The effect of a startle-based warning, age, sex, and secondary task on takeover actions in critical autonomous driving scenarios.

Introduction: In highly autonomous driving scenarios, it is critical to identify strategies to accelerate reaction times since drivers may take too long to take over control of the vehicle. Previous studies reported that an Acoustic Startling Pre-Stimulus (ASPS, i.e., a loud warning preceding an action) accelerated reaction times in simple ankle flexion exercises. Methods: In this study, we examined if an ASPS warning leads to shorter takeover reaction times in a sled-simulated evasive swerving maneuver. Twenty-eight participants (seven male adults, seven male teenagers, seven female adults, and seven female teenagers) were instructed to align a marker on the steering wheel with a marker on a lateral post as fast as they could as soon as the lateral sled perturbation (0.75 g) started. Four conditions were examined: with and without an ASPS (105 dB, played 250 ms before sled perturbation for 40 ms), and with and without a secondary task (i.e., texting). A catch trial (ASPS only) was used to minimize anticipation. Human kinematics were captured with an 8-camera 3D motion capture system. Results: Results showed that the drivers' hands lifted towards the steering wheel more quickly with the ASPS (169 ± 55 ms) than without (194 ± 46 ms; p = 0.01), and that adult drivers touched the steering wheel quicker with the ASPS (435 ± 54 ms) than without (470 ± 33 ms; p = 0.01). Similar findings were not observed for the teen drivers. Additionally, female drivers were found to lift their hands towards the steering wheel faster than male drivers (166 ± 58 ms vs. 199 ± 36 ms; p = 0.009). Discussion: Our findings suggest that the ASPS may be beneficial to accelerate driver reaction times during the initiation of a correction maneuver, and that autonomous vehicle warnings may need to be tailored to the age and sex of the driver.

Head excursions of rearward-facing child restraint systems in rear impacts.

OBJECTIVE: The aim of the current study was to quantify the head excursions of pediatric anthropomorphic test devices (ATDs) seated in rearward-facing child restraint system (CRS) models during rear impact sled tests and compare to roof heights of vehicles in the current fleet to assess the possibility of head contact against the vehicle roof. METHODS: Head excursions of ATDs seated in rearward-facing CRS models were analyzed from high-speed video data from 14 rear impact sled tests across two different series. Tests were conducted in rigidized vehicle seats from recent model year vehicles. Rearward-facing infant and convertible CRS models were tested with a variety of pediatric ATDs aged 12 months to 6 years in a variety of installation conditions (e.g., lower anchors or seat belt, anti-rotation features, etc). Maximum ATD head excursions in plane of the seatback were compared to previously measured roof heights of 87 different vehicles. RESULTS: The roof heights in all sedan seating positions (n = 58) and SUV/CUV/minivan seating positions (n = 60) were greater than the largest maximum ATD head excursions in plane of the seatback (792 mm). Head contact was possible in two of the pickup trucks which had roof heights of 730 and 775 mm. In all, 98% of vehicle seating positions measured in this study would accommodate all of the maximum ATD head excursions in plane of the seatback without contact. CONCLUSIONS: The risk of head contact against the vehicle interior roof appears low as maximum ATD head excursions in plane of the seatback were typically not great enough to reach the rooflines of the vehicles in the sample. Head contact appears possible in pickup trucks, where the window/roofline is directly behind the head restraint.

Repositioning forward-leaning vehicle occupants with a pre-pretensioner belt and a startle-based warning in pre-crash scenarios.

