Operational design domain of automated vehicles for crossing maneuvers at two-way stop-controlled intersections.

The departure sight triangle provides the view for the vehicle waiting to cross at the two-way stop-controlled intersection. The factors influencing the sight triangle for human drivers are considered in the 2018 AASHTO Green Book, but the Green Book lacks quantitative estimations for automated vehicles (AVs). Therefore, to guarantee the AV's operational safety, this study investigated the impact of intersection angle, speed, and crossing distance on the AV's intersection crossing maneuver. Using physics theorems and cosine law, formulae for the detecting angle (DA) and distance (DD), the two main components of the departure sight triangle, were developed for the acute- and obtuse-angle sides of the intersection for an AV approaching on the minor road; the minimum required DA and DD, with a given crossing distance, are thus proposed for the AV's operational design domain (ODD). Calculations indicate that the DD is mainly affected by the major road design speed and crossing distance, and that the DD increases very quickly as the speed and crossing distance increase. The intersection angle was found to have great impact on the DA on both the acute and obtuse sides, but its influence is negative on the acute side and positive on the obtuse side. On the acute side, the ODD detecting angle range is set as [83.4, 132.7], [80.7, 131.6], and [78.4, 130.7] degrees for major roads with 2, 4, and 6 lanes, respectively. On the obtuse side, the ODD is set as [57.4, 160.6], [70.6, 207.9], and [82.2, 249.1] m for the same respective roads. After comparing the DA and DD results, and depending on the intersection design attributes, it is concluded that most engineering attention should be paid to the DA on the acute side and DD on the obtuse side.

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.