Vehicle Envelopes 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

In the dialog box, move the mouse pointer over the controls to view the associated tooltip and then reference the controls described below.

Note: For the purposes of describing the software, it is assumed that Right-Hand Traffic is selected under Traffic Direction in Design Guidelines' General Category. If Left-Hand Traffic is selected, the descriptions with references to a right/left turn path should be interpreted in the opposite direction.

Name Section

Specify a name for the approach leg.

Lane Widths Section

Select how the lane widths are drawn. Different controls are available in the Edit Leg dialog box depending on which mode is selected:

• When Effective Lane Widths is selected, the Splitters & Crosswalks section displays controls to trim the splitter island envelope by minimum width or length. The Lane Taper Ratios section is available to adjust the taper ratios of the entry and exit lanes.
• When Fixed Lane Widths is selected, the Splitters & Crosswalks section displays controls to adjust the median. The Road Widening section is available to adjust the approach and departure tapers.

Effective Lane Widths

Select this option to have lane widths determined by adding the entry and exit lane offsets specified in the current Design Guidelines' Leg Offsets Category to the width of the vehicle’s off-tracking as it enters and exits the roundabout.

Fixed Lane Widths

Select this option to apply the fixed lane widths specified in the current Design Guidelines' Fixed Lane Widths Category.

Leg Options Section

Entry

Select this check box to draw entry lanes in the selected leg. The entry radius is displayed. Increase/decrease the number of entry lanes via the spinner control.

Button	Option	Click to...
	Configure Entry Path Radius and Offsets	When Effective Lane Widths is selected under Lane Widths: Override the entry path radius and offsets specified in the current Design Guidelines' Leg Arc Radii Category and Design Guidelines' Leg Offsets Category. When Fixed Lane Widths is selected under Lane Widths: Override the radius and fixed lane width settings. Note: This button is only available if an entry lane is turned on.

Exit

Select this check box to draw exit lanes in the selected leg. The exit radius is displayed. Increase/decrease the number of exit lanes via the spinner control.

Button	Option	Click to...
	Configure Exit Path Radius and Offsets	When Effective Lane Widths is selected under Lane Widths: Override the exit path radius and offsets specified in the current Design Guidelines' Leg Arc Radii Category and Design Guidelines' Leg Offsets Category. When Fixed Lane Widths is selected under Lane Widths: Override the radius and fixed lane width settings specified in the current Design Guidelines' Fixed Lane Widths Category. Note: This button is only available if an exit lane is turned on.

Bypass

Select this check box to draw a bypass lane in the selected leg.

Button	Option	Click to...
	Configure Bypass Lane	Override the bypass lane settings specified in the current Design Guidelines' Bypass Lane Category. Note: This button is only available if the bypass lane is turned on.

Leg Length

Specify the length of the selected approach leg.

Visibility and Configuration Section

Button	Option	Click to...
Visibilities and Configurations	Visibilities and Configurations	Set which aspects of the roundabout are drawn in the roundabout and allows certain aspects to be configured.

Calculated Output Section

Expand this section to view the widths of the entry, entry and exit lanes, the median, and the refuge as well as the entry angle measured using Method 1 and Method 2 (see Appendix -> Entry Angle Measurement).