Not only does it not apply the filter, the output is wildly incorrect. (which is a good thing, since i might not have noticed otherwise)
To extract one or more feature lines from the corridor select the corridor. On the context sensitive ribbon, Launch Pad panel, select Feature Lines [from] Corridor. The command line prompts you to select the Corridor feature line you would like to extract.In the Edit Feature Line Curve dialog box, edit the curve. Use the Radius edit box to specify the radius. Use the Maintain Tangency option to control the curve tangency state. The curve is highlighted and the arc start, center and end points are displayed with glyphs.
Editing Civil 3D Feature Line Geometry using "Fit Curve" and "Smooth" Feature lines represent one of the major components of a Civil 3D design. They can be used to define both existing and proposed 3D elements. Things like centerlines, edges of pavement, curb & gutter, breaklines, retaining walls, flow lines, etc.