## 3 Results and Discussion
### Braking Phase--Noise  
The average values of the equivalent sound pressure level (\(L_{Aeq}\)) during braking ranged from 58.7 dB for train B to 66 dB for train A (Figure A6). Train B recorded the lowest values at six points, while train A achieved the highest values by five times. Vehicle E was the only one to record extreme values at three different points, i.e., at point 1, it achieved the lowest value of all trains, amounting to 55.5 dB, and at points 5 and 10, it achieved the highest values of 62.9 dB and 66.2 dB, respectively. Train D, this time, achieved the lowest values at three points located in the third car. Train A obtained the highest maximum sound level (\(L_{pAFmax}\)) for the braking period, reaching 81.8 dB at point 7, while train D achieved the lowest average value of 66 dB. Comparative Assessment of the Metro Vehicles Structure from the Point of View of Recorded Vibrations and Noise  
In order to compare the vibroacoustic climate, two different methods were used; the first is [PERSON] psychophysical model [16] with root-sum-square (RSS) representation [24], and the second is the authors' combined relative measure. [PERSON] psychophysical law states that the subjective response increases exponentially with the objective physical magnitude of the stimulus. This can be expressed mathematically as follows:  
\[\psi=k\varphi^{n} \tag{7}\]  
where \(\psi\) is the subjective quantity, \(k\) is a constant, \(\varphi\) is the objective quantity of the stimulus, and \(n\) is the exponent dependent on the stimulus. The stimulus can be any continuum that can affect the human senses, such as the sound intensity, magnitude of vibration,temperature, or luminescence of light. When it comes to noise and vibration, the subjective quantity can be defined as follows:  
\[\psi_{s}=k_{s}\varphi_{s}^{n_{s}}\,, \tag{8}\]  
\[\psi_{v}=k_{v}\varphi_{v}^{n_{v}} \tag{9}\]  
where \(\psi_{s}\) and \(\psi_{v}\) represent the subjective magnitude of noise and vibration, \(k_{s}\) and \(k_{v}\) are constants for noise and vibration, and \(\varphi_{s}^{n_{s}}\) and \(\varphi_{v}^{n_{v}}\) are the physical magnitude of noise and vibration with their exponents, respectively. Using this relationship, the subjective magnitude of noise and vibration can be written in logarithmic form as an equation. \[\log_{10}\psi_{s}=\log_{10}k_{s}+n_{s}\log_{10}\varphi_{s} \tag{10}\]  
\[\log_{10}\psi_{v}=\log_{10}k_{v}+n_{v}\log_{10}\varphi_{v} \tag{11}\]  
Assuming \(L_{Aeq}\propto 20\log_{10}\varphi_{s}\), \(a_{VDV}\propto\varphi_{v}\) (or \(a_{RMS}\propto\varphi_{v}\)), and \(L_{Aeq}=L_{AE}-10\log_{10}\left(\frac{T}{T_{0}}\right)\), the follow is true:  
\[\psi_{s}=k_{s}10^{0.05n_{s}\ L_{Aeq}}, \tag{12}\]  
\[\psi_{v}=k_{v}(a_{VDV})^{n_{v}}. \tag{13}\]  
The root-sum-square model (RSS) assumes [24] that the total discomfort caused by combined noise and vibration can be predicted by taking the square root of the discomfort caused by noise alone and vibration alone, \(\psi_{c}=\sqrt{\psi_{s}^{2}+\psi_{v}^{2}}\), where \(\psi_{c}\) means total discomfort, \(\psi_{s}\) is the discomfort caused by the noise itself, and \(\psi_{v}\) is discomfort caused by the vibrations themselves. The lower the value of this indicator, the lower the overall nuisance and the better the comfort. A formula was used to evaluate the obtained measurement range:  
\[\psi_{c}=[\,(0.217\cdot 10^{0.039\ L_{Aeq}})^{2}+(245\cdot(a_{VDV})^{1.04}\,)^{2 }\,]^{0.5}. \tag{14}\]  
The second type of comparison was made using the relative measure \(R_{ij}(x,\,y)\) [-], where \(x\) is the reference value and \(y\) is the average value of the \(j\)-th indicator for the \(i\)-th train, determined for a set of \(n\) measurement points in a given train. The reference value \(x=A_{ij}^{max}\) is the maximum value from the set of values of a given indicator \(\overline{S}_{ij}\) for all trains. It follows that when \(x=y\), then \(R_{ij}(x,\,y)=0\); in any other case, \(R_{ij}(x,\,y)>0\) when the indicator's value is lower than the reference level \(x\).