OBJECTIVE: Pre-pretensioner (PPT) seatbelts have been found to be effective in controlling vehicle occupants' motion response to disturbances in optimally positioned occupants, but it is not clear how the PPT performs when the occupant is initially forward leaning. Previous work demonstrated that an acoustic startling pre-stimulus (ASPS) reduced trunk out-of-position in sled-simulated pre-crash maneuvers. Therefore, the aim of this study was to determine if coupling the PPT with the ASPS could reduce the needed magnitude and rate of belt tension of the PPT to reposition forward leaning occupants to their optimal position within the seatbelt. METHODS: Sixteen belt-restrained adult human volunteers (8 males and 8 females) restrained by a 3-point seatbelt on a vehicle seat in a forward leaning posture on a sled simulating pre-crash braking (approx. 1 g of maximum acceleration and 0.3 s duration) were exposed to sled perturbations with three belt configurations (low and high force PPT and no PPT), and two warning conditions (ASPS and no-ASPS). Head and trunk positions were extracted from the 3D motion-capture data. Repeated measure ANOVAs were used to understand the effect of sex, PPT, ASPS, and repetition on head and trunk positions. A survival analysis was also performed to understand the probability of the occupants moving rearward in the different conditions. RESULTS: The probability of the head and trunk to move rearward from the initial position was greater with the PPT than without the PPT (p = 0.01) and with the high force level than the low force level (p = 0.01). The interaction effect of ASPS x PPT showed that with no PPT, there was a greater probability for the head to move rearward from the initial position with ASPS than without ASPS (p < 0.03). The trunk shows a similar trend to the head, but the ASPS vs no-ASPS differences were not statistically significant (p = 0.06). No sex differences were found. CONCLUSIONS: The PPT, particularly the high level, may be an effective countermeasure on its own to reduce trunk and head out-of-position in forward leaning postures in pre-crash scenarios. The ASPS reduced the occupants' head forward position when the PPT was not available.

Interactions between rearward-facing child restraint systems and the front row seatback in frontal impact sled tests.

OBJECTIVE: Some child restraint system (CRS) manufacturers specify a minimum distance between the CRS and the seatback, whereas others require that the CRS may contact the seatback but cannot be "braced"; however, few studies have investigated these interactions. Therefore, the aim was to investigate the interactions between the front row seat and rearward-facing CRS models with and without a support leg during frontal crashes. METHODS: Sled tests using the FMVSS 213 frontal crash pulse were performed with the Q1.5 and Q3 anthropomorphic test devices (ATDs) seated in rearward-facing infant and convertible CRS models, respectively. A front row vehicle seat was in front of the test bench in three track positions: brace, touch and gap. For the touch condition, the front row seat was translated aftward until the seatback contacted the CRS. For the brace condition, the front row seat was translated 20 mm aftward. For the gap condition, the front row seat was translated 50 mm forward. Each condition was tested with and without the support leg of the CRS. RESULTS: The tests with a support leg were associated with significantly (p = 0.007) lower resultant linear head acceleration 3 ms clip compared to the tests without a support leg, but the reduction of head injury criterion 15 ms (HIC15) was not significant (p = 0.057). The Q1.5 ATD in the rearward-facing infant CRS with a support leg had the lowest injury metrics for the touch and gap conditions, whereas the Q3 in the rearward-facing convertible CRS had the lowest head injury metrics for the brace condition. CONCLUSIONS: The use of a support leg provided a clear benefit in terms of reducing head injury metrics for the Q1.5 in the rearward-facing infant CRS, especially for the touch and gap conditions. The rearward-facing convertible CRS in the current study appears to benefit from being braced against the front row seat. However, further tests are required to allow further statistical comparisons and determine if these preliminary findings extend to other rearward-facing CRS models.

Quantitative characterization of AEB pulses across the modern fleet.

OBJECTIVE: Characteristics of specific Automatic Emergency Braking (AEB) pulses can result in increased motion of the occupant, which can lead to the occupant being out-of-position such that when a crash occurs protection may be compromised. Quantifying these variations across the modern fleet is crucial to understand the loading environment to which vehicle occupants are exposed. Therefore, we categorized the AEB pulses based on acceleration pulse features such as deceleration magnitude, jerk, and ramp time. METHODS: A total of 2278 AEB vehicle tests (years 2013-2019) were extracted from the Insurance Institute for Highway Safety (IIHS) database and analyzed. The following pulse characteristics were extracted: Jerk (g/s), Ramp-time (s), and Maximum deceleration (g). A subset of tests in which the tested vehicle did not contact the foam target (n = 1665) was analyzed further, with the following additional variables extracted: Deceleration time (s), Steady-state deceleration (g), and Duration (s). Other non-pulse related features were also considered: Test speed (20 and 40 km/h), Curb weight (Kg), and Vehicle Model Year. Using machine learning methods, the pulses were categorized into clusters. One-way ANOVAs for continuous variables and X2 for categorical features were used to assess differences between clusters (p ≤ 0.05). RESULTS: Using the entirety of the AEB vehicle tests extracted (n = 2278), a total of 3 clusters were selected. The three clusters showed significantly different Jerk, Ramp-time, and Maximum deceleration (p < 0.001). Target contact decreased in AEB tests with more recent vehicle model years (rate of contact 66% in 2014 vs 1.7% in 2019). In one cluster, Jerk and Maximum deceleration increased with vehicle model year. Using the subset of tests in which there was no contact with the foam target (n = 1665), 4 categories of pulses were selected. In both sets of clusters, Ramp-time and Jerk showed moderate inverse correlation (r = -0.7), while all other features showed a low correlation. CONCLUSIONS: These results show that AEB technology improved over the years in obstacle avoidance. The identification of AEB pulse clusters is important in order to describe distinct approaches to achieving AEB and to be able to reproduce representative AEB pulses in the laboratory and understand the influences of those pulses on occupants' motion.

