## 2 Materials and Methods  
### Review of VTS Operation  
The VTS, which aids vessels to operate safely and efficiently at sea, started as the need for traffic management using onshore communication facilities and radar emerged because of the difficulties in properly operating port facilities with aids to navigation (AtoN) alone. The International Maritime Organization (IMO) adopted the guidelines at the 36 th meeting of the Maritime Safety Committee in 1990, requiring governments of the parties to make efforts to ensure that their vessels comply with or implement VTS regulations. Meanwhile, the International Convention for the Safety of Life at Sea (SOLAS) Chapter 5, Regulation 12 has stipulated the concept and purpose by stating, \"VTS contributes to the safety of life at sea, the safety and efficiency of navigation, and protects the marine environment from harmful environments that maritime traffic may cause, thus contributing to the protection of adjacent shores, workplaces, and offshore facilities\" [12]. As such, the IMO recognizes the value and importance of the VTS as a service that improves the safety and efficiency of vessel traffic and protects the environment. Moreover, when planning and installing a VTS, the parties are required to follow the \"Guidelines for Vessel Traffic Services (IMO Resolution A.857 (20))\" set by the IMO [13]. In addition to providing information for the safe operation of vessels, VTSs have become more actively involved in traffic management to improve port efficiency with an increase in traffic volume. However, to cope with navigational risks, the need for a VTS to obtain information on the planned entry route and navigation forecast information in advance has increased. The port management authority collects the vessel arrival and departure information and delivers it to the vessel to support the prediction of port traffic conditions. Consequently, the VTS is now in charge of both spatial and temporal coordination of vessel traffic, which is realized by controlling the arrival and departure times and vessel speed limits. The service provided by the VTS for vessel traffic coordination can be defined as the following services [13; 14]. Information service (INS) aids vessel navigators in using information necessary for navigation-related decisions in a timely manner. It provides essential information to assist the on-board decision-making process; however, it does not directly participate in the process. This service provides information, including mandatory reporting of changes in procedures and movements within the VTS area, such as the location, intention, destination, reporting lines, working frequency or channel, weather or navigation information, and information on overall traffic conditions associated with the vessel. Traffic organization service (TOS) aids in the prevention of dangerous traffic situations and maintain safe and efficient traffic. It can provide information to aid in the onboard decision-making process and supervise movements through advice, directives, and orders. It focuses on planning the traffic flow in advance, and is particularly useful when congested traffic conditions or the movement of a specific vessel interfere with the navigation of other vessels. This service establishes and operates procedures that prescribe priority for movement between vessels, allocation of routes, location reports, speed limits, and permits for passage. The navigational assistance service (NAS) helps navigators make effective decisions in water or situations when encountering difficulties in navigation. It can be employed in addition to the INS or TOS and may provide navigation-related recommendations or instructions. This includes providing information such as the effective course and speed of the vessel; the relative positions of routes and waypoints; the degree of proximity to navigational hazards; the name, position, and intention of the vessel in transit; and, if necessary, issuing warnings.