Roundabaut Crosssections

[GZE]

Our Client request us to submitt roundabout cross sections. I created crossections by sampling through central island alignments, the crossections looks fine exept where the circular region meets with the approach road the grades looks weird due to difference in crosslope directions between the central region and approach road regions. Am wondering how others present the crossections through roundabout.

Any suggestion is appreciated

[MikeEvansUK]

It's hard to see from the images but it looks like the cross slope on the entry / exits are very steep.

I'm not sure how you have modelled these entry / exit areas but it is usual (in the UK) to use a 1/3 or 2/3rds crown rule and design crown lines to intersect horizontally & vertically from each leg into and out of the roundabout edges. See image for this approach but you do not have to do this, the crown lines can be modelled at the channels.

Search in these forums for roundabout design and you should find some other posts.

One comment: I note that you are using the Roundabout tool and it has created all the centrelines intersecting at the centre of the roundabout. As a result one of your entry / exit curves is self intersecting hence why I do not use this. Not sure where in the world you are and what standards you are designing to but I would almost certainly design with an offset from the centre of the island to each approach leg to reduce this problem and increase the flare lengths & deflections etc.

[GZE]

Mike
I used a roundabout tool, I will try manual design to sort out the problem, I didn't understand 1/3 or 2/3rule our standards dont have much details on slopes rather than recommending 3% maximum approach grade.

[MikeEvansUK]

Here's a link to the UK DMRB for Roundabouts which would explain the 1/3rd 2/3rd part and the geometry a bit clearer but obvously you need to consult your design guide.