Roundabout Standard Editor: Arm Geometry: Splitter Island

Expand Arm Geometry and click on the Splitter Island tab.

The splitter island page is divided into three identical areas that relate to each of the three sides of the splitter island and a fourth that relates to the fillet radii.

The Island Length is the length of the splitter island from the point at which the approach centerline intersects the ICD to the approach fillet radius.

The Curb Radius is set by default to Tracking. This means that it is offset from the splitter definition line and that the offset changes linearly from the inner offset to the outer offset. If you wish to specify a fixed default radius then enter a value.

Note: If the end offsets are equal then the curb radius is a circular arc concentric with the splitter definition line.

The Inner Offset is the distance by which the splitter island is offset from the splitter definition line at the end closest to the center of the roundabout.

The Outer Offset is the distance by which the splitter island is offset from the splitter definition line at the end furthest from the center of the roundabout.

The Entry Offset and Exit Offset on the Roundabout Curb Line section are the distances by which the splitter island is offset from the inscribed circle at the entry and exit ends respectively.

The Entry Fillet Radius is the radius of the fillet at the intersection of the entry curb line and the roundabout curb line.

The Exit Fillet Radius is the radius of the fillet at the intersection of the exit curb line and the roundabout curb line.

The Approach Fillet Radius is the radius of the fillet at the intersection of the entry and exit curb lines.

Note: If the approach road has a central gap and the sum of the outer offsets at entry and exit is less than the central gap width then the island approach fillet will be omitted and the splitter island curb lines will be continued for form a central reservation.

In all cases the Max and Min values represent the limiting values from the adopted design standard and the Default value will be used when the roundabout is first placed. A default value MUST be provided but Max and Min may be blank if there is no limiting value.