Fundamental Diagrams of Commercial Adaptive Cruise Control: Worldwide Experimental Evidence

Recently, several experiments on commercial adaptive cruise control (ACC) vehicles have been conducted worldwide, providing an unprecedented opportunity to study the ACC behaviors. This paper has conducted a comprehensive empirical study on the ACC equilibrium behaviors using all available data to date and obtained the ACC fundamental diagrams. We find that ACC systems display a linear speed-spacing relationship, like human-driven vehicles, but the features of the speed-spacing relationships and the corresponding fundamental diagrams differ from human-driven traffic. ACC generally has very small spacing at minimum headway, resulting in much larger flow (and capacity) than human traffic, but the opposite occurs if maximum headway is used. Many ACC systems have extremely large wave speed, which may impose safety risk. Lastly, ACC jam spacing is much larger than human traffic, translating to much smaller jam density, which will reduce road storage capacity.