A survey of motor vehicle child restraint use found around 28% of children under the age of six using weight-inappropriate restraints. Many parents did not know when a child was likely to outgrow a booster seat nor the weight of their child, but they did know the child’s age. Anthropometric data show that, if advice on restraint transition, given solely in terms of age (6 months, 4 years, 8 years) were followed in Australia, incorrect restraint selection would occur in 5% of children under the age of six. Further analysis suggests how rewriting the Standard could reduce this number.

We present an argument for placing age-based transitions at the heart of the strategy to improve child restraint compliance. This may be superior to one based on the child’s weight or other anthropometric measurement. Our argument may be summarized as follows:​

1. 1 Age-based rules for selecting child restraints are simple, require less information to be retained, and might be more natural criteria for parents. They might have a greater chance of being adopted as norms, and of encouraging good peer cues. Anthropometric rules, on the other hand, assume that parents know the current dimensions of their children and have the tools at their disposal to measure these dimensions.
2. 2 The consequences of age-based promotion for the proportion of children in a restraint suitable for their weight can be estimated for alternative regulatory frameworks. We will report such Calculations below and show that this rate can potentially be very high.