# Temporal Instability Analysis of Injury Severities for Angle and Non-Angle Crashes at Roundabouts
## 6 Results and Discussion
### Predictive Comparisons (Prediction Simulations)
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Target Year**} \\ \cline{2-7}
**Base Year** & \multicolumn{2}{c}{**2014–2015**} & \multicolumn{2}{c}{**2016–2017**} & \multicolumn{2}{c}{**2018–2019**} \\ \cline{2-7}
**Angle Crash** & \begin{tabular}{c} **Non-Angle** \\ **Crash** \\ \end{tabular} & \begin{tabular}{c} **Angle Crash** \\ \end{tabular} & \begin{tabular}{c} **Non-Angle** \\ **Crash** \\ \end{tabular} & \
\begin{tabular}{c} **Angle Crash** \\ \end{tabular} &
\begin{tabular}{c} **Non-Angle** \\ **Crash** \\ \end{tabular} \\ \hline \multirow{3}{*}{2012–2013} & \(-\)0.0147 & \(-\)0.0203 & \(-\)0.0155 & \(-\)0.0210 & \(-\)0.0489 & \(-\)0.0340 \\  & (0.0069) & (0.0214) & (0.0062) & (0.0383) & (0.0721) & (0.0300) \\  & [0.0078] & [\(-\)0.0011] & [0.0093] & [\(-\)0.0173] & [\(-\)0.0232] & [0.0040] \\ \hline \multirow{3}{*}{2014–2015} & - & - & \(-\)0.0078 & \(-\)0.0013 & 0.0088 & \(-\)0.0099 \\  & - & - & (0.0026) & (0.0175) & (0.0016) & (0.0051) \\ \cline{1-1}  & - & - & [0.0052] & [\(-\)0.0162] & [\(-\)0.0104] & [0.0048] \\ \hline \multirow{3}{*}{2016–2017} & - & - & - & - & 0.0149 & \(-\)0.0098 \\  & - & - & - & - & (0.0021) & (\(-\)0.0090) \\ \cline{1-1}  & - & - & - & - & [\(-\)0.0170] & [0.0188] \\ \hline \hline \end{tabular} Note: The results in the table are the difference between predicted and ‘observed’ probabilities.  
\end{table} 
Table 7: Prediction results of angle and non-angle crashes for no injury, minor injury (in parentheses), and severe injury (in brackets). The differences in temporal shifts between the beginning and ending years are of particular interest [64]. Comparing 2012-2013 to 2018-2019, the distribution of injury severity for both angle and non-angle collisions showed a shift from minor injuries to no injuries and severe injuries (Angle collisions: no injury from 68.72% to 75.41%, minor injury from 28.91% to 21.67%, severe injury from 2.37% to 2.92%; non-angle collisions: no injury from 65.67% to 71.94%, minor injury from 30.05% to 23.62%, severe injury from 4.28% to 4.44%). For angle collisions, the predicted comparison trends of injury severity outcomes are consistent with the shift in statistical proportions. However, the two shifts are not exactly the same for non-angle collisions. As shown in Table 7, the 2012-2013 non-angle collision model predicted a decrease in no injury and an increase in minor and severe injuries relative to the 2018-2019 'observed' values. Both the temporal shift of the parameters and the specific characteristics may play a role in the temporal shift affecting injury severity, which deserves the attention of future studies. Figure 3: Differences between predicted and ‘observed’ probabilities of non-angle collisions (The red line indicates the position of the mean). **(a)** Difference between 2014–2015 ‘observed’ probabilities and predicted probabilities based on the 2012–2013 model; **(b)** Difference between 2016–2017 ‘observed’ probabilities and predicted probabilities based on the 2014–2015 model.