Sensitivity Analysis of Permitted Left - Turn Movement Delay Model in HCM

According to the HCM standards of signalized intersections, when there is a permitted phase, delay of left-turns will grow with increasing of through-turn volume of the opposing approach. In many countries, among them Iran, left-turn movement will not look for an acceptance gap and cuts into the through movement of opposing approach in a later time according to standards. Left-turn movements cause increasing the delay of through-turn movements of opposing approach. This fact will occur in a permitted condition, when volumes of left and through-turn movements prosper a certain limit. To determine these boundaries of left-turn movements and through-turn movements of the opposing approach, we should do the sensitivity analysis of “left-turn movement delay” against increasing of volumes of left-turn movements and through-turn movements of the opposing approach.According to accident statistics of many countries, %45 of accidents, at intersections, pertains to left-turn maneuvers. Most accidents occurr when left-turn movements are done in a permitted condition. Statistics indicate that %85 of these accidents will reduce, if permitted left-turn movements changed into protected left-turn movements.In addition, existence of permitted left-turn movements will increase the intersection delay. This paper presents relation between left-turn movements and volume of through-turn movements of opposing approach considering various numbers of opposing approach lanes and effective green time ratio (g/C).In this research, delay of left-turn movements is drawn in different charts with variables like left-turn movement volumes, effective green time ratio and opposing approach through-turn movement volumes and number of lanes, as a result of analysis with HICAP Software, for permitted condition. Also same-delay curves are drawn for three LOS es (D, E, F), according to volumes in different conditions. In comparison to delays, based on different volumes in permitted and protected conditions, we will present a proposed boundary that shows us when to use, which of these conditions.