urbanMSP

Considering that battery buses are almost a given at this point, a tunnel would not need the electric build-out or the specialized fleets that the Seattle Bus Tunnel and the Boston Silver Line have needed. Either a north-south or an east-west tunnel would be an amazing investment.

[*] An extension of the Downtown tunnel North across the River (probably by bridge? It was surprisingly difficult to find data on the riverbed and any prior attempts at tunneling) and a short distance into Northeast.

All you need to know: https://en.wikipedia.org/wiki/Hennepin_Island_tunnel