Human Lumbar Spine Injury Risk in Dynamic Combined Compression and Flexion Loading.

Anticipating changes to vehicle interiors with future automated driving systems, the automobile industry recently has focused attention on crash response in novel postures with increased seatback recline. Prior research found that this posture may result in greater risk of lumbar spine injury in the event of a frontal crash. This study developed a lumbar spine injury risk function (IRF) that estimated injury risk as a function of simultaneously applied compression force and flexion moment. Force and moment failure data from 40 compression-flexion tests were utilized in a Weibull survival model, including appropriate data censoring. A mechanics-based injury metric was formulated, where lumbar spine compression force and flexion moment were normalized by specimen geometry. Subject age was incorporated as a covariate to further improve model fit. A weighting factor was included to adjust the influence of force and moment, and parameter optimization yielded a value of 0.11. Thus, the normalized compression force component had a greater effect on injury risk than the normalized flexion moment component. Additionally, as force was nominally increased, less moment was required to produce injury for a given age and specimen geometry. The resulting IRF may be utilized to improve occupant safety in the future.

A naturalistic study of passenger seating position, posture, and restraint use in second-row seats.

OBJECTIVE: The objective of the current study was to increase scientific understanding of rear-seat passenger seating position, postures, CRS use, and belt use through a naturalistic study. A secondary objective was to compare data from vehicles used in ride-hailing with data from other vehicles. METHOD: Video cameras were installed in the passenger cabins of the vehicles of 75 drivers near the center of the windshield. The video data were downloaded after the vehicles were operated by their owners for two weeks. Video frames were sampled from near the ends and in the middle of each trip, and at five-minute intervals in trips longer than 15 min. A total of 7,323 frames with second-row passengers were manually coded. RESULTS: A total of 444 unique second-row passengers were identified in video frames from 1,188 trips taken in 65 of the 75 vehicles in the study. Two of the vehicles that were driven for commercial ride-hailing during the study period accounted for 199 (45%) of the passengers. Considering multiple passengers in some trips, a total of 1,899 passenger-trips were identified. For passengers not using child restraint systems (CRS), the belt use rate was 65% in the non-ride-hailing vehicles versus 32% among passengers in the ride-hailing vehicles. No CRS use was observed in the ride-hailing vehicles. Among children using backless boosters, the shoulder belt was lateral to the clavicle or under the arm in 26% of frames. Among belted passengers not using CRS, the belt was lateral to the clavicle or on the neck about 6% of the time. Belted passengers not using CRS were observed leaning to the left or right about 27% of the time, with leaning away from the shoulder belt more common than leaning into the belt. CONCLUSIONS: This study is the first to report seating position, posture, and belt fit observations for a large naturalistic sample of second-row passengers that includes adult occupants. The data suggest that low rear seat belt use rates remain a concern, particularly in ride-hailing vehicles. Non-nominal belt placement and posture may also be common in second-row seating positions.

Failure tolerance of the human lumbar spine in dynamic combined compression and flexion loading.

Vehicle safety systems have substantially decreased motor vehicle crash-related injuries and fatalities, but injuries to the lumbar spine still have been reported. Experimental and computational analyses of upright and, particularly, reclined occupants in frontal crashes have shown that the lumbar spine can be subjected to simultaneous and out-of-phase combined axial compression and flexion loading. Lumbar spine failure tolerance in combined compression-flexion has not been widely explored in the literature. Therefore, the goal of this study was to measure the failure tolerance of the lumbar spine in combined compression and flexion. Forty lumbar spine segments with three vertebrae (one unconstrained) and two intervertebral discs (both unconstrained) were pre-loaded with axial compression (2200N, 3300N, or 4500N) and then subjected to rotation-controlled dynamic flexion bending until failure. Clinically relevant middle vertebra fractures were observed in twenty-one of the specimens, including compression and burst fractures. The remaining nineteen specimens experienced failure at the potting-grip interface. Failure tolerance varied within the sample and were categorized by the appropriate data censoring, with clinically relevant middle vertebrae fractures characterized as uncensored or left-censored and potting-grip fractures characterized as right-censored. Average failure force and moment were 3290N (range: 1580N to 5042N) and 51Nm (range: 0Nm to 156 Nm) for uncensored data, 3686N (range: 3145N to 4112N) and 0Nm for left-censored data, and 3470N (range: 2138N to 5062N) and 101Nm (range: 27Nm to 182Nm) for right-censored data. These data can be used to develop and improve injury prediction tools for lumbar spine fractures and further research in future safety systems.

