Severe noise problems because of a sudden shockwave may appear when a high-speed train enters a tunnel. The solution was found in the King fisher, a skilful bird that hunts diving from the air to the water at high velocity without making any noise and injuring itself. Added to the total elimination of the problem of shockwaves in tunnels an important energy reduction was achieved when the shape of the bird was adopted for the train.
King fisher
King fisher diving moment
Shinkansen in Kyoto
Information Source: https://www.sciencedirect.com/science/article/pii/S1385894707001192
