Traffic Signal Design with an Increasing Queue Discharge Rate

Abstract

The traditional method of traffic signal design is based on the assumption of a constant queue discharge rate, also termed the saturation flow rate. However, a number of field studies conducted in Taiwan and the USA contradict this assumption because they reported a marginally increasing trend observed for the queue discharge rate toward the back of the queue. This paper reports on a field study conducted in Auckland, New Zealand at six signalized intersections. The field observations confirm the findings of previous research, namely that the queue discharge rate increases toward the back of the queue. Two empirical models are proposed to reflect the observed queue discharge behavior. One of them is implemented to calculate the capacity and signal timings. The proposed model shows the potential to overcome the shortcomings of the traditional method in practical applications.