Occupant kinematics in low-speed frontal sled tests: Human volunteers,Hybrid III ATD,and PMHS

A total of 34 dynamic matched frontal sled tests were performed, 17 low (2.5 g, Δv = 4.8 kph) and 17 medium (5.0 g, Δv = 9.7 kph), with five male human volunteers of approximately 50th percentile height and weight, a Hybrid III 50th percentile male ATD, and three male PMHS. Each volunteer was exposed to two impulses at each severity, one relaxed and one braced prior to the impulse. A total of four tests were performed at each severity with the ATD and one trial was performed at each severity with each PMHS. A Vicon motion analysis system, 12 MX-T20 2 megapixel cameras, was used to quantify subject 3D kinematics (±1 mm) (1 kHz). Excursions of select anatomical regions were normalized to their respective initial positions and compared by test condition and between subject types. The forward excursions of the select anatomical regions generally increased with increasing severity. The forward excursions of relaxed human volunteers were significantly larger than those of the ATD for nearly every region at both severities. The forward excursions of the upper body regions of the braced volunteers were generally significantly smaller than those of the ATD at both severities. Forward excursions of the relaxed human volunteers and PMHSs were fairly similar except the head CG response at both severities and the right knee and C7 at the medium severity. The forward excursions of the upper body of the PMHS were generally significantly larger than those of the braced volunteers at both severities. Forward excursions of the PMHSs exceeded those of the ATD for all regions at both severities with significant differences within the upper body regions. Overall human volunteers, ATD, and PMHSs do not have identical biomechanical responses in low-speed frontal sled tests but all contribute valuable data that can be used to refine and validate computational models and ATDs used to assess injury risk in automotive collisions.     

Finite element comparison of human and Hybrid III responses in a frontal impact

The improvement of finite element (FE) Human Body Models (HBMs) has made them valuable tools for investigating restraint interactions compared to anthropomorphic test devices (ATDs). The objective of this study was to evaluate the effect of various combinations of safety restraint systems on the sensitivity of thoracic injury criteria using matched ATD and Human Body Model (HBM) simulations at two crash severities. A total of seven (7) variables were investigated: 3-point belt with two (2) load limits, frontal airbag, knee bolster airbag, a buckle pretensioner, and two (2) delta-v's – 40 kph and 50 kph. Twenty four (24) simulations were conducted for the Hybrid III ATD FE model and repeated with a validated HBM for 48 total simulations. Metrics tested in these conditions included sternum deflection, chest acceleration, chest excursion, Viscous Criteria (V*C) criteria, pelvis acceleration, pelvis excursion, and femur forces. Additionally, chest band deflection and rib strain distribution were measured in the HBM for additional restraint condition discrimination. The addition of a frontal airbag had the largest effect on the occupant chest metrics with an increase in chest compression and acceleration but a decrease in excursion. While the THUMS and Hybrid III occupants demonstrated the same trend in the chest compression measurements, there were conflicting results in the V*C, acceleration, and displacement metrics. Similarly, the knee bolster airbag had the largest effect on the pelvis with a decrease in acceleration and excursion. With a knee bolster airbag the simulated occupants gave conflicting results, the THUMS had a decrease in femur force and the ATD had an increase. Preferential use of dummies or HBM's is not debated; however, this study highlights the ability of HBM metrics to capture additional chest response metrics.     

Influence of standing or seated pelvis on dummy responses in rear impacts

Objective

There is a question whether the standing or seated pelvis should be used in Hybrid III dummy evaluations of seats and belt restraint systems in severe rear impacts. This study compares the standing and seated Hybrid III pelvis in matched rear sled tests.

Methods

Sixteen sled tests were found at 10, 16 and 24 km/h rear delta V in Ford's archives where matched tests were run with the standing and seated pelvis in a belted Hybrid III dummy. Two new tests were conducted at 40 km/h rear delta V to extend the severity range. The head, chest and pelvis were instrumented with triaxial accelerometers and the upper and lower neck, thoracic spine and lumbar spine had transducers measuring triaxial loads and moments. Belt Loads were measured. High-speed video recorded different views of the dummy motion. Dummy kinematics and biomechanical responses were compared for all of the data with the two different Hybrid III pelvic designs.

