Effectiveness of Top Tether on Angular Kinematics of CRS and ATD in Side Impacts

Principal Investigator: Yun Seok Kang, PhD, The Ohio State University

Below is an executive summary of this project. Please note that this summary describes results and interpretation that may not be final. Final interpretation of results will be in the peer-reviewed literature.

Video capture from a sled test of a far-side impact in which no top tether was used in the installation.

Side impacts are less frequent than frontal impacts; but, given a side impact, the risk of injury is greater. Among side impacts, those far-side and near-side pose different injury risks, and age-appropriate child restraint systems (CRS) have been proven effective in reducing these risks in the event of a motor vehicle collision. The effectiveness of the CRS comes from its ability to distribute forces over the shoulders and hips of the child, while reducing head and chest excursion.

A critical component of optimal forward-facing CRS performance in the use of the Lower Anchors and Tethers for Children (LATCH) system, a standardized method of attaching child restraints to vehicle seats, is the top tether. Its effectiveness during frontal impacts has been well-documented, showing the ability to reduce head excursion, chest acceleration, and lower neck loads. Less is known, however, about the top tether’s effects during side-impact conditions. Previous research studies analyzed sled tests and finite element simulations in an effort to understand these effects, but had critical limitations. Some only collected limited data using anthropomorphic test devices (ATDs), or crash test dummies, while others only explored a few test conditions.

This study looked to further understand the effects of the top tether in side impacts. A series of near-side and far-side impact sled tests were performed with the Q3s dummy. Two CRS, the Evenflo Triumph and Symphony, and two impact direction angles, lateral (9°) and oblique (30°), were featured. Each scenario was performed with the presence and absence of the top tether.  Q3s responses were recorded, and Head Injury Criteria (HIC15) and Brain Injury Criteria (BrIC) values were calculated. Additionally, CRS angular kinematics were recorded and correlated to the Q3s responses.

For far-side impacts, the top tether increased resultant head accelerations by approximately 8 to 38 percent, and HIC15 values by approximately 20 to 140 percent. However, the top tether was effective in preventing lateral head excursion. For near-side impacts, the top tether resulted in less than a 10 percent increase in resultant head acceleration and HIC15 in the lateral impact direction. For oblique impacts, the top tether increased HIC15 by 17.3 percent for the Triumph and decreased it by 19.5 percent for the Symphony. This difference can be attributed to the design of the seats. The Symphony has side wings to provide extra padding during side impacts; the Triumph does not. Researchers observed noticeably larger Q3s head responses during the near-side impacts than during the far-side impacts. Additionally, the top tether proved beneficial in preventing forward and lateral CRS rotation and reducing lower anchor loads. These results provide critical insight into the effects of the top tether in various side-impact conditions and can aid CRS manufacturers in optimizing the design of child restraints that benefit from top tether usage.


Jordan Majstorovic, BS, The Ohio State University

IAB Mentors

Keith Nagelski, Britax Child Safety, Inc.; Eric Dahle, Evenflo Company Inc.; Agnes Kim, Ford Motor Company; Julie Kleinert, General Motors Holdings LLC; Kendal Fowler, Graco Children’s Products Inc.; Jerry Wang, Humanetics Innovative Solutions Inc.; Hiromasa Tanji, TK Holdings Inc.; Uwe Meissner, Technical Advisor