I like this underground autonomous cargo system better [1][2] (sorry in German, but you get the idea from the video images) It's autonomous, clean and inexpensive to build.
London used to have a similar system for distribution of mail throughout the city, officially known as the London Post Office Railway, or Mail Rail. I heard there were plans to open up some of the stations and tunnels to the public, not sure what they came of them though.
I used to work in Royal London House in Finsbury Square and the lowest subterranean level was sealed up but Royal Mail branded; given that it was a stones throw away from Mount Pleasant, I always wanted to gain access and see if it had access to Mail Rail or was even a station.
One station and a short section of tunnel are opening in 2017 as part of the Postal Museum. I forget all the detail, but the main limitation as to how far access is allowed is all down to the fact that evacuation was scarcely considered for the tunnels, given it wasn't really designed to carry passengers.
Here in Berlin they have been working to build 2.2 new kilometers of subway since 2010. They expect to finish around 2020, having spent 500 million Euros.
Building tunnels is really expensive. Barring radical longevity improvements, I don't think I'll live to see an underground transportation network.
At least from all the preliminary studies I've seen, electric power is not really practical for all but the smallest diameters. FYI I'm referring to the use of a rock-melting penetrator rather than a traditional cutting head. This is maybe just science fiction at this point, but it came to mind as the sort of technology that would make these sorts of projects economically feasible.
[1] https://www.youtube.com/watch?v=KSSO_QPgQTw [2] https://www.youtube.com/watch?v=r11X-zMF_pc [3] http://www.cargosousterrain.ch/de/