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 rather enter coordinates manually, use the Location field.
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.
The Inside Lane Offset is the gap between the edge of the roundel island (or the apron if one exists) and the inner most 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 Curb Offset is the distance from the definition line to the curb. A positive distance means that the curb is further from the center of the roundabout than the definition line. The curb offset applies to the outer roundabout curb and all curbs that merge with it.
The Outside Curb Offset is the gap between the edge of the outermost lane and the curb (i.e. from the road marking paint line marking the edge of the lane and the start of the curb).
The Inscribed Circle Diameter is the diameter of the definition line that represents the outer limit of the outer curb of the roundabout.