So overall CN traffic is light on this section of track; it just happens that as currently scheduled, its in conflict with optimally placed additional GO runs.
So the options (in theory) are:
1) Get CN to shift its schedule, if needed, to gain at least one additional slot (which you see as unlikely)
2) Build sufficient passing track at at least one location en route such that GO can move around the CN movement (cost being the key question here, I assume, since the majority of this sub was historically double-tracked, so the space is there.)
3) Find a different way to handle that peak demand
- Buses?
- Use CP via Welland and the spur to hit Niagara from the opposite side (requires investment in the spur, a minimum of one round trip clearance from CP and a platform/station in Niagara for off-loading passengers. (cost?) ?
The line still is majority double tracked. 52km out of 72 km (72%). The only portions which are single-tracked are east of Clifton (where most of CN's trains branch off anyway), and a 16.5 km segment between Grimsby and St Catharines. CN would presumably want to schedule meets at the Welland Canal (just east of St Catharines) so each bridge closure can be used by 2 trains simultaneously. So trains probably wouldn't be meeting between Grimsby and St Catharines anyway.
Double-tracked segments in green
Based on Paul's comment, our concept of adding an additional morning GO train would result in a total of 4 eastbound trains in the morning (2 GO, 1 VIA, 1 CN), and 3 westbound trains (2 GO, 1 CN).
The current passenger rail schedules are below.
Eastbound trains cross the canal at 10:03 and 10:35, and westbound at 11:33. If the eastbound CN train crosses at 11:33, then the new GO departure would need to depart Union at 10:51 and cross the canal at 12:33, to leave an hour to raise and lower the bridge between 11:33 and 12:33. If the CN train
doesn't cross at 11:33, that's a slot which could be used by an additional morning GO train, departing Union at 09:51 and skipping St. Catharines because there's no platform on the south track.
Given that the line over the canal is double-tracked, it seems like it would be practical to schedule 1 closure per hour, shared by 2 trains (1 per direction). Given the bridge is over a dual lock, each bridge raising would be useable by 2 boats (1 per lock).
I'm not sure what the capacity of the lock would be in the absence of the railway bridge, but I don't imagine it's much more than 1 boat per hour per direction anyway, given that
it takes 15 minutes to fill the lock, a few minutes to manoeuvre the boat out, 15 minutes to empty the lock for the next boat, and another few minutes to manouevre that boat in.
Conversely, the 30-minute gap between the Maple Leaf and the GO train might not be enough to raise and lower the bridge, in which case an additional slot for boats could be created by shifting one or both trips to create a 1-hour gap, to let 2 boats through.
Maybe the buses are key to solving some of the problem. You could have one express bus go from Burlington, and the other from West Harbour so it splits the traffic into 2. Or as crazy as it sounds, we could start a Ferry service which could save a lot in the long run. Looks like that is actually a thing that they're planning in the long run.
https://www.blogto.com/travel/2022/06/toronto-niagara-falls-ferry/
Buses may be key in the short term. I like your idea of a Hamilton-Niagara bus - the hourly Lakeshore West trains which turn back at Aldershot could have a 12B connection at Burlington, while the hourly trains which continue to West Harbour could have an express bus connection there. That would provide departures every 30 minutes from Toronto to Niagara. I'd suggest that the Niagara-Hamilton bus should start at Hamilton Centre so it provides a convenient new connection from Hamilton itself, in addition to providing additional frequency for the Toronto-Niagara route. That route would probably generate decent ridership in its own right.
In addition, perhaps the morning train could run non-stop from Union to Burlington, to force people coming from Exhibition, Port Credit, and Oakville to instead take the Lakeshore West local to Burlington, and then the 12B express bus to Niagara.
That option is actually just as fast anyway:
Exhibition - Niagara: 2h01 via route 12B, 1h59 via direct train
Port Credit - Niagara: 1h42 via route 12B, 1h46 via direct train
Oakville - Niagara: 1h28 via route 12B, 1h35 via direct train
June 2022 Route 12 timetable, highlighting the bus trip simultaneous with overcrowded train trip
So although people do prefer taking the train, taking the bus instead wouldn't actually be an inconvenience.