I NFLUENCE OF THE TYPE OF PLACE OCCUPIED BY A TRAM PASSENGER ON THE RIDE COMFORT

: In cities with developed transport infrastructure, many people use public transport in their everyday lives. In order for the passenger's journey to be comfortable and for the passenger to travel more willingly by tram than by car, many conditions must be met. A passenger must feel comfortable in a public transport vehicle, which includes, among others: appropriate temperature in the vehicle, no crowding, the possibility to seat, the possibility of a quick vehicle-change, short travel time, no noise and many others. A very important criterion from the point of view of travel comfort is also the level of vibrations in the tram. A tendency can be noticed that vehicles with a low vibration level are rated much higher by public transport passengers and citizens. Vibration itself can also be an indirect cause of noise. The greater the noise, the greater the dissatisfaction of the passenger which indicates the high role of vibrations as a factor of passenger satisfaction or dissatisfaction. The aim of the work is to test and evaluate the vibration level in the partially low-floor Moderus Beta MF 02 AC tram manufactured by the company Modertrans Poznań in Poland. Assessed was be the vibration comfort in selected points of the vehicle, including the floor and passenger seat. The level of vibrations in trams of the same type were compared. Due to the lack of specific Polish regulations regarding the permissible level of vibration in trams, an attempt was made to compare the obtained results with railway standards requirements or foreign countries requirements. The study proved that the level of vibrations differs in trams belonging to the same type. Significant damping of vibrations in the vertical direction by the passenger seat was observed. Maximum level of vibrations in the passenger area of the vehicle was ob- served on the floor above the bogie. It was found when comparing the values of vibration accelerations and comfort indi-cators with railway standards - that the Moderus Beta tram on the reference section of the track could be considered as a very comfortable vehicle.


Introduction
In Poland, in order for a given type of tram to be allowed for traffic, it must obtain approval, the rules of which are set out in the Regulation of the Minister of Infrastructure of 28 January 2011. However, it lacks specific requirements regarding the vibration level in vehicles. The word "vibration" appears once in the entire regulation and refers to external noise. On the one hand, it is a significant help for vehicle manufacturers, as vehicles do not have to be tested for vibration and comfort. On the other hand, the lack of an in-depth manufacturer's analysis may reduce passenger comfort, especially when a vehicle with a high level of vibrations is allowed to run in the city. There are railway standards describing the conditions in which a given rail vehicle may be allowed to operate, which include, among others, Standard PN-EN 14363 + A1: 2019-02E for testing and modeling the dynamic properties of rail vehicles before being allowed to run. It applies to railway vehicles, locomotives, freight and passenger carriages, empty and loaded. The passenger car is the closest to the tram, for which the permissible effective values of vibration acceleration in the transverse and vertical axis are 1.5 and 2.0 m/s 2 , respectively. However, the standard cannot be applied directly to tram-type vehicles. The Standard PN-EN 12299:2009 specifies methods of assessing comfort in rail vehicles. Again, however, it cannot be used directly for trams -it is necessary to modify the assumptions of the test method (e.g. driving speed or the length of the measuring window). Depending on the obtained results, it can be assessed with a given indicator whether, for example, a rail vehicle is comfortable or uncomfortable for a passenger (5- The RMS value of the vibrations was considered useful not only for the assessment of the vibration level and comfort (Wawryszczuk and Kardas-Cinal, 2021) but also for evaluation of the efficiency of tram articulations (Nowakowski et all, 2017). The link between the vibration level and noise was also found to be useful information (Haladin et all, 2021). The tests on trams of the 105N type in order to assess the noise in the passenger space, and thus the passenger's comfort, were carried out in Katowice too (Michta and Haniszewski, 2018). Noise level in tramway vehicles was also assessed in Romanian city Timisoara. Sound level and frequencies were verified (Bacria et all, 2018). In addition to directly examining passenger comfort, some research is also focused on the influence of the light condition of a rail vehicle on the level of vibrations while driving (Firlik and Czechyra, 2014). The online monitoring system for the condition of a light rail vehicle using information from installed sensors was to be used to monitor, among others, wear of suspension elements, damage to the wheel tread, current assessment of running stability, driving comfort, and safety against derailment. Vibration transducers, which were mounted on the 105N tram, allowed for the analysis of the bogie's vibration transmissivity in relation to the vehicle body (Czechyra et al., 2011). It was noticed that the design and the degree of wear of the running gear have a significant impact on the amount of energy transferred from the running gear to the car. The vibroacoustic approach was also used during the measurements of the Inspiro and Metropolis vehicles (Chudzikiewicz et al., 2016) in order to evaluate their dynamic properties. The analysis of the acoustic signal generated by the driving systems allowed for the conclusion that in the case of Inspiro, highfrequency components are excited, which was not observed in the case of the Metropolis vehicle. Vibration acceleration used for identification of lateral rail irregularities was tested on a rail track and rail vehicle intelligent monitoring system. Experiment was performed on the route between two Polish cities: Krakow and Wadowice (Uhl et al., 2010).
Studies were conducted to determine if the comfort of passenger is affected by the noise and vibration level of the Alstom CITADIS 402 (Khelf and Boukebbab, 2018), and also the ride discomfort caused by velocity fluctuation with proposal of the RDI (ride discomfort index) (Wang et al., 2001). In Poznań, which is another Polish city, the measurements were also connected with the internal noise of trams: 105N/105Na, Duewag GT6/GT8 and Tatra RT6-N1 (Tomaszewski and Orczyk, 2007). In Poznań there was also the trial of the implementation of on-board data recorders and their use to evaluate passenger ride comfort in city buses (Merkisz et (3), [49][50][51][52][53][54][55][56][57][58]2022 Moderus Beta MF 02 AC is partially low-floor tram, in which the external sections are high-floor, and the middle -low-floor. The area of the low-floor part constitutes 24% of the total floor area of the tram. The vehicle is based on four bogies with classic wheelsets. Each bogie has two motors and two gearboxes (on each axle of the vehicle).

