The weighted average log odds ratio (R) across all treated sites:

$R=\frac{{\displaystyle {\sum }_n{w}_i{R}_i}}{{\displaystyle {\sum }_n{w}_i}}=\frac{1005.99}{4187.19}=0.24$ (total crashes), and $R=\frac{{\displaystyle {\sum }_n{w}_i{R}_i}}{{\displaystyle {\sum }_n{w}_i}}=\frac{247.69}{814.66}=0.30$ (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 (*):

$\text{Safetyeffectiveness}=100\times \left(\text{1}-\text{OR}\right)=100\times \left(1-1.271\right)=-27.12\%$ (for total crashes)

$\text{Safetyeffectiveness}=100\times \left(\text{1}-\text{OR}\right)=100\times \left(1-1.355\right)=-35.53\%$ (for fatal and injury crashes)

The standard error of treatment effectiveness is:

$\text{SE}\left(\text{safetyeffectivenss}\right)=100\times \frac{\text{OR}}{\sqrt{{\displaystyle {\sum }_n{w}_i}}}=100\times \frac{1.271}{\sqrt{4187.19}}=1.96\%$ (for total crashes)

$\text{SE}\left(\text{safetyeffectivenss}\right)=100\times \frac{\text{OR}}{\sqrt{{\displaystyle {\sum }_n{w}_i}}}=100\times \frac{1.355}{\sqrt{814.66}}=4.74\%$ (for fatal and injury crashes)

The statistical significance of estimated safety effectiveness is assessed as:

$\text{Abs}\left(\left|\frac{\text{safetyeffectiveness}}{\text{SE}\left(\text{safetyeffectivenss}\right)}\right|\right)=\frac{27.12}{1.96}=13.80\ge 2$ , the treatment effect is significant at 95% confidence level (for total crashes).

$\text{Abs}\left(\left|\frac{\text{safetyeffectiveness}}{\text{SE}\left(\text{safetyeffectivenss}\right)}\right|\right)=\frac{35.53}{4.74}=7.49\ge 2$ , the treatment effect is significant at 95% confidence level (for fatal and injury crashes).