The six degrees of freedom motion of the human head, spine, and pelvis in a frontal impact.

OBJECTIVE: The goal of this study is to characterize the in situ 6-degree-of-freedom kinematics of the head, 3 vertebrae (T1, T8, and L2), and the pelvis in a 40 km/h frontal impact. METHODS: Three postmortem human surrogates (PMHS) were exposed to a deceleration of 15 g over 125 ms and the motion of selected anatomical structures (head, T1, T8, L2, and pelvis) was tracked at 1000 Hz using an optoelectric stereophotogrammetric system. Displacements of the analyzed structures are reported in the sagittal and the transverse planes. Rotations of the structures are described using the finite helical axis of the motion. RESULTS: Anterior displacements were 530.5 ± 39.4 mm (head), 434.7 ± 20.0 mm (T1), 353.3 ± 29.6 mm (T8), 219.9 ± 19.3 mm (L2), and 78.9 ± 22.1 mm (pelvis). The ratio between peak anterior and lateral displacement was up to 19 percent (T1) and 26 percent (head). Magnitudes of the rotation of the head (69.9 ± 1.5°), lumbar (66.5 ± 9.1°), and pelvis (63.8 ± 11.8°) were greater than that of the thoracic vertebrae (T1: 49.1 ± 7.8°; T8: 47.7 ± 6.3°). Thoracic vertebrae exhibited a complex rotation behavior caused by the asymmetric loading of the shoulder belt. Rotation of the lumbar vertebra and pelvis occurred primarily within the sagittal plane (flexion). CONCLUSION: Despite the predominance of the sagittal motion of the occupant in a pure (12 o'clock) frontal impact, the asymmetry of belt loading induced other relevant displacements and rotations of the head and thoracic spine. Attempts to model occupant kinematics in a frontal impact should consider these results to biofidelically describe the interaction of the torso with the belt.

Non-fatal and fatal crash injury risk for children in minivans compared with children in sport utility vehicles.

OBJECTIVE: To compare the fatal and non-fatal crash injury risk for children in minivans compared with midsize and large sport utility vehicles (SUVs). DESIGN: Three large population-based sources of US crash data were used--a nationwide cohort of sampled police-reported crashes (NASS-CDS) along with a census of fatal crashes (FARS), plus a large child crash surveillance system, Partners for Child Passenger Safety (PCPS)--collected in 16 states via insurance claim records and validated telephone survey. Each included: 2000-2006 data, occupants aged 0-15 years, traveling in minivan or (midsize/large) SUV, model year 1998-2007. Outcome of interest was parent/driver report of non-fatal injury (Abbreviated Injury Scale scores of 2 or higher) in PCPS and fatal injury in NASS-CDS/FARS. RESULTS: Compared with children riding in SUVs, those in minivans experienced a similar crude reduction in the relative risk of non-fatal injury (PCPS: unadjusted odds ratio (OR) = 0.55) and fatality (NASS-CDS/FARS cohort: unadjusted OR = 0.58). In PCPS, this reduction in injury risk changed little after adjustment for child, driver, and vehicle factors (adjusted OR = 0.56, 95% CI 0.38 to 0.82). Lower fatality risk in the NASS-CDS/FARS cohort was partially explained by the same factors (adjusted OR = 0.76, 95% CI 0.51 to 1.13). CONCLUSIONS: There may be important safety differences in vehicles during a crash that lead to fewer non-fatal injuries to child occupants of minivans compared with SUVs.

