The platooning of connected automated vehicles (CAVs) is a promising cooperative driving strategy, especially suited for freeway uninterrupted traffic. This paper presents a microscopic simulation approach to the modeling of CAV platooning on freeways, addressing the most relevant factors for the improvement of traffic throughputs. The paper introduces the algorithms to be added to current simulation software so that CAV platoons can be adequately modeled. The goodness of the proposed methodology has been tested through its implementation in the Aimsun Next software and with the application to a mixed traffic scenario consisting of a three-lane ring road with one on-ramp and one off-ramp, in which platooning is restricted to the leftmost lane. In this context, platooning has shown to increase traffic throughput significantly for CAV penetration rates of over 25%.For a 50% penetration rate the infrastructure baseline capacity more than doubles