Principal Investigator: John H. Bolte IV, PhD, The Ohio State University

Forward-facing child restraint systems (CRS) and high-back boosters are often tall enough to contact the vehicle seat head restraint when installed, but guidelines vary on whether or not head restraint interference is acceptable during CRS use. This project aims to study the effects of head restraint interference on dynamic child restraint system (CRS) performance by conducting sled tests simulating frontal and far-side impacts.

WHAT WAS THE PURPOSE OF THIS PROJECT? 

Previous compatibility studies and real-world experience have shown that forward-facing (FF) CRS and high-back belt positioning boosters (BPB) are often tall enough to contact the head restraint (HR) of the vehicle seat where they are installed. Having HR interference can create a gap behind the CRS or change the angle of the CRS on the vehicle seat. The goal of this study was to understand the dynamic effects of HR interference in frontal and far-side impacts. 

HOW WAS THE RESEARCH CONDUCTED? 

We ran a total of 24 sled tests (12 frontal impacts and 12 far-side impacts) using third row seats from a recent model year minivan. One FF CRS model and two different high-back BPB models were installed with and without HR interference by removing the HR for those tests. The FF CRS was installed using a variety of different methods (seat belt or lower anchor, with and without top tether) to see if the installation method would affect the outcomes. Our primary outcome metrics were ATD and CRS excursions as well as kinetic responses of the ATD. 

WHAT DID YOU FIND? 

In frontal impacts, the installations that had HR interference produced a small but consistent increase in most of the injury metrics, including frontal head excursion, head injury criterion (HIC), chest resultant acceleration, neck tension, neck flexion moment, and lap/shoulder belt loads. This difference can most likely be attributed to the HR initially positioning the CRS and occupant further forward on the vehicle seat. In the far-side impact tests, the results were less consistent. The presence of a top tether seemed to affect whether certain injury metrics were higher or lower with respect to HR interference

WHAT’S NEXT? 

This study showed that removing the HR to eliminate interference might reduce some injury metrics for CRS-seated children in frontal and far-side impacts. However, this study did not investigate rear impacts and the potential consequences of removing the HR in that crash mode, where support from the HR might be beneficial. It is not well documented whether the head support provided by the CRS or BPB alone would be sufficient in rear impacts. Future work in this area would create a more well-rounded dataset to help guide manufacturers’ recommendations regarding HR positioning in conjunction with CRS.

In frontal impacts, HR interference caused the occupant’s head to begin in an initially more forward position (~1.4 cm) on the vehicle seat (dark colored portion of the bars). During the crash event, the head displaced forward roughly equal amounts regardless of HR interference (light colored portion of the bars). Therefore, the overall forward head excursion (total height of each bar) was greater for CRS with HR interference, likely due to the more forward initial position of the head.

Co-Investigator

Julie Mansfield, PhD, The Ohio State University 

IAB Mentors

Jonathon Gondek, Calspan Corporation; Emily Thomas, Consumer Reports; Suzanne Johansson, General Motors Holdings LLC; James Fitzpatrick, Graco Children’s Products Inc.; Mark LaPlante, Graco Children’s Products Inc.; Bill Lanz, American Honda Motor Co., Inc.; Susan Mostofizadeh, American Honda Motor Co., Inc.; Jerry Wang, Humanetics Innovative Solutions Inc.; Russ Davidson, Lear Corporation; Steve Gerhart, Nuna Baby Essentials, Inc.; Jennifer Pelky, Toyota USA; Julie Kleinert, Technical Advisor; Uwe Meissner, Technical Advisor