Examining the Relationship Between Inner Circle Flow and Entry Lane Approach Flow to Identify the Theoretical Capacity of Roundabouts

The use of roundabouts for intersection improvements has been a common trend for many communities throughout central Indiana over the past 5 years. Although their use is a popular alternative to traditional methods of traffic control at intersections, there is much yet to be understood about the operational characteristics of roundabouts. In areas of relatively high growth, there is concern regarding the premature installation of roundabouts and the effect of post-developed traffic patterns on their future operational characteristics and level of service. By design, roundabouts slow traffic by their geometric configuration to function as a yield or two-way stop controlled intersection. The prime operational characteristic of a roundabout requires each user to assess gaps in vehicle headways within the circulating flow to maneuver the intersection. An example of the flow of traffic in a typical roundabout is shown is Figure No. 1. It is the intent of this paper to identify and review source material on the capacity of roundabouts and apply methodologies and information learned in the course to analyze and critique the source material.