Expand an arm and click Approach in the left hand pane. The Approach page is displayed.
The Design Speed can affect the turning capabilities of the vehicle if you have limited turning by lock-to-lock time. At higher speeds, vehicles will not be able to negotiate tight turns.
The Central Gap Width is the distance between the offside definition lines of the approaching lanes and the departing lanes.
Deflection, (or center line offset) is the distance that the alignment is adjusted to the left or right of the zero deflection point. Zero deflection occurs when the alignment meets the ICD on a bearing that passed through the center of the roundel. Deflection is used to adjust drivers speed.
Arm Base Alignment Curve Type Two calculation modes are available for the adjusted alignment approaching the roundabout. With Arc mode a tangential arc is created off the existing road alignment arcing to the ICD, in Spline mode a spline is used to the same transition.
Select the number of Approaching Lanes and Departing Lanes from the drop down list.
The Approaching Lane Width and Departing Lane Width are measured between definition lines. On a road with no center gap, the offside definition line is the centerline.
The Crown Line Blend Offset is the point at which the entry and exit crown lines merge with the arm centerline and is measured along the alignment from the intersection with the ICD.
The entry and exit Crown Line Entry Offset is the lateral offset of the crown lines at entry (or exit) measured from the nearside curb as a percentage of the width.
In all cases the Max and Min values represent the limiting values from the adopted design standard.