Visibility sightlines are calculated automatically by AutoCAD Civil 3D 2018 if the standard you have selected includes them. Because roundabouts must typically be checked for many sightlines which would be confusing if they were displayed all at once, they may be displayed individually. The visibility tab displays the sightlines and allows you to select them for display.
Click Visibility Analysis in the left hand pane. The Sightlines page is displayed.
The sightlines are grouped by arm and circulatory area. Click the [+] to list all the sightlines for a given arm.
Select the sightlines that you wish to display and click Apply. There’s no need to close the properties dialog but you can if you wish.
Alternatively, you may wish to use the Next Sightline and Previous Sightline buttons on the toolbar or ribbon to display the sightlines in sequence.
The Next Region and Previous Region buttons allow you to display the currently selected sightlines but for the next or previous arm.
Use the Select All and Clear All buttons to select or clear all the checkboxes.
Click View to display the settings of the currently selected sightline. The Visibility Sightline definition dialog is displayed in read-only mode.