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How to design a reverse curve on a curve

How to design a reverse curve on a curve

How to design a reverse curve on a curve

(OP)
I am designing a reverse curve on a curve with superelevation.

Does anyone have an equation or an idea of how to design this manually or on autocad?

Appreciate any info you can give.

Thanks

RE: How to design a reverse curve on a curve

The superelevation must runout to flat at the tangent section between the curves and then reverse to accomodate the reverse curve.  Some DOTs use centerline as profile grade and raise/lower the edges, others use an edge for profile grade line.  Spiral curves or a wider lane section during the curves makes a more driveable highway.

RE: How to design a reverse curve on a curve

I think you'll better off rough it out on paper / CAD.  I'm still not clear what you creating, a reverse curve from a single existing curve or introducing an "S" into a larger, single curve?  Post a sketch.  You might be better slopping in a spiral.

As far as super-elevation between the reverse curves, I've always set 0% cross slope at the PCC (point of compound curvature) and transitioned to full super using 50% on and 50% off for the transition lengths.  AASHTO suggests super transitions of 1/3 on and 2/3 off, but will allow 50/50.  I do not believe a tangent segment is required if you are not going back to normal crown.  You are dialing from full SE through 0% and back to full, i.e. -8% to 0% to 8%.

Ideally the reverse curves are the same radii and the same super.  Run outs on either end (PC and PT) should get the normal 1/3 - 2/3 transitions.
 

RE: How to design a reverse curve on a curve

(OP)
Thanks eea.

Because of the Reverse Curve (RC) being on a curve, the two radii will not be the same.  Are you saying the allowable ratio if not symmetrical is 1/3 - 2/3?

Or can the 2 curves on the RC be whatever radii that'll make it work?

Please advise.

Thanks

RE: How to design a reverse curve on a curve

Will:

The 1/3 2/3 is not a raduis ratio, it is how/where to locate the superelevation transition with respect to the PC or PT of a curve.

Eea is saying normally the superelevation transition is 1/3 in the curve and 2/3 outside the curve (usually on a tangent).

(eea also meant PRC - Point of Reverse Curvature, not PCC)

Because reverse curves don't have an adjacent tangent, anything that is outside one curve is inside the other. So splitting the transition 50/50 is about the best you can do.

To draw reverse curves in Autocad, Fillet Radius is a good tool in many cases, although it is not very scientific.
 

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