AutoCAD Civil 3D: Non-Compliant Intersections – Part 2

In the previous post, we created connected alignments for an intersection that did not qualify for the Intersection command. This post will walk you through creating an intersection out of connected alignments, i.e., a manual intersection. In the following steps, the regions below will be modeled.

Intersections are created from assembly sets. The geometry of the intersection will determine what type of assembly set is needed. There is usually an assembly describing the typical section be applied to the road:

Region 1

In this example, the primary roadway crown which is formed by the cross slopes of the left and right pavement sections will be maintained through the intersection. An assembly reflecting that will be used in Region 1. One side will be pavement only while the other side may have curb, sidewalk, shoulder or daylighting. This type of assembly is usually referred to as – Daylight Left or – Daylight Right depending on which side the daylight occurs.

Area 1 will require the definition of a baseline and a region. Remember that the definition of the baseline is the alignment and the associated profile where the assembly will be applied. There are already baselines defined in this corridor created by the Intersection tool that contain this alignment and profile, but my preference is to create a new baseline definition just for this intersection for organizational reasons.

Create Region 1 Baseline

1. Select the corridor.
2. On the contextual ribbon, click Add Baseline from the Modify Corridor panel.
   
3. In the Create Corridor Baseline dialog, with the Alignment and Profile option selected, select the centerline alignment of the primary road for this intersection. Click OK to continue.
   
4. In the Select a Profile dialog, select the finished grade profile for the centerline alignment. Click OK to finish.
   

Add Region 1

1. With corridor still selected, click Add Regions from the Modify Region panel on the contextual ribbon.
   
2. Hover over the centerline alignment to select the baseline. Notice the tooltip that says “multiple baselines”. Click on the centerline.
   
3. The Select a Baseline dialog opens because there are other baselines in this intersection containing this alignment and profile, but they were created for other intersections. In the Select a Baseline dialog, scroll down to the bottom of the baseline list. The most recently created will be at the bottom. Select the bottom baseline and click OK.
   
4. The command line prompts to select the start station for the region. The start station will coincide with the end point of the curb return radius along the offset alignment of the primary road. As a matter of fact, one could OSNAP to that point.
   
5. Next, the command line prompts to select the end station for the region which will coincide with the endpoint of the opposite curb return radius along the offset alignment of the primary road. Use an OSNAP here too.
   
6. In the Create Corridor Region dialog, select the appropriate assembly as discussed above. Click OK.
   
7. In the Object Name column of the Target Mapping dialog, click on next to Target Surface to select the existing surface for the daylight subassembly to target. The Pick a Surface dialog will open allowing you to do that. Click OK to continue.
   
8. The Widths and Slope targets could be configured to target the offset alignments and profiles in case of widening, but for this case we will proceed with no widening plans and click OK to close.
   
9. Rebuild the corridor and notice that Region 1 has been created.
   

Region 2

Region 2 requires a curb return assembly which will use the connected alignments and their profiles for the baseline. Because of this, the assembly is defined with the pavement on the left and the curb, sidewalk, shoulder, or daylighting on the right. This means that the direction of connected alignments must be running clockwise along the curb returns. Assigning a width to the pavement isn’t important since the pavement will be targeting other objects for width and slope.

Create Region 2 Baseline

1. Select the corridor.
2. On the contextual ribbon, click Add Baseline from the Modify Corridor panel.
   
3. In the Create Corridor Baseline dialog, with the Alignment and Profile option selected, select the connected alignment for the northeast curb return for this intersection. Click OK to continue.
   
4. In the Select a Profile dialog, accept the default presented for the finished grade alignment and click OK to finish.
   

Add Region 2

1. With corridor still selected, click Add Regions from the Modify Region panel on the contextual ribbon.
   
2. Hover over the connected alignment and click on the baseline.
   
3. The command line prompts to select the start station for the region. The start station will coincide with the start point of the curb return radius (remember that the connected alignment stationing is running clockwise). OSNAP to this point.
   
4. Next, the command line prompts to select the end station for the region which will coincide with the endpoint of the curb return radius. OSNAP to this point.
   
5. In the Create Corridor Region dialog, select the curb return assembly. Click OK.
   
6. In the Object Name column of the Target Mapping dialog, click on next to target surface to select the existing surface for the daylight subassembly as the target. The Pick a Surface dialog will open allowing you to do that. Click OK to continue.
   
7. In the Target Mapping dialog, click in the Object Name column next to Width Target to select the horizontal pavement targets.
   
8. In the Set Width or Offset Target dialog, select the primary road’s offset alignment that intersects the connected alignments and click Add. Then select the secondary road’s centerline alignment and click Add. Note that you can click on the green button to select them from the drawing. Click OK when done.
   
9. In the Target Mapping dialog, click in the Object Name column next to Outside Elevation Target to select the vertical pavement targets.
   
10. In the Set Slope or Elevation Target dialog, select the primary road’s offset alignment that intersects the connected alignments. You may opt to use the green button to select from the drawing. Once selected, select the profile and click Add. Repeat for the centerline of the secondary alignment.
    
11. In the Target Mapping dialog, click OK.
    
12. Rebuild the corridor and notice that Region 2 has been created. Region 2 is not finished. There is a gap in the region at the intersection of the primary road’s offset alignment and the secondary road’s centerline alignment. To fix this, we will add a section at this intersection point.
    
13. Hit Escape a few times to exit the Add Region command. With the corridor selected, on the contextual ribbon, click Add a Section on the Modify Corridor Sections panel.
    
14. The command line is prompting to select a baseline. Click on the baseline (connected alignment) for Region 2.
    
15. Use the intersection OSNAP to select the intersection of the primary road’s offset alignment and the secondary road’s centerline alignment. Press Enter to finish.
    
16. Notice the gap is now closed but to increase the precision of the corridor in this region, the frequency should be increased.
    
17. With the corridor selected, on the contextual ribbon, click Edit Frequency on the Modify Region panel.
    
18. Click inside the region.
    
19. In the Frequency to Apply Assemblies dialog, set Along Curves to By Curvature. Then set Mid-ordinate Distance to Define Curvature to 0.2. Click OK.
    
20. Rebuild the corridor to review the results.
    

Now it’s time to manually piece together Region 3…which will be a topic for another post.

There are times when intersections in our corridor do not meet the criteria for the intersection command to run. That’s when connected alignments can be used. Connected alignments will maintain dynamic relationships with their offset alignments which helps keep the corridor model in sync with centerline designs.

 – Cyndy Davenport