These pictures are rederings though.
https://portal.fo/dagur-36150/myndir-listaverkid-hja-trondi-...
I think this might also just be an effect of the fake high dynamic range on the pictures (i.e. a rather large amount of color bleed from an underexposed slice of the image was artificially enlarged to make it "pop" more).
I guess they could have chosen to dig 2 different tunnels, but that would probably have been more expensive because of the increase in kilometers, seeing how long they dig under land at the mouths in order for the tunnel to be deep enough at the banks/shores.