The weighted average log odds ratio (R) across all treated sites: $R=\frac{{\sum }_{n}{w}_{i}{R}_{i}}{{\sum }_{n}{w}_{i}}=\frac{1005.99}{4187.19}=0.24$ (total crashes), and $R=\frac{{\sum }_{n}{w}_{i}{R}_{i}}{{\sum }_{n}{w}_{i}}=\frac{247.69}{814.66}=0.30$ (fatal and injury crashes) The overall effectiveness of the treatment expressed as an odds ratio or CMF across all sites: $\text{OR}={\text{e}}^{R}={\text{e}}^{0.240}=1.27$ (for total crashes) $\text{OR}={\text{e}}^{R}={\text{e}}^{0.304}=1.35$ (for fatal and injury crashes) The overall safety effectiveness as percentage of change across all sites (*): $\text{Safetyeffectiveness}=100×\left(\text{1}-\text{OR}\right)=100×\left(1-1.271\right)=-27.12%$ (for total crashes) $\text{Safetyeffectiveness}=100×\left(\text{1}-\text{OR}\right)=100×\left(1-1.355\right)=-35.53%$ (for fatal and injury crashes) The standard error of treatment effectiveness is: $\text{SE}\left(\text{safetyeffectivenss}\right)=100×\frac{\text{OR}}{\sqrt{{\sum }_{n}{w}_{i}}}=100×\frac{1.271}{\sqrt{4187.19}}=1.96%$ (for total crashes) $\text{SE}\left(\text{safetyeffectivenss}\right)=100×\frac{\text{OR}}{\sqrt{{\sum }_{n}{w}_{i}}}=100×\frac{1.355}{\sqrt{814.66}}=4.74%$ (for fatal and injury crashes) The statistical significance of estimated safety effectiveness is assessed as: $\text{Abs}\left(|\frac{\text{safetyeffectiveness}}{\text{SE}\left(\text{safetyeffectivenss}\right)}|\right)=\frac{27.12}{1.96}=13.80\ge 2$ , the treatment effect is significant at 95% confidence level (for total crashes). $\text{Abs}\left(|\frac{\text{safetyeffectiveness}}{\text{SE}\left(\text{safetyeffectivenss}\right)}|\right)=\frac{35.53}{4.74}=7.49\ge 2$ , the treatment effect is significant at 95% confidence level (for fatal and injury crashes).