The pressure on the wall of a tunnel changes when a train or a pressure wave passes in the tunnel. When openings are provided in a tunnel, a long tunnel-entrance hood, or a hood linking tunnels such as a snow-shelter, the pressure change on the wall gives rise to airflow through the openings and a pressure wave is emitted outside. Though the magnitude of this pressure wave is small compared with that of the "micro-pressure wave" emitted from a tunnel exit, it may cause an environmental problem. A simple model is proposed to calculate the pressure wave emitted from the openings in the tunnel or the hood during propagation of the compression wave. The calculation results based on this model are compared with those of a 1/60 scale model experiment.
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