Many Subassemblies are provided "in the box" with Civil 3D 2005. They consist of several different types of roadway segments that can be snapped together, similar to lego pieces, to create a roadway cross-section.
The different types of segments include:
Medians - Primarily for divided highways
Lanes - Used for driving surfaces
Urban - These include different curb, gutter, and sidewalk types
Shoulders - For paved shoulders
Daylight - Many daylighting scenario segments
Generic - Many multipurpose links
Rehab - For Overlay sections with Milling or Leveling options
Bridge and Rail - For bridge or rail visualizations
Subassemblies have built in logic that tells them how to react, and what to connect to, under different conditions.