Anti-Rotation Load Leg Effects on Crash Injury Metrics Under Child Restraint System Misuse

Objective: Misuse (i.e., improper installation) of child restraint systems (CRS) remains alarmingly prevalent, with estimates ranging from 49% to 95%. Common misuse errors for rear-facing infant car seats include loose CRS installation in the vehicle and inadequate tightening of the child harness. These misuse errors compromise protection during motor vehicle crashes and intensify the risk of severe or fatal head and neck injuries (e.g., whiplash, traumatic brain, spinal, neck, chest contusions, other internal organs). Although anti-rotational devices, such as load legs, have shown potential in mitigating injury metrics, their efficacy for rear-facing infant CRS misuse conditions and condition combinations remains underexplored. Therefore, this research aimed to evaluate the use of load legs on head and neck injury metrics under two common misuse conditions: loose installations and loose harnesses. Methods: Dynamic frontal sled tests were conducted using a 12-month-old instrumented CRABI anthropomorphic test device (ATD). The ATD was secured in a rear-facing infant car seat, installed using the flexible lower anchor tether system, and tested on two distinct sled configurations: the Federal Motor Vehicle Safety Standard (FMVSS213) bench and the Consumer Reports CR35/35 bench, which replicates a more severe crash pulse. A full factorial 23 design of experiments (DOE) with no replication was executed to assess the effects of three categorical factors: load leg use, seat installation tightness, and harness tightness, yielding eight unique configurations per test protocol. Injury metrics analyzed included HIC36, HIC15, 3ms head clip, 3ms chest clip, neck resultant force, and neck resultant moment. Least squares regression modeling and ANOVA were used to assess main effects and trends across both protocols. Results: Across both test protocols, the load leg repeatedly emerged as a dominant performer in the reduction of head injury metrics, with effectiveness and tradeoffs varying by crash severity and installation quality. Under FMVSS213 (30 mph), a full factorial ANOVA (R20.84) with a percentage comparison of least squared means showed significant reduction in HIC36 by 16.3% (p=0.0253) but increased the 3ms chest clip by 12.9% (p=0.0059). HIC15, 3ms head clip, neck resultant force and neck resultant moment results were mixed, but none reached statistical significance (p>0.05). Under CR 35/35 (35mph), model fits remained strong (R20.86) and the load leg drove larger least squared means percentage reductions; HIC36 by 25.8% (p=0.0247), HIC15 by 27.8% (p=0.0174) and 3ms head clip by 14.1% (p=0.0185). Neck resultant force increased and 3ms chest clip and neck moment decreased, however these effects were not statistically significant. Kinematic overlays confirmed that the load leg reduced seat back rotation by 13o under proper installation and by 6o-19o across misuse cases. Head contact with the blocker plate was eliminated with load leg use across all condition except for the combined seat and harness misuse condition. In comparing FMVSS213 with CR35/35 protocols using eta squared (2), shows the 3ms chest clip effect size greatest under FMVSS213, whereas head and neck 2 metrics become more dominant under the CR35/35, the higher severity test. Conclusion: This study demonstrates that load legs improve CRS performance by reducing rotation and injury metrics under both ideal and misuse scenarios, though tradeoffs exist for mixed injury metrics. Their efficacy is more pronounced under high-energy crash conditions (CR35/35) for head and neck metrics and under lower severity crash conditions (FMVSS213) for thoracic injury. These findings validate the role of anti-rotation features as effective safety enhancements and highlight the importance of incorporating misuse-tolerant design features and user education into CRS safety strategies.

Author dc:creator

• Fernandes, Antonio S

Contributors dc:contributor

• Chowdhury, Suman
• Liang, Nade
• Yang, James
• Cross, Jennifer
• Tanushree Roy

Statement dc:rights

• Restricted until 09/2026. To request the author grant access, click on the PDF link to the left.

Language dc:language

English

Handle dc:identifier.uri

https://hdl.handle.net/2346/103262

OAI identifier oai:identifier

oai:tdl-ir.tdl.org:2346/103262