Effectiveness of Seat Belt Legislation on the Queensland Road Toll—An Australian Case Study in Intervention Analysis

The effect of seat belt legislation introduced in the state of Queensland was examined by using two approaches. The first approach consisted of modeling time series of road deaths before intervention (the legislation) as a Box-Jenkins univariate time series model. As we expected, this model proved to be inadequate in explaining the postintervention period, and the model was modified to incorporate the expected form of the intervention effects. Results showed that the legislation produced significant reduction in the road toll, but this analytical approach was limited in describing long-run effects. The second approach, involving causal model and incorporating a proxy explanatory variable and autoregressive-moving average error, was fruitful in overcoming the limitation of the previous approach. The long-run legislative effect was quantified, at a specific level of the explanatory variable, to be a 46 percent reduction in deaths.