Principal Investigator: Julie Bing, MS, The Ohio State University; John Bolte, 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.

CONTEXT

In frontal and oblique impacts, rear-facing (RF) CRS distribute crash forces across the occupant’s back and keep the head, neck, and spine safely aligned. However, in a rear impact, the overall kinematics of the crash are reversed.  The RF CRS rotates upward toward the back of the vehicle and the five point harness and vehicle seat back and/or head restraint become the primary loading surfaces for the occupant’s mass. Epidemiological studies show that injuries to children in most rear impacts are typically minor.  However, previous experimental studies of severe rear impact tests indicate that high head injury values may result from head strikes with the vehicle seat back and/or head restraint. Experimental data is sparse for more moderate, typical rear impact pulses.

OBJECTIVE

This study aims to define the performance of rear-facing child restraint systems (RF CRS) in moderate severity rear impacts.  The study also investigates whether certain RF CRS features may mitigate or exacerbate injury risk in this scenario.

METHODS

A series of twelve tests were conducted at a moderate severity rear impact sled pulse (approximately 28.2 km/h and 18.4 g).  Four different models of RF CRS were installed in the outboard positions of a popular compact sedan’s rear seats, which were affixed to a sled buck.  The CRABI 12-month-old (CRABI 12MO) and Hybrid III 3-year-old (HIII 3YO) anthropomorphic test devices (ATDs) were instrumented with head and chest accelerometers, head angular rate sensors, six-axis upper neck load cells, and a chest linear potentiometer (HIII 3YO only).  CRS kinematics were recorded with high speed video.  The test matrix investigated the effects of carry handle position, occupant size, presence of anti-rebound bar, Swedish style tethering, and lower anchor vs. seat belt installation.  Data were also analyzed for occupant injury criteria exceeding current pediatric injury assessment reference values (IARVs).

RESULTS

Head Injury Criterion (HIC15) values across all tests were small compared to current IARVs and US federal regulation limits, despite head contact against the vehicle head restraint in four tests.  Chest resultant accelerations (3ms duration) were also well below current thresholds.  In some CRS, the use of an anti-rotation device such as an upright carry handle or Swedish style tether increased neck loads compared to similar conditions with free rotation allowed, but all individual neck loads and combined axial force and moment (Nij) values were below current IARVs for all conditions. Other CRS models did not produce higher neck loads when anti-rotation features were used.

CONCLUSIONS

The results indicate that occupants of properly installed RF CRS are unlikely to suffer serious injuries in moderate severity rear impacts.  This study provides experimental data to address this crash scenario, which are currently lacking in the literature.  These conclusions are supported by epidemiological and field data which indicate that RF CRS are the safest type of CRS for young occupants considering all crash scenarios. 

IAB Mentors

Keith Nagelski, Britax Child Safety, Inc.; Emily Thomas, Consumer Reports; Eric Dahle, Evenflo Company Inc.; Fariba Famili, FCA US LLC; Mark LaPlante, Graco Children’s Products Inc.; Mladen Humer, Lear Corporation; Hiromasa Tanji, TK Holdings Inc.; Barbara Birkenshaw, Volkswagen Group of America; Uwe Meissner, Technical Advisor