Body mass index and injury risk among US children 9-15 years old in motor vehicle crashes.

OBJECTIVE: To determine the relationship between body mass index (BMI) and injury risk among US children in motor vehicle crashes. DESIGN: Cross-sectional study using data from the Partners for Child Passenger Safety study, a child-focused crash surveillance system. PARTICIPANTS: A probability sample of children, 9-15 years of age, involved in crashes in parent-operated vehicles between 1 December 2000 and 31 December 2006. MAIN OUTCOME MEASURE: The odds ratio of Abbreviated Injury Severity (AIS) 2+ injuries (overall and body region specific) by BMI category: underweight, normal, overweight, and obese. RESULTS: The study sample included 3232 children in 2873 vehicles, representing a population estimate of 54 616 children in 49 037 vehicles. Approximately 15% (n = 502) sustained an AIS 2+ injury to any body region; 34% of the children were overweight or obese. There was no overall increase in injury risk by BMI; however, body region differences were found. In multivariate logistic regression, compared with normal weight children, the odds of sustaining an AIS 2+ injury to the extremities for overweight and obese children was 2.64 (95% CI 1.64 to 4.77) and 2.54 (95% CI 1.15 to 5.59), respectively. CONCLUSIONS: Although overweight and obese children are not at increased overall risk of injury, they are at increased risk of injury to the lower and upper extremities. This increased risk may be due to a combination of physiology, biomechanical forces, and vehicle design.

Car safety seats for children: rear facing for best protection.

OBJECTIVE: To compare the injury risk between rear-facing (RFCS) and forward-facing (FFCS) car seats for children less than 2 years of age in the USA. METHODS: Data were extracted from a US National Highway Traffic Safety Administration vehicle crash database for the years 1988-2003. Children 0-23 months of age restrained in an RFCS or FFCS when riding in passenger cars, sport utility vehicles, or light trucks were included in the study. Logistic regression models and restraint effectiveness calculations were used to compare the risk of injury between children restrained in RFCSs and FFCSs. RESULTS: Children in FFCSs were significantly more likely to be seriously injured than children restrained in RFCSs in all crash types (OR=1.76, 95% CI 1.40 to 2.20). When considering frontal crashes alone, children in FFCSs were more likely to be seriously injured (OR=1.23), although this finding was not statistically significant (95% CI 0.95 to 1.59). In side crashes, however, children in FFCSs were much more likely to be injured (OR=5.53, 95% CI 3.74 to 8.18). When 1 year olds were analyzed separately, these children were also more likely to be seriously injured when restrained in FFCSs (OR=5.32, 95% CI 3.43 to 8.24). Effectiveness estimates for RFCSs (93%) were found to be 15% higher than those for FFCSs (78%). CONCLUSIONS: RFCSs are more effective than FFCSs in protecting restrained children aged 0-23 months. The same findings apply when 1 year olds are analyzed separately. Use of an RFCS, in accordance with restraint recommendations for child size and weight, is an excellent choice for optimum protection up to a child's second birthday.

Seat belt syndrome in children: a case report and review of the literature.

Characteristic patterns of injury to children in automobile crashes resulting from lap and lap-shoulder belts have been described for many years. These injuries are known as the "seat belt syndrome." We present a typical case of seat belt syndrome involving a 4-year-old boy and review the current literature on the topic, highlighting proposed mechanisms of intra-abdominal and spine injuries. In addition, recent research findings identifying a new pattern of injuries associated with inappropriate seat belt use in young children are reviewed. Emergency physicians must consider these seat belt-related injuries in the initial evaluation of any child involved in a motor vehicle crash who was restrained with the vehicle seat belt.

Protecting the child's abdomen: a retractable bicycle handlebar.

A surveillance system in the Emergency Department of a level 1 pediatric trauma center previously identified minor bicycle crashes as a cause of serious child abdominal injury. A discordancy exists between the apparently minor circumstances and serious injuries sustained by child bicyclists who impact bicycle handlebars. The objective of this work was to redesign the bicycle handlebar to reduce the forces transmitted to the child's abdomen during an impact with the handlebars. A retractable handlebar consisting of a spring-mass-damper system was designed to retract and absorb the majority of energy at impact (Patent pending). Because the child remains in contact with the bar after impact, the retracting system also includes a mechanism to damp the outward motion of the handlebar. This prototype will reduce the forces at impact by approximately 50% in a collision similar to those discussed above. A unique methodology of translating research findings into product design produced a novel handlebar that absorbs significant energy that otherwise would be transferred to the child's abdomen when impacting the handlebar.

