Effects of head restraint (HR) interference on child restraint system (CRS) performance in frontal and far-side impacts.

Forward-facing child restraint systems (FF CRS) and high-back boosters often contact the vehicle seat head restraint (HR) when installed, creating a gap between the back surface of the CRS and the vehicle seat. The effects of HR interference on dynamic CRS performance are not well documented. The objective of this study is to quantify the effects of HR interference for FF CRS and high-back boosters in frontal and far-side impacts. Production vehicle seats with prominent, removeable HRs were attached to a sled buck. One FF CRS and two booster models were tested with the HR in place (causing interference) and with the HR removed (no interference). A variety of installation methods were examined for the FF CRS. A total of twenty-four tests were run. In frontal impacts, HR interference produced small but consistent increases in frontal head excursion and HIC36. Head excursions were more directly related to the more forward initial position rather than kinematic differences caused by HR interference. In far-side impacts, HR interference did not have consistent effects on injury metrics. Overall, these results suggest only slight benefits of removing the HR in frontal impacts specifically. Caregivers should use caution if removing a vehicle HR to ensure that the current child occupant and all future vehicle occupants have adequate head support available in case of a rear impact.

Influence of initial belt torso contact on the kinematics and kinetics of booster-seated ATDs in frontal-oblique impacts.

OBJECTIVE: Varying initial belt torso contact (i.e., belt gap) on belt-positioning boosters may have implications for potential shoulder belt slip-off in low-speed evasive vehicle maneuvers and differences in dynamic outcomes in frontal sled tests. This study evaluated the influence of initial booster belt gap and belt fit conditions on the kinematic and kinetic outcomes during frontal oblique impacts. METHODS: Frontal oblique (+15° from frontal) sled tests (n = 18; 23.6 ± 0.1 g at 12.4 ± 0.1 ms) were conducted using the Q-Series 6-year-old (Q6) and 10-year-old (Q10) and the Large Omni Directional Child (LODC) anthropomorphic test devices (ATDs). Various initial belt fit and belt gap conditions were investigated by evaluating each ATD on 2 high-back (HB), 3 low-back (LB), and 1 low-profile (Low) booster. Initial belt fit and belt gap were quantified, and boosters were categorized as "smaller gap" or "larger gap" for comparison. RESULTS: Larger-gap boosters produced greater peak lumbar FY and MZ (HB: -23.2 ± 8.8 Nm, LB: -23.6 ± 9.7 Nm) compared to smaller-gap boosters (HB: -12.6 ± 4.4 Nm, LB/Low: -12.4 ± 7.2 Nm) for the LODC and Q10. Peak axial torso rotations were also observed for larger-gap LB (38.6°) compared to smaller-gap LB boosters (23.8°), and the LODC experienced greater peak thoracic rotations on larger-gap boosters compared to smaller-gap boosters. These results suggest that ATDs on larger-gap boosters experienced greater torso rotation and lumbar MZ due to lack of initial contact between the shoulder belt and inferior torso. No ATDs experienced complete shoulder belt slip-off; however, larger-gap boosters displayed more visual evidence of outboard shoulder belt positioning at the time of peak forward head excursion. CONCLUSION: This study provides a novel investigation on the role of initial belt fit and belt gap metrics on the dynamic response of booster-seated ATDs in frontal oblique impacts. Larger-gap boosters allowed the torso to undergo greater axial rotation before restraint was provided by the shoulder belt to the lower torso. Increased shoulder rotations may indicate greater propensity for shoulder belt slip-off in more severe crashes, in oblique maneuvers, or with variations in initial occupant posture. These results suggest the importance of continued evaluation of the implications of initial belt gap provided by boosters and the importance of evaluating lumbar FY and MZ and useful metrics for discrimination of differences in ATD response across booster designs.

Comparison of child and ATD belt fit and posture on belt-positioning boosters during self-selected, holding device, and nominal conditions.

