Models of critical gaps and follow-up headways for turbo roundabouts

Turbo roundabouts are the new generation of circular intersections. They offer numerous advantages, the main of which include relatively high flow capacity and high traffic safety, the latter being only slightly lower than in one-lane roundabouts, still incomparably higher than that of multi-lane intersections. The first ever turbo roundabout was designed in the second half of the 1990s in the Netherlands by L. Fortuijna. Ever since, intersections of this type have been designed in many countries all around the world, and one of those where turbo roundabouts are created is Poland. This article describes models used to estimate psychotechnical parameters, i.e. critical gaps and follow-up headways for turbo roundabouts and for different traffic organisation scenarios with regard to the area where a minor road enters the main carriageway. The models in question have been designed with reference to results of surveys conducted at turbo roundabouts in Poland.