Steady-state solutions and multi-class calibration of Gipps' microscopic traffic flow model

This study sought to make a contribution to the problem of calibration of Gipps’ microscopic traffic flow model. The approach followed in the paper consists in first deriving traffic stream models, in the form of steady-state solutions of car-following models, and then in fitting such models to stationary traffic data. To this aim, traffic stream models for the Gipps model were first attained and an explicit formula for the flow at capacity, as a function of microscopic parameters, is provided. Analysis of the models for different combinations of microscopic parameters explained the widely-held belief that the Gipps model is unable to reproduce unstable traffic phenomena. To be suitable for model parameter calibration in simulation practice, single-class models were generalized to a multi-class traffic scenario for which a calibration procedure was developed. Once applied to real motorway traffic data, the latter proved its effectiveness in terms of error statistics. Values of calibrated parameters were all significant and consistent with expectations. Moreover they were consistent with the observed aggregate measures (e.g. flow at capacity). Finally, unlike non-stationary, model-based approaches, the computing time required by the multi-class calibration presented is negligible, allowing us to calibrate a large number of parameters i.e. to calibrate different classes of vehicles.