A Comparison and Modification of Car-Following Models for Emission Estimation

The capability of car-following models to generate realistic vehicle trajectories for the emission estimation has been widely questioned. Gipps, Wiedemann and Fritzsche car-following models were selected and comparatively analyzed in this study, with the speed-specific VSP distribution as the evaluation index. The acceleration distribution and mean time headway generated by these models were compared. The comparison was based on massive field car-following trajectories and the numerical simulation of the models. It was found that the Gipps model generated rather realistic VSP distributions among the studied models and considerable errors were observed in the VSP distributions generated by Wiedemann and Fritzsche models. The errors of the VSP distribution were found to result mainly from the unrealistically generated accelerations. The Wiedemann car-following model was modified in order to produce more realistic VSP distributions, in which the parameters of the regime thresholds and acceleration models in the regimes were adjusted jointly. The field car-following data were divided into the regimes for the modification. It was indicated that the capability to generate realistic VSP distributions was improved. However, it was found that a great challenge exists to achieve both realistic VSP distributions and aggregated parameters in the regime structure of the Wiedemann model, which lacked a smooth transition over the regimes. A further investigation of the interaction between the parameters of the regime thresholds and acceleration models was recommended.