DETERMINATION OF THE FACTORS INFLUENCING THE EFFICIENCY PERFORMANCE OF ROUNDABOUTS:

Abstract

Roundabouts constitute special forms of space sharing roadway intersections that are known to enhance safety, reduce delay as well as being aesthetically pleasing. However, the factors influencing their capacities are many and their effects vary. In order to use them optimally in road network, these factors and their influences should be investigated. This is the focus of this work and a specific case study has been adopted. The roundabout studied is the Adeti roundabout in lIesa, Osun State. The roundabout, at peak periods of travel is characterized by long vehicle queues and long delays. Field observations of vehicles flow patterns at roundabout spanning 6am to 7pm daily for a period of five consecutive days (Monday- Friday) were undertaken. Various theories and design models used in different parts of the world were adopted as analytical tools. The results of the investigation showed that the vehicular flow in the roundabout corresponds well with the gap acceptance concept of the Highway Capacity (lower bound). It was found that when locally obtained values of drivers critical gap and follow up time were substituted into the Highway Capacity model, the corresponding ratio was 0.93. Thus, it is most likely that a totally customized Highway Capacity model would be most suitable for analyzing roundabouts in Nigeria.