How to Use Alignments to Design a Road in Civil 3D

Hi, I’m Charles Ellison. I’m a Civil 3D designer and trainer at autocadcivil3dtraining.com. Today we’ll be looking at how to use alignments to lay out a road design for residential development. Now, not only will we be finding out how alignments work, but we’ll gain an understanding of how they’re used to profile our existing grade, lay out the center line grade of our road, and use a road template to create a corridor surface. Now, I know many of these terms might seem overwhelming, but we’ll gain more confidence as we dive into it. So, let’s take a look.

So, let’s get right into it. You can see right here we’ve got our existing surface, which is listed right here as EG. we’ve got our existing contour shown from that. Then we also have an existing road. This is just 2D line work. There isn’t any 3D information assigned to any of this, so this is just an arbitrary road that I drew right here with a center line right here and the edge of the pavement. So, just real quick and dirty. Now, the next thing is before we actually get into alignments, we have to determine, okay, what are we actually using our alignments for? Our alignment for our road is the basis for our center line grade. When it comes to engineering you need to be able to set your center line grades for your road, and that’s the basis for your entire design, you know, when it comes to grading out to the gutter line, you know, determining your top of curb, and then grading out to your existing surface. So, let’s get started.

What I want you to do is I want you to go up to the alignment pull-down menu, click on that, and then click on alignment creation tools. We’ll get a little dialogue box here, and we need to name our alignment. I typically just name it our road, Maple Road. Everything looks good right here. Then click okay. Then we get this very overwhelming dialogue box, the alignment layout tools tab. Now, we’re only going to focus on two buttons on this dialogue box. So, what I want you to do is click on this drop-down menu on this button, and then click tangent to tangent, no curves. Now, for simplicity sake, I’m just going to draw in some arbitrary lines here, and I’m going to go perpendicular to the center line of my existing road. I’m going to press enter after doing that, and it automatically stations my alignment. Okay? Now, you can reverse the direction of these stations, but just for simplicity, we’re just going to leave that alone.

Next, I want you to click on this drop-down menu, next to this arc-like button, and then click on free curve fillet between two entities, and we’re going to give it a radius. We click on that, and then it asks us to click our first entity. We’re going to click right here and then the next right over here. We’re going to give a curve solution angle of less than 180. We’re going to stick with that. Then we’re going to type in our radius. We’re going to go with 200, and it fillets that nicely. Then we’re going to do that command again. Draw drop menu, click right here, first entity, next entity, less than 180. Then we’re going to put 50 instead of 200, but you know what? After I did that, you know what? This radius needs to be larger. How do I change that?

Well, if you click on the alignment itself, we get all these grips. Okay? Now, what I recommend that you do is to play around with them. See what happens when you click and drag and you have these things. Okay? It never hurts to play around. You’re not messing anything up by doing so. But what I’d like to do is I’d like to exit out of all this, undo what I just did. I want to go back to that 50-foot radius. I like that position, but I don’t like the radius. I’d like to change that. So, if I click on this arrow and I type in 200, it fillets that nicely with a 200-foot radius, and we’re also tying in tangent to our alignment. So, everything works out really, really nice.