## 5 Conclusions  
In this paper, the impact of frequency-weighting on the dynamic response of the railway vehicle carbody were analyzed at three relevant points of the vertical vibration behavior, positioned at the carbody center and above the two bogies. The dynamic response of the carbody is expressed in terms of the PSD of the acceleration. In the analysis, the numerical results are used for three cases: the unweighted PSD of the acceleration; the frequency-weighted PSD of the acceleration with the two weighting functions corresponding to the Sperling index method, namely the frequency-weighting function for RQ; and the frequency-weighting function for RC. Figure 14: RQ/RC index Wz at the carbody center: (**a**) for the bending eigenfrequency of 8 Hz; and (**b**) for the bending eigenfrequency of 6 Hz. Figure 15: RQ/RC index Wz: (**a**) above the bogie 1; and (**b**) above the bogie 2. Based on the results regarding the PSD of the acceleration, several important characteristics of the vertical vibration behavior of the vehicle carbody were identified, such as the following: the vibration level of the carbody is higher above the bogies than at its middle; and the asymmetry of the carbody vibration above the two bogies. Another important feature is the geometric filtering effect induced by the vehicle's wheelbases, due to which the vertical vibration of the carbody does not continuously intensify whit increasing velocity. It was highlighted that the geometric filtering effect becomes more intense at the carbody center and that it exhibits a selective character basing on vehicle speed and frequency, namely that the geometric filtering effect is more intense at low speeds, in the frequency range specific to the carbody bending vibrations. The dominant modes of vibration at the relevant points of the carbody were also identified. At the carbody center, the bounce is the dominant mode of vibration, but in the case of flexible carbodies, at velocities greater than 200 km/h, vertical bending becomes the dominant mode of vibration. Pitch is the dominant mode of vibration above the bogies. Based on the analysis of the effect of frequency weighting on the dynamic response of the railway vehicle carbody, the following important conclusions are summarized:  
* The dominant modes of vibration of the carbody are not changed by the frequency weighting;
* Both weighting functions corresponding to the Sperling index method reduce the carbody vibration level, with the following observations: the reduction in bounce vibrations is more effective in the case of weighting with the function for the RC function; the reduction in vertical bending vibrations is more effective in the case of weighting with the function for RQ; the reduction in pitch vibrations is not significantly different in the case of weighting with the function for RQ compared to the case of weighting with function for the RC. Based on the conclusions about the dominant modes of vibration of the carbody and those that emphasized the effect of frequency weighting with the two weighting functions on the carbody vibrations, the results on the Wz indices for RQ and RC were explained. The results presented in the paper and the conclusions synthesized based on them bring more knowledge in a field of research that has been insufficiently explored so far, in which the objectives of the studies are to identify the advantages and limitations of the RQ and RC evaluation methods, the correlation of the comfort indices obtained by different methods, and even the improvement of these methods from the point of view of applied methodology or interpretations. The paper outcomes contribute to a better understanding on the effect of the weighting functions corresponding to the Sperling index method upon the assessment of the RC and RQ using this method.