## 4 Test Results of the Active Steering Control
### Derailment Coefficient  
Deralment coefficient is a factor that indicates derailment safety when the vehicle is running and is defined as the ratio of the lateral force to the vertical force acting on the wheel. Figure 17 shows the measured derailment coefficient test data of the front outer wheel of the test vehicle according to the steering angle test conditions using the wheel force measuring wheelset.  
For the analysis of the derailment coefficients, the UIC 518 OR test standard used for wheel lateral force analysis was applied [17]. Figure 18 is the result of analyzing the derailment coefficients test data by subdividing 70 m into small sections and arranging them in the cumulative distribution order to extract 99.85% of the values as the representative sections of the small sections. Here, according to the test standard, the allowable limit of the derailment coefficient is 0.8 and all the results of the analysis are within the tolerance limit.  
Table 6 shows the mean values of the small section representative values for the analysis results in Figure 18 and the reduction rate for the derailment coefficient of each test case for the passive case.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Case** & **Force (kN)** & **Reduction (\%)** \\ \hline Passive & 14.99 & - \\ Active (25\%) & 7.53 & 49.8 \\ Active (50\%) & 4.68 & 68.8 \\ Active (75\%) & 3.20 & 78.6 \\ Active (100\%) & 2.46 & 83.6 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Mean lateral force for the circular section of the test section.  
Figure 17: Derailment coefficient test data according to steering control test conditions.  
The mean derailment coefficient of the wheel in a passive case with insufficient steering is 0.537. On the other hand, in the active steering control test condition, the derailment coefficient decreases as the steering angle implementation level increases. In the case of Active (25), the mean derailment coefficient is 0.232, which is 49.3% lower than the Passive case. In the case of Active (50) and Active (75), the mean derailment coefficients were 0.148 and 0.099, respectively, with 72.5% and 81.6% reduction rates.  
In the case of active (50) and active (75), the average derailment coefficients were 0.148 and 0.099, respectively, decreasing by 72.5% and 81.6%, respectively. In the case of Active (100) with 100% steering control, the mean derailment coefficient is 0.074, which is 86.3% lower than the passive case. This means that the derailment coefficient is naturally reduced if the wheel lateral force is reduced  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Case** & **Deraliment Coefficient** & **Reduction (\%)** \\ \hline Passive & 0.537 & - \\ Active (25\%) & 0.232 & 56.7 \\ Active (50\%) & 0.148 & 72.5 \\ Active (75\%) & 0.099 & 81.6 \\ Active (100\%) & 0.074 & 86.3 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Mean derailment coefficient for the circular section of the test section.  
Figure 18: Analysis results for derailment coefficient according to steering control test conditions.  
because the derailment coefficient is the ratio of the lateral force to the vertical force of the wheel. Accordingly, it can be seen that the wheel lateral force is reduced by the active steering control and the derailment coefficient, which is a vehicle running safety evaluation factor, is also significantly reduced.