# Collision Avoidance Behavior Mining Model Considering Encounter Scenarios
## 3 Results
### Case Analysis  
The model is now applied to collision avoidance behavior mining in the open waters east of the Yangtze River Estuary from 1 July 2023 to 31 August 2023. The area is defined by a longitude range of 122\({}^{\circ}\)53.831\({}^{\prime}\) E to 123\({}^{\circ}\)26.049\({}^{\prime}\) E and a latitude range of 30\({}^{\circ}\)29.193\({}^{\prime}\) N to 30\({}^{\circ}\)4.431\({}^{\prime}\) N. It contains a total of 2,228,774 vessel coordinate points, occupying approximately 162 MB of memory. The case area is shown in Figure 16.  
Figure 17 shows the extracted collision avoidance behavior information; the model identified a total of 827 valid collision avoidance cases, including 138 head-on, 414 crossing, and 275 overtaking scenarios. In the head-on scenarios, 113 cases took port-turn maneuvers and 25 cases took starboard-turn maneuvers. In the crossing scenarios, 75 cases took port-turn maneuvers and 339 cases took starboard-turn maneuvers. In the overtaking scenarios, 113 cases took port-turn maneuvers and 162 cases took starboard-turn maneuvers. The distribution of the earliest turning points of ships identified under each encounter scenario, after converting the relative distance and the bearing angle, is shown in Figure 18.  
In Figure 18, each concentric circle represents 1 nautical mile; red indicates starboard-turn collision avoidance by the first ship, while green indicates port-turn collision avoidance. In head-on scenarios, collision avoidance actions occur at distances between 2 and 6 nautical miles. When the relative bearing of the target vessel is within the [0\({}^{\circ}\), 6\({}^{\circ}\)] range from the  
Figure 15: The illustration of the ship encounter pairs identified by the model.  
first ship, the first ship is more likely to make a port-turn maneuver for collision avoidance. When the relative bearing of the target ship is within the [0\({}^{\circ}\), 6\({}^{\circ}\)] range from the first ship, the first ship is more likely to make a port-turn maneuver for collision avoidance. When the relative bearing of the target ship is within the [\(-354^{\circ}\), 0\({}^{\circ}\)] range from the first ship, the first ship is more likely to make a starboard-turn maneuver. In crossing scenarios, when the first ship is the give-way vessel, most ships made starboard-turn maneuvers within the [6\({}^{\circ}\), 90\({}^{\circ}\)] range, but in [6\({}^{\circ}\), 9\({}^{\circ}\)], some ships made port-turn maneuvers, which violates the COLREGs. This demonstrates that in small-angle crossing scenarios, ship operators may decide whether to deviate from the COLREGs based on their navigational experience in order to mitigate collision risks as quickly as possible. In [90\({}^{\circ}\), 112.5\({}^{\circ}\)], almost all ships chose a port-turn maneuver for collision avoidance. When the first ship is the stand-on vessel, collision avoidance actions occur at distances between 1 and 2.5 nautical miles, which shows that most ship operators followed the duty of the stand-on vessel and took emergency collision avoidance actions when the give-way vessel was no longer able to avoid the collision. These actions are mostly starboard-turn maneuvers. In overtaking scenarios, when the first ship is the give-way vessel, collision avoidance actions occur at distances between 1.5 and 6 nautical miles, while for the stand-on vessel collision avoidance actions occur at distances between 1 and 2 nautical miles. The choice of turning direction by ships is not clear in overtaking scenarios.  
Figure 16: The data distribution map of the case water area.