Abstract
According to the manuals for the capacity calculation and evaluation of roundabouts it is possible to calculate and evaluate the capacity of roundabout entries only under particular traffic conditions. However, it is not possible to simply determine the total capacity of roundabouts. For this reason, custom software tool, which allows total capacity calculation for different models of roundabouts under different traffic conditions, has been created. Results of the maximum capacity limits for some of the analyzed roundabouts at the most influencing traffic conditions settings are shown in the article. For better illustration, the results are compared with maximum capacity limits of simple unsignalized intersection.
Highlights
Modern roundabouts which were developed in the United Kingdom have started to be built in Slovakia after 1999
Tmin $ qk 3600 $ nc nc m where: G - basic capacity of a roundabout entry [pcu/h], qk - circulating traffic flow in front of the entry [pcu/h], nc - the number of circulating lanes [-], ne - parameter taking into account the number of entry lanes [-], ne=1.0 for single-lane entry; ne=1.5 for double-lane entry, tc - critical gap [s], tf - follow-up headway [s], tmin - minimum headway between the vehicles circulating in the circulating lane [s]
While the total capacity of roundabouts is increased by reducing of proportion of the traffic volume on the major entries – about 15% - 25% in dependence on left-turn percentage, the total capacity of unsignalized intersection is reduced to about 30%
Summary
Modern roundabouts which were developed in the United Kingdom have started to be built in Slovakia after 1999. For better illustration they are compared with capacity limits of simple unsignalized intersection – intersection with shared lanes on all legs
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