Abstract
Traditional multilane roundabouts have many branch lanes without traffic signs and channelization, which leads to a high tendency for traffic collisions. Turbo roundabouts are a new design that has the potential to reduce lane-change conflicts using canalization to force drivers to keep in specific lanes based on their intended destination. This paper evaluates the safety and efficiency performance of turbo roundabouts for the case of a five-leg roundabout called Lujiazui in Shanghai and provides design and construction guidelines when applying the turbo design. The models for the Lujiazui roundabout and the reconstructed turbo version were built in Vissim, and a comprehensive series of experiments under different traffic volumes and central island radii was performed. Afterward, the conflict statistics extracted from the trajectory files in the Surrogate Safety Assessment Model (SSAM) were analyzed using the conflict severity index (CSI) and were then integrated to calculate the modified conflict frequency (MCF) for safety performance evaluation. A comparative efficiency analysis was also conducted as a supplement. Based on the results, the relative characteristics for safety and efficiency between the turbo and original designs of the Lujiazui roundabout were analyzed. Suggestions to apply the turbo design on a five-leg roundabout are introduced.
Highlights
In a road network, intersections are recognized as the most dangerous and critical locations, as several points of conflict exist
The egg, basic, knee and spiral roundabouts are suitable for conditions when traffic flow from a single approach is predominant, while rotor or star roundabouts are recommended for equal traffic volumes at all entries [23]
The purpose of this study is to investigate the validity of turbo roundabouts in improving the safety performance under various traffic conditions based on a case study—the Lujiazui roundabout—and discuss the guidelines on implementing this new design on a five-leg roundabout regarding efficiency and safety
Summary
Intersections are recognized as the most dangerous and critical locations, as several points of conflict exist. Due to the lack of sign usage for route selection or other channelizing measures, there are several lane-change conflict points when vehicles are forced to decelerate based on the geometric size and curvature of the central island, which may cause side-by-side collisions and reduce road safety [12,13]. To address these problems, a new roundabout layout, called the turbo roundabout, was proposed in the Netherlands by Dutch researcher Dr Lambertus Fortuijn in 1996. Most are in the Netherlands (372), as this layout was developed there, and it is where the first turbo roundabout was built
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