Join Jeff Bartels for an in-depth discussion in this video Modeling an intersection, part 1: Approaches, part of Civil 3D Essential Training.
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- One thing that we know about roads is that they have to go somewhere. At some point, most every road design will need to connect to another road. Over the next couple of lessons, we'll look at a workflow for modeling intersections. This recording represents part one of the workflow. I'm gonna zoom in. Let me start by mentioning that Civil 3D has a tool that automates intersection creation and we'll look at that in just a little bit. The reason I'm showing you this manual method is because if you understand this, you can model anything you want. Let's take a quick tour. Here I have an existing surface called EG.
I have a pair of intersecting alignments. One's called Primary Street and the other one is called Second Street. I've already created finished grade profiles for these alignments. If we come over here we can see the finished grade profile for Primary Street and I have one for Second Street. Now when I created these finished grade profiles, it was important that the profiles intersect as well elevation wise. Let me show you how I did that. I'm gonna pan over. What I did was design the finished grade profile for Primary Street first.
Then when I was gonna create the finished grade profile for Secondary Street, I knew that I had to start at the same elevation as Primary Street. So, let's find that elevation. I'll do it by selecting the alignment and then I'll right-click, from the menu I'll choose inquiry. Let's close this for a second. When the inquiry tool comes up, I'll open the menu. We are automatically in the alignment group because I selected an alignment. I'm going to choose alignment station offset and profile elevation at point. That's what I'm looking for.
I'm interested in the Primary Street alignment. I'll select that and click okay. I would like to query the Primary Street finished grade profile so I'll select that and click okay. I will then come down and click this green box so I can pick a coordinate on screen and I'll grab the endpoint right here. If we look right down here, we can see the elevation of the finished grade profile for Primary Street is 798.71 in the area of the intersection. I'm gonna press escape. Let's pan this over. If we look right here, you can see that when I started my Second Street profile, I started at that same elevation.
So, we know our design intersects horizontally and vertically. Let me close the inquiry tool. We'll take a look at the assembly. I'm calling this full road section. I'm also using a simple daylight. I'm going to start by visualizing the lanes. I'm going to be using 12 foot pavement widths, that's what's defined in the assembly. To see that on screen, I'm going to launch the offset command and then I'll use a 12 foot offset. We'll offset the alignment up and down. We'll offset the other alignment to the left and right and I'll press escape.
Let's talk for a second about curb returns. I'd like to tie these pavements together with the radius of 25 feet so let's clean this up first. I'll launch the trim command and I'll select my geometry and press enter. I will then click to trim off the pieces I don't need and I'll press escape. I will then launch the fill it command. I'll come down and choose radius and I'll make sure that's set to 25 feet. I'll press enter and then I'll select these two objects. I'll press the space bar to go back into the command and I'll select these two objects.
So, this represents the geometry of my curb return. I'd like to keep these, although if I select this, you can see it's become one polyline now. Let me select both of them and then I'll come up and click explode and then I am going to select these tangent segments that I don't need and I'll press delete. This curb return geometry is going to be very important in just a second. Let's go ahead and create the corridor for Primary Street. I'll do that by clicking the corridor button. We'll call the corridor Primary Street.
I'm gonna be building it from the Primary Street alignment using the Primary Street finished grade profile. I'll be using the full road section assembly that uses daylighting so let's go ahead and target the existing ground surface. I'm gonna be running the assembly the entire length of the alignment so I don't need to see the dialogue box, I'll just come down and click okay. There's the corridor. As I look at this, I can see this typical section is perfect, nothing wrong with this until such time as I get down to the intersection area. Right here in the curb return is where the pavement starts pulling away so this part of the section isn't working.
Let's come down here. It also isn't working along here. As soon as I get outside the intersection, the typical section is perfect again, so my full section assembly that I'm using can model a lot of this, just the area of the intersection is where I have a problem. Let's create an assembly for this area. I'm gonna pan this over. When it comes right down to it, in the intersection, the left lane of the assembly is perfect, it's just the right lane I don't need. So, I'm gonna create a copy of this assembly. I'll come up and launch the copy command.
I'll select the assembly and the label and I'll press enter. I will then pick it up from a point on screen here and I'll pull it down and create a copy and I'll press escape. Now we'll make a few changes. I'm going to select everything here on the right side. I don't need that and I'll press delete, then we'll rename the assembly. I'll do that by selecting it. I'll come up and click the assembly properties icon and I'll call this half road section, I'll click okay, I'll press escape, and then we will edit the label as well.
I'll make this half road section and what I'll do now is split the corridor and we'll add the new assembly in the intersection area. We'll split the corridor by selecting it. I'll click the corridor properties icon and then here on the parameters tab, let me pull this over, we can see our baseline, here's the region where the assembly is copied. To split that I'm going to right-click and I'll choose split. This takes me into the drawing. We can see the jig there at my cursor. I would like to split the region at the endpoint of the curb return here and the endpoint of the curb return over here.
When I'm finished, I'll press enter. Let's slide this over. So, this region in the middle represents the area in the intersection. Let's click in the assembly field and I'll switch to the half road section in that area, I'll click okay, okay, and we'll rebuild the corridor. Let's back up and take a look. I'll press escape, this looks really good. At this point, I'm ready to start modeling Second Street. I'll do that by selecting corridor. We'll go back to corridor properties. Let me push this over, I'll collapse this up.
So we've got our main baseline. What if I was to create a baseline for Second Street? We can have more than one. I'll click the add baseline button. Now, what alignment do I want to use for that baseline? Let me open the menu, I want to use the Second Street alignment. I'll click okay, so now we have a new baseline. If I select that, we can see it on screen. What defines the baseline? Well, it's the alignment, that's what I just picked. Also the profile, let me choose click here and I'll select the finished grade Second Street profile for my baseline and I'll click okay.
What else do we need, we need a region. Let me right-click on this baseline and I'll choose add region, this is the area where the assembly is copied. I'm going to copy the full road section and I'll click okay. Let me slide this over. I'm gonna do one more thing. Remember the assembly targets a surface. Let's take the baseline, I'll click the ellipsis button here in the target column, and for this baseline I would like all of my daylight targets to target the existing ground surface. I'll click okay, and okay, and we'll rebuild the corridor.
I'll press escape, this looks good. As I look at this, I can see my typical section coming up to the intersection is perfect until such time as it meets the curb return. Let's fix this by changing the start station of the region such that it matches the curb return location. I'll do that by selecting the corridor. We'll go to corridor properties. Let's come down and find the region that we're working with. I will come over to the start station column and I'll click this icon. Since I don't know the exact station, by using this icon I can pick it on screen.
I'm going to select the endpoint right there. When I'm finished, I'll click okay and I'll rebuild the corridor. That looks really good. Let me show you a shortcut too. I adjusted the start station using the parameters dialogue box. Note if I select the corridor, we get a grip here at the end. Let me just pull this down a little and click. Notice I can use grips to edit these stations as well. Let me choose this grip and I'll pull it back to meet the endpoint of the curb return and I'll press escape. At this point, the bulk of our intersection model is finished.
The only thing left to model is these areas in the curb returns and we'll do that in our next lesson.
- Exploring the design data in drawings
- Creating, connecting, and grouping points
- Customizing label styles
- Defining existing ground surfaces
- Designing horizontal alignments
- Controlling alignment properties
- Creating profiles and profile views
- Sharing design data
- Creating and managing parcels
- Building assemblies
- Modeling advanced roadways
- Defining gravity-based pipe and pressure pipe networks
- Creating sections and section views
- Analyzing designs
- Generating plan sheets