Click Arm in the left hand pane. The Arm page is displayed.
The direction of the arm is shown in the Direction field. This is shown for convenience and is determined automatically from the whole circle bearing of the arm.
Enter a Name, Description and/or Notes for the roundabout arm.
AutoCAD Civil 3D 2018 works out which end of each of the picked arm centerlines is closest to the center of the roundabout and therefore the most logical direction of the road.
Click the + symbol to expand the Arm element.