A Model for predicting delay and capacity of right-turn traffic at closely spaced un-signalised junctions
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The study is centred on developing models to predict traffic delay and right-turning capacity of two successive signalised close junctions. Right-turn traffic at closely spaced un-signalised junctions is associated with delay and the resulting queuing since it cuts through main stream traffic. Through traffic volumes and spacing between junctions have significant bearing on the capacity and delay for right-turns. Limited studies have been conducted in the accessible literature to predict delay and capacity of right-turn traffic based on through traffic volume and spacing between closely spaced junctions. In this study, models for predicting delay and right-turning capacity of two successive unsignalised close junctions were developed. Traffic volume data from six paired junctions with intermediate spacing ranging between 30.0m and 185.0m on selected major roads in Kawempe Division of Kampala City were collected by video recording entered in Microsoft Excel and analysed using the RStudio modelling software. The critical right-turning traffic volume that yielded maximum queue length on the observed junctions was 220 vehicles irrespective of the spacing between junctions. A model to predict right-turning capacity between two successive unsignalised junctions basing on spacing between them, traffic volume discharged and merging traffic has been developed. It was observed that the delay of right turning traffic which impend the traffic flow on the main stream increased with decrease in the spacing between junctions. In addition, a model to predict average delay between junctions depending on spacing, right-turning traffic and queue length is suggested. The study recommends the use of aerial data collection methods, extending observation time and inclusion of geometric characteristics such as gradients and junction orientation in modelling.