It looks like it's too tight a squeeze, rather than a funky slope.
I make a bigger tunnel, then back fill. You should be ok with going under the tracks. The terrain will stick to it, right? So you won't mess that up.
I've found the terrain is more forgiving with sloped paths that it used to be. So, try going wider (tunnel) and see if that helps.
Or try using smaller width to see that the path will lay, then you'll know it's the tunnel width "obstructing".
In RCT raising land worked in increments and to get underground you had to dig a hole that was the equivalent of 2 stair cases. you look like your currently only half that with your slope. if you build a staircase of 2 meter paths that would probably be about the height of 2 or even 3 walls, thats how deep you have to go under the train
I agree with Fraggle, try using the "Flatten to surface" tool to make it hair wider while keeping that nice slope grade you made. The path should handle that slope just fine so it's gotta be the width that's the problem.
Edit: I just tried to do this myself. The path couldn't go down the slope straight due to the same error, I had to make it curvy,
No, it's not a width problem, it's a "the path system has had big problems since its inception" problem. It also works for me if I go curvy. I find more often than not I can do things with curvy paths that I can't do with straight paths, but I don't want a curve, I want a straight slope.
I don't understand why terrain can't just be shaped to meet the bottoms of paths.
Apples and oranges IMO, two different terrain systems. I do miss those hard edges though!
I think the best thing they could do is some kind of a terrain/path snap feature so if we raise/lower a path the terrain will deform and stick to it. I'd really like to see that for coasters/tracked rides too.
For anyone wondering "Why not just use a building to fill the gaps and/or create fake walls?" the reason is because you have to cover the tops of the gaps and there's no way to do that that doesn't look completely stupid, either.
This is basically just a big hole in the ground using a building to pretend the ground and walls are flush. But you have to cover the holes on top, that can't get close enough to the path to be covered without an entire chunk of flat roof.
I'm just doing workarounds. I don't want to do workarounds. [sad]
One way to make underground paths fairly easily is to build a coaster and use it to bore the tunnel, then after deleting the coaster track, replace it with your path.
When building the coaster use auto tunnel with no more then 9 degrees on the decline. I used somewhere between 8 and 9 degrees. It's nice being able to see the angle displayed as you build, that's new to the last update. [up]
Set the tunnel size to be 18 - 20 feet.
As you continue to build the coaster tracks, bore down to about 25ft and level out before making any turns. Keep your turn angle 30 degrees or less.
If you bring the coaster/ bore back to the surface, remember the incline should be between 8 and 9 degrees max.
Delete the coaster and add your path into the tunnel. You might need to hit the ground outside the entrance with some terrain smoothing to get the path started.
After laying your path, use the terrain tools to shape the entrance as you'd like.
I'm sure auto path tunneling will be added soon. If was spotted in the code during alpha and we could actually switch it on, however it was buggy, for example you could no longer connect paths to rides.