Results

In the 40 km/h sled tests, the dummy motion and excursion were essentially similar with the standing and seated pelvis. The similarities included the lap belt interaction with the pelvis and the leg movement upward flexing the hip joint. Overall, similar biomechanic and kinematic responses were found, including the pelvic acceleration, spinal forces and moments. For the lower speed tests at 10, 16 and 24 km/h, the motion sequence was also similar with the two different pelvises, including the upward movement of the legs as the seat was loaded and rebound kinematics. The biomechanical responses were similar. The seated pelvis involves only a small portion of the upper leg molded into the vinyl skin of the pelvis and does not limit leg rotation at the hip joint. Furthermore, lap belt loads were minimal during the rearward movement of the dummy.

Conclusions

The matched testing showed no significant difference in occupant kinematics or biomechanical responses between the standing and seated pelvis in rear sled tests. The Hybrid III dummy with the seated pelvis is suitable for FMVSS 301 and other testing of seats and belt restraint systems in severe rear impacts.     

The effect of hardhats on head and neck response to vertical impacts from large construction objects

We evaluated the effectiveness of hardhats in attenuating head acceleration and neck force in vertical impacts from large construction objects. Two weight-matched objects (lead shot bag and concrete block) weighing 9.1 kg were dropped from three heights (0.91 m, 1.83 m and 2.74 m) onto the head of a 50th percentile male Hybrid III anthropomorphic test device (ATD). Two headgear conditions were tested: no head protection and an ANSI Type-I, Class-E hardhat. A third headgear condition (snow sport helmet) was tested at 1.83 m for comparison with the hardhat. Hardhats significantly reduced the resultant linear acceleration for the concrete block impacts by 70–95% when compared to the unprotected head condition. Upper neck compression was also significantly reduced by 26–60% with the use of a hardhat when compared to the unprotected head condition for the 0.91 and 1.83 m drop heights for both lead shot and concrete block drop objects. In this study we found that hardhats can be effective in reducing both head accelerations and compressive neck forces for large construction objects in vertical impacts.     

The response of the adult and ATD heads to impacts onto a rigid surface

Given the high incidence of TBI, head injury has been studied extensively using both cadavers and anthropomorphic test devices (ATDs). However, few studies have benchmarked the response of ATD heads against human data. Hence, the objective of this study is to investigate the response of adult and ATD heads in impact, and to compare adult Hybrid III head responses to the adult head responses.     

Effects of vehicle seat and belt geometry on belt fit for children with and without belt positioning booster seats

A laboratory study was conducted to quantify the effects of belt-positioning boosters on lap and shoulder belt fit. Postures and belt fit were measured for forty-four boys and girls ages 5–12 in four highback boosters, one backless booster, and on a vehicle seat without a booster. Belt anchorage locations were varied over a wide range. Seat cushion angle, seat back angle, and seat cushion length were varied in the no-booster conditions.     

Determination of pre-impact occupant postures and analysis of consequences on injury outcome--part II: biomechanical study

This paper considers pre-impact vehicle maneuvers and analyzes the resulting driver motion from their comfort seating position. Part I of this work consisted of analyzing the driver behavior during a simulated crash in a car driving simulator. The configuration of the virtual accident led to an unavoidable frontal crash with a truck. The typical response to this type of emergency event was to brace rearward into the seat and to straighten the arms against the steering wheel, or, to swerve to attempt to avoid the impacting vehicle. In a turn crossover maneuvers, the forearm is directly positioned on the airbag module at time of crash. This position represents a potential injurious situation and is investigated in this Part II.Static airbag-deployment tests were realized in collaboration with Zodiac using conventional airbag (sewn cushion, pyrotechnical system and open event) and a Hybrid III 50th Male Dummy seated with the left arm positioned in the path of the deploying airbag. These experiments were numerically reproduced with Madymo^® and the ellipsoid Hybrid III dummy model. The dummy arm interaction with airbag was correlated with experiments. Then, a numerical simulation of a frontal collision at 56 km/h was realized. The results of the computational runs put forward injurious situations when the driver's arm was in front of the steering wheel. Indeed, in this case, the arm could hit the head under airbag deployment and induced serious neck bending and violent head launching.To mitigate head and neck trauma in this out-of-position situation, an airbag prototype (bonded cushion, two pure helium cold gas generators allowing mono- or multi-stage inflating, patented silicone membrane) was proposed by Zodiac. The results of static airbag-deployment tests with conventional and prototype airbags showed a significant reduction of the maximum linear head acceleration and neck bending with airbag prototype when a dual stage inflating was ignited, due to a reduced ‘flinging’ of the arm.     

