Assessment of saturation flow at signalized intersections: a synthesis of global perspective and future directions

Saturation flow assessment at signalized intersections is one of the key features for analysing various performance measures such as capacity, level of service, signal strategies and coordination, and prediction of traffic flow models. Thus, an accurate estimation of saturation flow value is more beneficial at signalized intersections. Several studies have focused on the estimation of saturation flow in different roadway, traffic and control conditions. Earlier, saturation flow estimation methods were developed purely based on homogeneous traffic, where vehicle interaction was relatively less. However, in mixed traffic, an uneven distribution can be observed due to different vehicle dynamics and manoeuvrability with weak lane discipline. Thus, many studies have been carried out to frame an appropriate saturation flow estimation method. This study presents a comprehensive review on various saturation flow estimation methods developed in different traffic conditions; the drawbacks of the each method are also summarized. Moreover, a list of influencing factors affecting saturation flow value is provided. The general challenges in saturation flow estimation followed by some future direction for improvement in prediction models are also highlighted.