Intersections in AutoCAD Civil 3D take a bit of time to get used to until they become second nature. Then when that happens, we find ourselves going all out creating assembly sets for each design scenario and municipality so that we are ready for anything. Then we are derailed when the Intersection command will not work in our real-world scenario. Alignments that intersect themselves, alignments with more than one intersection that alternate between the primary and secondary roles, or even intersections involving three alignments are scenarios where the intersection tool will not work. These situations are quite frustrating, especially since we’ve been asking for a solution for eons. And the only workaround is to create the intersection manually which is fun and ambitious but a lousy way to burn time.
Autodesk in their infinite generosity, rather than “reimagining” or “reinventing” the intersection tool, has given us a work around: Connected Alignments. A better way to refer to a connected alignment would be to call it a connected curb return. It is a tool for creating curb returns that are dynamic to offset alignments.
So, let’s walk through how a connected alignment works.
Let me introduce you to my data set. 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”. 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. As you can see below, 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. So, would the issue be that it cannot be primary in two intersections while being secondary in others? As a test, I deleted Road B’s only primary intersection to see if the last one would create. It didn’t work, but let’s get back to discussing connected alignments and how they will help complete this roadway model.
- The first step is to create offset alignments for Road B and Road D.
- In the Create Offset Alignments dialog, create one offset on both sides and limit the station range to the vicinity of the alignment. We will not be using any widening criteria or design check sets, but we will be creating profiles along the offsets at a 2% cross slope from the centerline.
The nice thing about working with the offset alignments and profiles is that they are dynamically linked to the horizontal geometry of the centerline alignment and the vertical geometry of the centerline profile. Any changes between the relationship of the offsets to their centerlines can be entered into their properties dialog.
- With the offset alignments created, create the connected alignments for each curb return.
- Civil 3D prompts to select the offset alignments for this connected curb return alignment to attach to. Curb return alignments should run in a clockwise direction so remember to select the offset alignments in that order. Next, the prompt says to pick the location for the connected alignment.
- The Create Connected Alignment dialog appears. For this scenario, no design criteria will be used. Enter the curve radius parameter and fill the check box to create a profile for the connected alignment.
- Now that the alignments have been created, it’s time to manually piece together the regions and targets for this intersection in the order depicted below…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