Expand Roundel and click Central Island in the left hand pane. The Island page is displayed.
We anticipate that users will generally position their roundabout using the mouse. However if you’d rather enter coordinates manually, use the Location field.
The Inscribed Circle Diameter is the diameter of the definition line that represents the outer limit of the roundabout. Note that if a curb offset has been defined then the actual curb will not coincide with the definition line.
The Center Island Diameter is the diameter of the island around which the vehicles turn. It does NOT include the apron or overrun area.
The Apron Diameter is the diameter of the overrun area.
The apron is often specified as a width so Apron Width just gives you an alternative way to enter its size.
In all cases, the Max and Min values represent the limiting values from the adopted design standard.