> There isn't much you can do other than spend tens of billions building a bridge or tunnel. Cars often get the ferry to make that journey.

There is a precedent for taking a train on the ferry [0]. Sure, a tunnel is preferable and it would've been constructed but the German authorities were dragging their feet for years[1].

[0]: https://en.wikipedia.org/wiki/Vogelfluglinie

[1]: https://en.wikipedia.org/wiki/Fehmarn_Belt_Fixed_Link