Experimental investigation of the effect of occupant characteristics on contemporary seat belt payout behavior in frontal impacts

Objective: The goal of this study was to investigate the influence of the occupant characteristics on seat belt force vs. payout behavior based on experiment data from different configurations in frontal impacts.

Methods: The data set reviewed consists of 58 frontal sled tests using several anthropomorphic test devices (ATDs) and postmortem human subjects (PMHS), restrained by different belt systems (standard belt, SB; force-limiting belt, FLB) at 2 impact severities (48 and 29 km/h). The seat belt behavior was characterized in terms of the shoulder belt force vs. belt payout behavior. A univariate linear regression was used to assess the factor significance of the occupant body mass or stature on the peak tension force and gross belt payout.

Results: With the SB, the seat belt behavior obtained by the ATDs exhibited similar force slopes regardless of the occupant size and impact severities, whereas those obtained by the PMHS were varied. Under the 48 km/h impact, the peak tension force and gross belt payout obtained by ATDs was highly correlated to the occupant stature (P =.03, P =.02) and body mass (P =.05, P =.04), though no statistical difference with the stature or body mass were noticed for the PMHS (peak force: P =.09, P =.42; gross payout: P =.40, P =.48). With the FLB under the 48 km/h impact, highly linear relationships were noticed between the occupant body mass and the peak tension force (R² = 0.9782) and between the gross payout and stature (R² = 0.9232) regardless of the occupant types.

Conclusions: The analysis indicated that the PMHS characteristics showed a significant influence on the belt response, whereas the belt response obtained with the ATDs was more reproducible. The potential cause included the occupant anthropometry, body mass distribution, and relative motion among body segments specific to the population variance. This study provided a primary data source to understand the biomechanical interaction of the occupant with the restraint system. Further research is necessary to consider these effects in the computational studies and optimized design of the restraint system in a more realistic manner.     

Investigation of occupant kinematics and injury risk in a reclined and rearward-facing seat under various frontal crash velocities

Introduction: The availability of highly automated driving functions will vastly change the seating configuration in future vehicles. A reclined and rearward-facing seating position could become one of the popular seating positions. The occupant safety needs to be addressed in these novel seating configurations, as novel occupant loading conditions occur and the current standards as well as regulations are not fully applicable. Method: Twelve finite element simulations using a series production seat model and a state of the art 50th percentile male human body model were conducted to investigate the influences of various parameters on the occupant kinematics and injury risk. The varied parameters included the seatback angle, impact speed, and seatback rotational stiffness. Results: The seat model shows a large seatback rotation angle during the frontal crash scenario with high impact speed. A reclining of the seatback angle leads to no significant increase of the injury risk for the assessed injury values. However, the reclining does affect the interaction among the occupant, seatbelt, and seatback. An increase of the seatback rotational stiffness helps reduce brain and chest injury metrics, while neck injury values are higher for the stiffer seatback.     

Belief about seat belt use and seat belt wearing behavior among front and rear seat passengers in the United States

Introduction: Unrestrained drivers and passengers represent almost half of all passenger vehicle occupant deaths in the United States. The current study assessed the relationship between the belief about importance of seat belt use and the behavior of always wearing a seat belt. Method: Data from 2012 ConsumerStyles were analyzed separately for front and rear passenger seating positions. Multivariable regression models were constructed to identify the association between seat belt belief and behavior (i.e., always wears seat belt) among adults. Models controlled for type of state seat belt law (primary, secondary, or none). Results: Seat belt use was higher in front passenger seats (86.1%) than in rear passenger seats (61.6%). Similarly, belief that seat belt use was very important was higher in reference to the front passenger seat (84.2%) versus the rear passenger seat (70.5%). For the front passenger seat, belief was significantly associated with seat belt use in states with both primary enforcement laws (adjPR 1.64) and secondary enforcement laws (adjPR 2.77). For the rear passenger seat, belief was also significantly associated with seat belt use, and two 2-way interactions were observed (belief by sex, belief by region). Conclusions: Despite overall high rates of seat belt use in the United States, certain groups are less likely to buckle up than others. The study findings suggest that efforts to increase seat belt use among high-risk populations, such as those who live in states with secondary or no seat belt laws and those who ride in rear seats (which include people who utilize taxis or ride-hailing vehicles) could benefit from interventions designed to strengthen beliefs related to the benefits of seat belt use. Practical applications: Future research that uses a theoretical framework to better understand the relationship between beliefs and behavior may inform interventions to improve seat belt use.     

