We were looking at a road widening the other day. AutoCAD Civil 3D has a few subassemblies to take care of this. We decided that since we had an existing ground surface representing the road surface and ground to each side, a centerline alignment, and not much else, we would use one of these subassemblies to widen the road. There was no superelevation data for the existing road, so we wanted the existing surface to control the pavement slope as we went along the alignment. There was no milling or overlay to the existing roadway, so we chose the OverlayWidenMatchSlope1 subassembly with an overlay thickness of zero,
This subassembly commonly is used to extend the width of one side of the road. The Sample Point usually is at the crown and the insert point at or near the existing EOP. There is no right or left to this subassembly; you specify positive or negative values for the offset to the Insert Point. This all works very well if you are doing one side of the road, but what if you want to do both sides at once?
What we wanted to do is show the datum surface and get some volumes. Here’s our assembly.
You can see what happens when we built the datum surface. Notice the triangular area caused by the crown in the roadway. Now, this wasn’t exactly what we wanted, but it is correct as far as the coding of the assembly goes. There is no Datum link between the Sample Point and the Insert Point, so the surface goes straight across the road. Not a problem if you are doing one side of the road.
We added a Basic Lane subassembly to the right and left of the crown point using 0.001m thickness for the pavement. The width was also set to 0.001m.
Now, here’s what we ended up with.
There’s some other trickery we could have used to obtain this result, but this was a pretty simple fix. It demonstrates how flexible these assemblies can be, and what you can do with a little effort. There may be some debate as to whether the existing road surface could actually be referred to as a datum surface, but I’ll leave that for another time. We got what we needed to show the surface.
I’m sure you’ve got other ways of dealing with this, and I’d love to hear them. So, leave a comment here. Maybe we can get a discussion going on this. Even an argument might be fun.
Comments