Calibration of the Platoon Dispersion Model by Considering the Impact of the Percentage of Buses at Signalized Intersections

Despite the wide use of Robertson’s platoon dispersion model, few studies have calibrated this model under different traffic conditions at signalized intersections. This study calibrated the platoon dispersion model on the basis of field data collected from Beijing; the impact of the percentage of buses was considered in the calibration. First, a video was made of the platoon dispersion at an intersection. The link travel time of the vehicles in the platoon was extracted from the video. Then, the parameters of the platoon dispersion model were estimated with the average and standard deviations of the fleet link travel times. It was found that the derived parameters varied, with the observed percentage of buses ranging from 0% to 6% or 15% to 22%. This factor showed the impact of the percentage of buses on platoon dispersion under specific conditions. Regression models were developed to reflect such an impact. To evaluate the effectiveness of the calibrated platoon dispersion model, the downstream flow profiles derived from the calibrated model were compared with the field-observed downstream flow profiles within the dispersion process. Finally, the influence of the time step on the calibrated platoon dispersion model was analyzed. The results show that the calibrated model has high accuracy. The calibrated platoon dispersion model can be used to represent the process of platoon dispersion at signalized intersections where the impact is affected by the percentage of buses. It can contribute to signal timing optimization of the intersections