Capacity of U-turn Junction at Midblock Median Opening on Urban Arterial Based on Balancing Volume-to-capacity Ratio

Abstract

U-turn at midblock median opening is frequently provided in developing countries to facilitate the local access. Movement capacity of such u-turns is of interest for deciding the necessary traffic management. HCM 2010 contains the methodology for u-turn capacity estimation, which is based on gap acceptance theory and assumption of major traffic headway distribution. This research evaluated the gap acceptance capacity model and proposed an adjustment method by v/c balancing. Data collection at a u-turn site was conducted for validation. The results showed that the gap acceptance capacity overestimated the field capacity in case of negative exponential headway distribution and underestimated in case of Erlang-2 headway distribution. The difference in driver behavior when responding to different conflicting headway could explain the situation. The proposed adjustment could provide the estimated capacity closer to the measured field capacity. The method also incorporated the interactions between the u-turn and through traffic streams.