Chest injuries of elderly postmortem human surrogates (PMHSs) under seat belt and airbag loading in frontal sled impacts: Comparison to matching THOR tests

Abstract

Objective: The goal of the study was to develop experimental chest loading conditions that would cause up to Abbreviated Injury Scale (AIS) 2 chest injuries in elderly occupants in moderate-speed frontal crashes. The new set of experimental data was also intended to be used in the benchmark of existing thoracic injury criteria in lower-speed collision conditions.

Methods: Six male elderly (age >63) postmortem human subjects (PMHS) were exposed to a 35?km/h (nominal) frontal sled impact. The test fixture consisted of a rigid seat, rigid footrest, and cable seat back. Two restraint conditions (A and B) were compared. Occupants were restrained by a force-limited (2.5?kN [A] and 2?kN [B]) seat belt and a preinflated (16?kPa [A] and 11?kPa [B]; airbag). Condition B also incorporated increased seat friction. Matching sled tests were carried out with the THOR-M dummy. Infra-red telescoping rod for the assessment of chest compression (IRTRACC) readings were used to compute chest injury risk. PMHSs were exposed to a posttest injury assessment. Tests were carried out in 2 stages, using the outcome of the first one combined with a parametric study using the THUMS model to adjust the test conditions in the second. All procedures were approved by the relevant ethics board.

Results: Restraint condition A resulted in an unexpected high number of rib fractures (fx; 10, 14, 15 fx). Under condition B, the adjustment of the relative airbag/occupant position combined with a lower airbag pressure and lower seat belt load limit resulted in a reduced pelvic excursion (85 vs. 110?mm), increased torso pitch and a substantially lower number of rib fractures (1, 0, 4 fx) as intended.

Conclusions: The predicted risk of rib fractures provided by the THOR dummy using the C_max and PC Score injury criteria were lower than the actual injuries observed in the PMHS tests (especially in restraint condition A). However, the THOR dummy was capable of discriminating between the 2 restraint scenarios. Similar results were obtained in the parametric study with the THUMS model.     

Computational investigation of the effects of knee airbag design on the interaction with occupant lower extremity in frontal and oblique impacts

Objective: The lower extremity of the occupant represents the most frequently injured body region in motor vehicle crashes. Knee airbags (KABs) have been implemented as a potential countermeasure to reduce lower extremity injuries. Despite the increasing prevalence of KABs in vehicles, the biomechanical interaction of the human lower extremity with the KAB has not been well characterized. This study uses computational models of the human body and KABs to explore how KAB design may influence the impact response of the occupant's lower extremities.

Methods: The analysis was conducted using a 50th percentile male occupant human body model with deployed KABs in a simplified vehicle interior. The 2 common KAB design types, bottom-deploy KAB (BKAB) and rear-deploy KAB (RKAB), were both included. A state-of-the-art airbag modeling technique, the corpuscular particle method, was adopted to represent the deployment dynamics of the unfolding airbags. Validation of the environment model was performed based on previously reported test results. The kinematic responses of the occupant lower extremities were compared under both KAB designs, 2 seating configurations (in-position and out-of-position), and 3 loading conditions (static, frontal, and oblique impacts). A linear statistical model was used to assess factor significance considering the impact responses of the occupant lower extremities.

