So, the other day, I was reading one of the discussion groups when I saw a post asking if a vertical curve could be created at the start of the profile without having to have a tiny little piece of tangent at the beginning. Someone responded back that you couldn’t do this and you had to have a little tangent piece between them. That seems to be a very common misconception about vertical curves. Read on to find out how to do this.

First off, how do you create a vertical curve at the beginning of your profile? Well, use one of the Fixed Vertical Curve options:

Fixed Vertical Curve Options

These curves do not need to be connected to anything in order to create them and they act very similar to the fixed curves in alignments. If you attach something to a fixed alignment curve, such as a free tangent between two curves, the curves will lengthen and shorten as needed. Profile curves will do basically the same (the few I’ve tested will shorten but won’t lengthen beyond how they were defined).

In the following example, I have three curves, the first curve is a Fixed Vertical Curve (Two points, grade at start point), the last vertical curve is a Fixed Vertical Curve (Three points), and the middle curve, which forms a double reverse curve, is a Free Vertical Curve (Parameter).

Profile with Curves Only

In this example, the fixed curves where made first, and then the free curve was placed between them. In the entity editor displayed in the panorama, there are no tangent lines, only curves. You can also, instead of placing a free curve between the fixed curves, place a tangent between them.

Free Tangent Between Two Fixed Curves

If you’re the type to read this blog, then you are probably also the type that likes to experiment with Civil 3D so, try some of this. Place a couple fixed curves and then put a free curve between them. Or, how about the floating curves and lines? Create a fixed curve, float another curve off it, float a line of the floating curve…

Fixed and Floating Curves and Tangents

I can see these fixed curves being very useful for roadway reconstruction. There is an existing curve at the beginning on the end of my project and I need to maintain the current geometry of that curve and tie my new design into it. Now get out there and design some exciting things!