Principal Investigator: Kristy Arbogast, PhD, Children’s Hospital of Philadelphia
Below is an executive summary of this line of research. Please note that each summary describes results and interpretation that may not be final. Final interpretation of results will be in the peer-reviewed literature.
The research objective was to quantify the influence of child restraint lower attachment method on head kinematics, head impact potential and head, neck, and thorax injury metrics for a child occupant secured in a forward-facing child restraint system (FFCRS) in oblique side impacts.
Fifteen sled tests were conducted with a Q3s seated in a FFCRS secured to the center position on a production small SUV bench seat. Three lower attachment methods were evaluated: rigid ISOFIX (RI), a flexible single loop LATCH webbing (SW) routed through the vehicle belt path of the FFCRS, and dual flexible LATCH webbing (DW) attachments on either side of the FFCRS. All were tested with and without a tether with one repeat test in each test condition. The same model FFCRS was used for all tests; only the attachment method varied. The vehicle bench seat was fixed on the sled carriage at 80 degrees (from full frontal). The input pulse was the proposed FMVSS 213 side impact pulse scaled to a 35 km/h delta-v. Two-way ANOVA was used to evaluate the effect of lower attachment and tether use on three outcome metrics: lateral head excursion, neck tension, and neck lateral bending.
Data included ATD head excursions, head linear accelerations and angular velocities, neck loads and moments, thoracic accelerations, lateral chest deflections, lower anchor loads, and tether webbing loads. ATD head kinematics were collected from a 3-dimensional motion capture cameras.
Results demonstrated a reduction in injury measures with the RI and DW attachment as compared to the SW attachment with decreased lateral head excursions (331 mm, 356 mm and 441 mm for the RI, DW, and SW systems respectively,( p<0.0001) neck tension (1.4 kN, 1.6 kN and 2.2 kN, p<0.01), and neck lateral bending (31.8 Nm, 38.7 Nm, and 38.0 Nm, p=0.002). The tether had a greater influence on lateral head excursion for the FFCRS with flexible webbing attachments than those with the rigid attachment with the tether forces being highest with the SW systems. Lateral head excursions were significantly lower and lateral neck bending moments were significantly higher with tether use (p<0.0001) across all lower attachments. The effect of tether on neck tension was mixed; only showing an increased effect with the RI system.
SIGNIFICANCE OF RESULTS
The CRS lower attachment system influenced occupant kinetics. The results indicate that CRS attached to the vehicle via rigid and dual webbing systems exhibit improved kinematics by reducing the rotation and tipping seen with the single webbing attachment. This leads to reduced lateral head excursions and neck tension values. The advantages of the tether in reducing lateral head excursion are most pronounced with the flexible webbing attachments. With tether use low in the US, a DW type FFCRS attachment system may be a better attachment method than SW and provide a simpler engineering solution than RI attachment.
Recent advances in child occupant protection have focused on mitigating fatalities and injuries to children in child restraint systems (CRS) in side-impact or oblique crashes. Although those in near-side seating positions have the highest injury and fatality risk in side-impact scenarios, injuries still occur to occupants seated center or far-side. For these occupants, the most common body region of injury is the head and neck, most frequently caused by head contact with the vehicle interior.
In the first year of this line of study, researchers observed the far-side seated forward-facing (FF) CRS yaw and roll in the oblique impact mode, leading to substantial head excursion of the anthropomorphic test device (ATD), or crash test dummy. This excursion was of the magnitude to lead to potential impact with a vehicle’s intruding components during a side-impact crash. The tests also suggested the tether can provide value in mitigating head excursion and pointed to the need for a more detailed look at the role of the tether. Based on the Year 1 findings, an extension of this work for a second year used a series of sled tests to explore the role of the tether and intrusion on the kinematics and injury potential of a 3-year-old occupant seated in the center seat in oblique side impacts.
Sled tests were conducted utilizing a Q3s ATD positioned in a FF CRS. CRS were attached to a rear seat from a small SUV via Lower Anchors and Tethers for Children (LATCH) flexible webbing in the center seating position; tests were conducted with and without the tether. The vehicle seat was secured to the sled at both 30 and 10 degrees from pure lateral, with a simulated intruded door secured left of the CRS – on the near side of the crash. 3D motion cameras collected ATD head excursion data, and head accelerations; head rotational velocities; neck loads, as well as webbing and tether loads.
All tests without a tether resulted in head to door contact, with the head rolling out of the FF CRS’s side wings and making contact with the intruded door halfway between top of door and the top of armrest. The tether reduced excursion and head injury values, indicating its importance for potentially preventing injury in side impacts to children seated center or far-side. In addition to elevated head injury metrics, neck injury metrics were above existing thresholds.