Factors influencing pediatric injury in side impact collisions.

BACKGROUND: Side impact collisions pose a great risk to children in crashes, but information about the injury mechanisms is limited. METHODS: This study involves a case series of children in side impact collisions who were identified through Partners for Child Passenger Safety, a large, child-focused crash surveillance system. The aim of the current study was to use in-depth crash investigations to identify injury mechanisms to children in side impact collisions. RESULTS: Ninety-three children in 55 side impact crashes were studied. Twenty-three percent (n = 22) of the children received an Abbreviated Injury Scale (AIS) score > or = 2 (clinically significant) injury. In these 22 children, head (40%), extremity (23%), and abdominal injuries (21%) were the most common significant injuries. Cases that illustrate body region-specific injury mechanisms are discussed. CONCLUSION: The cases revealed that serious injuries, particularly head injuries, occur even in minor crashes, and efforts should be made to make the interiors of vehicles more child occupant friendly. Lower extremity and abdominal injuries occurred because of contact with the intruding door. Design of vehicles to minimize crush should mitigate the occurrence and severity of these injuries.

Child occupant protection: a summary of current safety recommendations.

In 1998, 140 children younger than 1 year of age were killed in motor vehicle crashes, and nearly half of those children killed were restrained. Used correctly, child safety seats dramatically reduce a child's risk of death in a motor vehicle crash, but unfortunately, incorrect use of child seats is widespread. Obstetricians and gynecologists have a unique opportunity to counsel parents on the correct restraint for their infants and to provide recommendations for the proper restraint of older children as well. The recommendations for child occupant protection are updated with new information constantly. This article will provide an overview of the current recommendations for restraining children in motor vehicles and identify sources for up-to-date information for physicians and families.

The effect of seating position on risk of injury for children in side impact collisions.

The objective of this study was to evaluate the effect of seating position on risk of injury to children in side impact crashes. 5,632 children under age 16 in side impact crashes were enrolled as part of an on-going crash surveillance system which links insurance claims data to telephone survey and crash investigation data. Children seated in the front seat were at higher risk of significant injury than children seated in the rear (OR = 2.2 95% CI (1.2-3.8)). After adjusting for age, restraint use, and vehicle damage, children in the front seat were more likely to be injured (OR 2.6 95% CI (1.1-6.2)) than children seated in the rear when the child was sitting near the side of the impact. These results highlight the importance of evaluating the safety performance of both vehicles and restraint systems for children in side impact crashes.

Assessing child restraint misuse by parental survey.

OBJECTIVE: To determine the extent to which child restraint system (CRS) misuse can be evaluated by parental survey. METHODS: A cross sectional survey was conducted at eight CRS clinics from May to October, 1998. Before CRS inspection, parents were administered a structured interview to identify distinct characteristics of restraint use and misuse. After the interview, a certified child passenger safety technician team independently evaluated the restraint system and identified specific modes of misuse. Parent descriptions of CRS use were compared with observations of the technician and the degree of agreement between the two was assessed for several specific attributes of use. RESULTS: A total of 100 children restrained in convertible CRSs were included in the study. Parents were able to accurately report several aspects of child restraint use-in particular, the attachment and fit of the CRS, the use of the harness clip, and the CRS incline. Parents were less accurate in their characterization of the fit of the child in the CRS. For nearly every item assessed, parents were more accurate in their description of correct compared with incorrect use. CONCLUSIONS: Interview tools can be developed that enable parents to describe aspects of CRS use and that screen for correct CRS use. These tools could be administered by telephone to obtain a more representative estimate of the prevalence of CRS misuse or to screen for CRS misuse. This screening would assist in targeting time consuming and costly CRS clinics to those parents who need them the most.

Computer crash simulations in the development of child occupant safety policies.