Research methodology
The methodology was divided into preliminary and main research. The purpose of the preliminary tests was to verify whether the vibration level on individual seats is similar or perhaps significantly different, and whether any particular seat will experience the highest values of vibration acceleration. The preliminary test was carried out on one tram while driving at a constant speed of 40 km/h on the same straight section on the test track (Poznań, Franowo depot).
The instantaneous values of vibration accelerations occurring in selected 8 measurement points, shown in Figure 2, located on the seats in the first and third vehicle section. Then, the basic tests were carried out, the purpose of which was to verify whether the same level of vibrations would be observed in vehicles of the same type. It was initially assumed that the greatest vibrations in the vehicle would occur directly above the center of the bogie, i.e. the centre pin, while the smallest between bogies. In each of the 3 tested Moderus Beta MF 02 AC vehicles, 3 measuring points were located: two on the floor, one above the turning pivot of the third bogie, and the second between the third and fourth bogie (in the middle). One measurement point was also located on the passenger seat, which in preliminary tests showed the occurrence of high effective values of vibration acceleration. The measurement points included in the actual tests are shown in Figure 3.

Measuring Equipment
The measurement path consisted of the following elements:  Table 2 presents the effective values of vibration accelerations at the given measurement points and directions. The highest effective values of vibration acceleration were distinguished by points 5 (along the Z axis) and 7 (along the Y axis). Point 5 was selected for further analysis, i.e. the seat at the level of middle of the third bogie.     Table 3 shows example values for these calculations. The analysis shows that according to Standard PN-EN 12299 the vehicle is very comfortable, NMV values much lower than 1.5, and no higher than 0.3. Taking into account that the vibrations were measured "diagonally" in successive rows on the seats and assuming a similar level of vibrations on the left and right side seats at the same height, we can assume that all other seats in this vehicle are very comfortable. However, this would require an additional analysis which will be the subject of further research.

Main measurements results
The main measurements were carried out on the same test track in the Franowo depot and they were also carried out without passengers.    Only the values of vibration accelerations in the vertical and transverse axes were checked in the actual tests, disregarding the longitudinal axis. Such a limitation was decided due to the fact that in urban traffic the values of vibration accelerations in the longitudinal axis are strongly influenced by the driving style of the vehicle driver, and in the case of measurements in city traffic, random events occurring on the route, which could distort the measurement results. The values of the nine trips that were carried out as part of the tests of three different vehicles of the same type are summarized in Table 5 Tram 1 Tram 1 Tram 1 Tram 2 Tram 2 Tram 2 Tram 3 Tram 3 Tram 3  Point  Axis  Trial 1  Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Trial 7  Trial 8 Trial  effective value of vibration acceleration occurred at point 1 located on the floor above the pivot pin, in the vertical axis (Z). The highest resultant value (the Y and Z directions) also occurred in point 1. Figure 6 shows a diagram of the vertical vibration accelerations of tram no. 1, successively for all measuring points in this vehicle. There is a noticeable reduction in the value of vibration accelerations for point 3, i.e. the passenger seat, which proves that the passenger seat absorbs the vertical vibrations coming from the vehicle's bogie well. Hz there is a sharp and significant increase in the value of the acceleration of transverse vibrations, which can be justified by the excitation of the resonance frequency of the tram element. Due to the fact that the measuring point was above the center of the bogie of the vehicle, it can be concluded that the cause lies in one of the elements of the tram's running system, which should be further explored.

Summary
The work concerned the measurement of vibrations in the Moderus Beta MF 02 AC tram. Initial tests were first carried out to verify the level of vibrations in the seats and to identify seats with a higher level of vibrations. Eight seats in the tram were tested in three axes (longitudinal, transverse, vertical). Then, tests were carried out to verify vibrations in three points of the vehicle: on the floor above the pivot pin, on the floor in the middle between the bogies and on the seat, because it is these tram components (floor and seats) that directly transmit the vibrations to the passenger. During the actual tests, the measurements were collected along the transverse and vertical axis. The results from three measuring points and three different trams of the same type were compared. Based on the results and the analysis, the following conclusions were drawn: 6. In the Moderus Beta MF 02 AC vehicle the level of vibration acceleration in the transverse direction is lower than in the vertical direction. 7. Recorded attempts to drive the same tram on the same test track at the same speed allowed to obtain very similar results, and thus high repeatability and reliability were obtained. Thanks to the conducted study, it was possible to assess the level of vibrations in the Moderus Beta tram, to compare the level of vibrations on the floor and on the passenger seat, as well as to compare three different trams of the same type in terms of vibrations occurring in them. The analysis included in this article showed that each of the three verified vehicles of the same type showed different running properties. Due to the lack of applicable standards for the assessment of running properties of trams (both new and already in operation), it seems necessary to develop such a methodology, reflecting the actual operating conditions of trams. Striving to expand knowledge in this area will enable enterprises producing trams to create a higher quality product, and communication companies to verify and reliably evaluate the purchased vehicles.