Thirty years of the Gipps??? car-following model: applications, developments, and new features

Car-following models are widely used by researchers and practitioners for road traffic studies. Although dozens of them have been presented so far, the model proposed by P.G. Gipps in 1981 is still one of the most extensively used. However, many features of the model are still rather unknown or neglected in common applications. In this context, the present paper wishes i) to summarize and analyze the main findings available in the scientific literature for the Gipps??? car-following model and ii) to introduce some novel features of the same model that may improve its capability to reproduce real trajectory data. In particular, the structure of the acceleration component of the model is analytically investigated, in particular for what concerns the meaning of some parameters that in the common practice are usually kept to some empirically derived fixed values. Different possible versions of the Gipps??? model are presented and their performances to reproduce real vehicle trajectories are evaluated and compared. The results achieved show the necessity for these parameters to be calibrated in order to improve the predictive capabilities of the model.