In Autodesk Civil 3D 2005, corridor boundaries can be very useful for defining and displaying corridor surfaces.
The most important part is to define it properly. The trick is to pick each segment in the direction that you want them to connect.
Once a boundary is defined it is very useful to ask the software to verify that you defined a valid boundary. The software can also draw the boundary as it is defined on the screen. This can assist in reordering the segments or reversing their direction in order to make a valid boundary.