Determination of Adjustment Factors for Far Side and Near Side Bus Stops on Saturation Flow

Abstract

Saturation flow under mixed traffic conditions is affected by vehicular mix and its characteristics, approach grade, driver behaviour, roadway geometry, and road side frictions in the vicinity of intersection. Side friction arises from pedestrian movement, activities of public transport vehicles, and parking of vehicles on road premises. Due to the influence of these factors, realistic estimation of saturation flow is a complex task under heterogeneous traffic conditions. Road side friction arising from stopping of public transport adjacent to signalised intersection tends to interfere with vehicular discharge at intersections. This paper attempts to analyse the impact of far side (down stream side) and near side (upstream side) bus stops on saturation flow rate. As a first step towards quantifying the effect of bus stops, saturation flow of approaches that satisfies the base conditions set for the study were estimated in PCU/hr using area occupancy concept. Mathematical model for the prediction of base saturation flow was proposed. Effect of bus stops on saturation flow rate was then determined by analysing saturation flow rates of approaches where bus stops are located adjacent to intersections. Adjustment factors were introduced to incorporate the effect of far side bus stop (Ffb) and near side bus stop (Fnb) on saturation flow rate. Linear regression models were developed for the prediction of adjustment factors based on data generated using a micro simulation programme. The results of the study showed that adjustment factors vary with distance of bus stop from stop line, width of approach and proportion of green time blocked. The study also revealed that the reduction in saturation flow rate is more when bus stops are located in the upstream side (near side bus stop).