Efficient AutoCAD Civil 3D Cul-de-Sacs

Unfortunately, there is no Easy button in AutoCAD Civil 3D that makes adding cul-de-sacs to your corridors instantaneous. However, there are steps you can take that will help the process along.

Cul-de-sacs are usually modeled in corridors using an alignment created along the edge of pavement. Then you must create a surface profile, put it into profile view, then create a design profile for the alignment.

I find it easier to use a feature line instead. A feature line is one object that you can make dynamic to a surface and makes cul-de-sac work much more efficient.

Here is how it’s done.

1. Model your corridor all the way up to the corridor and create the corridor surface (be sure to add the surface boundary to your corridor).
2. Trace over the edge of pavement geometry with a polyline and overlap the corridor slightly at the polyline’s endpoints.
   
3. Use the Create Feature Lines from Objects command to turn the polyline into a feature line.
   
4. In the Create Feature Lines dialog, give the feature line a name that is easy to remember. Verify that the Assign Elevations checkbox is filled. Click OK to continue.
   
5. In the Assign Elevations dialog, choose the From Surface option and select the corridor surface. Also check the Relative Elevation to Surface option and verify that the relative elevation value is set to 0.00’. Click OK to finish.
   
6. Select the feature line and from the contextual ribbon tab, click Elevation Editor from the Edit Elevation panel.
   
7. In the Panorama on the Grading Elevation Editor tab, notice how the surface elevations have been assigned to the PIs of the overlapping segments. Click the Insert Elevation Point button and click on a location along the cul-de-sac feature line to insert a high point or low point.
   
8. Enter an elevation value in the Insert PVI dialog. Click OK to continue.
   
9. In the Panorama on the Grading Elevation Editor tab, hold down the shift key and click the second PI and then click the elevation point. Then click Flatten Grade or Elevations.
   
10. In the Flatten dialog, choose Constant Grade and click OK.
    
11. In the Elevation Editor, a continuous slope has been set along the selected range. Repeat steps 9-10 for the range between the elevation point and the second to the last PI to finish the vertical grading of the cul-de-sac.
    
12. Add the cul-de-sac to the corridor, select the corridor and click Add Baseline on the Modify Corridor panel of the contextual ribbon.
    
13. In the Create Corridor Baseline dialog, click the Feature Line option, then under Feature Line, select the cul-de-sac feature line. Click OK to continue.
    
14. With the corridor selected, click Add Regions on the Modify Region panel of the contextual ribbon.
    
15. Click over the feature line to select the baseline as prompted.
    
16. Then click the start and end station of the region as prompted. This will be at the edge of the adjacent region, not the endpoints of the feature line.
    
17. In the Create Corridor Region dialog, choose your curb return assembly.
    
18. In the Target Mapping dialog, choose the centerline road alignment and profile for this cul-de-sac as the width and elevation targets the lane subassembly. Be sure to configure any surface targets if needed. Click OK to finish.
    
19. Rebuild the corridor.
    

Taking the time to create alignments, profiles, and profile views for cul-de-sacs isn’t necessary for cul-de-sac modeling in our corridors because feature lines can serve as corridor base lines.  This relieves us of having to create a special profile view and maintain the geometry of both the alignment and profile in separate interfaces.  Also, with the ability of configuring a feature line’s PI points to remain relative to a surface, this ensures the start and end points of our cul-de-sacs never stray from our corridor surface which is a more efficient way to set up our corridor models.

 – Cyndy Davenport