Operational design domain of automated vehicles at freeway entrance terminals

The safe operation of automated vehicles (AVs) is now on the research agenda, with attention to the AV's operational design domain (ODD), which defines the conditions in which its driving automation system is designed to function. Due to the limited sight line on freeway entrance terminals, crashes involving AVs continue to occur during the merging operation. Considering that detecting range and detecting angle are critical parameters for the AV sensor's sight triangle and may differ from human driver requirements, it is urgent to provide initial ODD results to improve the AV's detection capabilities at entrance terminals. Based on sight triangle requirements, this study took a mathematical approach to quantify the relationships among AV sensor capabilities, design speed, and geometric design indicators separately for flat grades and 5 % grades. Required stopping sight distance (SSD) for the merging AV and travelled distance of the through-lane vehicle were calculated based on vehicle kinematics, common sensor capabilities, and Green Book parameter values. Using the law of cosines, the required detecting range and the detecting angle for AV sensors were calculated at various ramp and through-lane design speed combinations as the ODD constraint indicators. Two types of entrance terminals, the taper and the parallel, were considered in this study. Results show: 1) the maximum required detecting range and angle for AV sensors reached 185.0 m and 179.9 degrees, respectively; 2) the required detecting range and angle have only minor differences between the taper and parallel types; 3) the minimum acceleration lane length suggested for human drivers may not be available for AVs. These results provide two major contributions to safe operation of AVs: 1) for roadway design, the results provide general design references for acceleration lane length, merging angle, and sight-distance guarantee at freeway entrance terminals; and 2) for ODD management, results provide theoretical support for governments and traffic management departments to regulate AVs at these terminals, in some cases limiting the AV to manual driving or lower speed limits.