Roundabout Properties: Arm: Entry

Expand an arm and click Entry in the left hand pane. The Entry 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.

Select the Number of Lanes from the drop down list.

The Lane Width is measured between centers of lane markings. The innermost and outermost lane widths are measured to the nearside and offside definition lines respectively.

The Splitter Radius is the radius of the offside definition line at the splitter.

The Nearside Radius is the radius of the nearside definition line at the splitter.

The Inter-Leg Radius is the radius between the current leg and the next leg. Note that this is used to connect the nearside definition lines of two adjacent legs if the lines do not intersect on the Inscribed Circle.

The Additional Lane Length is measured from the yield line where it intersects the splitter line.

The Taper Lane Length is the distance over which the entry road width changes as it adjusts to accommodate the additional lane. This is normally a significant positive value to avoid a severe step in the nearside definition line.

The Flare Lane Width is the minimum width of any marked lane.

Select Equal Spacing Between Lanes to even out the lane width.

By default the ICD yield line is curved. To set a straight ICD yield line, select Straight Yield Line.

Some standards require individual lane yield lines set back from the ICD and roughly perpendicular to the lanes. Select Lane Yield Line if you require such markings.

If this exit is not relevant to flow calculations, e.g. it might be a service road, then select Ignore in Capacity Calculations.

In all cases the Max and Min values represent the limiting values from the adopted design standard.