Calibration of Robertson’s Platoon Dispersion Model in Non-lane Based Mixed Traffic Operation

Abstract

Once released from a signalised stop-line, vehicles normally proceed to the next intersection in bunches (called as ‘platoon’). While moving along a corridor, vehicle platoons disperses and therefore, the pattern of vehicle arrivals at a signal is different from the pattern of discharge from its upstream signal. Modelling of dispersion of vehicle platoon is an important consideration for coordinated operation of closely spaced traffic signals. In this regard, Robertson’s dispersion model has significant contribution towards design of coordinated signal system. However, successful application of Robertson’s model largely depends on calibration of the model for local roadway and traffic conditions. In this paper, calibration of Robertson’s model is carried out for an urban roadway scenario in India giving due consideration to level of heterogeneity in vehicle mix, variation in travel demand and link travel time. Data are collected from an urban arterial in Kolkata metropolitan area using videography. Using Robertson’s platoon dispersion model, downstream arrivals are predicted for observed upstream flow profiles at stop-line. Then, parameters of the Robertson’s platoon dispersion model (α and β) were calibrated using best fit approach. An empirical model is developed to express platoon dispersion factor (α) as a function of vehicle composition, normalised flow (flow to capacity ratio at stop-line), link travel time and modelling step size.