**4. Ride comfort index and rail and train maintenance identification**

Besides affecting passengers' comfort, vibration is also associated with safety. High safety levels, guaranteed by maintenance, are crucial to secure the reliability and longevity of rails and trains, furthermore nothing drives passengers away more than safety failures. Maintenance is performed by corrective and preventive interventions. The reactive action after failure recognition characterizes the corrective approach [13– 16]. In opposition, preventive interventions are defined as proactive measures to prevent and minimize failures at reduced costs.

Condition-based maintenance (CBM) is the traditional applied preventive track monitoring system. This is executed based on a defined schedule, allowing action to be taken when there is failure evidence. Inspection vehicles, such as EM 120 are usually applied to detect track failures [43–45]. These are expensive vehicles, and their passage introduces traffic disruptions, affecting the regular service operation [16, 44].

Railway track abnormalities influence rail vibration. Higher acceleration peaks are noticed on a defective rail compared to a healthy one. Thus, besides affecting safety, track abnormalities lead to increased passenger discomfort [15]. Due to the connection between vibration, track infrastructure abnormalities, and ride comfort, a new CMB methodology capable of identifying track abnormalities and rail vehicles maintenance needs was proposed. Based on the limitations of EN 12299 and Sperling's method, the ISO 2631 standard was defined as a reference methodology concerning ride comfort analysis. The main goal was to overcome the limitations of the current CBM methods, providing a complementary low-cost solution without disrupting the railway service. Thus, it was hypothesized that if multiple trains with different suspension systems

present floor discomfort at the same location, then the track infrastructure requires maintenance. Moreover, it was also considered that the train vehicle needs maintenance if a specific train presents low ride quality at the seat surface.

#### **4.1 Experimental procedure**

Different train series have different suspension mechanisms. Those are the critical mechanical structure affecting ride comfort. The suspension mechanism's function is to attenuate the vibration resulting from the train motion and wheel-track interaction. The primary suspension contains wheel-track interaction vibrations, whereas the secondary suspension suppresses the vibration transmission from the bogie to the carbody. This way, vibration is attenuated from the bogie to the seat, so if passengers feel discomfort, a track abnormality is identified [46–48].

Based on the mentioned assumption, it was assumed that the track infrastructure needs maintenance if trains with different suspension mechanisms reported floor discomfort at the same geographic location. Pendolino, Intercity and Urban trains vibrations were monitored for 18 journeys whilst running a passenger service. For the long-distance trains, nine measurements were taken for the Pendolino and six for the Intercity train. Measurements occurred at different places inside the train, namely at the lead, middle, and end cars. Regarding Urban rail, three records happened at the first seat in the motion direction. The experiments run on the Northern Line, downward direction, between Porto–Campanhã and Aveiro stations.

Following ISO 2631 recommendations, three-axial accelerometers were placed on the floor and seat surface and aided by a GPS, the train's geographic location was obtained. This way, track infrastructure maintenance sections were identified by matching the floor discomfort with the train geographic location. Vibration measurements were performed by three-axial seat pad accelerometers (PCE-VDL-24I 16 g) at a sample rate of 200 Hz, preventing aliasing and respecting Nyquist's theorem. Moreover, in addition to following ISO 2631 recommendations, the accelerometers also allow data recording on a μSD card [49].

The geographic location was obtained using a RedBoard Qwiic [50] connected with a GPS Logger Shield [51]. The equipment was programmed to retrieve the location, train velocity, and record the data on the μSD card at 1 Hz. Vibration and geographic measurements occurred synchronously.

#### **4.2 Track maintenance needs identification**

For this purpose, an algorithm was developed using MATLAB 2020a (from MATHWORKS) [52]. Following ISO 2631 approach, the analysis starts by calculating the instantaneous floor discomfort, corresponding to the total acceleration calculation at each second. Discomfort levels were divided into two categories: equal or under 0.315 m/s<sup>2</sup> , rated as "Not uncomfortable", and above the same threshold, ranked as "Uncomfortable". Once identified, the "Uncomfortable" locations were mapped.

The GPS device was installed in the train driver's cabin to get the best GPS signal. Therefore, a maximum distance of 158.9 m (Pendolino length) between acceleration and GPS measurements was observed for measurements taken at the end of the train. Moreover, considering the worst-case scenario where the Pendolino travels at 220 km/ h, around 61.1 m are achieved in 1 second. Therefore, a maximum 220 m offset was applied to obtain the matching segment.

*Railways Passenger Comfort/Discomfort: Objective Evaluation DOI: http://dx.doi.org/10.5772/intechopen.111704*

Considering all mentioned parameters, the matching locations and maintenance needs segments are those with less than 220 m distance between discomfort places of three different trains, **Figure 1**.

According to **Figure 1**, three maintenance segments were identified. The start and end geographic locations and the respective associated kilometer are presented in **Table 5** for each zone.

The listed locations match those defined by the Portuguese train company (IP) by passing the EM 120 inspection vehicle as requiring maintenance [53]. This way, the methodology reliability is proven, and ride quality as maintenance needs identification may be applied, resulting in a low-cost and non-disruptive CBM method.

**Figure 1.** *Illustrates the track maintenance segments identified by the MATLAB algorithm.*


#### **Table 5.**

*Maintenance segments geographic locations and line kilometer.*
