Modeling the fundamental diagram of mixed human-driven and connected automated vehicles

Traffic flow fundamental diagram (FD) is viewed as the basis of traffic flow theory and has various applications in transportation. However, the fundamental diagram of mixed human-driven vehicles (HVs) and connected automated vehicles (CAVs) traffic has not been well-studied. This paper derives the FD for mixed HV and CAV traffic considering the stochastic headway. Firstly, the deterministic FD of pure CAV traffic and pure HV traffic are built. Then the FD of mixed HV and CAV traffic is developed with CAV penetration and platooning intensity taken into consideration. A Gaussian mixture model (GMM) is applied to model the stochastic headway, based on which the stochastic FD is derived. Impact of CAV penetration and platooning intensity on the stochasticity of FD is studied. Results from theoretical analysis and case study show that increasing CAV penetration can reduce the scattering of FD, while higher platooning intensity may result in more scattering of FD.