## 5 Conclusions  
The causes of abnormal noise in light rail vehicles passing through sections with rail corrugation were identified, and the following observations were made:  
1. The measurement of interior noise in rail corrugation sections under different vehicle maintenance conditions indicated that the influence of the vehicle's age or maintenance conditions is minimal. Although the wear state of the wheels slightly reduces the interior noise, it is insufficient to solve the problem of abnormal noise.
2. An investigation of the rail corrugation section revealed that the corrugation wavelength was 24 mm, and vibrations in the 920 Hz range were induced when the vehicle operated at a maximum speed of 80 km/h.
3. The vertical vibrations of the axle box and car body strongly correlated with the abnormal interior noise frequency of 926 Hz.
4. The natural frequency test of the car body through excitation identified natural frequencies of 884.4 Hz and 926.6 Hz. The analysis of the interior noise effect through car body sweep excitation confirmed a relative increase in noise in the 920 Hz range, which corresponds to the car body's resonance frequency.  
Therefore, the abnormal noise that occurs when the vehicle passes through the rail corrugation section is induced by 920 Hz vibrations caused by the wavelength of the corrugation and the vehicle speed. These vibrations are transmitted to the car body, matching the car body's resonance frequency of 926.6 Hz, resulting in increased interior noise.  
Based on these results, reducing abnormal noise when passing through corrugated sections may require avoiding the 920 Hz resonance mode of the car body. However, this would require either replacing the car body or performing extensive maintenance to improve car body noise characteristics, which is challenging in practice. As an alternative, future studies will explore standard rail grinding methods or adjustments to vehicle speed and braking control when passing through corrugated sections to mitigate corrugation formation.  
Additionally, although corrugation typically occurs on curved sections, it was mainly observed on straight sections in this study. Further research is also needed to investigate whether the shorter wavelength of corrugation is related to the use of resilient wheels.  
Conceptualization, J.L. and D.A.; methodology, J.L.; software, J.L. and Y.P.; validation and formal analysis, D.A.; investigation, Y.P.; resources and data curation, Y.P.; writing--original draft preparation, J.L. and Y.P.; writing--review and editing, J.L. and D.A.; visualization, Y.P.; supervision, J.L. and D.A.; project administration, J.L.; funding acquisition, Y.P. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the National Research and Development Program (RS-2021-KA163504) funded by the Ministry of Land, Infrastructure and Transport.  
\begin{table}
\begin{tabular}{c l} \hline
**Equipment** & **Specification** \\ \hline FFT analyzer & [PERSON] \& Kjaer Lan-xi 3160-A-042 \\  & [PERSON] \& [PERSON], Naerum, Denmark \\ \hline Exciter & [PERSON] \& [PERSON] 4808 (frequency range: 5-10 kHz) \\  & [PERSON] \& [PERSON], Naerum, Denmark \\ \hline Impedance head & Dytran 58608 \\  & Dytran Instruments, Inc. Chatsworth, California, USA. \\ \hline Microphone & PCB 378B02 (frequency range: 3.75-20 kHz) \\  & PCB Piezotronics, Inc., Depew, New York, USA. \\ \hline Conditioning amplifier & [PERSON] \& [PERSON] 2690 \\  & [PERSON] \& [PERSON], Naerum, Denmark \\ \hline Accelerometer & PCB 393B04 \\  & PCB Piezotronics, Inc., Depew, New York, USA. \\ \hline \end{tabular}
\end{table}
Table 7: Specifications of the equipment for car body noise characteristics.