# Development and Operation of Track Condition Monitoring System Using In-Service Train
## 5 Improvement in Train Position Accuracy Based on Yaw Angular Velocity
### Position Correction Results and Track Condition Monitoring Results
#### 5.5.4 Track Condition Monitoring Results after Position Correction  
The track condition was monitored using the position-corrected data. Figures 15 and 16 show the track condition diagrams before and after the position correction for the section  
Figure 14: Estimated curvature with position correction. The color lines show the estimated curvatures for all runs with position correction.  
Figure 13: Estimated curvature without position correction. The color lines show the estimated curvatures for all runs without position correction.  
between stations, respectively. The lower parts of Figures 15 and 16 show histograms showing the threshold (1.0 [m/s\({}^{2}\)]) exceedance frequency. Additionally, as a reference value, the track curvature is shown as a red line, and the BTC and ETC positions used for position correction are shown as red points.  
The track conditions were monitored using position-corrected data. Figures 15 and 16 show the track condition diagrams before and after position correction for the section between the stations, respectively. The lower sections of Figures 15 and 16 present histograms that show the threshold (1.0 [m/s\({}^{2}\)]) exceedance frequency. The reference value is indicated by a red line in the track curvature, whereas the BTC and ETC positions used for position correction are shown as red points.  
First, we evaluated the acceleration occurring at approximately 4100 [m]. The variance and mean values were calculated before and after the correction. Before the correction, the variance was 104 [m\({}^{2}\)], and the mean value was 4105 [m]. After the correction, the variance was 75 [m\({}^{2}\)], the mean value was 4103 [m], and the data variation decreased owing to the position correction. Thus, the position where track irregularity occurs can be clarified via a position correction based on the curvature.  
Additionally, we verified whether track irregularity occurred at this point by comparing it with the measurement results obtained using track inspection equipment. The results show significant longitudinal-level irregularities of 24.7 [mm] at 3985 [m], 22.4 [mm] at 4110 [m], and 21.6 [mm] at 4185 [m], all of which appeared within the range of \(\pm\)10 [m] from the point indicated by the peak in the histogram of Figure 16. Furthermore, on-site confirmation of the point shows the occurrence of mud pumping at the rail joint, which is believed to have caused significant longitudinal-level irregularities.  
In the histograms shown in Figures 15 and 16, the acceleration caused by multiple track irregularities is superimposed; hence, an evaluation is difficult to perform. To evaluate the effectiveness of the proposed method appropriately, we set the threshold to 1.5 [m/s\({}^{2}\)] and extracted only relatively high accelerations caused by significant track irregularities (Figure 17).  
The results show that the position of the track irregularity can be identified more clearly via a position correction based on the curvature.  
Figure 15: Track fault identification without position correction.