This is the last entry in the three-part blog of the same title and over this series, the focus has been on how to create intersections when the Intersection command in AutoCAD Civil 3D rejects your intersecting alignments and throws you back to the command line.
Let me introduce you to my data set once again. I successfully defined all my intersections until I reached the last one in my data set which is the one labeled in the image below as “circular dependency” (Road B and Road D). The troubling thing about this is that Autodesk tells us that we cannot use one alignment as a primary in one intersection and as a secondary in another even though Road B, which is secondary in two intersections and primary in one, doesn’t have a problem. Road A is also secondary in two intersections and primary in one.
In Non-Compliant Intersections – Part 1, we discussed how connected alignments are actually manually created curb return alignments that connect to offset alignments and maintain a horizontal and vertical dependency to them. We created the connected alignments and started to piece together our intersection manually.
In Non-Compliant Intersections – Part 2, we discussed how to build the northeast quadrant region.
In this post we will complete the southeast quadrant region and finish off the intersection, highlighted in pink in the image below.
To create the southeast quadrant, we repeat the steps for creating Region 2 in the previous blog.
Create Region 3 Baseline
- Select the corridor.
- On the contextual ribbon, click Add Baseline from the Modify Corridor panel.
- In the Create Corridor Baseline dialog, with the Alignment and Profile option selected, select the connected alignment for the southeast curb return for this intersection. Click OK to continue.
- In the Select a Profile dialog, accept the default presented for the finished grade alignment and click OK to finish.
Add Region 3
- With corridor still selected, click Add Regions from the Modify Region panel on the contextual ribbon.
- Hover over the connected alignment and click on the baseline.
- 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.
- Next, the command line prompts to select the end station for the region which will not be at the endpoint of the curb return radius as it was for Region 2. When we created the offset alignment, we specified a 25’ overlap. This will cause the curb return alignment to extend past the endpoints of the radius by 25’. Since this intersection does not occur at a perfect 90°, both left and right curb returns are not symmetrical and if we created this region using the end points of the curb return, a gap would present itself. The intersection command would normally fill this gap with another region, but we can fill this in now in Region 3 using the intersection point of the connected alignment and the edge of the full section of Road D. OSNAP to this point.
- In the Create Corridor Region dialog, select the curb return assembly. Click OK.
- In the Object Name column of the Target Mapping dialog, click on <None> 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.
- In the Target Mapping dialog, click <None> in the Object Name column next to Width Target to select the horizontal pavement targets.
- 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.
- In the Target Mapping dialog, click <None> in the Object Name column next to Outside Elevation Target to select the vertical pavement targets.
- 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.
- In the Target Mapping dialog, click OK.
- Rebuild the corridor and notice that Region 3 has been created and is a gap in the region at the intersection of the primary road’s offset alignment and the secondary road’s centerline alignment; as it was for Region 2. To fix this, we will add a section at this intersection point.
- 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.
- The command line is prompting to select a baseline. Click on the baseline (connected alignment) for Region 2.
- 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.
- Notice the gap is now closed but to increase the precision of the corridor in this region, the frequency should be increased.
- With the corridor selected, on the contextual ribbon, click Edit Frequency on the Modify Region panel.
- Click inside the region.
- In the Frequency to Apply Assemblies dialog, set Along Curves to By Curvature. Then set Mid-ordinate Distance to Define Curvature to 2. Click OK.
- Rebuild the corridor to review the results.
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. Although it takes a little longer to manually build this type of intersection, in the long run, having a dynamic model will help us keep other elements of the design up-to-date.
– Cyndy Davenport