Create an Alignment with Curves from Line Segments
Chris Fugitt, author of the Civil 3D Reminders blog, details how to use the alignment by layout to take short line segments that make up a curve and turn it into a nice alignment curve in Civil 3D.
From the Chris' YouTube Channel.
Here's the Civil 3D Reminders blog link
Chris does the initial linear segment definitions By Object for the entire alignment in one pass - a powerful thing to know in Civil 3D.
Notice how newer versions of Civil 3D allow us to employ changes to Tangency Constraints to remove Best Fit data from the curves.
If you still get stuck, you can always employ LandXML out and in to remove the Best Fit data from the alignment definition.
This is a more common problem if you Best Fit an entire alignment or profile in Civil 3D.