Protective level of safety harnesses combined with some racing car seats in frontal impacts—A laboratory study

As a basis for a prospective modification of the present seat-belt regulation in Sweden, the protective level of safety harnesses compared with three-point belts has been studied. Biomechanical tests were carried out with different combinations of belts and seats. The results showed that a three-point belt on a conventional seat offered the best protection in frontal impacts. The geometry of the safety harness (inverted Y-harness and four-point belt) induces the lap belt to slide over the iliac crest and the restraining force will be on the abdomen (submarining). This may be prevented by the use of a six-point belt, where two crotch straps keep the lap belt in position. The safety harness induces strong rebounds on the head, owing to the fact that the shoulder straps stop the forward motion of the torso too fast. High accelerations and HIC-values were registered for the head. The shoulder straps of the safety harnesses also expose the wearer's shoulders and spine to high stresses in frontal impacts, which may induce injuries to the shoulders and compression injuries to the spine. Various solutions which may result in an increase of the protective level of the system safety harness and racing-car seat in frontal impacts are discussed.     

Geographic and sociodemographic variation in self-reported seat belt use in the United States

Background

With new data available, we sought to update existing literature on the prevalence of self-reported seat belt use by state, region, and rural/urban status and to estimate the strength of the association between seat belt use and rural/urban status adjusted for type of seat belt law and several other factors.

Methods

We examined data on self-reported use of seat belts from 50 states, the District of Columbia, and three territories using the 2008 Behavioral Risk Factor Surveillance System, a state-based random-digit-dialed telephone survey (n = 406,552). Reported seat belt use was assessed by state, U.S. Census regions, and U.S. Department of Agriculture (USDA) rural/urban continuum codes.

Results

Overall, 85% of adults in the United States reported they always used seat belts. Regionally, the West had the highest prevalence of persons who reported that they always wear seat belts (89.6%) and the Midwest had the lowest (80.4%). States with primary seat belt laws had the highest prevalence of reported seat belt use, compared with states with secondary or no laws. After adjusting for various sociodemographic characteristics, body mass index, and type of seat belt law, persons in the most densely populated metropolitan areas were significantly more likely to report always wearing seat belts than those in most sparsely populated rural areas (adjusted odds ratio = 2.9).

Conclusion

Our findings reinforce the evidence that primary enforcement seat belt laws are effective for increasing seat belt use, and suggest that upgrading to primary enforcement laws will be an important strategy for reducing crash-related fatalities in rural areas.     

Injury patterns in frontal crashes: The association between knee-thigh-hip (KTH) and serious intra-abdominal injury

Safety belts protect occupants in frontal impacts by reducing occupant deceleration and preventing the occupant from hitting interior vehicle components likely to cause injury. However, occupants moving forward during the impact may contact the safety belt webbing across their chest and abdomen. We hypothesized that if the occupant loaded their knee-thigh-hip (KTH) region with enough force to result in injury to this region—it might prevent compression (and injury) of their abdomen by the safety belt. Crash Injury Research and Engineering Network (CIREN) data were used to test the association between KTH and intra-abdominal injury related to safety belts. Odds ratios with 95% confidence limits (CL) and logistic regression models were used to assess statistical significance. Analyses were based on 706 CIREN adult, front seat occupants using their safety belt and injured in frontal crashes. Occupants with KTH injury were four times less likely (adjusted odds ratio = 0.25, 95% CL 0.10, 0.62) to have concomitant serious intra-abdominal injury caused by the safety belt. Although safety belts save lives and prevent serious injury, some occupants may sustain serious intra-abdominal injury when the abdomen is loaded by the safety belt during a frontal impact. These results may be useful to motor vehicle manufacturers and others who design and test motor vehicle safety systems.     

