Child Safety in Car Crashes

Doctoral thesis, 2012

Traffic related trauma is the most common cause of fatality and severe injury to children in developed countries. The majority of these fatalities and injuries are caused by frontal and side impacts. Researchers agree that the head is the most important body region to protect for all ages of children, while the thorax is equally important for older children. Injury epidemiology has shown that special attention is needed for the 3-year-olds in boosters and the 12-year-olds in seat belts only. The aim of this thesis is to develop mathematical frontal and side impact models and to use them to investigate and define the beneficial characteristics of restraint systems and other crash-related car parameters. It must be emphasized that children are better protected in rear-facing child restraints; they should remain rear-facing for as long as possible. Most children have outgrown the large rear-facing restraints by the age of about 4 years. This work concentrates on injury mitigation for those who have transited to forward-facing restraints. Models for two load cases were developed and validated. One of them was a frontal impact type, and the other was a near-side impact type. The frontal model was used both for a parameter study, to define beneficial restraint system characteristics for 3-year-olds, and for reconstructing three crashes in order to evaluate the head kinematics of the occupant model. The characteristics of the side impact load case were defined by analyzing real life crashes involving child occupants. The near-side impact model was used for a parameter study to define beneficial restraint system characteristics for 3- and 12-year-olds. It was also used to evaluate and propose improvements to the restraint systems within a range of common sitting positions for 12-year-olds. The validations carried out here showed that the models developed were suitable tools for conducting comparative studies of injury mitigation systems in both frontal and near-side impacts. The parameter studies showed that several of the restraint systems for adults also reduced the values measured by the child model. In the near-side impact, a curtain airbag, a thorax-pelvis airbag and a seat belt with a pretensioner reduced the head and chest injury measures of the two occupant models. To help mitigate injuries resulting from a frontal impact, the upper belt anchor point should be positioned so that the belt is routed near mid-shoulder (slightly toward the neck) and encloses the shoulder (tight fit). The lap belt anchor points should be positioned to make the lap belt angle as horizontal as possible without inducing submarining. Seat belts with pretensioners and load limiters also reduced the head injury measures for the 3-year-old occupant model. In side impacts, the results of the evaluation of common sitting positions suggested that extensive outboard, inboard and forward positions should be discouraged, while the restraint systems should be adapted to function with slight inboard, outboard and forward positions. This can be achieved with side supports integrated in the seat back, pre-impact (pre-brake) trigged seat belts, high performance full cell coverage curtain airbags, and/or thorax-pelvis airbags with an extended cover area. These findings are significant contributions to the continuous work of mitigating traffic accident induced injuries and fatalities to children.