Table 2

Results of the ARIMA intervention time-series analyses

 Collisions with injuries Quebec City* Collisions with material damages† Collisions with injuries for the rest of the province* β p Value β p Value β p Value AR1 – – 0.47 0.01 – – SAR1 – – −0.22 0.03 – – SAR2 – – −0.44 0.01 – – SAR3 – – −0.69 0.01 – – SMA1 0.55 0.01 – – 0.32 0.01 Intervention 8.75 0.02 −63.58 0.05 41.11 0.48 Trend – – 1.12 0.01 – – Constant – – 825.83 0.01 – – Model parameters (p,d,q) s(p,d,q)12 (0,0,0) (0,1,1) (1,0,0) (3,0,0) (0,0,0) (0,1,1) Test for autocorrelation Q‡ 0.44 (lag 1), p>0.51 0.03 (lag 1), p>0.86 1.95 (lag 1), p>0.16 Q‡ 13.75 (lag 12), p>0.32 10.29 (lag 12), p>0.59 10.96 (lag 12) p>0.53
• The interaction term (time×intervention) was not statistically significant and therefore pulled out of the three models.

• * Autoregressive and moving-average parameters were significant in the estimation stage but were no longer significant when the independent variables were included in the models. They were therefore discarded from the final models.

• When a linear trend was included in the model, 11 dummy variables for each month were added in the model to control for seasonal variations in the distribution of collisions (December=reference category).

• Box–Ljung test for autocorrelated residuals.