Japan Railways wants to ride its trains faster to compete with the airlines - so unlike in my country. They plan to increase the speed to 320km/h from current speed of 260 km/h. I don't even have a comment for this. For this, they have to do some work for the tunnel portals to protect them from sonic boom.

https://www.railwaygazette.com/high-speed/jr-east-to-speed-up-tohoku-shinkansen/57556.article