It was called the bullet train because it was rounded in front, but every time it went into a tunnel it would build up a pressure wave, and then it would create like a sonic boom when it exited.
E' stato chiamato bullet train (treno a pallottola) perché era tondeggiante davanti. Ma ogni volta che entrava in un tunnel accumulava un'onda di pressione. E poi creava come un'espansione acustica quando usciva.