Here is the latest information from Autodesk on their new Subassembly Composer:
This amazing tool will be a huge step in helping customers unleash the power of Civil 3D’s corridor modeling capabilities by giving the user the ability to easily create their own intelligent subassemblies. These real-world parametric BIM objects are the heart of the Civil 3D transportation design solution and access to project-specific subassemblies is a must for success. Beyond completely eliminating a common Civil 3D adoption barrier for transportation projects, Subassembly Composer for Civil 3D will also enable professionals working on other type projects such as levees, dams, breakwaters, tunnels, bridges, and retaining walls to begin to leverage a BIM-based workflow that is enabled via Civil 3D corridor models.
Key information to be aware of:
Available on subscription centre for Civil 3D subscribers (and any suites that include Civil 3D)
English only UI, but the tool can be installed with any language version of Civil 3D
Installation requires either Civil 3D 2011 or 2012
Content (subassemblies) created in the new tool can be used in Civil 3D 2011 or 2012
User assistance is available via Wiki help. (FYI - It’s our first Wiki for Civil 3D and we have high hopes that this will be a great way to expand and improve our user assistance perception and quality)
There are a number of videos on the web that demonstrate the tool. Dana Probert has a fun intro on YouTube that explains everything quite nicely.