take the edge off CIVIL 3D

• These kerb returns are not perfect - they’re just a first pass to get some quick volumes but they do more or less grade themselves automatically.
• They can also update (in vertical design) automatically.

They use a combination of existing subassemblies that come with the standard installation of Civil 3D.
This is just a brief overview of the concept. I’ll be covering the topic in detail on my AU session on Roundabout Reconstruction (even though the title refers specifically to roundabouts, the session is really just using a roundabout as a good example of some geometry with some interesting challenges and constraints).
The session is an easy one to remember - it’s the last one on the last day !

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So, in a nutshell…

In a nutshell, we use the overlay, widen subassembly with a generic link to position it on the road edge so it can grade back to the kerb alignment. The interesting part is that we get the initial design without designing the kerb profile at all.
- It’s a bit tricky to describe it in words but the pic below should show the idea:

The difference between this and just attaching the overlay assembly directly to the road edge is that we get the orientation of the kerb return alignment.
i.e. the sections go at 90 degrees to the kerb return alignment, not the road edge…

(I’ve taken a liberty in showing the generic link meeting the insert point instead of the sample point of the overlaywiden subassembly - anyone who has used this subassembly will know - I’ve mentioned it in another post here)

The general procedure..

• Start on a kerb alignment (Kerb 1)
• Sample the NS (or EG or any other surface)
• Use the generic link to get the data from the main/side roads

and (here’s the clever/weird part)

• Set the target alignment for the width of the overlay back to (Kerb 1)

How well does it work (really)?

It works well on string based jobs as the road edges are blended together already so when the grades are projected, they look reasonable. On non string jobs, there is quite a jump where the 2 road edges meet so the contours won’t be quite so smooth.

The reality is that ‘create profile from corridor’ feature will be used to extract the interpolated levels (from no. 3 in the diagram above) to form a properly smooth profile for the finished model.

However:

• Take an intersection designed with these quick kerb returns and make a change in vertical design. (in this case, we are raising the main road and then raising the strings of the crossing road to match)

• Rebuid the corridor of the quick kerb returns and they update straightaway so the new volume can be estimated and the new daylight line can be examined.

The DWG used here was a simplified one to just show the necessary concepts for training purposes - it looks a lot more funky when there are footpaths/sidewalks and batters/daylighting subassemblies added to the mix.

Conclusion?

This whole idea originated from a major presentation to a DOT. The job in the image below is a duplication of an existing road. Because the main control strings were defined carefully to match various criteria, the kerb returns were able to be graded quite accurately using the new quick method.

If anyone is after a sample drawing showing the concept, let me know.
I’ll be showing the procedure in the AU presentation with plenty of graphics to explain how it came about.

cheers,
SeanT