Assemblies and corridors
A corridor sweeps a typical cross-section (the assembly) along an alignment and profile to create a 3D road. It’s the heart of road design in Civil 3D.
In this lesson you will
- Build an assembly from subassemblies
- Create a corridor and control frequency
- Use targets for widening and daylight
- Create corridor surfaces and sample cross sections
Assemblies
An assembly is the typical cross-section: lanes, kerbs, footpaths, verges and daylight (the batter slope that ties the design into existing ground). It's made of subassemblies from the Tool Palettes (e.g. LaneSuperelevationAOR, UrbanCurbGutterGeneral, DaylightGeneral), each with parameters such as width, slope and depth.
Creating a corridor
- 1Home › Assembly › Create Assembly; add subassemblies on each side of the marker.
- 2Home › Corridor; choose the alignment, design profile and assembly.
- 3Set targets: the EG surface for daylight.
- 4Set frequency (e.g. every 10 m on tangents, more on curves).
- 5Build the corridor and inspect it in 3D and with the Section Editor.
Targets
Targets let subassemblies follow other geometry: a lane's edge can target an offset alignment or polyline to widen at an intersection or a bus bay; a kerb elevation can target a profile. Daylight targets the existing surface so batters find the ground wherever it is.
Corridor surfaces and sections
Create a corridor surface from links (e.g. Top or Datum) with an automatic boundary — the finished design surface. Sample lines along the alignment produce section views for each chainage, used for cross-section sheets and for earthwork volumes.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| Create Assembly | Home › Assembly | New typical section |
| Corridor | Home tab | Builds a corridor |
| Section Editor | Corridor contextual tab | Reviews/edits sections along the corridor |
| Sample Lines | Home › Sample Lines | Defines cross-section locations |
Common mistakes
Daylight doesn't reach the ground.
Set the daylight target to the EG surface and check the surface covers the area.
Jagged corridor on curves.
Increase frequency along curves.
Exercise
A two-lane road
- Build an assembly: 3.5 m lanes at -3%, kerb and gutter, 1.5 m footpath, daylight 1:3 cut / 1:4 fill.
- Create the corridor along your alignment and profile with EG as the daylight target.
- Create a corridor top surface.
- Create sample lines every 20 m and section views.
You should end up with: A 3D road model with sections.
Checklist
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Lesson quiz
What is an assembly?
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