Superel transitions for compound curves

[ACtrafficengr]

Most of my experience has been in traffic safey and operations, but now I'm involved in designing a rehab project for a rural highway. This is a moderately low volume rural collector. The traffic volumes don't justify the expense of realigning curves.

When dealing with compound curves on rural highways, how does one transition the banking from one curve to another? I didn't find the 2005 Green Book to be very helpful.

Thanks!

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"Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

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[Maury]

I encountered the same problem a while ago and didn't find a good solution. I ended up using as small a superelevation as possible, including reducing the posted speed (design speed) as much as possible, then doing the transitions totally on the curves rather than partially on the tangents, since there was no tangent. I would have preferred to realign the roadway, but like your project, that wasn't possible. Not the best solution, but better than no super at all.

 

[ACtrafficengr]

Maury,

Were you dealing with opposing curves? I should have specified that all but one of the compound curves are in the same direction. Should I put 1/3 of the transition on the sharper curve, and 2/3 on the wider curve?

Opposite direction compounds are in a sense easier since there isn't much else you could do.

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"Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

- Blair Houghton

 

[Maury]

My situation involved an s-curve (opposite directions) with no tangent in between, so all of the transition had to be on the curve. In your case, with the curves in the same direction, I would do as you suggest and put 2/3 of the transition on the larger radius curve. This most closely conforms with the design standard of having 2/3 on the tangent.