## 4 Results

Table 2: Scores on the test set for the general model. Figure 5: Graph showing the relationship obtained between static stiffness and dynamic stiffness for all tests. These results indicate a strong ability to predict the dynamic stiffness from the static stiffness and the experimental conditions to which the rail pads were subjected, even without considering the specific degradation condition of the test. Based on the results obtained, it is possible to conclude that dynamic stiffness values can be estimated under any condition solely from the mechanical parameters and static stiffness, with reduced error if the model identifies the type of rail pad as a variable. The model achieves an RMSE of 4.43 kN/mm for pad A, 27.09 kN/mm for pad B, and 21.83 kN/mm for pad C, demonstrating the robustness of the prediction, even when test conditions are not directly considered in the model. While it has been demonstrated that it is possible to estimate dynamic stiffness based on static stiffness and operating conditions, it is essential to deepen the study of rail pad degradation and its influence on prediction accuracy. Therefore, the type and degree of aging for each variable are now incorporated, independently analyzing the impact of each type of aging on each pad, with the objective of understanding the magnitude and nature of their influence on predictions. The main patterns observed in Figure 6 are described below:  
* Temperature Tests (Row 1): Rail pad A shows a linear relationship with little dispersion. In contrast, rail pad B appears to exhibit non-linear behavior under condition T1, while remaining mostly linear under condition T2. For Type C rail pads, under condition T1, the relationship between static and dynamic stiffnesses appears inversely proportional, with dynamic stiffness decreasing as static stiffness increases. This pad shows the greatest variation in behavior among the conditions. The stiffening effect observed under condition T2, related to the behavior of rail pads at low temperatures, has been noted by other authors. For example, [PERSON] et al. [22] observed that rail pads of types WJ-7, WJ-8, and Vossloh 300, used in high-speed railway systems in China, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Lark** & **Lasso** & **Ridge** & **RF** & **KNN** & **GB** \\ \hline \multirow{4}{*}{Pad A} & MSE (\(\lambda\)N\({}^{2}\)/mm\({}^{2}\)) & 55.64 & 58.38 & 55.61 & 30.15 & 55.03 & 31.98 \\  & MAE (kN/mm) & 4.88 & 4.66 & 4.86 & 3.36 & 4.60 & 3.70 \\  & R\({}^{2}\) & 0.904 & 0.897 & 0.905 & 0.9476 & 0.9045 & 0.9445 \\  & RMSE (kN/mm) & 7.45 & 7.64 & 7.45 & 5.49 & 7.41 & 5.65 \\ \hline \multirow{4}{*}{Pad B} & MSE (\(\lambda\)N\({}^{2}\)/mm\({}^{2}\)) & 1155.6 & 1131.6 & 1148.35 & 852.63 & 643.88 & 782.77 \\  & MAE (kN/mm) & 28.69 & 28.41 & 28.56 & 15.80 & 14.29 & 14.20 \\  & R\({}^{2}\) & 0.8473 & 0.850 & 0.8483 & 0.8873 & 0.9149 & 0.8966 \\  & RMSE (kN/mm) & 33.99 & 33.63 & 33.88 & 29.19 & 25.37 & 27.97 \\ \hline \multirow{4}{*}{Pad C} & MSE (\(\lambda\)N\({}^{2}\)/mm\({}^{2}\)) & 2796.3 & 2736.4 & 2782.40 & 992.29 & 2738.87 & 725.10 \\  & MAE (kN/mm) & 38.62 & 37.58 & 37.90 & 22.89 & 34.29 & 19.98 \\ \cline{1-1}  & R\({}^{2}\) & 0.8336 & 0.8371 & 0.8344 & 0.9499 & 0.8584 & 0.9568 \\ \cline{1-1}  & RMSE (kN/mm) & 52.88 & 52.31 & 52.74 & 31.50 & 48.77 & 26.92 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Scores on the test set for each type of rail pad. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Pad A** & **Pad B** & **Pad C** \\ \hline \multirow{2}{*}{MSE (kN\({}^{2}\)/mm\({}^{2}\))} & 19.64 & 734.25 & 476.68 \\  & 2.78 & 14.03 & 15.28 \\  & 4.43 & 27.09 & 21.83 \\  & 0.9665 & 0.9030 & 0.9716 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Metrics of the tests for each of the GB models. show a significant increase in dynamic stiffness at low temperatures.