Estimation of saturation flow rates on dual left-turn lanes

Signalized intersection capacity estimation and signal timing parameters optimization are directly related to the term 'saturation flow'. This parameter was the subject of numerous studies in which base saturation flow rates and its impact factors were estimated and analyzed. Also, analytical models for saturation flow estimation were developed. This paper presents an effort to investigate the base saturation flow rate on dual left-turn lanes. Data was collected on four intersections in Belgrade with protected dual left-turn lanes. Queue discharge rate research methodology was used and time headway data was collected via smartphones equipped with an application for that purpose. Results analysis showed that the saturation flow rates differ among left-turn lanes and a higher value is to be expected for the 'outer' lane, i.e. lane with bigger turning radius. However, a correlation between saturation flow rate and turning radius has not been demonstrated. Results showed that there was strong negative correlation between total saturation flow on both lanes and green time ratio. The paper also compares saturation flow rates obtained by field research and by models, and a model which is best suited for local conditions was identified