Investigation of Queue Discharge Behavior at Signalized Intersection Based on Analytical and Micro-simulation Models

Capacity is the most widely used concept in traffic engineering practice. Planning, design, and operation of signalized intersections often require estimates of lane capacities under prevailing road geometric, traffic and signal control conditions. The basic model of traffic operations at signalized intersections is based on the assumption that when a signal changes to green, the flow across the stop line increases rapidly to saturation flow rate, which remains constant until either the queue is exhausted or the green period ends. In recent years, this assumption has been challenged by some field observations conducted in Hawaii, Taiwan and the United States of America (USA). These observations showed marginal increase in queue discharge rate along the queued vehicles' position as average headway decreases. This paper investigates queue discharge behavior at signalized intersections based on video data collected from one of the busiest at-grade intersections in Auckland, New Zealand. The methods proposed in the Highway Capacity Manual (2000) and Australian Road Research Report 123 to estimate saturation flow rates were assessed against field observations. The intersection was then modeled in AIMSUN micro-simulation software. The results from field observations were similar to those observed in Hawaii, Taiwan and the USA., whereas the micro-simulation results went against some common perceptions that believed micro-simulation under represents queue discharge rate.