Kinematics, Injury Mechanisms and Design Considerations for Older Children in Adult Torso Belts

A gap in protection appears to exist for older children who have outgrown booster seats and are placed in some adult, 3-point belts with fixed shoulder belt anchorage points. Boys on average do not reach the 50^th percentile adult, male seated height until age 15 ½ and the average girl never reaches this height. The published minimum seated height and weight thresholds for use of three-point belts alone are inconsistent with the official recommendations by The National Transportation Safety Board and the majority of state seat belt laws. A shoulder belt with a fixed upper anchorage, which is typical in the rear occupant space, may create torso belt routing that can allow rollout from the shoulder belt in frontal oblique collisions. A belt trajectory that passes across the neck of an older child may create an artificial fulcrum in the cervical spine resulting in quadriplegia. Excessive webbing lengths can promote child occupant excursion, rebound and injurious head contact. The differences in older child protection reported in U.S. versus Australian car crashes suggest that safety improvements may be achieved with more rigorous state legislation and improved torso belt restraints, which appropriately accommodate both children and adults (i.e. “size-appropriate restraints”) in all positions occupied by child passengers. Further studies are indicated to fully elucidate the scope of the problem in U.S. crashes and the effectiveness of recommended design and public policy interventions.