OBJECTIVE: Pediatric anthropomorphic test devices (ATDs) are important tools for the assessment of child occupant protection and should represent realistic child belt fit and posture on belt-positioning boosters. Previous comparisons have been made to children in either self-selected or nominal postural conditions. This study compares belt fit and postural measurements between pediatric ATDs and a single cohort of children assuming different postures on boosters: self-selected, holding a portable electronic device, and nominal. METHODS: A cohort of children (n = 25) were evaluated in a stationary vehicle on five boosters and in three postural conditions: nominal, self-selected, and a representative holding electronic device position. The Hybrid III 6- and 10-year-old and Q-Series 6- and 10-year-old ATDs were evaluated in the same five boosters and in two postural conditions: nominal and a representative holding electronic device position. A 3D coordinate measurement device was used to quantify belt fit (shoulder belt score, lap belt score, maximum gap size, and gap length) and anatomic landmark positions (head, suprasternale, ASIS, and patella). Landmark positions and belt fit were compared between ATDs and children for each booster and postural condition, and Pearson correlations (r) were assessed across boosters. RESULTS: ATDs generally represented Nominal child postures across boosters. In the Device condition, ATDs were seldom able to be positioned to represent both the torso and head position of children, due to limited ATD spinal flexibility. When the torso position was matched, the ATD head was more rear by 63 mm. Correlations between Nominal child and ATD belt fit and belt gap metrics were generally weak and not significant, with the exception of lap belt score (all ATDs p < 0.07, r = 0.8549-0.9857). DISCUSSION: ATDs were generally able to represent realistic child postures and lap belt fit in Nominal and short duration Self-selected postures in a laboratory setting. However, these results display the potential difficulty of utilizing ATDs to represent more naturalistic child postures, especially the more forward head positions and flexed spinal posture associated with utilizing a portable electronic device.

Sociodemographic disparities in child restraint selection and variation in child passenger safety information sources.

PURPOSE: Marginalized and otherwise vulnerable groups remain at higher risk than their counterparts for not having all of their children appropriately restrained during vehicle trips. Little is known about potential sources of these disparities, however a commonly theorized factor has been where caregivers find or obtain information (i.e., their information sources). The objective of this study was to: (1) characterize caregivers' actual and preferred sources of information related to child passenger safety information, overall and within sociodemographic groups; and (2) determine if, and if so how, sources impact appropriate child restraint use (i.e., child/seat fit). METHODS: We conducted an online, cross-sectional survey of US caregivers. Caregivers answered questions about themselves, their child(ren), their child(ren)'s restraint use during trips, and their information sources to learn which seat their child should be using. We used Fisher's exact and Pearson chi-square tests to compare used and preferred sources of information across caregiver demographics (age, education, race/ethnicity), as well as to determine whether information sources were associated with caregivers' appropriate child restraint use. RESULTS: A total of 1,302 caregivers from 36 states with 2,092 children completed the survey. The majority (91%) of children were appropriately restrained. More caregivers from marginalized and otherwise vulnerable groups had children inappropriately restrained when compared with their counterparts. We identified multiple differences in both used and preferred information sources by caregivers' age, race/ethnicity, and education level. In addition, we found a trend that caregivers from populations with higher rates of inappropriate use seemingly used fewer information sources. Ultimately, information sources were not associated with appropriate restraint use; however, within vulnerable populations, almost all caregivers had all of their children appropriately restrained if they had used a Child Passenger Safety Technician (CPST)/Inspection Station or their Pediatrician. CONCLUSION: Our findings reiterate calls for more tailored interventions and efforts to combat widening disparities in child restraint use and crash outcomes and suggest one promising method may be providing more access to child passenger safety experts. Future studies must untangle the likely complex relationship between information sources and appropriate/accurate child restraint use.

Consumer usability of flexible vs. rigid lower anchor hardware in infant child restraint system (CRS) installations.

