This is something I wrote recently after hearing about the Ottawa/Gatineau Rail Loop - it's about a Bank Street O-Train Tunnel which the LRT & transit fans might enjoy:
Perhaps now is the time to begin discussions for the Ottawa Bank Street O-Train Tunnel? The city of Ottawa Gatineau with a population of 1,441,118 is nearing completion of it's O-Train East/West Confederation Line 1; and its Trillium Line 2 running North/South connecting the airport, EY Convention C
Non-Ottawans should be reminded that "The Bank Street Tunnel" is so far a fantasy concept with no basis in City planning. It might make some sense in a few decades but the technical problems with building a tunnel and stations along a Bank/Wellington/Rideau alignment would be huge.
When I heard that the branch line to the airport was going to be built, I thought about continuing it as a tunnel underneath Bank St towards the CBD and parliament. Continuing north it would run under the Ottawa River and terminate right by the Museum of History. This would serve the Museum and the federal workers at Place du Portage.
Bank would become an interchange station and the line would be very deep in order to run under the river.