# Indirect Assessment of Railway Infrastructure Anomalies Based on Passenger Comfort Criteria
## 5 Case Study: Portuguese Northern Line Condition Assessment
### Maintenance Needs Identified by the Indirect Method  
The data analysis identified railway track infrastructure maintenance sections by comparing the discomfort zones of the AP train versus those of the IC train. [PERSON] et al. [37] and [PERSON] [38] stated that a railway track infrastructure with isolated irregularities presents higher vibration levels at that location than a healthy one. Those higher vibrations will lead to increased discomfort levels. The developed methodology divided floor discomfort levels into \"Not uncomfortable\" and \"Uncomfortable\" categories depending on the instantaneous acceleration evaluation. Those under 0.315 m/s\({}^{2}\), corresponding to the ISO 2631 first discomfort level threshold, were grouped in the first category, while the second category comprised those above that discomfort threshold. Therefore, an abnormality in the railway track infrastructure was expected to present discomfort peaks higher than 0.315 m/s\({}^{2}\) at that location. Conversely, a healthy infrastructure should have instantaneous floor discomfort levels lower than that threshold. Ideally, those discomfort levels should present consistent behaviour. The reported trend was observed in the acceleration records and analysis. Figure 11 illustrates AP and IC trains' behaviour regarding the same locations (latitude). Vibration peaks capable of going through primary and secondary suspension systems cause passenger discomfort. AP and IC trains have different suspension systems and elements; thus, when the discomfort sections of both trains agree, it can be concluded that the railway track infrastructure requires maintenance. An example of that matching between both trains' discomfort levels is observed in Figure 11. The red mark illustrates \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Track Section**} & \multicolumn{2}{c}{**Kilometre Interval**} & \multirow{2}{*}{**Track Segment**} \\ \hline
**Start Station** & **End Station** & **Start** & **End** & **Track Segment** \\ \hline Alhandra & Castanheira do Ribatejo & 26 & 27 & A \\ Albergaria dos Doze & Alfarelos & 147 & 199 & B \\ Pampilhosa & Valega & 232 & 297 & C \\ Válega & Espinho & 297 & 316 & D \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Track segments’ maintenance needs identified by IP through the passage of EM 120 inspection vehicle (adapted from [56]). Figure 11: Instantaneous floor discomfort levels for AP and IC trains (where the red mark identifies a railway track infrastructure abnormality). the overlapping between the AP and IC discomfort levels. Thus, it can be established that an abnormality is presented at that specific location, and the railway track infrastructure requires maintenance. Figure 11 shows all maintenance required sections identified on the railway Northern Line using this algorithm, where AP and IC floor discomfort levels matched. Those below a 220 m distance between peak locations corresponded to the sections where maintenance was needed and are identified and illustrated. According to Figure 12, 12 maintenance zones were identified. For each zone, the start and end coordinates and their associated line kilometre are registered in Table 5, which also defines the matching with the IP-identified track sections. Due to the map resolution, some close zones appear to be just one. Blue and green markers define two sections that are, indeed, divided into small zones--1 and 2 for the blue marker and 3, 4, and 5 for the green section. The discomfort location obtained at the Porto (Campanha) train station is not numbered, as it was due to the acceleration to start the motion and not to a railway infrastructure abnormality. Ten listed locations match those that the Portuguese infrastructure manager company (IP) suggested to be subject to maintenance, identified by the EM 120 inspection vehicle [58]. Therefore, the obtained locations were critical points of the railway track infrastructure, thus validating this methodology. Moreover, two extra zones were detected: zones 10 and 11.