Effect of Temperature and Freezing on Human Adipose Tissue Material Properties Characterized by High-Rate Indentation: Puncture Testing.

The characterization of human subcutaneous adipose tissue (SAT) under high-rate loading is valuable for development of biofidelic finite element human body models (FE-HBMs) to predict seat belt-pelvis interaction and injury risk in vehicle crash simulations. While material characterization of SAT has been performed at 25 °C or 37 °C, the effect of temperature on mechanical properties of SAT under high-rate and large-deformation loading has not been investigated. Similarly, while freezing is the most common preservation technique for cadaveric specimens, the effect of freeze-thaw on the mechanical properties of SAT is also absent from the literature. Therefore, the aim of this study was to determine the effect of freezing and temperature on mechanical properties of human SAT. Fresh and previously frozen human SAT specimens were obtained and tested at 25 °C and 37 °C. High-rate indentation and puncture tests were performed, and indentation-puncture force-depth responses were obtained. While the chance of material failure was found to be different between temperatures and between fresh and previously frozen tissue, statistical analyses revealed that temperature and freezing did not change the shear modulus and failure characteristics of SAT. Therefore, the results of the current study indicated that SAT material properties characterized from either fresh or frozen tissue at either 25 °C or 37 °C could be used for enhancing the biofidelity of FE-HBMs.

Multidirectional mechanical properties and constitutive modeling of human adipose tissue under dynamic loading.

The mechanical behavior of subcutaneous adipose tissue (SAT) affects the interaction between vehicle occupants and restraint systems in motor vehicle crashes (MVCs). To enhance future restraints, injury countermeasures, and other vehicle safety systems, computational simulations are often used to augment experiments because of their relative efficiency for parametric analysis. How well finite element human body models (FE-HBMs), which are often used in such simulations, predict human response has been limited by the absence of material models for human SAT that are applicable to the MVC environment. In this study, for the first time, dynamic multidirectional unconfined compression and simple shear loading tests were performed on human abdominal SAT specimens under conditions similar to MVCs. We also performed multiple ramp-hold tests to evaluate the quasilinear viscoelasticity (QLV) assumption and capture the stress relaxation behavior under both compression and shear. Our mechanical characterization was supplemented with scanning electron microscopy (SEM) performed in different orientations to investigate whether the macrostructural response can be related to the underlying microstructure. While the overall structure was shown to be visually different in different anatomical planes, a preferred orientation of any fibrous structures could not be identified. We showed that the nonlinear, viscoelastic, and direction-dependent responses under compression and shear tests could be captured by incorporating QLV in an Ogden-type hyperelastic model. Our comprehensive approach will lead to more accurate computational simulations and support the collective effort on the research of future occupant protection systems. STATEMENT OF SIGNIFICANCE: There is an urgent need to characterize the mechanical behavior of human adipose tissue under multiple dynamic loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We performed the first series of experiments on human adipose tissue specimens to characterize the multi-directional compression and shear behavior at impact loading rates and obtained scanning electron microscope images to investigate whether the macrostructural response can be related to the underlying microstructure. The results showed that human adipose tissue is nonlinear, viscoelastic and direction dependent, and its mechanical response under compression and shear tests at different loading rates can be captured by incorporating quasi-linear viscoelasticity in an Ogden-type hyperelastic model.

Comparison of porcine and human adipose tissue loading responses under dynamic compression and shear: A pilot study.

Understanding the mechanical properties of human adipose tissue, and its influence on seat belt-pelvis interaction is beneficial for computational human body models that are developed for injury prediction in the vehicle crashworthiness simulations. While various studies have characterized adipose tissue, most of the studies used porcine adipose tissue as a surrogate, and none of the studies were performed at loading rates relevant for motor vehicle collisions. In this work, the mechanical response of human and porcine adipose tissue was studied. Two dynamic loading modes (compression and simple shear) were tested in adipose tissue extracted from the human abdomen and porcine back. An Ogden hyperelastic model was used to fit the loading response, and specific material parameters were obtained for each specimen. Two-sample t-tests were performed to compare the effective shear moduli and peak stresses from porcine and human samples. The material response of the human adipose tissue was consistent with previous studies. Porcine adipose tissue was found to be significantly stiffer than human adipose tissue under compression and shear loading. Also, when material model parameters were fit to only one loading mode, the predicted response in the other mode showed a poor fit.

