Saturation Flow Estimation by Traffic Subgroups

Abstract

A framework for the estimation of saturation flow rates at signal-controlled intersections is presented. The proposed framework is grounded in existing highway capacity theories found in U.S. and international highway capacity guides. It is intended to provide a high level of flexibility to the end user for analyzing complex approach configurations and signal control schemes. This flexibility is achieved through the decomposition of the traffic stream on an approach into a subset of homogeneous traffic subgroups, each of which has a unique average saturation flow headway. The proposed approach enables the analyst to produce saturation flow rates at multiple levels, ranging from turning-movement saturation flows on individual lanes (exclusive or shared) to overall approach estimates that can encompass multiple lane groups. The proposed framework can accommodate cases with uneven distribution of traffic across lanes because of lane impedance differentials or prepositioning. When assumptions similar to those found in the Highway Capacity Manual (HCM) were used, the model’s saturation flows were found to be virtually identical to those estimated by the 1997 HCM.