AbstractWith the advance of emerging vehicle technologies, more and more work has been devoted to analyzing the resulting impacts in traffic efficiency and energy savings, whereas relatively limited studies have investigated the impact of emerging vehicles on traffic safety. To bridge the research gap, this study selected two emerging vehicle technologies, adaptive cruise control (ACC) of automated vehicles (AVs) and cooperative and adaptive cruise control (CACC) of connected automated vehicles (CAVs), to analyze the impact of emerging vehicles on traffic safety in both homogeneous and heterogeneous traffic. In homogeneous traffic, theoretical linear stability analysis and simulation both indicated that CACC has more robust string stability and is safer compared to ACC due to the fact that CACC is able to transmit acceleration information to the following vehicle. For heterogeneous traffic, microscopic simulations with different vehicle classes were conducted with consideration of downgradation and platooning intensity. Simulation results showed that for mixed CAV and human-driven vehicle (HV) traffic, the collision risk tended to increase first and then fall with the market penetration rate (MPR) of CAVs, which indicates that the moderate deployment stage is the most dangerous stage. In addition, results showed that higher platooning intensity led to lower collision risk in both mixed CAV and HV and AV and HV traffic. As a consequence, this study suggests that vehicle platooning and strengthening the connectivity for emerging vehicles can improve the longitudinal traffic safety of emerging vehicles.

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