The turbo roundabout applies the vehicle envelopes design method to the unique turbo roundabout concept. The turbo roundabout design has spiraling circulating lanes and lane separators to allow drivers to quickly and safely navigate the roundabout, increasing throughput over traditional roundabouts. Drivers must choose the desired lane before entering the roundabout because lane changes within the roundabout are prevented by the raised lane separators. TORUS generates the turbo roundabout by applying design guidelines catered to drawing single, two, three, and four axes turbo designs to user drawn leg reference geometry. Building on the established design guideline concept in TORUS, additional categories have been added and existing categories adapted to cover all aspects of the turbo design: inner radius, number of spiral starts (axes), and spiral start type (straight, radius, or based on vehicle envelope); separate design vehicles for the circulating lanes and the circulating lane opening widths to the spiral starts; fixed circulating lane widths and offsets to determine effective circulating lane widths, separator widths and offsets; and mountable curbs.

The turbo block is the underlying geometry that determines the width of the circulating lanes, defines the principle spiral movements and the overall size of the turbo roundabout. The turbo block consists of construction lines which meet at axes lines maintaining symmetry sector by sector as the circulating lanes spiral outwards starting from the inner radius. The circulating lanes spiral out from the spiral starts (at spiral start legs), and exit the turbo roundabout at the spiral exit legs. The primary axis can be rotated to affect the overall size (footprint) of the turbo roundabout.

Note that for turbo roundabouts generated with the Effective Lane Width setting for Circulating Lane Widths, the changing radii in the principle spiral movements results in varying widths of off-tracking for the circulatory vehicle and thus the circulating lane widths are not a constant width (see Generate Roundabout - Circulating Lane Widths Section).