Prevalence of non-nominal seat positions and postures among front-seat passengers.

OBJECTIVE: Recent studies have suggested that a relationship exists between crash injury risk and occupant posture, particularly in postures different from those used with anthropomorphic test devices (ATDs) in crash testing. The objective of this study was to increase scientific understanding of typical front-seat passenger postures through a naturalistic study. METHOD: Video cameras were installed in the passenger cabins of the vehicles of 75 drivers. Reflective targets were attached to the seats and the seat position and seat back angle was moved through their available ranges during instrumentation. The video data, along with vehicle acceleration and location data, were downloaded after the vehicles were operated as usual by their owners for two weeks. Video frames were manually coded to identify characteristics of front-seat passenger posture and position. Seat position and seat back angle were estimated using the calibration data obtained during vehicle instrumentation. RESULTS: Video frames from a total of 2733 trips were coded for 306 unique front-seat passengers. For these trips, a total of 13638 frames were coded; each frame represents about four minutes of travel time. The head was rotated left or right in 33% of frames, and the torso was rotated left or right about 10% of the time and pitched forward in almost 10% of frames. No seat position or seat back angle change was noted in 40 (53%) of vehicles and the distributions of seat position and seat back angle on arrival were essentially unchanged during travel. The seat was positioned full-rear on the seat track about 23% of the time and rearward of the mid-track position in 92% of frames. The mean seat back angle was 25.4 degrees (standard deviation 6.4 degrees); seat back angle was greater than 30 degrees in 15% of frames and greater than 35 degrees in less than 1% of frames. CONCLUSIONS: This study is the first to report distributions of postures, seat positions, and seat back angles for front-seat passengers. Seat positions rearward of the middle of the seat adjustment range are common, but highly reclined postures are infrequent. Non-nominal torso and head postures also are nontrivial.

Comparison of three-point belt fit between humans and Hybrid-III anthropometric test devices in a driver mockup.

Objective: The Hybrid-III anthropometric test devices (ATDs) are widely used by the automotive industry to evaluate restraint system performance in standardized vehicle crash tests. The relationship between the belt fit measured for people in driving posture and the belt fit obtained with ATDs has not been reported in the literature. The present study compares lap and shoulder belt fit data from ATDs and to a statistical estimate for drivers using age, stature, and BMI.Methods: The lap and shoulder belt fits were measured for small-female and midsize-male Hybrid-III ATDs in a laboratory mockup of a midsize sedan. A range of lower and upper belt anchorage locations were used. The ATD belt fit data were compared with predictions from a regression model developed by data from 97 men and women measured in the same driving package conditions. Humans were free to position the belt comfortably, even if the position was not optimal.Results: The measurements of the ATD belt fit were obtained and compared to the regression estimate for a driver using age, stature, and BMI as predictors. For the small female, the ATD's lap belt was placed 46 mm further forward and 12 mm lower relative to the pelvis than the regression model estimates for a driver's lap belt placement. For the midsize male, the lap portion of the belt was placed 13 mm more rearward and 33 mm lower on the physical ATD than the regression model estimates for a similarly sized driver. The shoulder belt was placed an average of 66 mm more inboard and 11 mm more outboard on the small-female and midsize-male physical ATDs, respectively, compared with regression model estimates for drivers.Conclusions: Differences in the lap and shoulder belt fits were quantified between the physical ATDs and regression predictions for similarly sized humans in driving postures. The consequences of these differences should be investigated to help increase understanding of the relationship between belt fit and belt performance.

Passenger head kinematics in abrupt braking and lane change events.

