Impacts of commercially available adaptive cruise control vehicles on highway stability and throughput

Adaptive cruise control (ACC) vehicles are proving to be the first generation of automated vehicles. Although many studies have found that, theoretically, ACC vehicles may have positive impacts on traffic string stability and throughput, recent studies reveal that commercially available ACC vehicles are string unstable. However, it is still not clear what impacts on highway traffic these commercially-available ACC vehicles may have at higher market penetration rates. Therefore, the objective of this study is twofold: (i) investigate the impacts on highway traffic capacity of mixed human-piloted vehicles and theoretical ACC vehicles as well as commercially-available ACC vehicles at different market penetration rates; (ii) explore the potential relationship between string stability and highway throughput. We use the intelligent driver model with calibrated parameter values from car following data collected on commercially-available ACC vehicles and compare the simulation results to simulations conducted using a theoretical ACC vehicle model with parameter values obtained in the literature. The results show that when simulating ACC vehicles found in the literature,traffic flow is string stable and the bottleneck capacity increases by up to 7% at higher market penetration rates as compared to homogeneous human driven traffic. When commercially-available ACC vehicles are simulated, the traffic flow is string unstable and the bottleneck capacity decreases at higher market penetration rates with some scenarios resulting in a decrease in capacity of up to 35%. The analysis provides evidence that bottleneck capacity is substantially affected by string stability and inter-vehicle time gap, while downstream throughput is solely influenced by time gap.