OBJECTIVES: Child restraint systems (CRS) can be installed using the Lower Anchors and Tethers for CHildren (LATCH) system. Two different types of lower anchors (LA) are available on CRS in the United States: (1) traditional flexible webbing LA, or (2) rigid LA, which is similar to the European ISOFIX system. The objective of this study is to evaluate consumer usability of flexible vs. rigid LA on infant CRS bases. METHODS: Thirty adult volunteers were recruited to install one infant CRS base with flexible LA and one infant CRS base with rigid LA into two different vehicles apiece, for a total of four installations per participant. One vehicle had easily accessible LA hardware and the other vehicle had less accessible LA hardware. A Child Passenger Safety Technician (CPST) inspected each installation and recorded any misuse or errors. Participants were asked to share their opinions and preferences on the two types of LA via written survey and verbal interview. Outcome variables include the number of errors committed, consumer preference, and ease of use (measured by time spent on each installation and participant feedback) of each LA system. RESULTS: Rigid LA installations resulted in higher rates of correct installation compared to flexible LA (72% correct vs. 47% correct, χ2 = 7.761, p = 0.0053). Participants reported better physical ease-of-use and higher confidence with rigid LA compared to flexible (Likert scale with Wilcoxon signed rank test, two-tailed, for paired data: p = 0.0326 and p = 0.0023, respectively). Rigid LA was faster to install during users' second installation of each CRS compared to flexible (p = 0.0007) but was not faster during the first installation (p = 0.1165, matched-pair two-tailed t-tests). This indicates that each CRS required about the same amount of time for participants to familiarize themselves with the system, but once familiar, the rigid LA system was faster to install. Overall, 24/30 participants (80%) preferred rigid LA to flexible. Self-reported sociodemographic factors suggest that the participant sample was skewed toward highly-educated, white, native English speakers. CONCLUSIONS: The rigid LA system was preferred by this group of consumers for installation of the base of infant CRS. The lower rate of installation errors suggests that rigid LA may help reduce the reported high rates of incorrect LA installation in vehicles in the US.

Biomechanical effects of a halo orthotic on a pediatric anthropomorphic test device in a simulated frontal motor vehicle collision.

Objective: Cervical spine injuries in children under 10 frequently involve the craniocervical junction. In patients too small for conventional spinal instrumentation, treatment may involve placement of a halo orthotic, and these patients will frequently be discharged home in a halo orthotic. To date, little research has been done on the biomechanics of motor vehicle collisions involving young children in halo orthotics. To better understand possible safety concerns, we applied a halo orthotic to an appropriately sized anthropomorphic test device (ATD, or crash test dummy) on an acceleration sled to simulate a frontal motor vehicle collision.Methods: For the tests, a Hybrid III 3-year-old ATD was instrumented with head and chest accelerometers, head angular rate sensors, a six-axis upper neck load cell, and a chest linear potentiometer. Four tests were conducted on an acceleration sled, and kinematics were recorded with high speed video. Testing variables included 1) with or without a halo orthotic and 2) with a standard booster seat or a commercially available harness vest.Results: The halo orthotic reduced flexion and extension but was associated with increased rotation, especially in the condition of a halo orthotic with a standard booster seat. Increased cervical distraction was noted with the halo orthotic, and this was especially increased in the condition of a halo orthotic with the harness vest.Conclusions: The biomechanics of a child involved in a motor vehicular collision may be dramatically altered with a halo orthotic, as modeled by an acceleration sled test. While cervical spine flexion and extension are reduced with the halo orthotic, rotation appears to increase. Immobilization from a halo orthotic also appears to increase cervical distraction, especially when used in conjunction with a harness vest. Further testing is needed to determine the safest restraints for this small, but at-risk, population.

Evaluation of LATCH vs. non-LATCH installations for boosters in frontal impacts.

OBJECTIVES: The objective was to understand how the use or nonuse of the Lower Anchors and Tethers for Children (LATCH) system affects the performance of booster seats during frontal impacts. METHODS: Sixteen frontal impact sled tests were conducted at 24.8 ± 0.3 g and 50.1 ± 0.2 kph. A production vehicle seat buck was attached to the sled. Four high-back boosters or combination seats in high-back booster mode and two backless booster models were tested. Each booster model was installed two different ways: using the LATCH system ("LATCH" installation) and without using the LATCH system ("non-LATCH" installation). All installations used a 3-point seat belt with retractor in emergency locking mode (ELR) to restrain a Hybrid III 6-year-old anthropomorphic test device (ATD). The retractor, belt webbing, buckle, vehicle seat cushion, and booster were replaced after each test. Some conditions were tested twice to establish repeatability. ATD and booster responses were compared between LATCH and non-LATCH tests. RESULTS: Using LATCH reduced the forward movement of the booster itself by 32.3% to 71.5% compared to non-LATCH installations. Differences in most other metrics were small and often within the range of normal test-to-test variation. Forward movements of the ATD head and heel were similar between LATCH and non-LATCH tests (typically less than 10% difference). HIC36 values trended slightly higher for LATCH installations compared to non-LATCH installations (0.8% to 17.2%). Chest resultant accelerations were typically 7.3% to 21.2% higher for LATCH installations, except for one booster for which it was lower with LATCH. Chest deflections trended higher for LATCH installations compared to non-LATCH installations for the backless boosters (6.9% to 14.1%). For high-back boosters, chest deflection was similar between installation conditions (less than 5% difference). Shoulder belt loads showed the greatest reductions when LATCH installations included a top tether (12.9% to 20.8%). Instances of the ATD submarining under the lap belt were not observed in these tests. CONCLUSIONS: Overall, the differences in kinematics and injury metrics were small between boosters installed using LATCH vs. non-LATCH.