OBJECTIVE: A test track study was conducted to quantify patterns of adult front seat passenger head motion during abrupt vehicle maneuvers. METHOD: Eighty-seven men and women with a wide range of body sizes and ages participated in data collection on a closed test track in a passenger sedan under manual control by a test driver. Because a primary goal of the study was to gather "unaware" data, the participants were instructed that the study was concerned with vehicle dynamics and they were required to read from a questionnaire taped to the top of their thighs as the drive began. The first event was a hard brake (approximately 1 g) to a stop from 35 mph (56 kph). Within the space of approximately 5 min the participants also experienced an aggressive lane change, a sharp right turn with simultaneous hard braking, and a second hard braking event. A Microsoft Kinect v2 sensor was positioned to view the area around the front passenger seat. Head location was tracked using the Kinect data with a novel methodology that fit 3D head scan data to the depth data acquired in the vehicle. RESULT: The mean (standard deviation) forward excursion of the estimated head center of gravity (CG) location in the first braking event was 135 (62) mm. The forward head CG excursion in the second braking event of 115 (51) mm was significantly less than that in the first, but the difference was small relative to the within-condition variance. Head excursion on the second braking trial was less than that on the first trial for 69% of participants. The mean maximum inboard head excursion in lane-change maneuvers was 118 (40) mm. Forward head excursions in braking were significantly smaller for older passengers and those with higher body mass index, but the combined factors accounted for less than 25% of the variance. Inboard head excursion in the lane-change event was significantly related to stature, but only about 7% of variance was related to body size. Head excursions for men and women did not differ significantly after accounting for body size. DISCUSSION: This is the first quantitative occupant dynamics study to use a large, diverse sample of passengers, enabling the exploration of the effects of covariates such as age and body size. CONCLUSIONS: The data demonstrate that a relatively large range of head positions can be expected to result from abrupt vehicle maneuvers. The data do not support simple scaling of excursions based on body size.

Driver head locations: Considerations for head restraint design.

OBJECTIVE: U.S. FMVSS 202a requires that a vehicle head restraint lie within a specified distance (55 mm) from the physical headform on the head restraint measurement device (HRMD). Smaller values of this distance, known as backset, are frequently associated with improved protection against neck injury in rear impact. In some vehicles, small backsets are also associated with complaints of head restraint interference with drivers' preferred head positions. The objective of this study is to examine head/head restraint distances using data from a lab study of driving posture to provide guidance for safe and comfortable head restraint design. METHODS: Head positions were measured for 88 U.S. drivers in a laboratory mockup using a seat from a mid-size sedan. The head restraint was removed to allow measurement of drivers' preferred head locations without interference from the head restraint. Rates of disaccommodation, defined as interference between predicted possible head restraint locations and drivers' preferred head locations, were analyzed at HRMD-referenced backsets of 25, 50, 75, and 100 mm measured at 22° and 25° seat back angles. RESULTS: With HRMD-referenced backsets of 25 mm and 50 mm measured at 25°, the head restraint intersected the preferred head locations of 17.9 and 5.2% of the drivers, respectively. An HRMD-referenced backset measured at 22° produced larger accommodation rates than the same backset measured at 25°. CONCLUSIONS: The reported distribution of occupant head positions and the resulting restrictions on comfortable head restraint position at various HRMD-referenced backsets and seat back angles help provide guidance for head restraint design. Knowing the actual mean driver-selected seat back angle for a particular vehicle seat and the model presented in this work, a manufacturer can choose a head restraint location that will have a high likelihood of complying with FMVSS backset requirements while also achieving minimal disaccommodation. The findings in this study support the flexibility in the current FMVSS 202a that permits testing at more upright seat back angles than the 25° originally proposed.

Evaluating an intervention to improve belt fit for adult occupants: Promoting positive beliefs.

INTRODUCTION: Seat belt use provides significant public health benefit, however, most public awareness campaigns have generally focused on seat belt use rather than encouraging adults to improve seat belt fit with belt placement. This study provides an evaluation of a video-based intervention to improve adult belt fit assessing whether a video-based intervention can target beliefs and knowledge of seat belt placement and be perceived as relevant by the target audience. METHOD: An intervention group of 29 adults (15 women and 14 men) and a comparison group of 99 adults (41 women and 47 men) participated. RESULTS: The intervention group had significantly more favorable beliefs around belt fit than the comparison group related to Health Belief Model constructs of higher self-efficacy, greater benefits, and fewer barriers. The intervention group was also significantly better at accurately drawing belt fit than the comparison group. The video intervention was described as relevant, interesting, and the intervention group favored the provision of a diverse sample of models in the intervention. CONCLUSIONS: Overall, the study provides insight into relevant target beliefs for an intervention focused on belt fit and suggests that a brief video-based intervention in the style of a public service announcement may be effective in promoting positive beliefs and knowledge around belt fit. Future efforts should confirm these findings with a larger sample size spanning multiple geographic and demographic areas. PRACTICAL APPLICATIONS: These findings can help better inform intervention initiatives to improve occupant belt fit.

