OK, I stand corrected. I have never seen any of those and in my country (USA) I have never heard of a tunnel that had many exits. But they may exist here and I am sure someone will let me know. (Thanks Hallux) To answer the first post, I suspect that most GPS signals can't penetrate the earth above the tunnel so you loose that feature while in the tunnel. Maybe some tunnels may have a GPS receiver installed outside the tunnel which then sends the signal with wire to a receiver inside the tunnel and then uses a transmitter that re-broadcasts the GPS signals to your car GPS receivers or smartphones.