I was given a template that is intended to place 2 lanes of pavement on the left carriageway. I found that it didn't serve my purposes as well as I liked. It places 14' of pavement to each side of the baseline: 12 feet of lane plus 2 feet of shoulder with full depth pavement. I want to add a point that represents the edge of travel way (ETW) and then set the pavement edge (EP) 2 feet outside that.
The above establishes that superelevation is pinned to the EP in the template that was provided. I haven't changed it.
I'm adding points called ETW-L and ETW-R. I constrained each to be offset from the centerline, with an appropriate label for parametric constraints. I constrained each to Vector-Offset (0') between the centerline and the edge of pavement (which, as noted, is how superelevation is set).
The EP points as provided were constrained horizontally from the CL (14') and by slope from CL (2%). In the process, I re-set the horizontal constraint (the first constraint) on the EP points: Setting it to be derived from the near ETW then pressing Apply, I get the message: "ERROR: The first constraint could not be placed because: Invalid Parent - Causes recursive constraints".
The workaround is that on the ETW, I need to change from Vector-Offset to Slope, and use the same CL and EP points to establish the slope. At that point on the EP I don't get the recursive constraint message when I set the horizontal constraint to the ETW. This workaround isn't a great deal of work, but surprising, as it is not obvious. And if this recursion had been deep enough, it might not be obvious where it started.
In the end, I suppose I'm asking that this error be fixed or explained.