Operational design domain of autonomous vehicles at skewed intersection

Sight distance is an important indicator of vehicle safety at intersections. Traditional intersection design methods might be not suitable for the autonomous vehicle (AV) because its perception differs from that of the human driver, on which AASHTO Greenbook 2018 are based. Since, to guarantee future operational safety, intersection design needs to consider the impact of the AV, this study investigates and quantifies the relationships between intersection angle on skewed intersections. The operational design domain (ODD) is defined as the required detecting angle and distance within the skewed intersection's speed range. Calculations for acute-side detecting angle, obtuse-side detecting angle, and obtuse-side detecting distance formulae were developed based on sine theorem and inverse trigonometric function; leg length of the sight triangle along an intersection's major road was calculated by multiplying the design speed by the time gap. Calculation results show that the current design criteria cannot provide sufficient sight distance for the AV if the approach speed is not controlled. The AV's higher approach speed, even when controlled, can improve both intersection safety and efficiency. The ODD requires different detecting angles and distances for the intersection angles of 55, 60, 65, 70, 75, 80 degrees. Intersection angle was found to have greater influence on the detecting angle when the road design speed was higher than 40 km/h, and the obtuse-side detecting distance increased rapidly when speed on the major road reached 50 km/h. For AV safety performance, engineers should incorporate the AV's detecting angle, distance, and time gap into the skewed intersection design criteria. AVs technology needs to comply with the ODD defined by the intersection geometrics.