Abstract
Although two-lane roundabouts theoretically exhibit excellent operating performance, in practice, safety problems arise because of inappropriate driving behavior. Turbo roundabouts, which are characterized by a much higher level of safety, are alternatives to classic two-lane roundabouts, but the capacity-related benefits derived from such roundabouts remain an open issue. Accordingly, this study uses an equilibrium traffic flow allocation approach to evaluate multi-lane roundabout capacity based on gap acceptance theory. Capacity levels are calculated and compared for different gap acceptance parameters, including local parameters, and different traffic flow scenarios. It is found that the capacity of minor approaches on turbo roundabouts is always higher than on two-lane roundabouts, but that the main approaches on two-lane roundabouts exhibit better performance in terms of fully equilibrium traffic allocation. This state, however, cannot be achieved for every demand scenario. The results depend strongly on traffic movements and gap acceptance parameters indicating the need for local calibration processes.
Highlights
Roundabouts have been operating for over 100 years worldwide, but there is still debate about which is the best type in terms of capacity, safety, environmental issues, and geometric features, among other aspects
We determined the increase in the v/c ratio in the most optimistic case. This value was compared with the turbo roundabout capacity obtained at full traffic flow allocation, with the assumption of improved utilization of the inner lane
This paper has presented a detailed description of capacity estimation for multi-lane roundabouts, with particular application to two-lane and turbo roundabouts
Summary
Roundabouts have been operating for over 100 years worldwide, but there is still debate about which is the best type in terms of capacity, safety, environmental issues, and geometric features, among other aspects. These intersections continue to evolving, resulting in new variants, such as turbo, flower, dog-bone, and turbo-square roundabouts. The geometric layout of two-lane roundabouts enables drivers to change between circular lanes, regardless of lane markings This means that vehicles go through at excessively high speeds as they use both circular lanes and aggressively cut through traffic flow on the outer lane when exiting from the inner one. The need for a solution to these safety issues prompted the development of turbo roundabouts
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