Effect of Platoon Formation Policy and Platoon Size for Connected Autonomous Vehicles on Mixed Traffic Capacity

Recent technological development allows a queue of vehicles to be driven safely close to each other, which increases road utilization and reduces air drag, thus, resulting in significant energy savings. The queue of vehicles that follow one another in close succession is called a vehicle platoon. In the early stages of connected autonomous vehicles (CAVs) platooning, CAVs are expected to form platoons at their departure point according to an appropriate platoon formation policy. However, the effect of platoon formation policy on traffic capacity is rarely considered. This paper analyzes the effect of platoon formation policy and platoon size on the capacity of mixed traffic flow with CAVs, autonomous vehicles, and human-driven vehicles. First, given platoon size distribution, we derive the probability mass function for the position of an arbitrary CAV within a platoon and obtain mixed traffic capacity as a function of CAV penetration rate and average platoon size. The platoon size is heavily influenced by platoon formation policies. So, the platoon size distributions are derived for several platoon formation policies and are applied to obtain the mixed traffic capacities under the platoon formation policies. Some numerical examples are also provided to demonstrate how the key parameters of platoon formation policies affect the mixed traffic capacity.