The comms working throughout the tunnels thing is going to be a real problem - and TETRA won't even touch that. Getting comms working through the tunnels, in conditions where there are obviously already serious problems is going to be even tougher. Frankly they might do better to have a TETRA relay box in each station which someone grabs and pushes into the tunnel - hooking it to the tunnel comms wires (pair of wires that runs along the tunnels for emergency use) - that would also knock out the power should someone try and restore it.