Abstract: Under the context of intelligent network，vehicles can enact cooperatively at a small headway，and con- tinuous connected vehicles will be in platoon configurations by information interaction of vehicle-to-vehicle or vehi- cle-to-infrastructure communication． Thus，the road capacity will be improved effectively． Considering the traffic flow randomly mixed with regular vehicles and connected vehicles，4 types of car-following characteristics and its spatial distribution probability in heterogeneous traffic flow were analyzed． Then the fundamental diagram model and the passenger car equivalents ( PCE) were obtained． And the sensitivity analyses on penetration rate of connected vehicle and platoon size were carried out．Research results show that the improvement of the penetration rate of the connected vehicles and the increase of the platoon scale will help enhance the traffic capacity and reduce the PCE． Moreover，the positive impacts will be more obvious with the increase of the penetration rate of the connected vehi- cles． When the vehicle platoon scale is larger than 4，its impact on the traffic capacity improvement and the PCE reduction will decrease significantly．

Key words: highway basic segment, mixed traffic flow, connected vehicle platoon, penetration rate, platoon size, traffic capacity