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Reverse Curves

Is there a way in InRoads to create a reverse curve without having a tangent in between the curves?


Example, I am making a 400' (radius) curve that goes to the left and has a 400' (radius) curve that goes to the right with no tangent.  It is making an "S" shape. 


When I create this layout in MicroStation I can import the alignment by going File -> Import -> Geometry -> From Graphics and selecting the Horizontal Alignment from the drop menu.  I use the "Check Integrity" of the alignment to make sure it is in right. But this is a hassle to do once the alignment is already created and you are making changes to it.


Once I have the alignment already loaded and try to make an "S" curve it gives me "Solution overlaps or contains discontinuities".  If I make my curves have a 399.9' radius then it will work with a very small tangent in between, but I don't want any tangent I want an "S" shape.  Any solution??  Hopefully that makes sense.

5 Replies (Most Recent Reply)

  •  Hi,

    You can use Multiple Horizontal Element Regression Analysis to acomplish this task. You may need to activate this tool from (Tools/ApplicationAdd-Ins). To create reverse curve select the first and the last tangent element and and add two curves between. Choose free parameters and enter  'first guess' values for curves lengths.Hit Apply and Inroads will compute curves for you. This is really powerfull tool.

    good luck.



  • In reply to Adam Wieczorek:

    There is also the Horizontal Element Tools these tools give you full control over the elements allowing the creation of compound curves. Below is an explanation of some Geometry Layout Methods.


    Mike Longstreet
    Vermont Agency of Transportation
    Civil Engineering Technical Support
    VTCAD Help

  • In reply to Adam Wieczorek:

    Another alternative is the Horizontal & Vertical Elements Application Add-in. It must be InRoads or InRail for this to be available.

    With these tools, you can build all sorts of compound and reverse curves. Once your tangents are in place, use the Place Free Curve tool. It's the InRoads equivalent of the Fillet tool. Radii are either + or - so if the first attempt seems to go the wrong direction, try the opposite sign. Sometimes you have to use the check integrity tool to re-order the elements or to occasionally reverse the direction of elements. 

    These are powerful tools worth learning - including the vertical elements tools.

    CADDCOP (Chuck Rheault)

    • MicroStation user since IGDS!
    • InRoads user since TDP!
    • Dragged kicking and screaming into the world of Civil 3D, too!

  • In reply to caddcop:

    In the New Geometry tools to be released with Select Series 1, you can do this.  There is a reverse curve tool in which one of the lockble inputs is the tangent length. 

    Naturally, Radius1, Radius2 and Tangent length are interdependent and locking two of them will require that third adjust if the reference elements between which the reverse is built are parallel. 

    If the based elements are curved or non-parallel, then it might be possible to lock all three and still get a solution. 

    Robert Garrett
    Senior Product Engineer
    Bentley Systems Inc.

  • In reply to caddcop:

    Thanks y'all for the help.  I ended up using the "Free Curve" option that caddcop suggested.  I want to dive into the Multiple horizontal Element but just don't have the time.  I tried using it but didn't know what I was doing.  I'll have to read up on it in the Help

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