Leveraging Corridors and Feature Lines Within Civil 3D

Over the past few releases of AutoCAD Civil 3D there has been a lot of emphasis on Corridor modeling, corridor modeling techniques and advanced modeling workflows.  Much of this is because of Department of Transportation’s getting deeper into Civil 3D workflows and larger companies pushing for things to behave a certain way.  But even for those doing “simple” site plans and subdivision roads, Civil 3D has a great way to increase your productivity and help streamline your workflows.

This article helps you walk through a couple scenarios of when you could possibly use feature lines in your corridor modeling.  If you would like the data used for this article, please email me and I will send the files.


In addition to alignments and profiles, feature lines now can be used as corridor baselines. This change was made in 2018, I believe.  Feature lines can also be selected when creating the corridor and when adding baselines.

A parking lot is a good example of where to apply this new workflow.  When I design a parking lot, I typically design the edge of pavement in order to see true slopes of asphalt. I then use the stepped offset command to give me flow line and/or back of curb elevations, and sometimes I may use grading objects to keep some level of dynamics.  But now you can add the feature line to a corridor along with a curb & gutter assembly and have a much more dynamic and accurate surface.

An intersection is also a great example of using feature lines within your corridor model. Many people use feature lines for intersections, but up until now it was more of a manual process and not very dynamic.  Extracting and targeting these feature lines is very simple and easy to use in corridor modeling.

The functionality of extracting feature lines, and keeping them dynamic, has been in Civil 3D for as long as I can remember.  However, this functionality has now been enhanced with many new options.  The options for selecting which feature lines to extract include:

  • Extract all feature lines at once
  • Select them one by one
  • Define Station Range
  • Select a subset based on a corridor region or a simple polyline

By selecting a polyline, you will then be given the option on which feature lines to include/exclude for the extraction procedure.  Select the settings option to choose whether or not to dynamically link them to the corridor.  You can choose to add them to a site, or now use the “Siteless” feature line options.


We will need to create an assembly for our curb & gutter. We will use this assembly for both examples. This will typically be a simple assembly and can even be a copy/modification of your corridors full assembly. Below is a screenshot of what I will be using:


Yes, we could use the intersection tool to create this, but sometimes that just does not accomplish what we want it to do. Sometimes you need just a bit more control, and feature lines will allow you to do so.

Let’s take a 4-way intersection for example. I first start with extracting the centerline feature lines as a dynamic link to either my profile or corridor. In this case I chose to use my FG profile as the feature to extract a feature line f rom (We will keep both crowns maintained).

1. From the Home tab > Create Design panel > Feature Line drop-down > Create Feature Lines f rom Alignment

2. Select your alignment, then select the profile you wish to dynamically link to. You will then have a dynamic feature line, therefore when your Alignment and/or Profile changes, your feature line does as well.

3. Create your feature lines along the Lip of Gutter (Edge of Asphalt) using either a polyline and create f rom objects command, or manually draw in your feature line.

4. Set the grades as you would like along that feature line. For this example, I will assume you know how to do so.

The example I am using would look something like this. The corridor has already been started, with gaps for the intersection area to be modeled.

Once we have our assembly created and our feature lines in place, we are ready to begin modeling the intersection.

5. Select the Corridor, go into your Corridor Properties and select the Parameters tab.

6. From the Parameters tab, select ADD BASELINE. The Create Corridor Baseline dialog box will appear, select FEATURE LINE from the Baseline type.

7. Use the icon next to the Feature Line dropdown to select your feature line from the screen.Once selected, you may be prompted to name the feature line, I chose to name mine NW Quad INT 1. Select OK.

8. The Baseline is now added to your corridor and we need to add the region and select the assembly.

9. Right click on the new baseline and select ADD REGION.

10. Choose your assembly and select OK. Rebuild corridor if needed.

This will no put in the assembly along that feature line. And no need to do a stepped offset!!  Pretty good so far, right?  Let’s finish up the intersection quadrant by targeting our centerline feature lines for width and elevation.  I use the contextual ribbon for some very useful shortcuts. Use these to really speed up your corridor modeling workflows!

11. Select your corridor from the screen.

12. From the contextual ribbon for said corridor, select EDIT TARGETS from the Modify Region panel.

13. Select within the region for the intersection.The Target Mapping dialog box will appear.

14. We first will select the targets to set our Width.Select NONE next to Width Target for the asphalt portion.

15. Set the object type to FEATURE LINES, SURVEY FIGURES AND POLYLINES.Then select both centerline feature lines from the screen.

16. Select OK.

17. We now need to select the same feature lines for the Outside Elevation Target. Select NONE next to Outside Elevation Target and follow the same steps as outlined about for setting width targets.

18. Select OK to exit the Target Mapping dialog box and Select OK to complete the Corridor edits.

Repeat all the about for each intersection. Remember to use your contextual ribbon to assist.  There is a MATCH PARAMETERS command that is very helpful in this case. This will allow you to set similar targets without going through all the same steps.

Your resulting intersection should look something like this.  You may need to reverse feature lines from time to time as well, keep that in mind.


This is a question I probably get at least once a month... "Should I use corridors for parking lots?”. Before now, in order to corridor a parking lot, you would end up with numerous alignments, profiles, assemblies, etc. And it just was not worth the hassle of managing all that data, and a lot of times resulted in a lot of re-work.

Now, for parking lots of any shape and size, you can simply add each feature line to the corridor as a baseline (not separate corridors) and apply the correct assembly. You also get the extended data a corridor offers with different materials and surface, something that cannot easily be done with just feature lines and stepped offsets. The workflows are practically the same as I outlined within the intersection example, so I will not repeat everything, but a quick outline of this new workflow is below:

1. Add features lines to corridor as a baseline and apply the assembly.

2. Repeat as needed for all curbing.

3. After the first couple are in place, create a surface f rom your corridor model for the finished grade.

4. As you add additional baselines, you can see your parking lot take shape! You can allow the surface to tin f rom island to island, or even target using an asphalt subassembly.

5. If the surface/corridor seems to be upside down, you simply need to select the feature line and use the reverse tool f rom the contextual ribbon.

6. One common issue in corridor modeling is inside and outside corners. Avoiding “bowties” and “non-mitered” issues have always been painful. Inspect some of the island and parking areas to see how Civil 3D has now fixed the majority of those issues!

Try this on your next site design to really see the benefit of using corridors in this situation. I would love to see your final product!


There are many ways to model a corridor and corridor intersection. Some like to create alignments and profiles, some like to use the intersection tool and modify f rom there and some just ignore the intersection (I have time to time). It was my attempt to display a workflow that you may try and see if it fits your needs. So hopefully this gives you a little direction to at least give the feature line as baseline a shot within your Corridor Modeling workflows.

As always, I am interested to hear what you think and see how we can improve upon this topic.

Good luck and Happy Modeling!!

Shawn has been a part of the design engineering community for roughly 15 years in all aspects of design, construction, and software implementations. He has implemented and trained companies across the Country on Civil 3D and other inf rastructure tools and their best practice workflows. Shawn can be reached for comments or questions at

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