The longest undersea tunnel is 8.9km and it goes to a city with a population of 8,215. It goes to an entire island though, so a few more people than that benefit.
Your overall point is completely right, but might as well get the facts straight, so people can compare and don't recite wrong information.
It's not really common. They only have one tunnel that's 24.5km ( https://en.wikipedia.org/wiki/List_of_tunnels_in_Norway ) and it's not under the sea. The remaining are 10km or shorter.
The longest undersea tunnel is 8.9km and it goes to a city with a population of 8,215. It goes to an entire island though, so a few more people than that benefit.
Your overall point is completely right, but might as well get the facts straight, so people can compare and don't recite wrong information.
Norway doesn't actually show up much on the list of longest tunnels: https://en.wikipedia.org/wiki/List_of_longest_tunnels