ABSTRACT The traffic mixed by manual vehicles (MVs) and automated vehicles (AVs) will appear in the future. While the quantitative analysis of variation trend of penetration rate affecting traffic efficiency and safety is insufficient. This paper aims to study the influence of some typical factors on the mixed traffic flow by extensive simulation experiments. In particular, with the aid of VISSIM, the trend of traffic efficiency with the change of AVs’ penetration rate is discussed. An intelligent driver model (IDM) and classic psycho-physiological following model Wiedemann99 are introduced to describe the characteristics of AVs and MVs, respectively. Then, the influence on traffic safety is studied in the case of different time headways, which is a parameter in IDM model parameters. Simulation results illustrate that under the condition of low penetration rate of AVs, the traffic efficiency will increase, but no more than 15%. When the AVs’ penetration rate reaches the peak, the traffic efficiency can increase by 40%. Additionally, with the increase of time headway, the improvement of traffic efficiency will trend to be stable, and the driving safety, which is evaluated by peaks of vehicles’ deceleration, will be improved as well. In conclusion, the introduction of AVs will improve the traffic efficiency of mixed traffic flow. KEY WORDS: Mixed traffic flow, Traffic simulation, Intelligent driver model, Car-following model, VISSIM

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