Evaluation of static belt fit and belt torso contact for children on belt-positioning booster seats.

Objective: Previous studies have indicated that gap between the seatbelt and torso (reduced belt torso contact) for children on belt-positioning booster seats (BPBs) may lead to less torso engagement and increased likelihood of shoulder belt slip-off during evasive vehicle maneuvers, potentially increasing injury risk during crashes. However, current BPB belt fit measures do not quantify belt gap and may not be able to fully discriminate between designs which provide good vs. poor dynamic outcomes. The goal of this study was to evaluate both novel (belt gap characteristics) and conventional measures of seatbelt fit for BPB-seated children.Methods: Ten BPBs and three seatbelt anchor locations were investigated. Fifty volunteers (4-14 years) were recruited and each evaluated on six unique combinations of BPB and seatbelt anchor location on a vehicle rear seat in a laboratory setting. A 3 D coordinate measurement system quantified positions of anatomic, seatbelt, BPB, and vehicle reference points. Novel belt gap (gap size, length, location, and percent torso contact) and conventional belt fit (position of belt on shoulder and pelvis) metrics were calculated using anatomic and seatbelt landmarks. Variation in belt fit and belt gap outcomes due to BPB, seatbelt anchor location, and anthropometry were investigated.Results: BPBs produced significantly different outcomes, while seatbelt anchor location did not. BPBs with features that directly routed the lower portion of the shoulder belt more forward on the buckle side produced the largest (29.3 ± 12.6 mm) and longest (106.9 ± 68.2 mm) belt gap on average, while BPBs that pulled the belt less forward or did not directly route the belt produced the smallest (13.9 ± 6.7 mm) and shortest (16.9 ± 33.9 mm) gap on average. Belt gap outcomes were not strongly correlated with conventional belt fit metrics, indicating that evaluation of belt gap may provide additional insight when attempting to discriminate between BPBs which provide good vs. poor seatbelt engagement during vehicle maneuvers and crashes.Conclusions: This is the first study to evaluate belt gap characteristics for BPB-seated children. Results suggest that belt fit and belt gap are influenced by BPB design, particularly lower shoulder belt routings, and may have implications for belt engagement during dynamic events.

System providing automated feedback improves task learning outcomes during child restraint system (CRS) installations.

OBJECTIVES: The objective was to build and test an automated, interactive educational system to teach adults how to install a child restraint system (CRS) into a vehicle seat. METHODS: The automated feedback system (AFS) consisted of a mockup vehicle fixture, convertible CRS, and doll. Sensors were implemented into the equipment so that forward-facing (FF) CRS installation errors could be detected. An interactive display monitor guided users through the CRS installation process and alerted them when steps were done incorrectly. Sixty adult volunteers were recruited and randomized into either the treatment group or the control group. The treatment group used the AFS to guide them through a practice installation. The control group also completed a practice installation using the same equipment fixture without the feedback feature turned on; they only had standard printed instruction manuals to guide their tasks. Then, participants from both groups completed a second CRS installation in a real vehicle with standard instruction manuals only. The frequencies and types of errors in all the installations were evaluated by a Child Passenger Safety Technician (CPST). Error rates were compared between the treatment and control groups using lower-tailed t-tests and Pearson's chi-square tests. Error rates were evaluated considering minor and serious errors together and also considering serious errors alone. RESULTS: Compared to the control group, participants who trained with the AFS exhibited fewer overall errors (minor and serious) in their fixture installations (p < 0.0001) as well as their follow-up vehicle installations (p < 0.0001). Specifically, participants in the treatment group had fewer errors in choosing an installation method, locking the seat belt (SB), tightening the SB or lower anchors (LA), and tightening the harness (p = 0.0002, p = 0.0003, p = 0.0084, and p = 0.0098, respectively, compared to control group during follow-up vehicle installations). The treatment group also performed significantly better than the control group when only serious errors were considered. CONCLUSIONS: An automated feedback system is an effective way to teach basic CRS installation skills to users.

