FDOT Geometric Design Method

Add approach legs to the roundabout, and edit approach legs' parameters.

Note: This tool requires existing CAD geometry in the drawing to act as the leg reference geometry. The geometry may consist of lines, arcs, or polylines/complex chains. Lines and arcs can be combined within the polylines/complex chains.

Add Leg / Edit Leg Dialog Box

Approach Radius 1 Generation Section

Radius

Specify the radius value of the Approach Radius 1 arc.

Start

Specify the starting point value of the Approach Radius 1 arc. This is measured from the intersection of the Inscribed Circle Diameter and the leg reference geometry to the starting point of the arc.

Approach Radius 2 Generation Section

Radius

Specify the radius value of the Approach Radius 2 arc.

Outer Offset

Specify the offset value. This is measured from the leg reference geometry to the splitter island envelope.

Inner Offset

Specify the offset value. This is measured from the leg reference geometry to the splitter island envelope.

Inner-Outer Offset

Specify the offset value. This is measured between the Outer Offset and the Inner Offset.

Angle

Specify the rotation angle of the Approach Radius 2 arc.

Note: This value is applied after the Inner Offset and Offset Values and overrides the Inner Offset and Outer Offset values.

Approach Radius 3 Generation Section

Approach Radius 3

Specify the radius value of Approach Radius 3 arc.

Outer Entry Radius

Specify the radius value of the outer entry arc.

Inner Exit Radius

Specify the radius value of the inner exit arc.

Outer Exit Radius

Specify the radius of the outer exit arc.

Lane Widths Section

Entry

Select this check box to draw the entry lane and specify the width of the entry lane.

Exit

Select this check box to draw the exit lane and specify the width of the entry lane.

Intermediate Path Section

Radius

Click this button to add an arc between the entry and exit paths and specify it's radius value.

Offset Left Section

Distance

Specify the offset distance value. This is an offset of the leg reference geometry to determine one end point of the TAN 2 extension line. It is at the intersection of the offset of the leg reference geometry and a line perpendicular to the TAN 2 extension line running through the center of the roundabout or the end of the leg reference geometry element if the leg reference geometry does not extend to the center of the roundabout.

Splitter Island Start Section

Distance

Specify the distance value of the splitter island nose arc. This is measured from the intersection of the Inscribed Circle Diameter and the leg reference geometry to the extents of the arc.

Nose Radius

Specify the radius of the splitter island nose arc.

Leg Section

Length

Specify the length of the selected approach leg.

Bypass Section

Dedicated Entry

Select this check box to add a dedicated entry lane to the entry lane side of the approach.

Dedicated Exit

Select this check box to add a dedicated exit lane to the exit lane side of the downstream approach.

Select Bypass Alignment

Click this button to pick the user-drawn bypass geometry in the drawing.

Lane Width

Specify the bypass lane width value.

Entry Width

Specify the width at the entry of the bypass lane. This is measured parallel to the leg reference geometry at the entry of the bypass lane.

Exit Width

Specify the length of the exit of the bypass lane. This is measured parallel to the leg reference geometry at the exit of the bypass lane.

Outputted Results Section

Displays the calculated output for the splitter width, tangent lengths, and entry and exit widths.