###### Abstract
A reliable and high-quality automated visual inspection is a relatively expensive technique to carry out and are difficult to mount and maintain on an in-service train as they are integrated in the operation and are subjected to brightness fluctuations and motion blurring during high-speed travel and can reduce the accuracy of detection. In Sweden around 298,080 euros \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Fasteners**} & **Rail** & **Rail** & **Rail** & **Rail Wear** & **Insulated** & **Track** & \multirow{2}{*}{**Total**} \\  & & **Corrosion** & **Defects** & & & **Joints** & **Foreign Object** & & \\ \hline
2010 & 18 & 6 & 792 & 1 & 10 & 11 & 838 \\
2011 & 70 & 2 & 313 & 1 & 6 & 96 & 488 \\
2012 & 17 & 0 & 397 & 6 & 22 & 10 & 452 \\
2013 & 10 & 0 & 372 & 10 & 12 & 6 & 410 \\
2014 & 13 & 1 & 479 & 37 & 21 & 18 & 569 \\
2015 & 13 & 14 & 476 & 4 & 9 & 30 & 546 \\
2016 & 50 & 7 & 686 & 1 & 17 & 18 & 779 \\
2017 & 1 & 0 & 540 & 1 & 118 & 13 & 673 \\
2018 & 7 & 0 & 393 & 0 & 49 & 6 & 455 \\
2019 & 4 & 0 & 456 & 30 & 4 & 2 & 496 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Delay in hours due to failure of track components. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Fastener**} & \multirow{2}{*}{**Crossings**} & **Middle** & **Check** & **Rail** & **Rail** & **Rail Wear** & **Insulated** & **Turnout Foreign** & \multirow{2}{*}{**Total**} \\  & & & **Part** & **Rail** & **Corrosion** & **Defect** & & **Joints** & **Object** & \\ \hline
2010 & 8 & 93 & 1 & 1 & 6 & 260 & 3 & 0 & 22 & 509 \\
2011 & 13 & 21 & 0 & 0 & 9 & 200 & 5 & 0 & 33 & 344 \\
2012 & 1 & 38 & 0 & 1 & 6 & 282 & 105 & 0 & 51 & 592 \\
2013 & 2 & 83 & 0 & 0 & 10 & 499 & 14 & 0 & 55 & 760 \\
2014 & 29 & 37 & 86 & 0 & 31 & 274 & 36 & 0 & 40 & 643 \\
2015 & 8 & 72 & 0 & 14 & 10 & 521 & 19 & 0 & 50 & 811 \\
2016 & 18 & 94 & 3 & 1 & 12 & 602 & 33 & 2 & 39 & 948 \\
2017 & 8 & 40 & 3 & 4 & 13 & 456 & 72 & 0 & 33 & 747 \\
2018 & 9 & 43 & 0 & 1 & 18 & 491 & 20 & 1 & 49 & 780 \\
2019 & 12 & 84 & 0 & 3 & 4 & 332 & 19 & 1 & 50 & 568 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Delay in hours due to failure of components in switches and crossings. alone was spent in 2014 to inspect two lines with a total track length of ca. 300 km, of which more than 75% was utilised to inspect track components that exhibit magnetic characteristics (rail fastening, weld joints, rail surface etc.) [25]. With the increasing demand for safety and cost-effectiveness, maintenance managers are striving to cut these operations and maintenance cost through effective condition-based maintenance while assuring the quality and capacity of the rail services. In earlier research, the authors proposed a train-based differential eddy current sensor [25] for fastener inspection that can overcome the major challenges mentioned above. Eddy current sensors are not affected by the presence of nonconductive materials in the sensor-to-target gap and can be used in dirty environments, water, oil etc., where other inspection systems fail. The proposed inspection technique using a differential eddy current sensor was able to detect fastener signature from a distance of 65 mm above the railhead. The individual fastener signatures were easily distinguishable from the 1-D time signal plots. The sensor uses two driving fields with frequencies 18 kHz and 27 kHz respectively and the fastener signatures obtained from both the channels exhibited very good correlation. The sensor concept and working principle of the sensor is explained in Section 2 of the previous publication [25]. The results presented in the previous literature was based on study carried out for a short track section. However, when considering other track sections with an increased likelihood of disturbances, it was found that relying on one feature could generate a decrease in accuracy for detection.