Impact of Saturation Flow Changes on Performance of Traffic Lanes at Signalised Intersections

The paper presents analysis of saturation flow variability in traffic signal cycles during periods of congestion on the basis of empirical measurements. The purpose of this study was to investigate the impact of adverse weather conditions on the capacity of entry lanes. The empirical research was conducted in period 2007 - 2009 in three Polish cities. Investigated were lane groups with through traffic and geometrical characteristics corresponding to basic conditions in calculation methods and focused on detailed analyses of departure headways between vehicles, especially during the middle interval of the green signal of variable length, depending on drivers' behaviour. It was shown that saturation flow in traffic signal cycles at individual intersections is a random variable which can be described by gamma or normal distribution. Measurements' results show noticeable impact of different weather conditions on the saturation flow. The last part shows regression analyses which were conducted to accommodate numerous saturation flow determinants. The paper presents practical, aggregated models for prediction of basic saturation flow together with a proposed scale of efficiency of driver's behaviour, which is largely determined by traffic conditions. Simulation research enabled the authors to determine capacity variability and its impact on traffic performance (delay and vehicle queues). (C) 2011 Published by Elsevier Ltd.