Sub-optimal restraint use, particularly the incorrect use of restraints, is a significant and widespread problem among child vehicle occupants, and increases the risk of injury. Previous research has identified comfort as a potential factor influencing sub-optimal restraint use. Problems with comfort may lead the child to misuse the restraint in their attempt to achieve better comfort whilst parent-perceived discomfort has been reported as a driver for premature graduation and inappropriate restraint choice.

This thesis consists of four related studies that have focused on the relationships between comfort and optimal child restraint use. These studies have examined the relationships between parent perceived comfort and both appropriate restraint choice and correct child restraint use as well as the relationship between child experienced comfort and correct restraint use.

The results of these studies indicate that there is no link between parent perceived comfort and appropriate restraint choice. However, there is a relationship between parent perceived comfort and restraint misuse, particularly active misuse of the harness or seat belt. A method for measuring and quantifying comfort experienced by the child was identified and used to compare the level of comfort experienced by the child in an add-on restraint system and an integrated restraint system.

These results suggest that while some parents report concern about their child’s comfort, parent-reported comfort levels were not associated with age appropriate restraint choice. However, parent reported comfort is important for the correct use of restraints. There is evidence to support the notion that the comfort experienced by the child is important for correct restraint use. The method we have developed for studying real comfort can be used in naturalistic studies involving child occupants to further understand this relationship. Overall the results of this body of work indicate comfort experienced by children in child restraints may be related to errors in use that occur through interaction between the child and the restraint system. It is recommended that naturalistic studies be conducted to confirm the relationships between child experienced comfort and restraint misuse as well as the relationship between specific restraint design features and comfort.