Slip Lanes are bypass lanes that join the entry to the next exit and are built off the outer edge of the travel way.
Slip lanes can only be created if:
Click Slip Lane in the left hand pane. The Slip Lane page is displayed.
Select Slip Lane to add a slip lane to your roundabout.
In the Lanes drop down, select either Single Slip Lane or Double Slip Lane.
The Overall Road Width set the road width for the slip lane.
The Inner Lane Width sets the width of the lane closest to the roundabout.
The Outer Lane Width applies when Double Slip Lane is selected and sets the width of the lane furthest from the roundabout.