Creat another surface "Void-1". Paste the non-roadway surface into it. Add a boundary that matches the void area inside the roadway. Paste the three surfaces into your combined surface in this order: "Non-roadway surface", "roadway surface", "Void-1 surface".
this is the approach I'd take although just check that the triangles form correctly at all common boundaries. They usually do but occasionally you might have a gap which can be closed by adding a show boundary.
neilyj (No connection with Autodesk other than using the products in the real world)
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