I had some trouble finding your geometry because it was so far from the origin. But I found that if you do this:
you get this:
which looks like this closer up:
What if you divided each of the track’s edge curves into the same number of points, then made a line between each corresponding pair of points, found the ruled surface’s closest point to each of these, and then found the normal to the ruled surface at each of these points.
I remember reading an article about designing roller coaster paths that dealt with the G forces at various points. The idea was to not exceed a G force higher than about 5, because higher ones can result in heart attacks and/or blackouts. The key to the article was that the method used, as it’s points of reference, were points called “heart points”, which are where rider’s hearts would be relative to the track, and not the standard method of “head points”, which are where their heads would be. Apparently that made a significant difference to the final track design.
internalized geometry roller coaster-bb1.gh (546.0 KB)