Evaluating an intervention to improve belt fit for adult occupants.

INTRODUCTION: Previous laboratory studies have demonstrated that some drivers position their seat belts suboptimally. Specifically, the lap portion of the belt may be higher and farther forward relative to the pelvis than best practice, and the shoulder portion of the belt may be outboard or inboard of mid-shoulder. This study evaluated the performance of a video-based intervention for improving the belt fit obtained by drivers. METHOD: Twenty-nine adult drivers participated in this study. Belt fit was measured before and after the intervention in participants' vehicles and in a laboratory mockup. RESULTS: Data from both the in-vehicle and laboratory belt measures found that 95% of participants sampled improved some aspect of lap belt fit. For the in-vehicle test conditions, participants who lowered the lap belt location (Z) after the intervention showed an improvement of 26 mm on average. Among those participants who shifted the horizontal lap belt location rearward (closer to the pelvis), an average improvement of 36 mm was observed. No significant differences were observed between baseline and post-intervention shoulder belt fit. CONCLUSIONS: The results provide preliminary evidence that an intervention improves driver belt fit. More research is needed to establish what aspects of this intervention affected behavior and how effective such an intervention is in the context of public health. PRACTICAL APPLICATIONS: These findings can help better inform intervention initiatives to improve occupant belt fit.

Comparison of three-point belt fit between humans and ATDs in rear seats.

OBJECTIVE: The anthropomorphic test devices (ATDs) in the Hybrid III family are widely used as human surrogates to test the crash performance of vehicles. A previous study demonstrated that passenger belt fit in rear seats was affected by high body mass index (BMI) and to a lesser extent by increased age. Specifically, the lap belt was worn higher and more forward as BMI and age increased. The objective of this study was to compare passenger belt fit to the belt fit achieved when installing the small female and midsize male Hybrid III adult ATDs using standard procedures. METHODS: The ATDs were installed using standardized procedures in the same conditions previously used with volunteers. Belt fit was measured using methods analogous to those used for the volunteers. Comparative human belt fit values were obtained by using regression analysis with the volunteer data to calculate the mean expected belt fit for people the same size as the ATDs. RESULTS: For the small female ATD, the upper edge of the lap belt was on average 59 mm forward and 11 mm above the anterior-superior iliac spine (ASIS) landmark on the ATD pelvis bone. In contrast, the belt position for similar size passengers was 17 mm forward and 22 mm above the ASIS. For the midsize male ATD, the belt was 34 mm forward and 10 mm above the ASIS. For similar size passengers, the position was 38 mm forward and 44 mm above the ASIS. For context, the belt width in this study was 38 mm. DISCUSSION: The results suggest that the lap belt fit obtained by ATDs is more idealized but more repeatable compared to that achieved by similar size passengers. Future standardization efforts should consider investigating whether new belt-positioning procedures with ATDs may improve the biofidelity of ATD response.

Development, Evaluation, and Sensitivity Analysis of Parametric Finite Element Whole-Body Human Models in Side Impacts.

Occupant stature and body shape may have significant effects on injury risks in motor vehicle crashes, but the current finite element (FE) human body models (HBMs) only represent occupants with a few sizes and shapes. Our recent studies have demonstrated that, by using a mesh morphing method, parametric FE HBMs can be rapidly developed for representing a diverse population. However, the biofidelity of those models across a wide range of human attributes has not been established. Therefore, the objectives of this study are 1) to evaluate the accuracy of HBMs considering subject-specific geometry information, and 2) to apply the parametric HBMs in a sensitivity analysis for identifying the specific parameters affecting body responses in side impact conditions. Four side-impact tests with two male post-mortem human subjects (PMHSs) were selected to evaluate the accuracy of the geometry and impact responses of the morphed HBMs. For each PMHS test, three HBMs were simulated to compare with the test results: the original Total Human Model for Safety (THUMS) v4.01 (O-THUMS), a parametric THUMS (P-THUMS), and a subject-specific THUMS (S-THUMS). The P-THUMS geometry was predicted from only age, sex, stature, and BMI using our statistical geometry models of skeleton and body shape, while the S-THUMS geometry was based on each PMHS's CT data. The simulation results showed a preliminary trend that the correlations between the PTHUMS- predicted impact responses and the four PMHS tests (mean-CORA: 0.84, 0.78, 0.69, 0.70) were better than those between the O-THUMS and the normalized PMHS responses (mean-CORA: 0.74, 0.72, 0.55, 0.63), while they are similar to the correlations between S-THUMS and the PMHS tests (mean-CORA: 0.85, 0.85, 0.67, 0.72). The sensitivity analysis using the PTHUMS showed that, in side impact conditions, the HBM skeleton and body shape geometries as well as the body posture were more important in modeling the occupant impact responses than the bone and soft tissue material properties and the padding stiffness with the given parameter ranges. More investigations are needed to further support these findings.

