It was also interesting that the GSMR presumably had no problems in the tunnel reaching the outside world but the radios brought by emergency services did.
The SECAmb Airwave manual describes the steps needed to take to switch a vehicle's set to act as a repeater and to get the hand held units to connect to that. The example given for this was operation within a tunnel.
I could imagine that parking a vehicle by that cutting in a position where it could effectively relay being a challenge - unlike a road tunnel you can't just park at the entrance.