Comparing the Fundamental Diagrams for Electric vs. Internal Combustion Vehicles: Case Study of ACC

Abstract: Automated vehicles (AVs) have been highly anticipated due to their potential to reduce congestion. The first generation of AVs using Adaptive Cruise Control (ACC) has become commercially available in recent years and is now available in the increasingly popular electric vehicle (EV) market. Understanding the fundamental traffic flow characteristics is critical for the future of traffic operations and planning as ACC-equipped EV market penetration increases. To provide a better understanding of traffic flow characteristics for commercially available ACC, this study conducted microscopic simulations using well-designed ACC car-following models that are validated by a comprehensive set of full-speed range car-following field experiments. Varying combinations of internal combustion and electric vehicle market penetrations were tested, with the vehicles that are all ACC-equipped, and the fundamental diagrams for each combination were constructed. This study addresses the previous gap in research, which relied on either speculative simulations or field data from a few vehicles to generate the fundamental diagram. Findings of this study show that as the EV market penetration increases, the capacity and jam density significantly increase, to nearly 2400 veh/hr/ln and 65 veh/km/ln, respectively, at 100% market penetration. Also, the shape of the diagram become more triangular rather than nonlinear and trapezoidal at higher EV market
penetrations, due to the unique EV powertrain characteristics that deliver swift and constant acceleration and deceleration over a broader range of speeds.