Parallel, curved edge

I didn’t find a solution after googling many different phrases, so I decided to ask, as I’m basically stuck with my project.

I’m improving a model (intersection prefab) for ETS2 - I think it doesn’t really matter here.

What’s my problem?
This part needs to be 1 meter wide everywhere.
As you can see, I aligned the inner edge with road’s shoulder but how do I make the outer edge parallel (the same curvature)?
It’s not nicely curved right now, as I was doing it manually just to see how bad it looks.

Here’s an example of the original part, that is nicely rounded:

Any ideas?

Thanks in advance!

Convert it to quads, edge slide with even option on. Could also enable edge lengths from mesh display. Edge slide with clamp option off to move it outside the edge boundary but along the parallel edges. Looptools addon: space to even out the spacing between the vertices.

Keep inner edge and start from there. A few examples: Offset edges addon, extrude depth and Solidify modifer, convert to curve and curve extrude.

From what I understand from your explanation, you can just delete those tris and get the normal for the inner edge, then extrude a new ring of faces 1 meter out from the normal.

or a simple fill then inset