ATD Responses in Rear-facing/Forward-facing Configurations in Frontal and Rear Impact Sled Tests

Principal Investigator: Declan Patton, PhD, Children’s Hospital of Philadelphia


Some European rear-facing CRS can accommodate larger children up to age 6 years. These child restraints have support legs, also known as load legs, to reduce rotation during frontal impacts, and some have lower tethers to reduce rotation during rear impacts. Our aims for this project were two-fold: 1) to investigate the effects of these anti-rotation devices during sled tests, and 2) to compare a convertible CRS in forward-facing (FF) and rear-facing (RF) configurations during frontal and rear impacts. This project builds upon prior CChIPS work led by Dr. Aditya Belwadi, which investigated the effect of load legs in infant seats using a 12-month-old and an 18-month-old ATD in frontal impacts.


We used sled testing to investigate the performance of three exemplar CRS models: one RF infant CRS with flexible lower anchors (LATCH) and a support leg, one RF infant CRS with rigid lower anchors (ISOFIX) and a support leg, and one extended-use convertible CRS attached via a seat belt with a retractable support leg and lower tethers. We tested a variety of different scenarios. The two RF CRS were tested with 12- and 18-month-old ATDs, with and without load legs in frontal impacts. The convertible seat was tested with 3- and 6-year-old ATDs in frontal and rear impacts – in frontal impacts the seat was tested FF and RF, with and without load legs, and in rear impacts the seat was tested FF and RF, with and without lower tethers.



We found a safety benefit – reductions in head injury metrics and non-injurious levels of neck injury metrics – associated with the support leg in frontal impacts across all ATDs and RF CRS models. For the convertible CRS, the lower tethers reduced rotation of the CRS during rear impacts. While previous research had similar findings for the 3-year-old ATD, we were able to demonstrate that those safety benefits can extend up to 6 years old. For the extended-use convertible CRS, we found elevated neck injury metrics for FF child occupants and elevated head injury metrics for the RF CRS in the frontal impacts. The elevations in head injury metrics for RF occupants in frontal impacts were attributed to interactions with the blocker plate, intended to represent the front seat in a vehicle. These interactions need to be further investigated in tests using an actual vehicle seat to accurately represent the dynamic response of the front seat back.


This study provides valuable information to CRS manufacturers regarding the design and development of anti-rotation devices, such as support legs and lower tethers, and also supplements epidemiologic studies regarding child seat policy.

Project Team Members

Kristy Arbogast, PhD, Children’s Hospital of Philadelphia; Aditya Belwadi, PhD, Children’s Hospital of Philadelphia (current affiliation: Tesla, Inc.)

IAB Mentors

Farid Bendjellal, Britax Child Safety Inc.; Mark Pitcher, Britax Child Safety Inc.; Allison Schmidt, Britax Child Safety Inc.; Jonathan Gondek, Calspan Corporation; Mike Kulig, Calspan Corporation; Mark LaPlante, Graco Children’s Products Inc.; Jason Stammen, National Highway Traffic Safety Administration; Uwe Meissner, Technical Advisor