Analysis of innovative roundabout treatments in WA

Managing unbalanced traffic flows at roundabouts presents particular challenge to traffic engineers. Installation of traffic signals at one or more roundabout approaches is increasingly becoming an option to treat the problem of excessive queuing and delays caused by highly directional flows. Depending on the roundabout size and its geometric characteristics there is two possible avenues to pursue in terms of roundabout signalisation: 1. Part-time roundabout metering signals which operate only during peak periods and revert back to normal priority operation outside peaks. This arrangement consists of metered and controlling approaches usually positioned at opposite sides in different peaks to cater for traffic flow direction change in the morning and in the afternoon. There has been a dozen of roundabout metering signal applications in Australia predominantly in Melbourne, Victoria. 2. Full roundabout signalisation of all approaches with signal heads along the circulatory part of the roundabout which operate on a permanent basis. This arrangement is not very common and is applied in situations where the roundabout inscribed diameter is particularly large (100 meters and over). The ability of fully signalised roundabout to handle the traffic demand is highly dependent on the sufficient storage space in circulating lanes for the right turning vehicles. The storage space is a function of the roundabout size preventing this arrangement on smaller roundabouts. A number of fully signalised roundabout have been implemented in Queensland. The Eelup roundabout in Bunbury is the first such application in Western Australia. The purpose of this paper is to present VISSIM microsimulation analysis of the permanent and part time roundabout signals using two case studies in Western Australia. In cases where the roundabout signals have been implemented the paper will cover the issues and findings that werenrt as obvious during the analysis and modelling.