Response corridors for the medial–lateral compressive stiffness of the human arm: Implications for side impact protection

The biofidelity of side impact anthropomorphic test devices (ATDs) is crucial in order to accurately predict injury risk of human occupants. Although the arm serves as a load path to the thorax, there are currently no biofidelity response requirements for the arm. The purpose of this study was to characterize the compressive stiffness of male and female arms in medial–lateral loading and develop corresponding stiffness response corridors. This was accomplished by performing a series of pendulum tests on 18 isolated post-mortem human surrogate (PMHS) arms, obtained from four male and five female surrogates, at impact velocities of 2 m/s and 4 m/s. Matched tests were performed on the arm of the SID-IIs ATD for comparison. The arms were oriented vertically with the medial side placed against a rigid wall to simulate loading during a side impact automotive collision. The force versus deflection response data were normalized to that of a 50th percentile male and a 5th percentile female using a new normalizing technique based on initial arm width, and response corridors were developed for each impact velocity. A correlation analysis showed that all non-normalized dependent variables (initial stiffness, secondary stiffness, peak force, and peak deflection) were highly correlated with the initial arm width and initial arm circumference. For both impact velocities the PMHS arms exhibited a considerable amount of deflection under very low force before any substantial increase in force occurred. The compression at which the force began to increase considerably was consistent with the average tolerable medial–lateral arm compression experienced by volunteers. The initial stiffness (K1), secondary stiffness (K2), peak force, and peak deflection were found to significantly increase (p < 0.05) with respect to impact velocity for both the non-normalized and normalized PMHS data. Although the response of the SID-IIs arm was similar to that of the female PMHS arms for both impact velocities, the SID-IIs arm did not exhibit a considerable toe region and therefore did not fall within the response corridors for the 5th percentile female. Overall, the results of the current study could lead to improved biofidelity of side impact ATDs by providing valuable data necessary to validate the compressive response of the ATD arm independent of the global ATD thoracic response.     

Hybrid III anthropomorphic test device (ATD) response to head impacts and potential implications for athletic headgear testing

The Hybrid III 50th percentile male anthropomorphic test device (ATD) is the most widely used human impact testing surrogate and has historically been used in automotive or military testing. More recently, this ATD is finding use in applications evaluating athletic helmet protectivity, quantifying head impact dosage and estimating injury risk. But ATD head–neck response has not been quantified in omnidirectional athletic-type head impacts absent axial preload. It is probable that headgear injury reduction that can be quantified in a laboratory, including in American football, boxing, hockey, lacrosse and soccer, is related to a number of interrelated kinetic and kinematic factors, such as head center of gravity linear acceleration, head angular acceleration, head angular velocity, occipito-cervical mechanics and neck stiffness. Therefore, we characterized ATD head–neck dynamic response to direct head impacts in a series of front, oblique front and lateral head impacts.     

Improving seat belt use among teen drivers: Findings from a service-learning approach

Background

Low seat belt use and higher crash rates contribute to persistence of motor vehicle crashes as the leading cause of teenage death. Service-learning has been identified as an important component of public health interventions to improve health behavior.

Methodology

A service-learning intervention was conducted in eleven selected high schools across the United States in the 2011–2012 school year. Direct morning and afternoon observations of seat belt use were used to obtain baseline observations during the fall semester and post-intervention observations in the spring. The Mann–Whitney U test for 2 independent samples was used to evaluate if the intervention was associated with a statistically significant change in seat belt use. We identified factors associated with seat belt use post-intervention using multivariable logistic regression.

