Expand Roundel and click Dimensions in the left hand pane. The Dimensions page is displayed.
We anticipate that users will generally position their roundabout using the mouse. However if you’d prefer to enter coordinates manually, use the Location field.
The Centre 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.
The Inside Lane Offset is the gap between the edge of the roundel island (or the apron if one exists) and the innermost lane of the roundabout (i.e. from the road marking paint line marking the edge of the lane and the start of the apron).
In all cases, the Max and Min values represent the limiting values from the adopted design standard.
Select the number of Circulatory Lanes from the drop down list.
Enter the Lane Width for up to four lanes.
In all cases, the Max and Min values represent the limiting values from the adopted design standard.
The Circulatory Width is the total width of all the lanes (standards sometimes define max and min values).
The roundabout is set out using definition lines. The Kerb Offset is the distance from the definition line to the kerb. A positive distance means that the kerb is further from the centre of the roundabout than the definition line. The kerb offset applies to the outer roundabout kerb and all kerbs that merge with it.
The Outside Kerb Offset is the gap between the edge of the outermost lane and the kerb (i.e. from the road marking paint line marking the edge of the lane and the start of the kerb).
The Inscribed Circle Diameter is the diameter of the definition line that represents the outer limit of the outer kerb of the roundabout.