Bus Rapid Transit, Safety, and Roundabouts

Evaluation of design solutions for roundabouts with Bus Rapid Transit based on safety and level of service of all modes

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The popularity of Bus Rapid Transit (BRT) has been growing rapidly over the past years, where more and more cities add BRT to their public transport systems. Roundabouts are also growing and are popular intersection designs because they are one of the safest types of intersections and improve traffic flow. It is, therefore, likely that in some cities a BRT route will go through a roundabout.
To keep the priority of BRT and the safety effects of a roundabout, the evaluation of roundabouts with BRT based on safety and level of service (performance) of all modes is investigated. Some countries have already developed and built solutions for roundabouts with BRT, where the priority of the buses can differ. One solution, often called throughabouts, is where the exclusive bus lanes go through the centre island of the roundabout, giving full priority to the buses. However, few guidelines have been developed on roundabout solutions with BRT and there seems to be a disagreement about the effectiveness of these types between some countries.
This thesis aims to reduce this research gap by developing an evaluation methodology that compares and evaluates different design solutions of roundabouts with BRT based on the safety and level of service of all modes. The evaluation methodology is also able to determine which design solution is the most optimal.
The methods used to compare and evaluate the designs in the methodology are literature review, multicriteria analysis (MCA), microsimulations and calculations, and a case study.
A case study of a roundabout in Reykjavik, Iceland is used to illustrate and test the methodology. Three design solutions are compared and evaluated where the priority configuration of the BRT is changed for each design. Design 1 is a regular roundabout where the buses drive through the intersection in mixed traffic. Design 2 is a throughabout where there are traffic signals for all entering traffic, and design 3 is a throughabout where there are traffic signals for the conflicting traffic. These designs are evaluated based on the traffic performance indicators of total throughput, travel time, and variation in travel time, and the safety indicators of number and types of conflicts for vehicle – vehicle conflicts and active mode – vehicle conflicts, and costs. These indicators are obtained by the output of a VISSIM model and using SSAM for the safety calculations. MCA is used to compare and evaluate the designs.
This results in that throughabouts with traffic signals for conflicting traffic prove to be the most optimal designs for roundabouts with BRT. They are also both the safest and best performing design solution.
This thesis addresses the research gap of disagreement of the effectiveness of the roundabouts by showing that throughabouts are effective, however, to determine their full effectiveness, further research is recommended on comparing throughabouts with other types of intersections. This thesis developed an evaluation methodology which can be used to evaluate and compare different design solutions which can be used to decide which design is the most optimal for intersections.