrogate types, two crash severities, and seven modern, real-world vehicle environments. Ultimately, this study found substantive gaps in occupant protection in the rear seats of modern vehicles for mid-sized adult male occupants. Tatem, W. M., and Gabler, H. C. (2019). Differential fatality risk between rear and front seat passenger vehicle occupants in frontal crashes. In Proceedings of the 2019 International IRCOBI Conference on the Biomechanics of Injury (pp. 554–560). / Doctor of Philosophy / Historically, the rear seat has been considered safer than the front seat for restrained occupants in frontal crashes. However, with advances in safety systems for the front seat, studies have found that the front seat might be safer for older adult occupants. The objective of this study is to investigate submarining protection and abdominal injury risk for rear-seated mid-sized male occupants in frontal crashes. Submarining occurs when the lap belt slips off of the pelvis and directly loads the abdomen, potentially producing severe abdominal injuries. Twenty-four sled tests were conducted with the THOR-50M and Hybrid III 50th-percentile male anthropomorphic test devices (ATDs) in three crash conditions and seven modern vehicles. The vehicles selected included a minivan, SUVs, compact SUVs, and sedans from the US vehicle fleet. Three of the vehicles had advanced restraints in the rear seat and four had conventional restraints. The three crash conditions were a generic low speed test and a low and high-speed vehicle-specific crash pulse. Eight tests were conducted with eight different post-mortem human surrogates on a subset of four vehicles (2 with advanced restraints, 2 with conventional restraints) using the high-speed crash condition. The Hybrid III never submarined, but the THOR submarined in 16 out of 24 tests (5 out of 7 vehicles). Three out of eight PMHS submarined, in two of the four vehicles. Three heavier PMHS sustained pelvis fractures, and all but one PMHS had sustained damage to the abdominal viscera. Restraint type was not an indicator of submarining risk in the rear seat, suggesting that other seat and vehicle design variables contribute to submarining risk. Comparison of the responses of the ATDs with the PMHS suggests that the THOR is a more reasonable surrogate than the Hybrid III for submarining assessment in the rear seat. Inclusion of data from other body regions is necessary to make a definitive determination of the appropriate ATD for the assessment of occupant protection for a mid-sized male in the rear seat during frontal crashes. Overall, this study suggests that protection against submarining and injury to the pelvis and abdomen for mid-sized male passengers in the rear seat of modern vehicles in the US fleet could be improved.

Le sous-marinage, apparaissant lorsque la ceinture pelvienne glisse au-dessus des épines iliaques antérosupérieures (E.I.A.S.) du bassin, est la cause principale des lésions abdominales sévères. Ce phénomène, conditionné par l’angle relatif entre la ceinture pelvienne et le bassin, est fortement lié à la cinématique du bassin au cours du choc. Cette dernière dépend des efforts et moments qui y sont appliqués, provenant principalement de la colonne lombaire, des hanches, du contact avec l’assise du siège ainsi que de la ceinture pelvienne. L’objectif est de caractériser le comportement de la population au regard du sousmarinage. Cela passe par l’identification des paramètres individuels influents sur le phénomène et par l’étude de leur distribution sur la population. Pour cela, neuf essais sur sujets humains post-mortem (S.H.P.M.) ont été effectués dans un environnement simplifié. Trois configurations de choc, chacune testée sur trois sujets, ont été définies. Les résultats ont ensuite servi de base pour la validation d’un modèle éléments finis d’être humain. Le modèle a été amélioré de façon globale vis-à-vis des corridors définis par les réponses S.H.P.M. et personnalisé au niveau de la géométrie, de la répartition des masses et du comportement de la colonne lombaire pour correspondre à chacun des neuf sujets. La personnalisation de ces paramètres a permis de reproduire les comportements observés en essais. Enfin, le modèle a été utilisé dans une étude numérique pour approfondir la compréhension de la cinématique du bassin, d’une part, et identifier les paramètres individuels influençant le sous-marinage, d’autre part. La répartition des masses, la raideur de la colonne lombaire et l’orientation initiale du bassin influencent l’apparition du sous-marinage. L’ouverture des ailes iliaques, la position des E.I.A.S par rapport au point H, la profondeur de l’échancrure iliaque et l’épaisseur des tissus entre le bassin et la ceinture jouent aussi un rôle. / Submarining occurs in frontal crashes when the lap belt slides over the anterior superior iliac spine (ASIS) and is the principal cause of AIS 3+ abdominal injuries. Submarining is the consequence of the pelvis kinematics relative to the lap belt, driven by the equilibrium of forces and moments applied to the pelvis. The four main components playing a role in the pelvis kinematics are the lumbar spine, the hips, the seat pan and the lap belt. The purpose is to characterize the population behavior regarding submarining. This requires to identify individual parameters having an effect on submarining and to examine their distribution among the population. A nine post-mortem human subject (PMHS) sled test campaign was carried out on a simplified environment. Three test configurations were defined. Each configuration was realized on three PMHS. The test results were used as reference data for a human finite element model validation. The model was improved to better fit the PMHS corridor responses and then personalized regarding the geometry, the mass distribution and the lumbar spine behavior to obtain nine models matching each PMHS. The personalized models responses were consistent with the PMHS ones. Finally, the human model was used in a numerical study. The numerical study was aimed at deepen the understanding of the pelvis kinematics on the one hand, and investigate the influence of several individual parameters on submarining on the other hand. The mass distribution, the lumbar spine stiffness and the initial pelvis orientation have revealed an influence on the submarining observation. The iliac wing angle, the position of the ASIS relative to the H-point, the iliac notch depth and the thickness of the soft tissues between the pelvis and the lap belt were also identified to have an effect on submarining.