The technology preview Corridor Solids for AutoCAD Civil 3D 2012 has been available from the Autodesk Labs site. This allows Civil 3D users to create solids from corridor subassembly shapes that will span corridor regions. This is very helpful for better visualization of the 3d nature of corridors and for use in other products (i.e. Navisworks for construction timelining and clash detection).
Be sure to watch the videos on the page to get a good understanding of how to best use this preview.
BE BETTER!! ...do someone a solid.