For those still going to work - TfL (London Transport) - is using leaky feeder technology to provide 4G coverage (all 4 major providers) on the underground. The pilot program is up and running on the Jubilee Line between Westminster and Canning Town, so usefully for commuters between Waterloo Railway Station and Canada Water.
How fast? 230 Mbps is a reality.
So I'm looking at wiring up some Lithium batteries, in series, and testing the Z3C whilst in the Underground tunnel. (aside how robust is the Z3C if the Amps are over spec?).
Lets hear it for leaky feeder tech!🤣