Statistical Models for Predicting Automobile Driving Postures for Men and Women Including Effects of Age.

BACKGROUND: Previously published statistical models of driving posture have been effective for vehicle design but have not taken into account the effects of age. OBJECTIVE: The present study developed new statistical models for predicting driving posture. METHODS: Driving postures of 90 U.S. drivers with a wide range of age and body size were measured in laboratory mockup in nine package conditions. Posture-prediction models for female and male drivers were separately developed by employing a stepwise regression technique using age, body dimensions, vehicle package conditions, and two-way interactions, among other variables. RESULTS: Driving posture was significantly associated with age, and the effects of other variables depended on age. A set of posture-prediction models is presented for women and men. The results are compared with a previously developed model. CONCLUSION: The present study is the first study of driver posture to include a large cohort of older drivers and the first to report a significant effect of age. APPLICATION: The posture-prediction models can be used to position computational human models or crash-test dummies for vehicle design and assessment.

A statistical model including age to predict passenger postures in the rear seats of automobiles.

Few statistical models of rear seat passenger posture have been published, and none has taken into account the effects of occupant age. This study developed new statistical models for predicting passenger postures in the rear seats of automobiles. Postures of 89 adults with a wide range of age and body size were measured in a laboratory mock-up in seven seat configurations. Posture-prediction models for female and male passengers were separately developed by stepwise regression using age, body dimensions, seat configurations and two-way interactions as potential predictors. Passenger posture was significantly associated with age and the effects of other two-way interaction variables depended on age. A set of posture-prediction models are presented for women and men, and the prediction results are compared with previously published models. This study is the first study of passenger posture to include a large cohort of older passengers and the first to report a significant effect of age for adults. The presented models can be used to position computational and physical human models for vehicle design and assessment. Practitioner Summary: The significant effects of age, body dimensions and seat configuration on rear seat passenger posture were identified. The models can be used to accurately position computational human models or crash test dummies for older passengers in known rear seat configurations.

Evaluation of the Kinematic Responses and Potential Injury Mechanisms of the Jejunum during Seatbelt Loading.

High-speed biplane x-ray was used to research the kinematics of the small intestine in response to seatbelt loading. Six driver-side 3-point seatbelt simulations were conducted with the lap belt routed superior to the pelvis of six unembalmed human cadavers. Testing was conducted with each cadaver perfused, ventilated, and positioned in a fixed-back configuration with the spine angled 30° from the vertical axis. Four tests were conducted with the cadavers in an inverted position, and two tests were conducted with the cadavers upright. The jejunum was instrumented with radiopaque markers using a minimally-invasive, intraluminal approach without inducing preparation-related damage to the small intestine. Tests were conducted at a target peak lap belt speed of 3 m/s, resulting in peak lap belt loads ranging from 5.4-7.9 kN. Displacement of the radiopaque markers was recorded using high-speed x-ray from two perspectives. Marker trajectories were tracked using motion analysis software and projected into calibrated three-dimensional coordinates to quantify the seatbelt and jejunum kinematics for each test. Five of the six tests resulted in jejunum damage. Based on the autopsy findings and the assessment of the belt and jejunum kinematics, it is likely that direct abdominal interactions with the seatbelt resulting in compression and stretch of the jejunum are components of the mechanisms of crash-induced jejunum injuries. In addition, the presence of fluid or air in the portion of the jejunum in the load path appears to be necessary to create jejunum damage in the cadaver model. Overall, the kinematics and damage data generated in this study may be useful for future restraint system development.