Results: The presence of a KAB had a significant influence on the lower extremity kinematics compared to no KAB (P <.05) by providing early restraint and distributing contact force on the legs during airbag deployment. For in-position occupants, the KAB generally tended to decrease tibia loadings. The RKAB led to greater lateral motion of the legs compared to the BKAB, resulting in higher lateral displacement at the knee joint and abduction angle change (51.2 ± 21.7 mm and 15° ± 6.0°) over the dynamic loading conditions. Change in the seating position led to a significant difference in occupant kinematic and kinetic parameters (P <.05). For the out-of-position (forward-seated) occupant, the earlier contact between the lower extremity and the deploying KAB resulted in 28.4° ± 5.8° greater abduction, regardless of crash scenarios. Both KAB types reduced the axial force in the femur relative to no KAB. Overall, the out-of-position occupant sustained a raised axial force and bending moment of the tibia by 0.8 ± 0.2 kN and 21.1 ± 8.7 Nm regardless of restraint use.

Conclusions: The current study provided a preliminary computational examination on KAB designs based on a limited set of configurations in an idealized vehicle interior. Results suggested that the BKAB tended to provide more coverage and less leg abduction compared to the RKAB in oblique impact and/or the selected out-of-position scenario. An out-of-position occupant was associated with larger abduction and lower extremity loads over all occupant configurations. Further investigations are recommended to obtain a full understanding of the KAB performance in a more realistic vehicle environment.     

Attitudes toward a primary seat belt law among adults in a rural state with a secondary seat belt law

Problem

Enforced primary seatbelt laws can reduce morbidity and mortality associated with motor-vehicle crashes. Constituent support is an important factor associated with legislator voting behavior toward injury prevention laws. Little is known about attitudes toward a primary seat belt law among adults in rural states without a primary seat belt law.

Methods

Data from the Behavioral Risk Factor Surveillance System (BRFSS) survey, a telephone survey of a representative sample of adults in Montana, were used to assess attitudes toward a primary seat belt law.

Results

Sixty-one percent of respondents supported a primary seat belt law. Using multiple logistic regression analyses, women (AOR 1.87; 95% CI 1.49-2.36), persons aged 65 years and older (1.45; 1.06-1.96), American Indians (2.71; 1.55-4.75), those with health insurance (1.51; 1.07-2.14), and those who reported always wearing their seat belt (4.05; 3.14-5.21) were more likely to support a primary seat belt law than respondents without these characteristics.

Conclusions

The majority of adults in a rural state support a primary seat belt law.     

The use of seat belts in cars with smart seat belt reminders--results of an observational study

Recently, smart seat belt reminders (SBR) have been introduced in cars. By increasingly reminding drivers and passengers if they are not using the seat belt, the intention is to increase the belt use to almost 100%. OBJECTIVE: The objective was to study if there were differences in driver's seat belt use between cars with and without SBR. METHODS: Drivers of cars with and without SBR were observed concerning seat belt use. The case (cars with SBR) and the control group (cars without SBR) were similar in all major aspects except SBR. In all, more than 3,000 drivers were observed in five cities in Sweden. RESULTS: In cars without SBR, 82.3 percent of the drivers used the seat belt, while in cars with SBR, the seat belt use was 98.9 percent. The difference was significant. In cars with mild reminders, the use was 93.0 percent. CONCLUSION: It is concluded, that if the results can be generalised to the whole car population this would have a dramatic impact on the number of fatally and seriously injured car occupants.     

Influence of seat foam and geometrical properties on BioRID P3 kinematic response to rear impacts

