About Approach Roads for Roundabouts

Before you can create a roundabout, you must create at least one alignment to represent an approach road.

This is the alignment to which an approach will be dynamically connected. If you change or move this base approach alignment, the roundabout approach is dynamically updated.

The Create Roundabout - Approach Roads dialog box provides parameters that let you define the approach road geometry. It creates three alignments that define the approach road. The following table lists the default naming convention that is used to name the approach road alignments. You can change the “Approach_” prefix to something that better suits your project’s needs. However, you cannot edit the “_EW_EDGE_LEFT” suffix during creation.

Approach Road Alignment	Alignment Name
alignment that defines the center of the approach road	Approach_EW
alignment that defines the left edge of the approach road	Approach_EW_EDGE_LEFT
alignment that defines the right edge of the approach road	Approach_EW_EDGE_RIGHT

Note: In the above example, “EW” in the alignment name identifies the alignment as the “East-West” alignment. This two-letter naming convention is based on the alignment direction, and not on the roundabout approach road direction. For example, NW is used for an alignment that runs from the north to the west, and so on.

These approach road alignments (1 = Approach_EW_EDGE_LEFT, 2 = Approach_EW, and 3 = Approach_EW_EDGE_RIGHT) are shown in the following illustration.

The island, construction triangle, and pavement markings on the approach road are constructed as polylines.