Kinematics and shoulder belt engagement of children on belt-positioning boosters during evasive steering maneuvers

ABSTRACT

Objective: To increase the protection of child passengers in crashes preceded by evasive steering, understanding of how children interact with the seat belt in such situations is essential. This study aims to quantify child kinematics and describe child-to-restraint interaction during evasive steering maneuvers.

Methods: Eighteen child volunteers (aged 5–10) were seated on the rear seat of a passenger vehicle. A professional driver made repeatable sharp turns at 50 km/h. Children were restrained by the seat belt on a booster cushion (BC) and on an integrated booster cushion (IBC). Kinematics of the nasion and upper sternum were analyzed with video tracking software and shoulder belt (SB) engagement and position were evaluated.

Results: Children moved laterally inboard, and SB-to-body interaction was influenced by booster and stature. Shorter children displayed initial SB positions closer to the neck with less instances of gap between the SB and the lower torso, resulting in more curved belt paths on the IBC. On the BC, shorter children had less of the SB in contact with the torso and straight belt paths were observed throughout steering. Taller children generally had the SB initially mid-shoulder with less instances of gap, resulting in curved belt paths at initial and maximum displacements on both boosters. Children loaded the shoulder belt by axially rotating their torso into the SB more often on the IBC compared to BC. The SB generally stayed on the shoulder, with 89% of slip-off instances occurring for shorter children on the BC. Shorter children on the BC had the largest average inboard nasion displacement (120 mm). Taller children on the BC had the lowest average inboard displacement of the nasion (100 mm). All children initially displaced on average 90 mm inboard with their upper sternum.

Conclusions: Initial SB position on the shoulder and torso differed with booster and stature, which influenced how children engaged with the seat belt during steering. Children with less SB initially in contact with the torso moved laterally behind the belt, resulting in straighter SB paths and outboard motion of the SB on the shoulder (often ending far out or slipped off). When more of the SB was initially in contact with the torso, children tended to engage the SB more, moving with the belt and causing the SB path to become more curved, resulting in less inboard head displacement and less outboard motion of the SB on the shoulder. Enhanced understanding of how evasive steering affects the kinematic response of children provides valuable data for protection of children in real-world situations.

KEYWORDS:

• Child safety
• occupant kinematics
• rear seat
• seat belt
• child restraints
• booster seat
• shoulder belt engagement

Acknowledgments

The authors thank all of the participating children and their families. We especially thank Thomas Alfredsson at Stora Holm's test track for providing safe rides for the children. Thank you also to Volvo Cars Safety Centre, especially Håkan Gustafson, for instrumentation of the vehicle and extraction of data. Special thanks also to Ida Hansson, Laure-Lise Gras, and Jean-Adrien Develet at Chalmers for helping with data collection. The authors also acknowledge everyone in the research group within the Swedish national research project “Safety for Children in the Rear Seat” at SAFER. This study was carried out at the SAFER Vehicle and Traffic Safety Centre at Chalmers University of Technology, Sweden.

Funding

This study was financed by FFI (Strategic Vehicle Research and Innovation) by VINNOVA, the Swedish Transport Administration, the Swedish Energy Agency, and their industrial partners, Sweden.