Getting a Sense of Assembly Sets

Part of your AutoCAD Civil 3D customization should consist of assembly sets. Assembly sets are used to create intersections. If created ahead of time, roadway modeling can be expedited. But what are assembly sets?

AutoCAD Civil 3D uses each member of the assembly set to create the regions of the intersection corridor.

To understand assembly sets, we must first identify the characteristics of an intersection that influence assembly sets.

• The Intersection command in AutoCAD Civil 3D recognizes 3-way or 4-way intersections composed of two alignments:
  • Main – the alignment with the governing centerline profile (crown).
  • Side – the alignment that will inherit some of its vertical geometry from the profile of the main alignment.
  • (Note: In versions prior to AutoCAD Civil 3D 2023, Main is referred to as Primary, and Side referred to as Secondary).
• The intersection alignments can form right angles or acute angles.
  
• There are two types of intersections:
  • Primary (main) road crown maintained – maintains the pavement section of the Main alignment forcing the side alignment profile to revise and “shrink wrap” over the top of the Main alignment pavement. Primary syntax remains in alignment type name in 2023.
  • All crowns maintained – maintains the crown elevation of the Main alignment at the point of intersection revising the crown elevation of the side alignment to adhere to Main profile at the point of intersection.

The type of intersection used, the type of angle formed at the intersection of the alignments, and the number of intersecting roadways entering the intersection determine what assemblies compose the assembly set. There are basically ten types of assemblies in an assembly set.

• CurbReturnSection – Used in every intersection regardless of the characteristics. The assembly baseline coincides with the edge of pavement and the opposite edge of pavement will tie into the side road profile and either the main road profile or edge of pavement, depending on the intersection type.
  
• ThroughRoad – Used in intersection type Primary Road Crown Maintained, 4-way intersection. The assembly represents the pavement only of the main road in the intersection between the outer end points of the curb returns. There are no incidentals (curb, sidewalk, daylighting, etc) on the left and right sides.
  
• MainRoadTypicalSection and SideRoadTypicalSection – Used in every intersection regardless of the characteristics. Both assemblies represent the full section of the main or side road entering the intersect from both directions. These assemblies can be the same assembly regardless of pavement width.
  
• MainRoadFullSectionDayLightLeft and MainRoadFullSectionDayLightRight – Used in intersection type Primary Road Crown Maintained on 3-way at right and acute angles, and 4-way intersections at acute angles. This is a full section without incidentals on the opposite side referred to in the assembly type.
  
• MainRoadHalfSectionDayLightLeft and MainRoadHalfSectionDayLightRight – Used in intersection type All Crowns Maintained on 3-way at right and acute angles, and 4-way intersections at acute angles. This is half of a full section with incidentals representing the side referred to in the assembly type.
  
• SideRoadHalfSectionDayLightLeft and SideRoadTypicalSectionDayLightRight – Used in both types of intersections with right and acute angles, 3-way, and 4-way. This is half of a full section with incidentals representing the side referred to in the assembly type. These assemblies can be the same assemblies used in MainRoadHalfSectionDayLight version regardless of pavement width.

Assembly sets can represent typical sections particular to a municipality or development type. When these assembly sets are created ahead of time and placed in a central location, each designer can proceed with intersection creation without having to construct these tools from scratch each time a roadway design is started.

– Cyndy Davenport