## 5 Discussion  
To summarize the abovementioned considerations, Table 10 was developed, showing the level of difficulty in implementing the provisions of the analyzed regulations introduced by the IMO [13] and European Parliament [14]. The following values were used for the assessment:  
* 3--indicated considerable difficulty in performing functions or implementing changes;
* 2--indicated medium difficulty in performing functions or implementing changes;
* 1--indicated low difficulty in performing set functions or implementing changes.  
The assessment was carried out based on the authors' knowledge and experience. Among the analyzed VTS systems, the VTS Swinoujscie-Szczecin system is by far the least susceptible to the implementation and realization of changes. This is due to the complexity of decision-making processes, location, parameters of the fairway, whose sensitivity to hydrometeorological factors and the occurrence of \"bottlenecks\" have an impact on the disruption of ship traffic and, consequently, on navigation safety. On the other hand, the VTS Swinoujscie-Szczecin has the great impact on shaping vessel traffic safety and efficiency.  
It should be noted that presented research has a number of limitations:  
1. The provided assessments show the authors' opinion on investigated issues, based on their knowledge and experience. In future research studies, the involvement of greater number of experts will be essential.
2. Seven criteria were identified for the comparative analysis of the operation of the VTS systems. However, this limited number of criteria may impact the reliability of achieved results. Increasing the number of assessment criteria may be considered by authors when conducting future studies.
3. While assessing the adjustment of the VTS systems operating in Poland to current regulations introduced by the IMO and European Parliament, two documents were analyzed. Selection of other EU regulations for the detailed analysis will be taken into account by authors in their future work.
4. The assessment of risks related to vessel traffic in the area covered by the VTS systems was based only on the calculation of the probability of collisions related to default causation factors. More detailed analysis of vessel traffic risks is planned.
5. The AIS data collected for the period 01.01.2021. to 30.09.2021. was used to analyze the probability of collision at each section of the described VTS systems. Repeating the study using year-round data can give a better overview of current changes in shipping safety in the areas managed by the VTS systems.
6. The research study focuses on the assessment of VTS systems operating in Poland. Therefore, the comparative analysis of VTS systems operating in Poland and other countries will be considered.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Analyzed Regulations**} & **VTS Zatoka** & **VTS Lawica** & **VTS Swinoujscie–** \\  & **Gdanska** & **Slupska** & **Szczecin** \\ \hline Regulation (EU) No. & & & \\
1315/2013 & 1 & Not considered & 2 \\ \hline Resolution A.1158(32) & 1 & 3 & 3 \\ \hline Total points per VTS & 2 & 3 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Assessment of the level of difficulty in implementing the provisions under review.