The Eysturoy tunnel is an Y-shaped tunnel, connecting three islands of the Faroe. (Edit: Not entirely true, as two of the mouths are actually on different peninsulas of the same island Eysturoy.)

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.