Fascinating, and now I learned another new thing! Thank you for sharing.
> Basically what happens is when a train enters a tunnel at high speed, the air in front of it is compressed and does not have enough time to flow past the trains body. When all released at once, the pressure causes a shockwave that goes boom!
This is basically a very rudimentary version of the piston effect: https://en.wikipedia.org/wiki/Piston_effect