Evaluation of interventions to make top tether hardware more visible during child restraint system (CRS) installations.

Objectives: The objective of the study is to determine whether specific child restraint system (CRS) or vehicle conditions improve top tether attachment rates during volunteer installations. Methods: A factorial randomized controlled trial was designed to evaluate 4 different experimental categories: (1) Color of tether adjuster casing (black or red), (2) labeling on tether adjuster casing (labeled with "Tether: Use for forward-facing" or unlabeled), (3) storage location of tether (bundled in a rubber band on the back of CRS or Velcroed over the forward-facing belt path), and (4) labeling in vehicle (labeled under head restraint and below anchor or unlabeled). Ninety-six volunteers were randomly assigned to one combination of conditions. One installation per volunteer was completed. The primary outcome measure was acceptable attachment of the top tether to the tether anchor. The secondary outcome measure was overall secureness of the installation. Pearson's chi-square tests were used to identify significant predictors of acceptable outcomes and logistic regression was used to investigate interaction effects. Results: A total of 66/96 subjects (68.8%) attached the top tether in an acceptable manner, with either zero errors (n = 50) or minor errors (n = 16). A total of 30/96 subjects (31.2%) had unacceptable tether outcomes, with either major errors (n = 10) or nonuse the tether at all (n = 20). None of the 4 experimental categories significantly affected tether outcomes. Subjects who opted to install the CRS with the lower anchors (LAs) had higher rates of acceptable tether attachment compared to subjects who installed using the seat belt or those who used both LA and seat belt together (χ2 = 6.792, P = .034). Tether outcomes were not correlated with previous CRS experience, use of instruction manual(s), age, or sex. Only 15.6% of subjects produced overall correct and tight installations. Of those who used the seat belt in some manner, 70.2% neglected to switch the retractor into locking mode. Conclusions: Conditions in this study including tether color, tether labeling, storage location, and vehicle labeling did not significantly affect tether attachment rates. High rates of tether misuse and nonuse warrant further exploration to find effective solutions to this usability problem.

Usability of non-standard lower anchor configurations for child restraint system (CRS) installation.

OBJECTIVES: The objective of this study was to determine whether the amount of tension required for proper child restraint system (CRS) installation varies with lower anchor spacing and to determine whether nonexperts can produce adequate tension on wider-than-standard lower anchor configurations. METHODS: CRSs were installed by certified child passenger safety technicians (CPSTs; n = 6 subjects, n = 72 installations) and nonexperts (n = 30 subjects, n = 120 installations) on a mock-up vehicle seat fixture with lower anchors set at 11 (standard), 15, 19, and 23 in. apart from one another. Each CPST installed a rear-facing (RF) infant base, RF convertible, and forward-facing (FF) convertible into each of the 4 spacing configurations in random order. The CPSTs were instructed to tighten the lower connector strap until the tension was exactly at the threshold between passing and failing the 1-in. test. Each nonexpert installed one CRS model into all 4 spacing conditions in random order. Nonexperts were instructed to install the CRS to the best of their ability. The tension produced on the lower connector strap was recorded via load cell in the lower anchor assembly of the vehicle seat. Resultant tension magnitudes were compared across spacing conditions using matched pair t-tests. The CPSTs' mean 1-in. test threshold values were compared to tensions produced by nonexperts. Installations were visually evaluated for errors and qualitative usability feedback was collected via survey. RESULTS: CPSTs installed the infant base with higher tensions in the 15-, 19-, and 23-in. configurations compared to the standard 11-in. configuration (P = .034, .032, and .003, respectively). The nonexperts installed the infant base with higher tension in the 15- and 23-in. configurations compared to the 11-in. configuration (P = .004 and .026, respectively). The RF convertible and FF convertible installations showed no significant differences in tension among any of the spacing configurations for either group. Only 19% of the nonexperts' installations were tight enough to pass CPST thresholds, and the pass rate did not vary with respect to lower anchor spacing. In feedback surveys, the nonexpert group did not show a consistent preference for either standard or wider-than-standard lower anchor configurations. CONCLUSIONS: The amount of tension required to pass the 1-in. rule did not vary with lower anchor spacing configurations for the RF and FF convertible CRS, but the infant base required more tension in wider anchor configurations. Nonexperts tended to produce less than ideal tension in all configurations, although their tension magnitudes increased for the infant base in wider configurations.