On what basis did you figure out the required clearance for the Richmond Hill GO Corridor?
Perhaps my math is off...........
But I'm getting a number closer to 14% grade.
Keep in mind the require thickness of the base supporting the tracks, at elevation.
Then there's another issue.........did you notice the high-voltage Hydro Pylon just beyond the Richmond Hill tracks? In the pic, below, the near-side pylon is shown, but the wires end up on the riverside just to the south.
There's not a very big clearance window between over the Richmond Hill tracks and under the Hydro lines.
Alignment from
www.reliefline.ca