- Create your toposurface as normal - making sure your elevations, etc are nailed down prior to moving on the the next step. :)
- Use the Split Surface tool to split the surface into 3 parts, forming your road - you'll have to do this twice as the Split Surface tool only allows you to split the surface into two parts each time.
- On each side of the road, use the Split Surface tool again to split the surface into (2) 6" (or whatever your specs) pieces or slivers outward from each side of your road - this will later become the top of your curb and your gutter.
- Go to an elevation view and move the road, and the two inside most 6" pieces (your gutters) down your required curb height.
- Assign the appropriate materials to the roadway, curbs and topo (asphalt, concrete and grass) - now you can see things shaping up.
- Now, using the Split Surface tool again, Split each of the four 6" spaces 1/8" from the their shared edge - creating (2) 1/8" slivers of curb in between each of the two 6" pieces.
- Finally, go to a 3D view and use the Merge Surfaces tool and select the lower 1/8" curb piece and then the upper 1/8" curb piece - this will join the two 1/8" pieces to create your curb wall.