These results point to the need for further research examining potential CRS attachment design and vehicle interior protection countermeasures to limit head and neck injury, including ways to better contain the head in oblique crashes. Additional padding or inflatable curtains below the vehicle’s window sill also may help better protect small occupants and children.
This testing illustrated relevant side-impact crash circumstances where side wings do not provide the desired head containment for a 3-year-old ATD seated far-side or center in a FF CRS. In a center or far-side seating configuration, the absence of a door structure immediately adjacent to the CRS may allow the rotation and tipping of the FF CRS towards the impact side and the roll-out of the head around the side wing structure. Results suggest other prevention measures, in the form of alternative side-impact structure design, FF CRS vehicle attachment, or a combination of safety technology provided by both the vehicle and the FF CRS and the vehicle, may be necessary to protect children in oblique side impact crashes.Side-impact collisions are the second most common crash mode, accounting for 26 percent of fatal crashes for all occupants, and 40 percent of fatalities to children between 0 and 8 years of age. As such, the National Highway Traffic Safety Administration has identified child restraint systems (CRS) protection in a near-side configuration as a safety priority.
Few studies have examined the injury potential to children in side-impact crashes in positions other than the near-side position, such as center seating locations, because they are generally considered safest for the pediatric occupant. For the center- or far-side seated CRS in particular, the potential of CRS to yaw or roll into intruding vehicle components (especially in small-size vehicles) has not been addressed. This line of research is intended to spur development of safety improvements for children in side impacts and is in alignment with recent efforts to meet the safety needs of adults seated in front row positions, during side impacts that are far side to the occupant.
This project aimed to quantify the kinematics and injury potential for anthropomorphic test devices (ATDs) representing a 3-year-old occupant in a far- or center- seated position in an oblique side-impact crash. The project test series examined the influence of side-impact protection features, such as side wings, of a forward-facing CRS (FF CRS), vehicle seat type, and tether routing.
Sled tests were conducted utilizing a Q3s dummy positioned in a FF CRS with large side wings that were removed. The CRS were attached via Lower Anchors and Tethers for Children (LATCH) on two different vehicle seat fixtures – a small SUV rear bench seat with a fixed head restraint, and a minivan rear bucket seat with an adjustable head restraint. The vehicle seats were secured to the sled at 20 degrees from lateral.
Results indicated the side wings have little influence on head excursions and ATD response. Researchers observed primary differences in head response between the two vehicle seat fixtures due to the vehicle seat head restraint design. The bench seat integrated head restraint forced the top tether to be routed over the head restraint. Due to the lateral crash forces, the tether moved laterally off the head restraint reducing webbing tension and increasing head excursion (477 mm median). In contrast, when the tether was routed under the bucket seat’s adjustable head restraint, it maintained a tight attachment and helped control head excursion (393 mm median).
Project Team Members
Hans W. Hauschild, MS, Medical College of Wisconsin (Y1, Y2, Y3); Bruce Kaufmann, MD, Children’s Hospital of Wisconsin & Medical College of Wisconsin (Y1, Y2, Y3); Matthew R. Maltese, PhD, Children’s Hospital of Philadelphia (Y1, Y2, Y3); Frank A. Pintar, PhD, Medical College of Wisconsin (Y1, Y2, Y3); Narayan Yoganandan, PhD, Medical College of Wisconsin (Y1, Y2, Y3)
John R. Humm, Medical College of Wisconsin (Y1, Y2, Y3); Jared Koser, Milwaukee School of Engineering (Y3); Paul Gromowski, MS, Medical College of Wisconsin (Y1).
Keith Nagelski, Britax Child Safety, Inc. (Y2, Y3); Eric Dahle, Evenflo Company Inc. (Y1, Y2, Y3); Amanda Taylor, Federal Aviation Administration; Neeharika Anatharaju, FCA US LLC; Lan Xu, FCA US LLC; Mark LaPlante, Graco Children’s Products Inc. (Y1, Y2, Y3); Jerry Wang, Humanetics Innovative Solutions Inc. (Y1, Y2, Y3); Mark Humer, Lear Corporation; Sara Seifert, Minnesota HealthSolutions; Hiromasa Tanji, TK Holdings Inc. (Y1, Y2, Y3); Uwe Meissner, Technical Advisor (Y2, Y3); Audrey Eagle,FCA US LLC (Y1,Y2); Julie Kleinert, General Motors Holdings LLC (Y1,Y2); Schuyler St. Lawrence, Toyota USA (Y1,Y2); Barbara Birkenshaw, Volkswagen Group of America (Y2); Rodney Rudd, National Highway Traffic Safety Administration (Y2); Mike Kulig, Calspan Corporation (Y1); Agnes Kim, Ford Motor Company (Y1)