As the primary interface with the human body during rear impact, the automotive seat holds great promise for mitigation of Whiplash Associated Disorders (WAD). Recent research has chronicled the potential influence of both seat geometrical and constitutive properties on occupant dynamics and injury potential. Geometrical elements such as reduced head to head restraint, rearward offset, and increased head restraint height have shown strong correlation with reductions in occupant kinematics. The stiffness and energy absorption of both the seating foam and the seat infrastructure are also influential on occupant motion; however, the trends in injury mitigation are not as clear as for the geometrical properties. It is of interest to determine whether, for a given seat frame and infrastructure, the properties of the seating foam alone can be tailored to mitigate WAD potential. Rear impact testing was conducted using three model year 2000 automotive seats (Chevrolet Camaro, Chevrolet S-10 pickup, and Pontiac Grand Prix), using the BioRID P3 anthropometric rear impact dummy. Each seat was distinct in construction and geometry. Each seat back was tested with various foams (i.e., standard, viscoelastic, low or high density). Seat geometries and infrastructures were constant so that the influence of the seating foams on occupant dynamics could be isolated. Three tests were conducted on each foam combination for a given seat (total of 102 tests), with a nominal impact severity of Delta V = 11 km/h (nominal duration of 100 msec). The seats were compared across a host of occupant kinematic variables most likely to be associated with WAD causation. No significant differences (p < 0.05) were found between seat back foams for tests within any given seat. However, seat comparisons yielded several significant differences (p < 0.05). The Camaro seat was found to result in several significantly different occupant kinematic variables when compared to the other seats. No significant differences were found between the Grand Prix and S-10 seats. Seat geometrical characteristics obtained from the Head Restraint Measuring Device (HRMD) showed good correlation with several occupant variables. It appears that for these seats and foams the head-to-head restraint horizontal and vertical distances are overwhelmingly more influential on occupant kinematics and WAD potential than the local foam properties within a given seat.     

Organizational policy and other factors associated with emergency medical technician seat belt use

INTRODUCTION: The purpose of this study was to determine factors associated with seat belt usage among Emergency Medical Technicians (EMTs). METHODS: As part of biennial re-registration paperwork, nationally registered EMTs completed a survey on the safety and health risks facing Emergency Medical Services (EMS) providers. Respondents were asked to describe their seat belt use while in the front seats of an ambulance. They were categorized as "high" in seat belt use if it had been more than a year since they had not worn their seat belt or "low" in seat belt use if they had not worn their seat belt at least once within the past 12 months. A logistic regression model was fit to estimate the association between seat belt use, organizational seat belt policy, type of EMS organization worked for, EMT certification level, and the size of community where EMS work is performed. RESULTS: Of the 41,823 EMTs that re-registered in 2003, surveys were received from 29,575 (70.7%). A significant interaction between organizational seat belt policy and type of EMS organization was found to exist. Participants reporting no organizational seat belt policy had lower odds of seat belt usage when compared to individuals that do have a seat belt policy. Odds Ratios ranged from 0.20 (95% CI 0.10-0.40) for military organizations to 0.59 (95% CI 0.38-0.93) for private EMS organizations. Paramedics and those working in rural areas also had lower odds of seat belt use. CONCLUSION: Several factors were found to be associated with seat belt usage among EMTs while in the front compartment of an ambulance. However, it appears that only one, organizational policy, is a modifiable characteristic.     

Whiplash-associated disorders in frontal impacts: influencing factors and consequences

This multidisciplinary in-depth investigation of accidents using 24 occupants with neck symptoms shows the complexity of whiplash-associated disorders (WAD) in frontal impacts with respect to factors that influence occurrence as well as duration of symptoms. Several different occupant kinematics have been identified, all resulting in symptoms classified as WAD. Compared to occupants restrained only by a seat belt, occupants with arm resistance influence showed a greater representation of symmetrical neck symptoms. Two cases of unbelted occupants with a neck compression mechanism far from conventional "whiplash" motion were found. Posture as well as physical and psychosocial factors such as strong negative reactions, bad prognosis expectation, and stressed daily activities influenced the duration of symptoms. Occupant characteristics and sitting posture and behavior at the time of impact are important factors when analyzing and understanding WAD.     

Factors contributing to serious and fatal injuries in belted rear seat occupants in frontal crashes

Abstract

Objectives: Earlier research has shown that the rear row is safer for occupants in crashes than the front row, but there is evidence that improvements in front seat occupant protection in more recent vehicle model years have reduced the safety advantage of the rear seat versus the front seat. The study objective was to identify factors that contribute to serious and fatal injuries in belted rear seat occupants in frontal crashes in newer model year vehicles.

