Agreed. Local LRT would be a better investment, and would serve far more destinations as Niagara attractions are somewhat distributed.
That said, there is a potentially interesting solution in the ~$2B range. CN services that small industrial area near Thorold Town Line Road and Welland River, and CP has a short bit of rarely used track leading to the falls just on the other side of Welland River. A new station adjacent to the Marriott could be serviced by filling in that gap and bridging over the river.
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I've thought of variations of that myself, as have others as
@Willybru21 notes above.
The challenge is both the extent of any track upgrades required, and the face that the CP route out of Hamilton doesn't serve as much population en route.
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That said, since you reminded me of the CN industrial trackage.......... I got to looking to see if one repurposed that, whether a shorter connection route could be found on mostly public land. I don't want to stray too far into fantasy territory....but to contribute to the sub thread at hand.........one could consider this:
CN Industrial track almost right to the falls via the Hydro corridor. (we know Hydro would love this idea, but a cursory ground-truthing suggests a single-track could be built w/o passing under existing pylons.
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There's also a potential route along the Hydro Canal which has/had rail along some of it in the past. But that involves ~2km more track, and would likely displace a recreational trail.
Finally, I considered connecting the CN industrial track via the 420 ROW.
A very cursory assessment suggests there is room, though there would be at least one complex and costly fly under, and maybe 2.
It would cross a couple of major roads at-grade, but if service were only hourly, that doesn't seem unreasonable. A station could be sited within 2 blocks or so of the Rainbow Bridge.
That would shave 1.5km off the distance between The Falls tourist zone and the current station.
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To be clear, I'm not backing any of these at the moment, I'll stick by the suggestions I made above; that said, there may be something to consider which if any of these choices merits consideration in the distant future and making sure to future-proof for same.