Using the Civil 3D 2016 Extract Corridor Feature Lines Tool
How to Use the Civil 3D 2016 Extract Corridor Feature Lines Tool
A video from a Jeff Bartel's YouTube channel see the Autodesk Civil Immersion blog.
Since the C3D 2013 Productivity Pack is included in Civil 3D 2017 this is also listed and a new feature in 2017.
Jeff does a better or more detailed job of showing how it works here. You will say "ooooo" at the interactive border section.
If you deal with grading interaction issues and complex corridors this tool is better than hot sliced bread, butter, and wild clover honey.
Spend a little time and invest in a proper Code Set Style. That helps you from being overwhelmed. See the Flines Only one in InstantOn.