# Railway Track Monitoring Using Train Measurements: An Experimental Case Study
## 5 Fault Detection on Dublin-Belfast Route
### Comparison of Results with Track Recording Vehicle Data  
The locations in Figure 13 where the amplitudes exhibit high energy are inspected in this section for the purpose of fault detection. There are four main zones in Figure 13b that show high energy levels: around 3100 m, 3900 m, 6000-7000 m, and 7550 m. Irish Rail's Track Recording Vehicle (TRV) monitored the track shortly after the acceleration measurements were taken. The TRV data are used here as a baseline to check the effectiveness of the proposed damage indicator.  
The scaled amplitudes around the second peak close to 3900 m are shown in Figure 14 with the corresponding TRV data. The TRV data includes eight track properties, named here using the colloquial terms and being represented by colour bars. The properties shown in this output (from the top) include 'Gauge' (track gauge), 'Twist 3' (3 m twist), 'Twist 10' (10 m twist), 'Align Down' (alignment (horizontal) of the down rail), 'XL' (cross level), 'Align Up' (alignment (horizontal) of the up rail), 'Top Down' (longitudinal level (vertical alignment) of the down rail), and 'Top Up' (longitudinal level (vertical alignment) of the up rail). These properties are defined in detail in EN 13848. The blue colour implies no irregularity or defect, while yellow, orange, and red indicate the alert and intervention limits that are defined by the standard.  
The TRV data clearly show some defects between 3800 and 4000 m corresponding to the dominant peak in the scaled Hilbert amplitudes. The cross level parameter, 'XL', in the TRV data shows that the intervention limit has been exceeded at this location. Cross level is a measure of the difference in height of the running tables of both rails. It can be observed that this is caused by two changes in the longitudinal level of the up rail, which also manifests itself as a 3 m twist. This defect in the longitudinal level would have caused significant vertical motion of the bogie frame, which was measured by the sensor attached to the bogie. The resulting scaled amplitudes show a strong correlation between the Hilbert amplitude and recorded TRV damage.  
Figure 15 shows the scaled amplitudes and TRV data between 5800 to 7200 m, where there are also high energy levels. Again, the deviations in the vertical alignment of the up rail produce defects, which are also measured as defects in cross level and 3 m twist. The good match between the energy indicator and the TRV data confirms that the idea of drive-by train monitoring has good potential for railway track monitoring while using an in-service vehicle.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{5}{c}{**Average Standard Deviation**} \\ \hline
**Range** & **2000–3000 m** & **3000–4000 m** & **4000–5000 m** & **5000–6000 m** & **6000–7000 m** & **7000–8000 m** \\ \hline Not-scaled & 3.42 & 6.68 & 4.43 & 4.20 & 8.15 & 4.82 \\ Scaled & 2.96 & 5.80 & 3.49 & 2.92 & 6.61 & 3.95 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Statistical properties of the signals before and after rescaling.  
Figure 14: The Track Recording Vehicle (TRV) data and scaled amplitudes.  
Figure 15: The TRV data and scaled amplitudes.  
Figures 14 and 15 are two samples that show the effectiveness of the proposed method. However, further work is needed to improve the accuracy of the locations and also find the types of the faults detected by this method. For example, the accuracy of the defect locations is a function of the performance of the GNSS under different train forward speeds. This could create some levels of mismatching between different passes. There is also some error in the PBD process in terms of the accuracy of the peak locations. However, there is reasonable consistency over several passes, which indicates acceptable performance.