OBJECTIVE: To address the predictability of injury from air bag activation by use of crash simulation software. METHODS: Using current, validated crash simulation software, the effect of air bag activation on injury risk was assessed for the 6-year-old child, both restrained and unrestrained. Results were compared with those for adult occupants in similar crash scenarios. RESULTS: For the unrestrained child passenger, crash simulations predicted serious head, neck, and chest injuries with air bag activation, regardless of crash severity. For the restrained child passenger, crash simulations predicted similar severe injuries for high-severity crashes only. No serious injuries were predicted for unrestrained male adults exposed to air bags or for child passengers restrained in the rear seat for the crash scenarios simulated. CONCLUSIONS: Using current crash simulation software, this study demonstrated that the risk of air bags to school-aged children could be predicted. Our results confirmed the previously identified risks to unrestrained children and provided the first evidence that air bags, in their current design, are not beneficial to restrained children. This study illustrates that computer crash simulations should be used proactively to identify injury risks to child occupants, particularly when limited real-world data are available.

Misuse of booster seats.

OBJECTIVE: To describe several aspects of booster seat use and misuse in a sample of children attending child safety seat clinics. METHODS: Booster seat practices were assessed at 76 child safety seat clinics held between April 1997 and January 1999 in Pennsylvania and southern New Jersey. At each assessment, a child passenger safety team evaluated the booster seat and identified modes of misuse. RESULTS: Altogether 227 booster seats were observed. Sixty eight per cent (68%) of shield boosters and 20% of belt positioning boosters were misused. Thirty two per cent of the children using a shield booster weighed more than 40 lb (18.1 kg); 68% of children in shield boosters and 63% in belt positioning boosters weighed less than 40 lb. CONCLUSION: This study identified a relatively high rate of booster seat misuse. Shield boosters were more likely to be misused than belt positioning booster seats. Significant numbers of children weighing more than 40 lb were using possibly dangerous shield boosters. The majority of children in this study were less than 40 lb. In this weight range, a convertible child restraint system provides better protection than a booster seat. Booster seat use should only be initiated once the child has completely outgrown their convertible child restraint system.

Factors influencing pediatric injury in side impact collisions.

Side impacts collisions pose a great risk to children in crashes but information about the injury mechanisms is limited. The heights and weights of children vary widely and as a result, the injury patterns may vary across the pediatric age range. This study involves a case series of children in side impact collisions who were identified through Partners for Child Passenger Safety, a large child-focused crash surveillance system. The aim of the current study was to use in-depth crash investigations to identify injury mechanisms to children in side impact collisions. 93 children in 55 side impact crashes were studied. 23% (n = 22) of the children received an AIS > or = 2 (clinically significant) injury. In these 22 children, head (39%), extremity (22%), and abdominal injuries (17%) were the most common significant injuries. The cases revealed that serious injuries occur even in minor crashes. Cases that illustrate body region-specific injury mechanisms are discussed.

A fiber-reinforced composite model of the viscoelastic behavior of the brainstem in shear.

Brainstem trauma occurs frequently in severe head injury, often resulting in fatal lesions due to importance of brainstem in crucial neural functions. Structurally, the brainstem is composed of bundles of axonal fibers distinctly oriented in a longitudinal direction surrounded by an extracellular matrix. We hypothesize that the oriented structure and architecture of the brainstem dictates this mechanical response and results in its selective vulnerability in rotational loading. In order to understand the relationship between the biologic architecture and the mechanical response and provide further insight into the high vulnerability of this region, a structural and mathematical model was created. A fiber-reinforced composite model composed of viscoelastic fibers surrounded by a viscoelastic matrix was used to relate the biological architecture of the brainstem to its anisotropic mechanical response. Relevant model parameters measured include the brainstem's composite complex moduli and relative fraction of matrix and fiber. The model predicted that the fiber component is three times stiffer and more viscous than the matrix. The fiber modulus predictions were compared with experimental tissue measurements. The optic nerve, a bundle of tightly packed longitudinally arranged myelinated fibers with little matrix, served as a surrogate for the brainstem fiber component. Model predictions agreed with experimental measures, offering a validation of the model. This approach provided an understanding of the relationship between the specific biologic architecture of the brainstem and the anisotropic mechanical response and allowed insight into reasons for the selective vulnerability of this region in rotational head injury.