It takes four hours because they are on different Islands that aren't near each other or connected well. You are insinuating that it is just a slow train.

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.

A train has to travel in the opposite direction, across several islands and then back up. 4 hours is pretty good considering that. Even then there is so little demand for this journey it is infrequent.

https://goo.gl/maps/SZeteqJRc1ng49go8

Actually, it seems to only take 2h:50min by train Copenhagen to Aarhus[0], while by car it takes 3 hours with the ferry from Sjællands Odde to Aarhus[1].

[0]https://www.google.com/maps/dir/Copenhagen/Aarhus,+Denmark/@...

[1]https://www.google.com/maps/dir/Copenhagen/Aarhus,+Denmark/@...

> 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

Gothenburg to Stockholm is longer and takes 3 hours by train, and that is with a train from 1990. That is of course the prime route in Sweden, but it still isn't fast.

My point was that Denmark is a very small country, and the solutions used there might be interesting for certain small cases, but may be difficult to generalize for larger cases.

I lived in Brussels, Belgium for almost eight years, and they have many of the same issues with regards to scale.

Brussels has international high speed trains to London, Paris, Amsterdam, Cologne.