Assessment of Turbo and Multilane Roundabout Alternatives to Improve Capacity and Delay at a Single Lane Roundabout Using Microsimulation Model Vissim: A Case Study in Ghana

A single lane roundabout characterized by long queues during morning and evening peak periods was chosen as our study site. The objective of this study was to 1) Model and calibrate the vissim simulation model for the roundabout and 2) to model roundabout alternatives to improve capacity and assess the delay. A two hour video data collection was undertaken on a typical morning peak from which the traffic demand and turning movement data were extracted. The vissim micro simulation model was calibrated using the west approach as the target and the analysis was done for the existing single lane roundabout. A Turbo roundabout and a conventional double lane roundabout alternatives were also assessed. The capacity of the single lane roundabout was estimated as 2990 pcu/h and was performing at an ICU level of service H. Average Delay on the west approach was 232 seconds. The intersection capacity was 4392 pcu/h when the turbo roundabout alternative was assessed. Westbound vehicles experienced average delay of 87 seconds (inner lane) and 74 seconds (outer lane). The capacity of the conventional double lane roundabout was estimated to be 3690 pcu/h. The turbo roundabout concept will deliver a comparatively higher capacity and could be the most effective alternative to reduce congestion and delay.