Safety for Children in Cars – Focus on Three Point Seatbelts in Emergency Events

Doctoral thesis, 2016

Child safety in vehicles has improved over time. One of the main factors is due to the increased restraint use by children. Nevertheless, studies show that although children are restrained, injuries still occur indicating that restraint systems have the potential for further improvement. This thesis focuses on emergency events that may precede a crash, and how these events influence the kinematics of child occupants restrained by a three point seatbelt. Real world data was analyzed and the results identified that a substantial portion of drivers attempted an avoidance maneuver prior to crash. Volunteer tests were carried out to investigate children’s motion during emergency braking and steering maneuvers in a passenger vehicle, and the current child crash test dummies were evaluated with respect to child occupants. In addition, a countermeasure was evaluated by activating an electrical reversible seatbelt retractor (pre-pretensioner) prior to run-off road events with child crash test dummies. The results of the volunteer tests emphasize the need for considering large areas of the vehicle’s interior as part of potential head impact surface. Maximum forward excursion is influenced by initial shoulder belt position and type of booster used in the braking events. A steering maneuver is an unstable restraint situation for children in the rear seat and a great variety in lateral displacement and seatbelt position on the shoulder were seen in different restraint configurations. Influencing factors include child age, anthropometry, initial seated posture and initial shoulder belt position on the shoulder. This thesis confirms that children can be exposed to sub-optimal postures due to emergency events. It provides evidence that a pre-pretensioner has considerable potential in maintaining different sizes of rear-seated occupants well restrained. The braking and steering maneuvers with child volunteers carried out in this thesis provide novel and unique knowledge of possible pre-crash postures of children across a variety of restraint systems in vehicle emergency maneuvers. Test tools are needed to better replicate the real world seated postures and injury causation scenarios. This thesis evaluated the available physical child test tools in low acceleration conditions when exposed to emergency events and highlighted the limitations in capturing child kinematics in emergency events with existing crash test dummies. Extending previous research, this thesis has resulted in deeper knowledge of how children are affected by emergency events prior to crash, in terms of quantifying the frequency of vehicle maneuvers in real world data, measuring the kinematics of children and child crash test dummies in these scenarios and exploring a possible countermeasure to improve safety. The output has the potential to positively impact child safety in cars through the development of active safety systems, enhanced rear seat restraints, and improved test methods and test tools.