Effects of driver characteristics on seat belt fit.

A laboratory study of posture and belt fit was conducted with 46 men and 51 women, 61% of whom were age 60 years or older and 32% age 70 years or older. In addition, 28% of the 97 participants were obese, defined as body mass index ≥ 30 kg/m^2. A mockup of a passenger vehicle driver's station was created and five belt anchorage configurations were produced by moving the buckle, outboard-upper (D-ring), and outboard-lower anchorages. An investigator recorded the three-dimensional locations of landmarks on the belt and the participant's body using a coordinate measurement machine. The location of the belt with respect to the underlying skeletal structures was analyzed, along with the length of belt webbing. Using linear regression models, an increase in age from 20 to 80 years resulted in the lap belt positioned 18 mm further forward relative to the pelvis, 26 mm greater lap belt webbing length, and 19 mm greater shoulder belt length. An increase in stature of 350 mm (approximately the range from 5th-percentile female to 95th-percentile male in the U.S. population) was associated with the lap belt 14 mm further forward relative to the pelvis, the shoulder belt 37 mm more outboard relative to the body centerline, and 38 mm less shoulder belt webbing length. Among the driver factors considered, body mass index had the greatest effects. An increase of BMI in 20 kg/m^2, which spans approximately the central 90% of U.S. adults, was associated with the lap belt being placed 102 mm further forward and 94 mm higher, relative to the pelvis, and increases in lap and shoulder belt webbing length of 276 and 258 mm, respectively. Gender did not have important effects on the analyzed belt fit measures after taking into account stature and body mass index. These results offer important considerations for future crash safety assessments and suggest that further research is needed to consider belt fit for older and obese occupants.

Prediction of visceral response to multi-directional loading as measured by the chestband.

Thoracic and abdominal injury outcomes are correlated to chestband-derived uniaxial metrics in post-mortem human specimen (PMHS) experiments. Yet, uniaxial metrics may neglect deformations remote from the measurement site which still may be relevant to injury risk in motor vehicle crashes. Using 2D chestband contours from PMHS experiments, visceral strain and strain energy density responses were examined using a planar viscoelastic finite element model. The model was exercised by applying to the periphery 21 subject-specific PMHS chestband deformation patterns representing four boundary conditions: (a) lateral impact with close-proximity torso airbag, (b) stationary close-proximity torso airbag loading, (c) flat rigid lateral impact, and (d) antero-lateral oblique rigid impact. ANOVA determined that mean peak responses were dependent on boundary condition (p<0.002). Using matched-pair experiment injury outcomes, 50% risk of visceral trauma corresponded to localized strain and strain energy density of 1.55 and 33.0 kJ/m(3) (p<0.1). Although strains were large, model response demonstrated sensitivity to impact boundary conditions and observed PMHS trauma. This model formulation is useful for comparative examination of injury risk from torso deformations measured experimentally using the chestband device.

Injury differences between small and large overlap frontal crashes.

Because small overlap impacts have recently emerged as a crash mode posing great injury risk to occupants, a detailed analysis of US crash data was conducted using the NASS/CDS and CIREN databases. Frontal crashes were subcategorized into small overlap impact (SOI) and large overlap impact (LOI) using crash and crush characteristics from the datasets. Injuries to head, spine, chest, hip and pelvis, and lower extremities were parsed and compared between crash types. MAIS 3+ occupants in NASS/CDS and CIREN demonstrated increased incidence of head, chest, spine, and hip/pelvis injuries in SOI compared to LOI. In NASS/CDS, subgaleal hematoma represented 48.6% of SOI head injury codes but 27.6% in LOI. Cervical spine posterior element fractures also represented greater proportions of SOI spine injuries (e.g., facet fractures: 27.8 vs. 14.0%), and proximal femur fractures represented a greater proportion of hip/pelvis injuries (e.g., intertrochanteric fracture: 32.5 vs. 11.8%). Tarsal/metatarsal fractures were a lesser proportion of lower extremity injuries in SOI compared to LOI. Occupant contact points inducing these injuries were observed in CIREN cases in some instances without compartment intrusion. These injuries suggest the substantial role of occupant kinematics in SOI which may induce suboptimal occupant restraint interaction.