###### Abstract
However, this task is also a very difficult one because each RC evaluation method has different expressions, and the comfort indices depend on the way in which the railway vehicle vibrations are measured and processed. Thus, a research area was established, in which several reference papers can be found. One of these is that of [PERSON] et al. [5], in which the relationships between several methods for the evaluation of the RC of the railway vehicles was analyzed. These methods are the Sperling index method, the mean comfort method according to the UIC 513 and the EN 12299, and the method based on RMS acceleration (root mean square of the acceleration) in accordance with ISO 2631. [PERSON] and [PERSON] [18], as well as [PERSON] and [PERSON] [19], made a correlation between RC indices for vertical vibrations calculated according to EN 12299 and the Sperling index method based on the similarity between the sensation of comfort and the values of the indices corresponding to the two methods. [PERSON] et al. [20] evaluated the RC for two positions of the passenger--the seated position and the standing position by the method corresponding to EN 12299--and the results obtained were validated based on the Sperling method. [PERSON] et al. [21] examined the advantages and limitations of the mean comfort index method and the Wz index method using experimental data. To identify an optimal method for evaluating RC in trans, [PERSON] et al. [22] compared three methods of RC evaluation, namely the equivalent vibration level method according to ISO 2631, the Wz index method, and the mean comfort method. Starting from the premise that each RC evaluation method has certain advantages and disadvantages that depend on the running conditions of the railway vehicle, [PERSON] and co-authors [23] used two methods in parallel--the Sperling index method and the mean comfort method according to UIC 513--to test the effectiveness of a new magneto-rheological damper installed in the secondary lateral suspension system of a high-speed vehicle. [PERSON] et al. [24] applied the RMS acceleration method, according to ISO 2631 and the mean comfort method according to EN 12299, to evaluate RC in a tram in the city of Cuenca, Ecuador. The results obtained with both methods showed that the tram is pleasant and that oscillations are barely perceived by the passengers. [PERSON] et al. [25] noticed that the issue of carbody hunting instability has rarely been considered in RC evaluation. In addressing this issue, different RC evaluation methods, namely the Sperling index method, the mean comfort method, and the continuous comfort method, are compared. In this context, using experimental results, the advantages and limits of these methods are analyzed and the most suitable method for evaluating the carbody hunting instability is determined. Recently, a team of researchers from Spain raised the issue of improving the current methods for evaluating RC, both in terms of methodology and interpretations [26]. Reference was made to the Sperling index method and the mean comfort method on the EN 12299 standard, which, in the current context of increasing speeds and the use of light structures, seem to be outdated. The research on the Sperling index method developed by [PERSON] and co-authors [27] is also in the same line. They investigated the dependence of the Sperling index on the calculation algorithms used and showed that the results obtained based on the analysis in the time domain and based on the analysis in the frequency domain can be inconsistent in some situations. In a recent paper, [PERSON] et al. [6] published a review paper in which they conducted a systematic analysis on RC assessment. In this paper, they dedicated a large section to RC analysis. In the first part of this section, the most well-known RC assessment methods are presented, namely the ISO 2631 method, the mean comfort method, and the Sperling index method.