A method for estimating saturation flows at signal-controlled junctions

A knowledge of saturation flow of an approach at a traffic signal is of fundamental importance for the determination of signal settings for minimising delays and maximising capacity. Therefore, accurate derivation of model parameters is of great importance both for research purposes and for practical design analysis. All methods currently used require saturation rate profiles similar to a plateau shape, which has limited the application of these methods to unopposed movements. A new method of deriving saturation flow and lost time based on the best fitting of the rectangular model of the departure process to the cumulative histogram of observed departure rates is described in this paper. The proposed method allows estimation of saturation flow values for lanes carrying unopposed traffic streams as well as opposed and mixed streams in shared lanes. Preliminary measurements have been conducted at 11 lanes in order to validate this method in practice. Some results of saturation flow measurements are also presented in the paper.