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# Drawing Spiral Curves Roadway Alignment

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01-14-2014 09:21 PM

I am needing to recreate a highway centerline alignment in order to calculate angle points on a property boundary. I know the centerline stationing that corresponds to the angle points, but i don't know how to put together the centerline. Unfortunately whover laid out the centerline originally used a spiral transistion curve. I have a record survey that has the spiral curve data and the centerline bearing at the PS and PT, what is the best way to draw the curve in autocad? I have been looking into old DOT refrences on spiral curves, and i am pretty sure i can do it the old way with linework and my calculator. THere has got to be a better way though... Below is some of the given information:

4degree curvature

delta = 45deg12'18" (PS to PT)

Tangent= 977.26'

a = .533

I think its best if i attach a tiff image of the survey as well, as it's always easiest to get a grasp on this kind of stuff with a picture to help explain. My curve is on page 4 of the attached document PS= 395+47.88, PT= 414+28.00

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Message 2 of 2 (115 Views)

# Re: Drawing Spiral Curves Roadway Alignment

01-15-2014 05:11 PM in reply to: andy7918

Andy:

I haven't done spirals for some time but here is what I did.

1.  Draw the two tangents and make an alignment (you have bearings for each tangent given on the plan).  Go ahead and have it labeled.

To make it easier to keep up with I designed the alignment start station to begin with Sta 390+00.00.

2.  Rt. click this alignment (made of just two tangents) and select Edit Alignment Geometry.  Then select "Add Free Spiral-Curve-Spiral" icon then select    "Free Spiral-Curve-Spiral (Between two entities)"

Then you will be asked a few questions and the spiral to curve to spiral will be drawn.  (Use two 750' spirals)

Any questions?

Bill

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