About Creating Subassemblies
Add subassemblies to a drawing using the subassemblies provided through the Autodesk Civil 3D tool palette or tool catalog, or create your own custom subassemblies.
About Inserting Subassemblies on Right and Left Sides of a Corridor
Some subassemblies use a Side input parameter to specify inserting the subassembly on the right or left side of a corridor; other subassemblies allow you to do this by specifying a positive or negative value for the insertion point input parameter.