Evaluation of the effects of signalisation on roundabout capacity using VISSIM: A case study of the Suame roundabout in Kumasi, Ghana

Thumbnail Image
November, 2016
Journal Title
Journal ISSN
Volume Title
Increasingly, many roundabouts in Ghanaian cities are becoming problematic due to capacity challenges resulting from rapid traffic growth. Signalisation is known to improve capacity, shorten queue length, and reduce delay at roundabouts but this option has not been used in Ghana. In this study, three model options for signalising roundabouts, namely Approach-by-Approach Control, Metered Approach, and Full Signalisation, were explored for analysis and comparison of their effects on roundabout in Kumasi as a case study. The aim of the study was to establish the model option that best addresses traffic problems at the Suame Roundabout in terms of improved capacity, reduced delays and queue lengths. Field traffic volume studies for the entire roundabout’s approaches were performed. Travel time and delay studies together with queue lengths measurement for the subject approach (South East Approach) were also undertaken. Geometric data as well as data from the field study described earlier were used to calibrate a model for the existing situation. Capacity, delay, queue length and degree of saturation were observed for the signalised options and existing un-signalised. The results indicated that the Full Signalisation Model produced the best parameter results and the Approach-by-Approach Model the worst among all the models including the calibrated existing model. Full signalisation of the Suame roundabout is recommended to improve capacity and reduce vehicular delays and queue lengths. However, under budgetary constraints, the Metered Approach option may provide more consistency in operations at the roundabout as compared to the current situation where movements at peak periods are traffic-warden controlled.
A thesis submitted to the Department of Civil Engineering, College of Engineering in partial fulfillment of the requirements for the award of the degree of Master of Science in Road and Transportation Engineering,