This category allows you to view and edit the turbo block's inner radius, primary axis angle and number of spiral starts as well as set the spiral start type for turbo roundabouts generated with these design guidelines.

Design Guidelines' Turbo Block 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.

Turbo Block Section

Inner Radius

Specify the inner radius. The inner radius is the distance from the center of the sector's central island to the inside edge of the innermost circulating lane.

Primary Axis Angle

Specify the primary axis angle. The primary axis angle is the angle measured between the spiral start leg that the primary axis is assigned to and the primary axis.

Number of Spiral Starts

Specify the number of spiral starts. The number of spiral starts value is how many unique circulating lane starting points there are in the turbo roundabout. This number also determines the number of axes lines, and therefore the number of sectors, that there are in the turbo roundabout.

Spiral Start Type Section

Straight

Select this option to have the start of the inner lane drawn as a straight continuation of the spiral start leg's lane edge.

Radius

Select this option to have the start of the inner lane drawn as an arc of the specified radius.

Envelope

Select this option to have the start of the inner lane drawn as an offset of the Opening Width design vehicle's tire track offset (see Vehicles Category: Opening Width and Circulating Lanes Category: Internal Circulatory Offset).