Results

Overall seat belt use rate increased by 12.8%, from 70.4% at baseline to 83.2% post-intervention (p < 0.0001). A statistically significant increase in seat belt use was noted among white, black, and Hispanic teen drivers. However, black and Hispanic drivers were still less likely to use seat belts while driving compared to white drivers. Female drivers and drivers who had passengers in their vehicle had increased odds of seat belt use.

Conclusion

A high school service-learning intervention was associated with improved seat belt use regardless of race, ethnicity, or gender, but did not eliminate disparities adversely affecting minority youth. Continuous incorporation of service-learning in high school curricula could benefit quality improvement evaluations aimed at disparities elimination and might improve the safety behavior of emerging youth cohorts.     

Usage patterns and misuse rates of automatic seat belts by system type

This study examined seat belt usage in North Carolina by drivers of 4,151 late model cars equipped with a variety of restraint system types. We measured usage by restraint type (automatic belt, air bag, manual belt), by make/model and by driver characteristics (age, sex, and race). Usage ranged from a high of 94.2% for motorized shoulder belts (but with only 28.6% lap belt usage in these cars) to 73.9% usage of manual lap/shoulder belts in cars equipped with air bags. Various types of misuse of the shoulder belt (e.g. excessive slack, detachment from the door, placement under the arm) were observed in nearly 6% of the sample.     

Increased risk of driver fatality due to unrestrained rear-seat passengers in severe frontal crashes

While belt usage among rear-seat passengers is disproportionately lower than their front-seat counterpart, this may have serious consequences in the event of a crash not only for the unbelted rear-seat passenger but also for the front-seat passengers as well. To quantify that effect, the objective of the study is to evaluate the increased likelihood of driver fatality in the presence of unrestrained rear-seat passengers in a severe frontal collision. U.S.-based census data from 2001 to 2009 fatal motor vehicle crashes was used to enroll frontal crashes which involved 1998 or later year vehicle models with belted drivers and at least one adult passenger in the rear left seat behind the driver. Results using multivariate logistic regression analysis indicated that the odds of a belt restrained driver sustaining a fatal injury was 137% (95% CI = 95%, 189%) higher when the passenger behind the driver was unbelted in comparison to a belted case while the effects of driver age, sex, speed limit, vehicle body type, airbag deployment and driver ejection were controlled in the model. The likelihood of driver fatality due to an unrestrained rear left passenger increased further (119–197%) in the presence of additional unrestrained rear seat passengers in the rear middle or right seats. The results from the study highlight the fact that future advances to front row passive safety systems (e.g. multi-stage airbag deployment) must be adapted to take into account the effect of unrestrained rear-seat passengers.     

Methods to mitigate injury to toddlers in near-side impact crashes

This research focuses on the injury potential of children seated in forward-facing child safety seats during side impact crashes in a near-side seated position. Side impact dynamic sled tests were conducted by NHTSA at Transportation Research Center Inc. (TRC) using a Hybrid III 3-year-old child dummy seated in a convertible forward/rearward child safety seat. The seat was equipped with a LATCH and a top tether and the dummy was positioned in forward-facing/near-side configuration. The test was completed using an acceleration pulse with a closing speed of 24.1 km/h, in the presence of a rigid wall and absence of a vehicle body. A fully deformable finite element model of a child restraint seat, for side impact crash investigations, has been developed which has also been previously validated for frontal and far side impacts. A numerical model utilizing a Hybrid III 3-year-old dummy, employing a similar set-up as the experimental sled test was generated and simulated using LS DYNA. The numerical model was validated by comparing the head and the chest accelerations, resultant upper and lower neck forces and moments from the experimental and numerical tests. The simulation results were observed to be in good agreement to the experimental observations. A numerical model of the near-side laboratory tests, utilizing a Q3s child dummy, was also created for parametric studies regarding different ISOFIX configurations. Further, numerical simulations were completed for both the dummy models with rectangular and cross-shaped sections of rigid ISOFIX systems. In addition, studies were conducted to confine lateral movement of the dummy's head by adding energy absorbing foam on the side wings in the vicinity of the contact region of the CRS. It was observed that the use of rigid ISOFIX system reduced the lateral displacement of the CRS and different injury parameters. Addition of energy absorbing foam blocks was effective in further reducing the lateral displacement of the dummy's head. The lateral displacement of the head was reduced by 68 mm by using cross-shaped section ISOFIX with energy absorbing foam near the vicinity of the head of the Hybrid III 3-year-old dummy compared to the flexible LATCH configuration without foam. For the Q3s dummy, the lateral displacement of the head was reduced by 48 mm by utilizing a cross-shaped section rigid ISOFIX system with the addition of energy absorbing foam compared to the flexible LATCH configuration.     

