Planar Rehab Corridor Between Gutters
Alan Gilbert of Autodesk explains that given the gutter lines on both sides of a centerline,
you can quickly create a straight graded roadway corridor that ignores a crown.
For example - maybe you must match an existing superelevated road.
from the Civil Imersion blog.
Alan's use of a vanila link subassembly to make a classic AOR subassembly do the work from the targeting is well worth understanding.
Civil 3D Assembly construction seems to often be a form of civil engineering design art.
Autodesk also provides some generic and more elaborate Rehab subassemblies you can also use.