The Civil Side: Intersection Design Wizard How-To

November 30th, 2010

An intersection object created by the Intersection Wizard builds and manages various object data, including alignments, profiles, corridors, assemblies, subassemblies, and surfaces. In previous versions of AutoCAD Civil 3D, in order to create a simple intersection you would need a bare minimum of six alignments (one for each main road (two) and each curb return (four); six corresponding profiles; and at least two assemblies, one for main road and one for curb return intersection design).

The new intersection design wizard has streamlined the complicated process of intersection design. Not only does the wizard create an intersection object, but also gives you the ability to add the newly created intersection to an already generated corridor model or keep the intersection object as a standalone design alternative. Let's take a closer look!

What you will need to get started

To create a 3D intersection that includes a corridor, you will need to first create the road geometry (road centerline alignments and profiles) and existing ground surface in your drawing. Once these components exist in the drawing, you can proceed with using the Create Intersection wizard. The wizard prompts you to select the location in the drawing where the two road centerline alignments intersect.

You can start with the following data combinations:

  • two intersecting centerline alignments
  • two intersecting centerline alignments with one or more road edge offset alignments and or their profiles

You can have profiles already defined, or not. If profiles are not available, however, then features that are associated with 3D modeling will not be available on the wizard. For example, if you begin creating an intersection object with no profiles, then the following wizard options will not be available for selection: creating offset alignment and curb return profiles, as well as the ability to create a new corridor, or to add to an existing corridor in the intersection area.

With any of the scenarios just described, you can start the Create Intersection command, select the point where the centerline alignments intersect, and proceed with creating an intersection using the Create Intersection wizard.

Note: If you are creating a T-shaped (3-way) intersection, you must ensure that the alignments snap together precisely and do not overlap. If there is any overlap between the two alignments, a 4-way intersection will be created.

Where to find the Intersection Design Wizard

In AutoCAD Civil 3D 2010 located on your Home tab, Create Design Panel, Select the icon labeled Intersection (see below).

How do I use the Intersection Design Wizard?

You will then be prompted to select the exact point where your two alignments intersect and then select the "main road" alignment. This will be used to determine how the intersection is ultimately warped: are you going to hold crown for the main road or warp the entire intersection?

After making those two selections, your Create Intersection – General dialog box will appear where you are then prompted to give your intersection a name, description, marker, and label style and determine how the road is to be crowned (see below).

Click "Next."

Let's begin to explore the power and ease of use of the wizard by first checking the "Create or specify offset alignments" and select the Offset Parameters button (see below).

This will create your curb return alignments and then you can generate profiles in order to manipulate the design of your intersection as needed.

Next check the "Create curb return alignments" box and select the Curb Return Parameters button (see below).

Within this dialog box, you can specify the radius of EACH quadrant of the intersection separately. You can also choose to add a widening for incoming or outgoing lanes, if you happen to check these options highlighted at the top of the above screen capture, then you can specify how far of an offset and what the transition widening length is supposed to be per your design.

On the Create Intersection – Geometry Details dialog box, now you want to check the "Create offset and curb return profiles" box and select the Lane Slope Parameters button (see below).

Within the above dialog box you will have the ability to vary your cross fall from the centerline of your roadway design. You can chose to vary it with a constant cross fall of, say, 1.5 percent or link the cross fall to an already generated profile for vertical transitioning.

When you have completed the Intersection Lane Slope Parameters, select OK and NEXT to the Create Intersection – Geometry Details dialog box.

Above is the last step before AutoCAD Civil 3D will create your intersection object for you. At the top of the Create Intersection – Corridor Regions dialog box, you can first determine if you want to create a new corridor out of your intersection or if you want to add the data to an already created corridor model that you have run up to the start point of the intersection.

Next, if your corridor model has a daylight subassembly built into it, you can choose which surface object to which you wish to daylight. Finally, you can choose an already defined assembly set to use for your roadway design. If you have created all the necessary assemblies for your design, you can path them to the correct portion of the intersection and hit the "Save as a set…" button to make these assemblies in your drawing available for other intersection design projects.

Happy designing!

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About the Authors

Melanie Santer


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