ANALYSIS OF SATURATION FLOW RATE FLUCTUATION FOR SHARED LEFT-TURN LANE AT SIGNALIZED INTERSECTIONS IN JAPAN: A CASE STUDY

摘要

In urban corridor performance evaluation, saturation flow rate (SFR) is regarded as one of thekey parameters in estimating the capacity and delay at signalized intersections. In Japan, wherevehicles travel on the left side of the road, the SFRs of shared left-turn lane usually showcomparable fluctuation, due to different departure characteristics of through and left turningvehicles as well as complicated interactions with pedestrians and bicycles. Therefore, thereliability of lane group capacity, even intersection capacity would be potentially affected.For a better evaluation of corridor performance, this study investigates stochastic SFRsstarting from shared left-turn lane and empirically explores its implications. Results show thatefficient utilization of shared lane by through traffic can significantly improve SFRs. At lower orhigher pedestrian-bicycle volumes, SFRs are relatively reliable. While at middle levels ofpedestrian demands, more random arrivals and interactions between pedestrians and vehicleslead to rather unstable SFR fluctuation. Moreover, it is found that identical SFR values can beachieved under different turning proportions and pedestrian volumes. In other words, single SFRvalue cannot solely determine one traffic state in shared lane. For the shared lane with a largerleft turning radius, its SFRs display a stable trend since more turning vehicles can be storedwithin turning bays, thus a smaller chance of total lane blockage and a bigger chance ofachieving higher SFRs. A comparative analysis of observed SFRs and HCM estimations indicateHCM usually overestimates the SFRs in shared left-turn lane in Japan.