## 5 Conclusions  
In this study, we focus on the bridge-borne noise induced by the freight EMU with the speed of 350 km/h, we study the mechanism of bridge-borne noise is, and the noise reduc  
Figure 12: Insertion losses distributions under the noise wall heights of (a) 4 m, (b) 6 m, and (c) 8 m at 9 Hz; (d) 4 m, (e) 6 m, and (f) 8 m at 71 Hz; (g) 4 m, (h) 6 m, and (i) 8 m at 82 Hz.  
tion effect of the noise wall is further investigated. The characteristics of the bridge-borne noise under different loading conditions are analyzed, and the mechanism of radiation noise is revealed. Moreover, the effects of setting noise walls on bridge radiation noise are studied, and the influences of the noise wall height are investigated. The main conclusions are as follows:  
1. Compared with the condition of the empty containers, the accelerations of the bridge deck increase slightly under the loaded condition. Correspondingly, the bridge sound power and SPLs have a small increase in the frequency range below 20 Hz and above 125 Hz, and the maximum increments of the sound power and SPLs are 6.8 dB and 2.5 dB, respectively.
2. The structure resonance, intense local vibrations, and high acoustic radiation efficiency of the bridge are related to the strong bridge radiation noise. The vibration of the deck is dominant, and the modes of the deck are conformed to the surface mode when the structural vibration frequency is greater than the critical frequency, which leads to high acoustic radiation efficiency.
3. The bridge radiation noise is attenuated when transmitting the noise wall, resulting in a good noise reduction effect in the sound shadow zone, but the noise in local areas between the bridge and the noise wall increases due to the sound wave reflection of the noise wall. The ground reflection affects the superposition of transmitted, reflected, and diffracted sound waves, which causes nonlinear relationships of noise reduction effects with the noise wall height.
4. The loudness levels of typical field points increase with frequency in the range of 20-80 Hz, while they fluctuate slightly within 40-60 phon in the frequency range above 80 Hz. Compared to the condition without the noise wall, the reductions of loudness level are within 10 phon under the 4 m noise wall condition, and the maximum reductions under 6 m and 8 m noise wall conditions attain 20 phon.  
This paper only presents a simple simulation case of noise walls; full-scale or reduction-scale experiments should considered for further investigation when conditions permit them to be carried out. Moreover, future research should emphasize sound-absorbing materials to achieve better noise reduction effects.  
Conceptualization, M.D. and X.Z.; methodology, X.Z.; software, M.D.; validation, M.D. and X.Z.; formal analysis, M.D. and X.G.; investigation, M.D.; resources, K.W. and X.Z.; data curation, M.D.; writing--original draft preparation, M.D.; writing--review and editing, X.G., K.W. and X.Z.; visualization, M.D. and X.G.; supervision, K.W. and X.Z.; project administration, K.W. and X.Z.; funding acquisition, K.W. and X.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by [PERSON] and [PERSON] The grant numbers are U19A20110, 52362049, 22 JR5 RA344, 22 JR11 RA152, 22 ZY1 QA005 and LZJTU-ZDYF2302. And APC was funded by U19A20110.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
Author [PERSON] was employed by the company CRRC Qingdao Sifang Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.