Grading an eyebrow/bulb with a Corridor, target perpendicular to alignment.

[Anonymous]

I am trying to use a corridor to grade this bulbous little half cul-de-sac eyebrow type roadway. I am having trouble with the return of the bulb as it runs back North, it is too perpendicular to the alignment/corridor. I have tried changing the 2-dimensional shape of the bulb slightly but I can't change it enough to help the issue I'm having. I have also changed the frequency of the offset target curve and that helped smooth it out but it is still overlapping some in that area, not really bow-tie though. 

Looking for the best course of action to fix it, I am almost debating just splitting the corridor regions over that span and connect the two regions with Feature Lines along that return. Otherwise some sort of offset alignment or something should be able to help I think? Any help would be appreciated! Thanks. 

[KMercier_C3D]

Treat it similar to an intersection with a curb return alignment around the base of curb and use a curb return subassembly to keep your shoulder analyzed perpendicular to the perimeter instead of perpendicular to the centerline alignment. 

[sboon]

You need to think about how the finished surface is to be sloped.  Does the bulb have a low point where runoff is supposed to collect, or do you want to create a swale along the outside edge of the travel land and carry the water around the corner?

Steve
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[Anonymous]

Well now that you got me thinking about it more, (thanks) I am thinking as the bulb happens I will have to stop the crown in the road and sheet flow from the south to the North until it gets out of the bulb and then go back to crowned to the north. I probably froze too much context from the drawing in an attempt to simplify things. The bulb is going to be about the highest elevation in the site and the water is going to run to the North end of the site where I have ponds on either side of the road.

[sboon]

Something like this?

You can use superelevation from the road centerline to get it draining in the right direction.  Extract the edge of lane featureline from that corridor. (white)  Create an alignment around the perimeter of the bulb as @KMercier_C3D suggested, making sure that the profile matches the featureline elevations where they tie into each other.  You will also need a centerline alignment/profile for the bulb (yellow) so that your assembly has a target when it projects inward from the curb line.

Once you have the bulb corridor built you will have to adjust the profiles to get it flowing in the right directions.

Steve
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[Anonymous]

sboon, thanks for the suggestions, I think I'm close but there are a few things that aren't quite lining up, the contours in the bulb don't look good and the corridor region sort of overlaps itself. I am not sure if I did the superelevation correctly or what it was that I did wrong.  I have attached a few screenshots as well as the drawing if that is easier. 

[sboon]

It took a while, but I think I've got it now.

Your corridor has targeting issues, and problems with duplicate alignments and profiles etc.  You should probably spend some time editing object names and deleting extra stuff before you go much further with this drawing.  I've re-exported the lane edge featureline and edited the other alignments and profiles to get a mostly smooth pavement surface.

I'm not sure which version you're using so I've added an xml with the edited alignments and profiles.

Steve
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[Anonymous]

Wow that looks so much better than what I had! I'm sorry the project has changed a few times and I should have cleaned the drawing more before uploading it. So really what you did was edit the alignments and profiles while watching the surface and the corridor updating to get the surface smooth? I'm sorry this feels like a dumb question, what exactly did extracting the featureline from the corridor do for us? Just give us an elevation that we have to tie back to? You've really helped me out, I'm just trying to understand what I need to do in order to do it myself next time. Also on the West side as we start the curve before switching regions, there is a low spot in the (I got rid of the low spot on the East side.) Is that low spot from the transition back from sheet flow to crowned? How do I fix that? I really appreciate the help. 

[sboon · Accepted solution]

A corridor cannot target itself, so if the featureline is not extracted (and the dynamic link broken) then it cannot be used as a target for your corridor.  Note - you could have created the bulb as a separate corridor, in that case the second corridor could target the featureline of the first one.

You had some weird issues with targeting in the bulb, so I deleted a bunch of stuff and recreated it.  I made sure that the ends of the cds profile matched the featureline, then added VPI's at the start and end of the bulb to get the cross slope of that area working right, and finally added more VPI's in the transition areas to smooth them out.

For the curve you didn't extend use the superelevation parameters of the alignment.  If you had then you would find that the transition from normal crown to full super extends beyond the limits of the horizontal curve.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

ProTip - Avoid edits or extra data to a corridor surface if at all possible.  It makes diagnosis of the corridor errors much more difficult.  Use a separate surface for displaying final grades; paste the corridor surface plus other work into that.