Methods: A case series review of belted rear seat occupants who were seriously injured or killed in frontal crashes was conducted. Occupants in frontal crashes were eligible for inclusion if they were 6 years old or older and belted in the rear of a 2000 or newer model year passenger vehicle within 10 model years of the crash year. Crashes were identified using the 2004–2015 National Automotive Sampling System Crashworthiness Data System (NASS-CDS) and included all eligible occupants with at least one Abbreviated Injury Scale (AIS) 3 or greater injury. Using these same inclusion criteria but split into younger (6 to 12 years) and older (55+ years) cohorts, fatal crashes were identified in the 2014–2015 Fatality Analysis Reporting System (FARS) and then local police jurisdictions were contacted for complete crash records.

Results: Detailed case series review was completed for 117 rear seat occupants: 36 with Maximum Abbreviated Injury Scale (MAIS) 3+ injuries in NASS-CDS and 81 fatalities identified in FARS. More than half of the injured and killed rear occupants were more severely injured than front seat occupants in the same crash. Serious chest injury, primarily caused by seat belt loading, was present in 22 of the injured occupants and 17 of the 37 fatalities with documented injuries. Nine injured occupants and 18 fatalities sustained serious head injury, primarily from contact with the vehicle interior or severe intrusion. For fatal cases, 12 crashes were considered unsurvivable due to a complete loss of occupant space. For cases considered survivable, intrusion was not a large contributor to fatality.

Discussion: Rear seat occupants sustained serious and fatal injuries due to belt loading in crashes in which front seat occupants survived, suggesting a discrepancy in restraint performance between the front and rear rows. Restraint strategies that reduce loading to the chest should be considered, but there may be potential tradeoffs with increased head excursion, particularly in the absence of rear seat airbags. Any new restraint designs should consider the unique needs of the rear seat environment.     

A comparison of volunteers and dummy upper torso kinematics with and without shoulder belt slack in a low speed side/pre-roll environment

OBJECTIVE: The objective of this study was to compare the occupant and dummy kinematics in a low-speed lateral environment with and without shoulder belt slack. METHODS: A buck of a small European car was mounted on a side impact sled. The parameters evaluated were pulses, sitting location, and belt slack. A total of 24 tests were carried out. Three 50th-percentile male volunteers and one Hybrid III 50th-percentile male were tested. The pulses consisted of Pulse 1:+/- 0.7 g's pulse and Pulse 2: a -0.9 g pulse to simulate low-speed pre-roll/side events. Both pulses had a duration of 500 msec. RESULTS: The peak lateral head excursion was higher in the far-side occupants than in the near-side occupants. Furthermore, for the far-side volunteers, lateral head displacements were lower in the no-slack condition than in the slack condition, at 388 +/- 64 mm and 455 +/- 84 mm respectively for Pulse 1 and at 138 +/- 2 mm and 207 +/- 70 mm for Pulse 2. The timing required to reach peak lateral displacement was higher in Pulse 1 than in Pulse 2. In comparison to the volunteers, the Hybrid III dummy lateral motion was lower. The peak lateral displacement in Pulse 1 was 231 mm with slack and 194 mm without and 98 mm and 107 mm for Pulse 2, respectively. CONCLUSIONS: The results obtained in this study indicate that removing seatbelt slack would be more beneficial for far-sided occupants than near-sided. They also point to the lack of biofidelity of the Hybrid III dummy in low g lateral pulses.     

