# Indirect Assessment of Railway Infrastructure Anomalies Based on Passenger Comfort Criteria
## 1 Introduction
Moreover, railway track infrastructure maintenance also improves the interaction performance of the rail vehicle and the overhead infrastructures, such as the pantograph-catenary interaction, which leads to a more safe, stable, and comfortable journey [23]. It is known that there is a significant difference in vibration levels when comparing a healthy railway track infrastructure with a defective one, which is characterised by higher peak values. Thus, besides affecting safety, isolated and continuous infrastructure defects lead to poor passenger comfort due to increased vibration levels [9]. Once comfort is significantly affected by vibration, which is mainly caused by train motion and rail track infrastructure irregularities, passengers are subjected to discomfort throughout their journey due to contact with the seat and floor. Therefore, vibration is transmitted through all passenger-seat and passenger-floor contact surfaces; this is generally defined as whole-body vibration (WBV). Besides causing discomfort, this can also lead to fatigue and, in some extreme cases, diseases. Due to the adverse consequences of WBV, it is vital to classify vibration levels in the rail environment. One of the international reference documents is the ISO 2631 standard, which precisely quantifies WBV regarding comfort, human health, and motion sickness [24; 25; 26; 27]. Up to this date, passenger comfort levels have not been used for possible damage detection. Based on the close connection between railway track infrastructure conditions, induced vibrations, and passengers' discomfort levels, it was possible to develop a new CBM methodology to identify critical railway track infrastructure locations. The goal was to provide a low-cost solution to improve maintenance needs detection and increase infrastructure availability. The present method overcomes the limitations of traditional railway infrastructure maintenance detection methods as it does not cause a disturbance to railway operations. This study considers the railway track infrastructure to require maintenance actions if multiple trains with different dynamic characteristics present floor discomfort at the same GPS location. Based on the limitations of previous experiments, this study aims to offer clear contributions regarding some aspects that, presently, according to the authors' knowledge, are not sufficiently addressed in the existing literature, particularly the following:  
* Development of a methodology capable of detecting rail track infrastructure abnormalities or damages based on measurements on in-service trains. This way, the service runs under regular operation without disruption or interference. * Development of a methodology that is easy to adapt and implement and can be applied in any in-service rail vehicle. This way, the limitations of the accelerometer installation in the axle box, which imposes difficulties on the processes of installation, maintenance, and dismounting, can be overcome. The results of the present methodology are not dependent on the vehicle type. Thus, it can be applied to passenger trains with different characteristics. This was stated based on the results of multiple measurement campaigns proving the methodology's accuracy and precision.