Northern Light
Superstar
Even if Hunter Street could be twinned, can GO push enough trains through Bayview Junction in both directions to justify it, while also maxing the potential of a completed east exit from West Harbour?
I feel like that's a @reaperexpress question.
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Side note, right now the single track section of the approach is ~1.2km. Of that a bit more than 800M is the tunnel, with a bit less than 400M being east of the tunnel, in an open-cut, assuming the bridges (pedestrian and road) over the open cut allowed sufficient clearance for two double-stack tracks, or could be cost-effectively replaced to allow such, the two 'hard' pinch points would the Junction and the Tunnel (as is).
If you have a way of doing so please feel free to share. As of right now the Hunter Street tunnel only has a single track that has the responsibility of running both CP and GO in and out of hamilton. Whilst the tunnel is theoretically wide enough to support two tracks, the tunnel isn't tall enough to support double-stack freight trains in such a configuration (hence why its single track currently). If you want to expand the tunnel to offer more service, there are 2 general ways to do so: Make the tunnel taller so that a track on the side of the tunnel could support double stacks, or make the tunnel wider. The former cannot be done whilst also preserving CP's access to Hamilton GO, so you'd have to somehow build some sort of temporary bypass that CP trains could use whilst work is being done on the tunnel. Then you could theoretically move the track to a side of the tunnel, and deepen the tunnel one half at a time (I'm not an engineer, and there's a really high chance this isn't even feasible, but I'm working with extremely optimistic scenarios here). Even then work could probably be done way faster by just... closing the tunnel and not doing half a tunnel at a time.
The one 1/2 at a time strategy is fine, in theory, but even if the tunnel dimesions and safety permit it, that obviously requires the track shifted to one side, during which time it would not be able to handled double-stack freight, until the first 1/2 of the modification is complete.
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A tunnel by-pass isn't realistic, at that point, you're literally building a new tunnel, on a new alignment. But you made me laugh, I pictured forcing CP and GO to street-run on Hunter Street!

You could widen the tunnel, but that would almost certainly have to be done using cut and cover construction, and expropriating/paying heavy easements to all of the residents/business owners along hunter street, and once again while it might be possible to keep current CP/GO service levels here, doing so would almost certainly jack up the construction timeline, and thus increase cost.
I don't have the drawings showing the exact alignment of the tunnel, but I imagine, the large apartments on either side of Hunter St. at various points have underground parking that must come awfully close to the tunnel walls. .....