ION - Waterloo Region's Light Rail Transit

[jamincan]

This is the most important bit. I don't see why tunneling here would be technically not possible, but I do know that it would not be achievable politically. We had a significant fight to get LRT; a more expensive system that involved tunnelling in some but not other parts of the line would not have achieved the necessary support.

The two cities are in completely different contexts. Many more middle-class and professional Ottawans take transit and have experienced how having buses operate in mixed traffic downtown wastes time and resources. A completely separate right of way is probably much easier to sell to them.

Tunnelling here would be possible, as it is pretty much anywhere except maybe through the core of an active volcano or something like that. However, it would be ridiculously expensive. Through Uptown, it would have to go under the creek, which means either very tricky tunnelling through muck or going very deep, either of which is expensive. Given the traffic levels and the availability of space on the surface, this simply doesn’t make sense, and as pointed out by others, would have led to non-approval of the project.

In Ottawa the traffic levels are enormously higher. Also, the tunnelled section is high ground consisting of rock, and only a small fraction of the route. As a result, the tunnel more or less continues the grade of the non-tunnelled portion so they could just start digging in from the side. Because it is all rock, they were able to mine it; to my knowledge Ottawa didn’t use any tunnel-boring machines.

You're correct that the Ottawa tunnel was mined. It wasn't entirely straightforward, though. There was a section just east of the Rideau Canal that crossed an old river bed that is now basically just sand. They had quite a bit of trouble getting through that section, including dealing with a massive sinkhole. https://obj.ca/article/rideau-sinkhole-c...ity-report