Operational Design Domain of Automated Vehicles at Freeway Exit Terminals

Abstract

With the advancement of automated driving technology, ensuring the operational safety of automated vehicles (AVs) has become a research focus. AVs at freeway exit terminals face high risks due to diverging operations and limited sight distance. Currently, exit terminal design relies on sight distances adequate for human drivers’ perception abilities. However, since detecting angle and range are key parameters in the sight triangle and differ between AVs and human drivers, the existing design may not adequately accommodate AVs. To address this gap, this research adopts a strictly mathematical approach to compute operational design domain (ODD) constraints based on the sight triangle at exit terminals. Required stopping sight distance (SSD) or required detecting range, and required detecting angle were quantified as ODD indexes for diverging AVs at various exit ramp and through-lane design speed combinations, based on vehicle kinematics theorems and the sine law. Both flat grades and grades over 3% were considered. Results indicate that (1) the largest required detecting range and angle are 303.0 m and 50.45 degrees, respectively; and (2) some diverging AVs may fail to meet the detecting range requirements, particularly at higher design speeds. Three contributions are provided: (1) the computed ODDs can serve as general references for ensuring sight distances and designing deceleration lanes at exit terminals suitable for AVs; (2) the criteria can improve the geometric design of exit terminals within usual ODD constraints; and (3) it benefits AVs’ ODD management by governments and traffic departments.