Autodesk Labs, which provides access to previews of new technology, has made available "Bridge Modeler for AutoCAD Civil 3D 2010". This preview add-on can be installed on Civil 3D 2010 and Civil 2010.
The overview states:
"Bridge Modeler for AutoCAD Civil 3D 2010 is a Civil 3D add-in module which can create simplified bridges directly from a Civil 3D corridor object. It is a technology preview project at Autodesk Labs derived from a subset of Bridge Extension for Revit Structure 2010, a part of Subscription Advantage Pack 2010, which provides more robust bridge modeling capability and works with Bridge Modeler for AutoCAD Civil 3D 2010.
With this add-on, Highway Engineers and Bridge Engineers are treated separately to assume requirements for design practice and preference of technologies. For more information, see the Getting Started Guide (PDF).
The Bridge Modeler for AutoCAD Civil 3D expires on March 15, 2010."
The intention of a technology preview is for anyone, that wishes, to use the technology and provide feedback to help shape how it evolves.
Be Better! ...build bridges whenever possible.