The development of a new gap acceptance model based on limited priority for the major-stream is discussed. Field observations were done to identify the merging mechanism taking place at unsignalised intersections under congested conditions. A limited priority system is proposed based on the assumption that the major-stream vehicles could be slightly delayed to accommodate the minor-stream vehicles. Equations for capacity in the limited priority system were presented assuming that the major-stream vehicles have a bunched exponential headway distribution and the minor-stream drivers are both consistent and homogeneous. The gap acceptance model based on the limited priority was then applied to the performance of roundabouts. It was found that the limited priority merge can have a significant effect on the entry capacity at two-lane roundabouts. The relationship between the entry capacity and the circulating stream flow at two-lane roudabouts was very close to the straight-line relationship that has been found in the U.K. using an empirical method.(A)
Abstract