## 4 Collision Avoidance Decision-Making Method
### Collision Avoidance and Manoeuvre Principle  
1. Collision avoidance principle  
The OS in this work is an ordinary power-driven vessel sailing in the Chengshantou TSS. While the OS sails in the recommended traffic flow direction, all TSs are classified as ordinary power-driven vessels and special ships described in Table 2. What is more, ordinary power-driven vessels are classified as whether they sail along recommended traffic flow direction.  
The responsibility of taking avoidance actions of OS can be identified as per \"COLREGs\" when the TS poses a risk of collision. Although certain target vessels have the obligation of not impeding, when the OS and special ships pose a risk of collision, the OS remains a give-way ship. For ordinary power-driven vessels, it can be determined by the encounter situation identification model.  
When the OS is unable to sail in the general direction of traffic flow for any reason, she should resume sailing in that direction as quickly as practical.  
2. The principle of collision avoidance  
On condition that the OS is running at sea speed in the Chengshantou TSS, a head-on situation may appear if the TS violates the ship's routing provisions and sails in the opposite direction. The OS shall normally alter course to the starboard side and pass from the TS's port side.  
If the minimum distance between the OS and the TSS boundary line is very small, a violation of the ship's routing may therefore occur after the OS alters course to starboard and invades the boundary line, and the collision avoidance action may be different. When the TS is far away, and there is no risk of collision (but PCR exists), altering the course to the port side can also be accepted. However, when a collision risk exists, the OS can only alter course to the starboard side, according to the COLREGs and the requirements of good seamanship.  
When the OS is a give-way vessel in an overtaking situation, she should stay out of the way of the overtaken vessel and can choose to overtake in a direction with a smaller diversion. In a crossing situation, the OS can only alter course to starboard by a large margin and avoid crossing the fore of the stand-on vessel.  
In the early stages of a developed collision risk, while the OS is a stand-on vessel, she should keep course and speed. If the give-way vessel does not behave according to the COLREGs until \(CR>0.2\), the OS will alter course to starboard to avoid collision in a crossing situation. In an overtaking situation, the OS can choose an anti-collision action with a smaller course alteration amplitude. The master can set the parameter \(CR\) to match the actual situation, and the system will execute it automatically. Collision avoidance details can refer to the previous research [7].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Category**} & **Vessel Engaged** & **Vessel Restricted in** & **Not under** \\  & **in Fishing** & **Her Ability** & **Command Vessel** \\ \hline \multirow{4}{*}{Characteristics} & A vessel is small in size & The vessel is restricted in her & A vessel whose main \\  & and engaged in fishing, & ability to maneuver and & engine, steering gear, etc., \\  & and a large safety distance & cannot give way to & is out of control and \\  & needs to be maintained & another vessel & cannot give way to \\ \hline \hline \end{tabular}
\end{table}
Table 2: Classification of special ships.