Effectiveness of Load Legs on Rear-Facing Only Child Restraint Systems (CRS) in Frontal Sled Tests

Abstract

Introduction: Load legs are a safety feature that brace child restraint systems (CRS) against the floor of the vehicle. Previous research has identified potential benefits in terms of energy absorption and injury metric reductions with this safety feature. The goal of this study is to establish the efficacy of a wider range of load leg designs and performance outcomes in frontal impacts compared to identical tests without load legs. Methods: The Consumer Reports test buck with front row blocker plate was used with a frontal impact pulse of approximately 34.5 g and 62.1 kph. One CRS model was tested with both an experimental "dampening" load leg design and an experimental "stiff" load leg design. Additionally, six different models of rear-facing only (RFO) infant CRS were tested with and without their load leg in position for three or more repetitions each, for a total of 55 tests. The Child Restraint and Airbag Interaction (CRABI) 12-month-old anthropomorphic test device (ATD) was used as the occupant in all tests. Results: The dampening and stiff load leg designs had similar injury metric outcomes to one another. Across the full sample, load legs significantly reduced the occurrence of CRS shell and ATD head contact against the blocker plate. On average, load legs reduced the rotation angle of the CRS by 10.3° (47.9%, p<0.0001), HIC15 by 1339.7 (73.3%, p<0.0001), head resultant acceleration by 69.3 g (50.8%, p<0.0001), and chest resultant acceleration by 14.6 g (19.8%, p<0.0001) compared to corresponding tests without load legs. Although the load legs collapsed in several tests, many injury metrics were still significantly reduced in these cases compared to corresponding tests without load legs. However, collapsed load legs were less effective at reducing CRS rotation, which might be an important factor in preventing head strikes in real-world crashes. Conclusions: Load legs provided significant benefits to the CRABI 12-month-old occupant in RFO CRS. Load legs that maintained their structural integrity produced the best results, but load legs that collapsed under loading still provided significant benefits to CRS occupants. These results support the use of load legs in families' vehicles when possible.