This category allows you to choose the default lane width type and view or edit the circulatory offsets for effective lane widths and the fixed lane width settings. In a turbo roundabout the circulating lanes are the spiraling lanes that begin at the spiral starts (at spiral start legs), spiral outwards, and exit the turbo roundabout at the spiral exit legs.

Design Guidelines' Circulating Lanes Category 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.

Effective Lane Widths

Select this option to have the circulating lane widths determined by adding the internal and external circulatory offsets to the width of the circulatory design vehicle’s off-tracking. Note that in a turbo roundabout, the widths of the circulating lanes will change somewhat due to the difference in the vehicle's off-tracking on the different radii.

Fixed Lane Widths

Select this option to have TORUS draw the circulating lanes based on the specified lane widths.

Circulatory Offsets for Effective Lane Widths:

External Circulatory Offset

Specify the external circulatory offset. The external circulatory offset is the distance from the circulatory design vehicle's outer tire track to the outer construction line/circulatory lane separator.

Internal Circulatory Offset

Specify the internal circulatory offset. The internal circulatory offset is the distance from the circulatory design vehicle's inner tire track to the inner radius/circulatory lane separator.

Apron Width

Specify the width of the apron. The apron width is the width dimension of the drivable portion of the Central Island, which will accommodate wheel tracking of large vehicles.

Minimum Lane Width

Specify the minimum lane width. This is the lane width that will be used in the event that a calculated lane width is less than the minimum.

Rounding

Select the amount of rounding to be applied to the calculated lane widths from the list.

Legend

For a description of the elements drawn in the turbo roundabout in this category, see Turbo Roundabout Illustration Legend.