Principal Investigator: Yoganand Ghati, MS, Children's Hospital of Philadelphia
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.
This study builds upon findings from a previous CChIPS study that analyzed New Car Assessment Program (NCAP) data for various vehicles over model years and showed that the magnitude of the accelerations experienced by rear-seated occupants increased as the cars got newer. At the same time, these
newer vehicles received a better NCAP star rating, which is based on the driver and right front-seated passenger risk of injury, indicating improved protection over older cars. Better star ratings, despite higher accelerations, are primarily due to better restraints (advanced air bags, seat belts with pretensioners and load limiters) available to passengers in the front seat but not in the back seat.
The rear-seated occupant population is diverse and consists of children and older adults who may have different injury risks than typical front seat occupants. The diversity of rear seat occupants’ size and age and associated injury tolerance limits make it more challenging to design and optimize restraint systems for rear-seated occupants. This study was designed to evaluate and optimize advanced restraint systems, such as those used in the front seat, for different-sized anthropomorphic test devices (ATDs) in typical vehicle rear-seat conditions using computational modeling techniques.
Baseline computational models of rear-seated occupants of different age groups using advanced restraint systems (pretensioners and load limiters) with typical vehicle interiors were created using MADYMO. The effect of variations in vehicle and restraint parameters — such as seat buckle height, seat cushion ramp height, and shoulder belt anchor locations — on injury metrics and occupant kinematics were assessed. Results showed that the use of a load limiter and retractor pretensioner has the highest effect on injury metrics and ATD kinematics, while the buckle pretensioner’s effect is negligible for all ATDs. The D-ring, belt buckle, and seat cushion ramp were not found to be as significant for optimizing safety.
These findings suggest that while designing vehicles for the optimum safety of rear-seated occupants, careful consideration should be given to the load limiter level and the use of the retractor pretensioner. Technologies implemented in the front seat may not be exactly transferable to the rear seat due to different occupant sizes.
John Combest, Nissan; Hiromasa Tanji, TK Holdings Inc.