Civil 3D: Build a partial Intersection manually

February 22, 2023 Simmie Graves

The site requires an access driveway to a parking lot.  This is a short driveway with different radii for the curb returns.  The west side will use a 35ft radius and the east side will use a 50’ radius.  The corridor will need to be split in multiple areas to accomplish the desired model.

This method is effective when you want to match at the edge of an existing road.

  1. Develop your assemblies for the primary corridor and the curb returns. 
    1. You will need the subassemblies that are dynamic so the pavement sections can use targets.
    2. Use the daylight subassembly from the basic road assembly.


  1. Establish Corridor control lines (I prefer to use feature lines for this purpose, but you can use alignments and profile definitions).  You’ll create feature lines for the following entites:
  • Edge of travelways (South edge of the East/West road, West and East edges of driveway).
  • Centerline of Road / Driveways
  • Curb Returns


  1. Create the primary corridor from the base Centerline.

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  1. Extract ETW feature lines from each side of the corridor.  Make sure that the Dynamic Link is Unchecked.


  1. Let’s build the NE portion:

Add a baseline to the Corridor.

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  1. Select the feature line on the NE side.

  1. Next, Select the Baseline, right click and select add region:

  1. Set the start station for the Region.  For the NE side. The start of the region is Station 0+15.03
    1. Select the Curb Return assembly for the region
  2. Set the targets:
    1. EG1 for the Surface.
    2. Select the Edge of Travel ways for both the width and elevation targets (these will be the same 2 feature lines for both targets).

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  1. When you close the dialog box, rebuild the corridor.
  2. Split the Driveway Corridor for the West side at the beginning of curve.  The station is: 0+28.06'

  1. Modify the assemblies for the Driveway Corridor.
  • Right side, the full Roadway Assembly with Daylights are used from Station 0+00 to 0+15.03. Target the surface EG1 for Right and Left sides.

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  • Left side, the Assembly will use the Daylights from Station 0+15.03 to 0+28.06 Only target the left side surface EG1

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  • From 0+28.06 to 0+63.09 do not target the existing surface.  The corridor will produce the results shown below:

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NE Quadrant of intersection completed (Shown below):


  1. Repeat the steps above to add a baseline and region for the NW Quadrant.

The completed corridor is shown below:

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The Parameters for the completed corridor are shown below:

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  1. The final edit is to modify the Roadway section where the South edge of the corridor meets the parking lot feature line.  We want the First Section (0+00) assembly template slope to match the parking lot.

  1. Open the Section Editor In the Modify Corridor Sections.

  1. Go to Station 0+00 and set the default slope for that station to 0%.  This will flatten the driveway to match the parking lot slope.


  1. The custom (partial) intersection is complete.  The surface created from this corridor can be composited into the parking lot grading surface.

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Final Corridor for the North Driveway.

About the Author

Simmie Graves

Infrastructure Applications Expert<br><br>Simmie has diverse experience in Civil Engineering design and Survey Mapping support since 1979. He has been involved in key projects from Civil Site, Subdivision, Rail Transit, Airports, Highway, Utility Infrastructure, and Utility Scale Solar Farm site layouts. His start with a small surveying firm as a drafter in Oakland, CA provided a good base for transitioning and becoming a designer / engineering technician utilizing Computer Aided Design software. He quickly learned proprietary computer engineering systems such as Wang – Holguin, Vango and MS Dos based AutoCAD which transitioned from SoftDesk to Land Development Desktop to Civil 3D. <br><br> Simmie has a solutions-based focus that has served his clients very well. The vast majority of projects he has been involved in have been permitted and built.

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