Vehicle automation technologies open new avenues for improving present transportation networks. It is predicted that Autonomous vehicles (AVs) and Connected Vehicles (CVs) will improve the traffic flow though increasing road capacities and reducing travel time and congestion to a great extent. According to the studies, AVs and CVs benefits will likely to more increase with their penetration rates and level of automation and cooperation. Eventually it might accelerate the expected evolution in car mobility in which the gradual transition from regular human driving to automated driving will occur. This paper summarizes the recent studies on the impact of vehicle automation in traffic flow. Although many factors are considered to affect traffic flow under the use of vehicle automation. This study has selected four main factors, these are travel behavior factor, the effect of platooning, travel time factor, and the effect of intersection control. The reviewed studies relevant to these keywords have been extensively argued and thoroughly discussed in this paper. Furthermore, the different applied models and the analytical frameworks which have been used to achieve various results and outcomes, are described in an illustrative table. Finally, all findings which have been demonstrated from this paper emphasize a great contribution of the developed vehicle automation technology to the future of our transportation system.