Investigating cervical muscle response and head kinematics during right, left, frontal and rear-seated perturbations

Objective: Whiplash research has largely focused on rear collisions because they account for the majority of whiplash injuries. The purpose of this study was to evaluate the effects of 4 perturbation directions (anterior, posterior, right, and left) on muscle activity and head kinematics to provide insight into the whiplash mechanism of injury. Methods: The effects of 4 perturbation directions induced by a parallel robotic platform, with peak acceleration of 8.50?m/s(2), were analyzed on 10 subjects. Surface electromyography (EMG) measures were collected from the sternocleidomastoid (SCM), trapezius, and splenius capitus muscles. Kinematics of the head, thorax, and head relative to thorax were also measured. Results: We observed stereotypic responses for kinematics and SCM EMG for the various perturbation directions; the trapezius and splenius capitus muscles showed amplitudes that were less than 5 percent maximum voluntary contraction (MVC). Rear perturbations elicited the smallest onset latencies for the SCM (30?ms) and kinematic variables and greatest linear head center of mass (COM) accelerations. Frontal perturbations resulted in an average SCM onset latency of 143?ms and demonstrated the greatest magnitude of head translations and rotations relative to the thorax. Left and right perturbations demonstrated similar kinematics and SCM onset latencies (55 and 65?ms, respectively). Conclusions: Compared to frontal, left, and right directions, rear perturbations showed smaller SCM onset latencies, greater SCM amplitudes, and larger head accelerations, relating to a greater potential for injury. We suggest that the greater contact area and stiffness of the seatback, in the posterior direction, compared to restrictions in other directions, led to increased peak head accelerations and shorter SCM onset latencies.     

Influence of ATD versus PMHS reference sensor inputs on computational brain response in frontal impacts to advanced combat helmet (ACH)

ABSTRACT

Objective: This study analyzed the influence of reference sensor inputs from anthropomorphic test devices (ATDs) versus postmortem human subjects (PMHSs) on simulations of frontal blunt impacts to the advanced combat helmet (ACH).

Methods: A rigid-arm pendulum was used to generate frontal impacts to ACHs mounted on ATDs and PMHS. An appropriately sized ACH was selected according to standard fitting guidelines. The National Operating Committee on Standards for Athletic Equipment (NOCSAE) head was selected for ATD tests due to shape features that enabled a realistic helmet fit. A custom procedure was used to mount a reference sensor internally near the center of gravity (CG) of the PMHS. Reference sensor data from the head CG were used as inputs for the Simulated Injury Monitor (SIMon). Brain responses were assessed with the cumulative strain damage measure set at 10%, or CSDM(10).

Results: Compared to ATD tests, PMHS tests produced 18.7% higher peak linear accelerations and 5.2% higher peak angular velocities. Average times to peak for linear accelerations were relatively similar between ATDs (5.5?ms) and PMHSs (5.8?ms). However, times to peak for angular velocities were higher by a factor of up to 3.4 for PMHSs compared to ATDs. Values for were also higher by a factor of up to 13.1 when PMHS inputs were used for SIMon.

Conclusions: The preliminary findings of this work indicate that small differences in ATD versus PMHS head kinematics could lead to large differences in strain-derived brain injury metrics such as CSDM.     

Ninety five percent: an evaluation of law, policy, and programs to promote seat belt use in Washington state

Seat belt use in Washington state was 83% in 2001. In 2002, a series of law, policy, and program initiatives coalesced to produce a dramatic increase in seat belt use. Washington enacted a primary enforcement seat belt, the Chief of the Washington State Patrol made safety belt enforcement one of the core missions of that agency, and Washington participated in the national Memorial Day Click It or Ticket program during May 2002 and continued the program into 2003. Evaluation of these initiatives was accomplished through observation surveys of seat belt use, analysis of seat belt violation data, and analysis of data on traffic deaths of motor vehicle occupants. The major findings were that there was a two- to three-fold increase in enforcement of the seat belt law, belt use rates increased to 93% in 2002 and again to 95% in 2003, and motor-vehicle occupant fatalities decreased by 13%. IMPACT ON PRACTICE AND POLICY: The primary seat belt law and Click It or Ticket program activities were critical factors in increasing belt use in Washington state. Media and enforcement programs targeting seat belt use can be very effective in raising the belt use rate, but a long-term commitment to continuation of these program activities is essential. Other states implementing new primary seat belt laws should consider delivering a Click It or Ticket campaign prior to the effective date of the primary law and continuing these activities during subsequent months and years.