## 4 Results Analysis
### Noise Pattern Analysis  
We utilized the DBSCAN algorithm to perform a clustering analysis on the noise assessment metrics of the driver's cab of Lanzhou Urban Rail Transit Line 1. In total, we found 10 distinct types of noise, which can be approximately categorized into two major groups: high-intensity and low-intensity. The high-intensity noise clusters include Cluster 1, Cluster 3, Cluster 4, Cluster 8, and Cluster 9, all of which exhibit higher average \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Metric** & **Mean** & **Std** & **Max** & **Min** \\ \hline \hline Leq & 87.12 & 8.52 & 117.33 & 53.43 \\ L\({}_{\text{max}}\) & 101.11 & 8.15 & 132.05 & 67.98 \\ L\({}_{\text{min}}\) & 29.54 & 14.21 & 78.78 & 0.00 \\ L\({}_{10}\) & 96.72 & 8.39 & 126.05 & 63.01 \\ L\({}_{25}\) & 93.71 & 8.41 & 124.24 & 59.83 \\ L\({}_{50}\) & 89.19 & 8.51 & 119.74 & 55.34 \\ L\({}_{75}\) & 82.87 & 8.71 & 115.76 & 48.73 \\ L\({}_{90}\) & 74.97 & 8.95 & 110.14 & 40.68 \\ LR & 71.57 & 11.88 & 124.87 & 36.32 \\ MF & 24.68 & 20.26 & 100.00 & 10.00 \\ TE & 7,753,212.22 & 1,480,296.53 & 13,831,022.73 & 2,948,416.30 \\ NE\({}_{70}\) & 27.76 & 15.81 & 97.00 & 0.00 \\ NE\({}_{75}\) & 30.72 & 16.43 & 99.00 & 0.00 \\ NE\({}_{80}\) & 30.97 & 17.90 & 109.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The estimation results of noise assessment metrics. Among the high-intensity noise clusters, Cluster 1 and Cluster 4 exhibit similar Leq values (90.12 dB and 91.87 dB) and significant fluctuations. Cluster 1's main frequency component (MF) is 14.47 Hz, while Cluster 4's MF is 69.70 Hz, indicating a distinct frequency divergence. This pattern suggests that the noise originates from mechanical operations and wheel-rail interactions, especially during acceleration and deceleration, as these processes are known to produce both low-frequency and high-frequency noise. The frequent high-frequency components and noise events (NE\({}_{70}\), NE\({}_{75}\), NE\({}_{80}\)) in Cluster 4 likely correlate with the operation of traction motors and braking systems, which are characteristic sources of high-frequency noise [50]. The characteristics of Cluster 3 and Cluster 8 indicate they likely originate from wind noise and track noise generated at high speeds. Cluster 3 has a Leq of 94.20 dB, a Lmax of 106.98 dB, and a main frequency component of 15.76 Hz, while Cluster 8 has a Leq of 101.92 dB, a Lmax of 114.07 dB, and a main frequency component of 18.78 Hz. The observed characteristics align with typical noise patterns from these sources, where aerodynamic and frictional forces at high speeds generate substantial noise levels within these frequency ranges [42]. The noise characteristics of Cluster 9 indicate an Leq of 93.75 dB, an Lmax of 107.73 dB, a dynamic range of 94.10 dB, a main frequency component of 17.89 Hz, and an energy accumulation of 8,900,800.27 joules. This type of noise is likely associated with the noise generated when the train passes through track crossings or switches since the complexity of track structures and the diverse operating conditions of trains in these areas may generate high-intensity and frequent low-frequency noise. In contrast, the low-intensity noise clusters include Cluster 2, Cluster 5, Cluster 6, Cluster 7, and Cluster 10. These clusters exhibit comparatively lower average and maximum sound pressure levels, larger dynamic ranges, and lower energy accumulations. Cluster 2 has an Leq of 75.60 dB, with a dynamic range of 70.91 dB and a main frequency component of 17.60 Hz. It is primarily attributed to background noise generated by the air conditioning system or other electrical equipment within the train carriage [22]. These devices produce continuous but relatively low-frequency noise during operation, with significant fluctuations in noise intensity, reflecting the operational instability and complexity of the noise sources. The noise in Cluster 5 and Cluster 7 might be categorized as the operational noise of the train at low speeds.