A retrospective analysis of chest injuries in 280 seat belt wearers

The usefulness of seat belts is today well documented. The purpose of the present study was to analyse the factors which caused the fatal outcome of 207 seat belt wearers, a chest injury being recorded as the main cause of death. The control material consisted of 73 seat belt wearers who sustained severe chest injury in the same kind of traffic accidents. The basic material consisted of 3,468 traffic accidents investigated by the Boards of Traffic Accidents Investigation of Insurance Companies in Finland. Since 1972, the Boards have investigated accidents involving one or more victims dying within 30 days of the accident. In the group of fatally injured victims drivers outnumbered passengers statistically (p less than 0.01), this being the case especially in frontal impact collisions. In those frontal crashes the part of the car causing injury was the steering wheel in 28.6% of the cases, but in lateral collisions the injury was in 4.8% due to impact by steering wheel (p less than 0.001). In lateral impact collisions there were more fatalities compared with other directions of impact (p less than 0.001) and only 3.3% survived in the front seat on the side impact. The injury mechanism on the body was grouped as follows: deceleration, contusion, and crushing force. Crushing force was the most common mechanism leading to the fatal outcome and was statistically more common in lateral impact collisions than in other types of crashes (p less than 0.001). Improving the constructions of steering assembly and strengthening side panels of the cars can be considered one of the main priorities in the prevention of fatal chest injuries.     

Seat back and head restraint response during low-speed rear-end automobile collisions

Automobile seat backs and head restraints play a key safety role during low-speed rear-end collisions, yet few studies have explored the effect of collision variables on seat response. In this study, the effects of vehicle speed change and seat belt use on dynamic seat back and head restraint response during low-speed rear-end automobile collisions were examined. Four human subjects were repeatedly exposed to vehicle-to-vehicle rear-end collisions with speed changes of 2, 4, 6 and 8 km/h. Seat back force and deflection, and head restraint force were measured. The point of application of the resultant force applied to the seat back and head restraint were determined. The magnitude and time of peak kinematic and kinetic response parameters were used in a two-way repeated-measures analysis of variance (ANOVA) for speed change and seat belt use. The results showed that 20 of the 24 seat back and head restraint response parameters varied with speed change and none of the parameters varied with seat belt use. Head restraint forces, seat back forces and seat back deflections increased approximately linearly with speed change, whereas time to peak response, direction and moment arm of the forces remained either constant or varied only slightly over the range of speed changes tested.     

Construction and evaluation of thoracic injury risk curves for a finite element human body model in frontal car crashes

There is a need to improve the protection to the thorax of occupants in frontal car crashes. Finite element human body models are a more detailed representation of humans than anthropomorphic test devices (ATDs). On the other hand, there is no clear consensus on the injury criteria and the thresholds to use with finite element human body models to predict rib fractures. The objective of this study was to establish a set of injury risk curves to predict rib fractures using a modified Total HUman Model for Safety (THUMS). Injury criteria at the global, structural and material levels were computed with a modified THUMS in matched Post Mortem Human Subjects (PMHSs) tests. Finally, the quality of each injury risk curve was determined. For the included PMHS tests and the modified THUMS, DcTHOR and shear stress were the criteria at the global and material levels that reached an acceptable quality. The injury risk curves at the structural level did not reach an acceptable quality.