Resumen
Roundabouts are commonly used as a means of intersection control for moderate traffic flows and junctions having variations in the intersection geometry. It facilitates an orderly movement of traffic in a circular motion around a central island which is generally circular in shape. The circulating traffic is considered to be the priority stream and entering traffic waits for a suitable gap in the circulating traffic. In this fashion, it reduces the stopped delays as observed on the signalized intersections, as well as reduces the crashes and expenditure required for maintenance of traffic signals. This paper examines the entry capacity of a roundabout under different circulating flows by measuring the field entry flows. Queue formation in the approach is taken as an indicator that the approach is operating at capacity. Relationship between entry flow and circulating flow is found following negative exponential distribution. This is compared with the entry capacity estimations based on HCM, 2010. The field entry flows are found to be higher than that given by the HCM, 2010 equation. This is due to the lower critical gap acceptance behavior shown by the Indian drivers under mixed traffic compared to the homogenous traffic modeled in the HCM, 2010. An adjustment factor, multiplicative to the entry flow estimation based on HCM, 2010 equation, is proposed which can be used by field engineers directly. This will be simpler than the approach based on critical gap computation, which is tedious and difficult.