A compression wave is generated ahead of a high-speed train, while entering a tunnel. This compression wave propa- gates to the tunnel exit and spouts out as a micro pressure wave, causing an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a tunnel must be understood and experimental information on these phenomena is required. An experimental and numerical in- vestigation is carried out to clarify the mechanism of the propagating compression wave in a tube. The final objective of our study is to understand the mechanism of the attenuation and distortion of propagating compression waves in a tun- nel. In the present paper, experimental investigations are carried out on the transition of the unsteady boundary layer induced by a propagating compression wave in a model tunnel by means of a developed laser differential interferometry technique.
 S. Ozawa, T. Maeda, T. Matsumura and K. Uchida, “Countermeasures to reduce micro-pressure waves radiating from exits of Shin-kansen tunnels,” Proceedings of 7th International Symposium on Aero-Dynamics and Ventilation of Vehicle Tunnel, Elsevier Science Publishers Ltd., London, 1991, pp. 253-266.
 K. Matsuo, T. Aoki, H. Kashimura, M. Kawaguchi and M. Takeuchi, “Attenuation of Compression Waves in a High-Speed Railway Tunnel Simulator,” Proceedings of 7th International on Aero-Dynamics and Ventilation of Vehicle Tunnel, Elsevier Science Publishers Ltd., London, 1991, pp. 239-253.
 T. Fukuda, S. Ozawa, M. Iida, T. Takasaki and Y. Wakabayashi, “Distortion of the Compression Wave Propagating Through a Very Long Tunnel with Slab Tracks,” JSME International Journal Series B, Vol. 71, No. 709, 2005, pp. 36-43.