Abstract
“Standard” roundabouts, for example those designed in some European countries, can often be characterized by low levels of safety or capacity and a high degree of sustainability. Given the proliferation of newer layouts, it is of interest to explore whether design practices could be improved by capitalizing on the experience gained internationally. Operational aspects of some of these designs have been explored previously, but there is a need to compare both the operational and safety performance of new designs to that of standard roundabouts. The objective of this paper is to evaluate the safety and operational implications of various potential alternatives to the standard roundabouts that proliferate in Europe and elsewhere. Microsimulation is used to simulate traffic operations at roundabout layout alternatives at the same levels of volume to capacity (V/C) ratio and also with the same traffic flow. Operational performance measures include the common level of service parameters, while measures of safety are based initially on time to collision (TTC) values. Threshold values of TTC were then applied in defining conflicts that are used for crash-based safety evaluation by applying crash-conflict models estimated in published research. Interesting insights were revealed, suggesting that the newer layouts should be considered where warranted by cost-benefit considerations.
Highlights
In the last decade, new roundabout types of great practical interest from a sustainability perspective have been designed or proposed to overcome some of the problems related to average speed, level of service, conflict points, and crashes that arise with standard roundabouts
The objective of this paper is to evaluate the safety and operational implications of various potential alternatives to standard roundabout layouts that proliferate in Italy and elsewhere
The target roundabout has the largest queue length when traffic volume is 80% of its capacity
Summary
New roundabout types of great practical interest from a sustainability perspective have been designed or proposed to overcome some of the problems related to average speed, level of service, conflict points, and crashes that arise with standard roundabouts. The alternatives of interest for this paper are turbo roundabouts, flower roundabouts, and target roundabouts Such intersections offer potential safety benefits and, under certain traffic conditions, have been shown to provide higher capacity and better operation than equivalent standard roundabouts. Building on previous research where the issue of alternative roundabouts was investigated [1,2], microsimulation is used to simulate traffic operations at roundabouts with standard and newer layouts at various levels of traffic volume. Performance measures include emissions and level of service, as well as measures of safety, including conflicts and speeds, both estimated from trajectories generated in the microsimulation. Microscopic traffic simulation has the potential to provide a safe and flexible test environment for the a priori estimation of traffic safety and performance effects brought about
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