Influence of child restraint system design features on comfort, belt fit and posture

Abstract

ObjectiveThis study examined the relationship between restraint design features and comfort, posture and seat belt position of children in booster seats during a driving trial. The relationship between comfort and errors introduced by a child throughout a trip were also explored. MethodFifteen children were recruited in this study. Due to technical issues affecting video capture of three participants, the comfort, belt fit, errors and posture of twelve Australian children aged 4–8 years were analysed during two, one hour on-road drives in an instrumented study vehicle fitted with in-vehicle video monitoring equipment. Each child sat in two different types of booster seats, which varied markedly in design. Restraint 1 featured an adjustable headrest, sash belt guide and side wings, whilst Restraint 2 had a longer cushion length (R1: 29 cm, R2: 34 cm), no sash belt guide or side wings. Three five-minute video segments were analysed per seating condition; at the beginning, middle and end of the trip. The Discomfort Avoidance Behaviour (DAB) rate, DAB time, errors and average participant trip time observed in shoulder belt, sagittal torso and head positions were quantified. ResultsThe average DAB rate was higher in R2 than R1 (R2 = 2.79 vs. R1 = 1.85, p = 0.009) and the average number of errors across time points was greater in R2 than R1 (R2 = 0.81 vs. R1 = 0.38, p = 0.01). The DAB rate was associated with increases in the number of child induced errors (log (errors in use) = −2.07 + 0.57 × DAB, p < 0.0001). Whilst both seating conditions most commonly displayed mid-shoulder belt position, a greater proportion of time was observed in R1 than R2 (R1 = 74% vs. R2 = 50%, p = 0.020). On average, children in R2 spent more time with the sash belt contacting the neck (R2 = 36% vs. R1 = 15%, p = 0.038). In R2, a greater proportion of trip time was spent with the head against the head rest (R2 = 48% vs. R1 = 25%, p = 0.005), whilst a greater proportion of trip time in R1 was observed with the head upright relative to the torso (R1 = 71% vs. R2 = 45%, p = 0.002). Children in R2 spent a greater proportion of time with their back and shoulders against the backrest (R2 = 79% vs. R1 = 61%, p = 0.003), whilst more time was spent by children in R1 with their entire back but not shoulders against the backrest (R1 = 36% vs. R2 = 16%, p = 0.001). ConclusionsThe design of a restraint and its influence on comfort, errors, shoulder belt fit and posture may provide an effective avenue to enhance the correct use of child restraints throughout a trip.