Creating an Intersection with a Corridor (12:19 min)

Alignments, profiles and assemblies are not all you need to know when it comes to becoming efficient in designing roads. In this lesson, you’ll learn a few tips and tricks when it comes to corridor modeling – specifically creating an intersection within a corridor.

There are several methods to do this:

  • Manual: Add feature lines and/or alignments along the curb return, using grading objects or adding a feature line in the corridor.
  • Intersection Design Tool: A tool from the “Home” tab in Civil 3D.

How to create an intersection manually:

Before we begin:

In Civil 3D, we start with a feature line that has its elevation set based on the existing raod and going into the parking lot at about 1%. We also have a corridor that helps show the intersection is half of a road. We want to turn the two curb return polylines into a feature line and then grade the feature lines with an assembly into the corridor.

We’ll build the assembly first:

1. Select “Assembly” in the ribbon and choose “Create Assembly”.

2. Name the assembly and click “OK” (leave all of the default settings as is).

3. Place the assembly to the side.

4. Create a lane by using the “Tool Palettes” on the left and selecting “LaneSuperelevationAOR”.

5. In the “Properties” tab on the left, change the “Side” to “Left” and the “Width” to “2.00’”. Select the assembly to apply.

6. Add a curb by returning to the “Tool Palettes” on the left and clicking on the “Curbs” tab.

7. Choose “UrbanCurbGutterGeneral” and add that to the assembly.

Return to the model to turn our curb returns into feature lines:

1. Select “Feature Line” from the ribbon and click “Create Feature Line from Objects”.

2. Choose both yellow lines on the curb return (these are the edge of the asphalt).

3. Hit “Enter”.

4. A window titled “Create Feature Lines” will appear. Click the checkbox for “Style” and select “Basic Feature Line” in the drop-down menu.

5. Uncheck the box for “Erase existing entities” and check the box for “Assign elevations”.

6. Click “OK”.

7. A new window titled “Assign Elevations” will pop up. Assign the elevation based on the entrance road by selecting it from the drop-down menu.

8. Uncheck the box for “Insert intermediate grade break points”.

9. Click “OK”.

10. Select one of the curb returns and click on the “Quick Elevation Edit” tool. If you hover over the curb returns, you’ll see the elevations are set on both sides.

11. Click on one of the curb returns again and select the “Set Grade/Slope between Points” tool.

12. Choose the point where the curb return ties in with the road and drag the mouse all the way up the curb return. Set the slope to 1%.

13. Repeat steps 11 – 12 for the opposite curb return.

14. Now we can add this to our corridor. Select the corridor, right click and go to “Corridor Properties”.

15. A window titled “Corridor Properties” will appear. Select “Add Baseline” under the “Parameters” tab.

16. A new window titled “Create Corridor Baseline” will pop up. Under “Baseline Type” select “Feature line”.

17. Next to the “Feature line:” drop-down menu, click on the green icon so select the feature line from the screen.

18. Click on one of the curb returns, name it and click “OK”.

19. Hit “OK” in the “Create Corridor Baseline” box that will re-appear.

20. The “Corridor Properties” window will re-appear. Repeat steps 15 – 19 for the opposite curb return.

21. Now we need to add regions to each baseline that we just created. In the “Corridor Properties” window, right-click on one of the baselines as select “Add Region”.

22. In the “Assembly” drop-down menu, use the curb you created earlier. Click “OK”.

23. Repeat steps 21 – 22 for the other baseline.

24. Now we are going to change the starting station for each curb return. Click the “+” icon on the left of one of the baselines and click on the arrow icon in the “Start Station” section of that baseline.

25. Place the Start Station at the PC.

26. Repeat steps 24 – 25 for the other baseline.

27. A window titled “Corridor Properties – Rebuild” will appear. Click “Rebuild the corridor”.

28. In some cases, like this one, our curb return is backwards. To fix this, select one of the feature lines and click on the “Reverse” icon. Do this on both sides.

29. Now we’re going to change some frequencies. Click on the corridor and select “Edit Targets” from the top.

30. Click on “Edit Frequency” in the ribbon and click on one of the curb returns.

31. A window titled “Frequency to Apply Assemblies” will appear. Change “Along tangents” and “Curve increment” to “2.5’”. Click “OK”.

32. Repeat steps 29 – 31 for the other curb return.

33. Now let’s target width. Select the corridor and choose “Edit Targets”.

34. Click within the region of that corridor.

35. A window titled “Target Mapping” will appear. Add a “Width Target” by clicking on “<NONE>” and selecting “Feature lines, survey figures and polylines” in the drop-down menu.

36. Click “Select from drawing” and click on the center of the intersection road.

37. A window titled “Target Mapping – Target to Feature Lines” will pop up. Select “Name the feature lines using the default name template”.

38. Go back to the “Target Mapping” window and add another “Width Target” but select “Alignment” instead of “Feature lines, survey figures and polylines.”

39. You can pick the alignment from the screen by clicking the green icon or choosing it from the drop-down list in the window.

40. Click “Add>>” and then “OK”.

41. Back in the “Target Mapping” window, add an elevation target by clicking on “<NONE>” next to “Outside Elevation Target”.

42. In the “Set Slope or Elevation Target” window that appears, click “Select from drawing”, select elevation target on the drawing and click “OK”.

43. Now select the alignment from the drawing by choosing “Profile” from the drop-down menu at the top of the “Set Slope or Elevation Target” window and adding your profile.

44. To do the same to the opposite corridor, select the corridor and click on “Match Parameters” from the “Modify Region”.

45. Match the corridor we just targeted to the opposite corridor and hit “Enter”.

How to use the Intersection Tool:

1. Under the “Home” tab, select “Intersections” and then click “Create Intersection”.

2. Select the intersection point.

3. A window titled “Create Intersection – General” will appear. For this example, leave the settings as the default settings, but change the “Intersection corridor type” to “Primary Road Crown Maintained”.

4. Select “Next”.

5. In the next window, “Geometry Details”, select “Offset Parameters”.

6. Change the left and right offset parameters on the primary road to 20’.

7. Change the left and right offset parameters for the secondary road to 14’.

8. Select “OK”.

9. Back in the “Geometry Details” window, select “Curb Return Parameters”.

10. Select the quadrant (in our example, we chose the southeast quadrant) and check the box for “Widen turn lane for incoming road”. In this case, we’re going to leave the default settings as they are. Hit “OK”.

  • You can also modify the settings for the “Lane Slope Parameters” and the “Curb Return Profile Parameters”. For our example, we’re not going to change any of the default settings.

11. Back in the “Create Intersection” window, select “Corridor Regions” on the left.

12. In “Corridor Regions” you have the option of creating a new corridor or adding an existing one. In our example, we’re creating a new one.

13. Under “Select assembly set to import”, if you have a pre-set list already, you can re-use those. If not, the items on the list give you options of different assemblies and where it’s going to be applied to. For this example, select “Primary Road Full Section” and hit “Create Interesction”.

14. This will quickly generate the corridor with alignments, profiles, widening and all of the information associated with that.

This may be a lot of information to manage, but if you go to “Corridor Properties”, the corridor information will appear in a pop-up window. This is a lot of information created easily and quickly, helping you avoid losing time by doing it manually.