## 4 Discussion  
The applied solution involves the preparation of a detailed model on a microscopic scale. Because each infrastructure element and each road user influences the simulation results, a tremendous amount of input data should be considered. This model would show even more accurate results if equipped with modules of an adaptive traffic control system and not based on fixed-time programs. However, access to this type of connection is impossible for people who are not road managers. The presented model has been correctly calibrated and validated against the GEH [21; 27] statistics. Thus, the results obtained are probable and possible to consider. Due to the linear infrastructure in the analysed city, road users who want to get to the northern districts of the town are forced to share the infrastructure with heavy goods vehicles. Constructing a new road with parameters like the existing one would result in a completely different distribution of road traffic. In this analysed case, drivers do not have alternatives. Thus, the road network in the vicinity of the port and the entire city of Gdynia is vulnerable to congestion. It, in turn, translates into the so-called carbon footprint. Therefore, it is of great importance for the traffic volumes indicated in the simulation model presented in Section 3. In addition, public transport loses its efficiency and profitability in the event of congestion on its routes. Let us discuss the level of vulnerability of the transport network as it stands and after the construction of the road connecting the port with the Chylonia junction. Figure 11 represents the simplified graph theory [26] model of the road network given in Figure 1.  
Considering the domination theory in the graphs presented in Section 2, the vertices \"City Centre\" and \"Morska-Estakada\" constitute the minimum dominating set. Thus, the domination number is equal to 2. It means that both nodes are critical from an urban road network point of view. They are heavily loaded and, therefore, prone to congestion--as evidenced by the daily rush hours in Gdynia. Moreover, they are the only nodes through which heavy goods traffic from the port may be directed to Tri-City Bypass. If, for the smallest domination set chosen in this way, we remove the edge between the nodes \"Morska-Estakada\" and \"Gdynia Chylonia\", then it will be necessary to add the last vertex to the smallest dominating set, and thus increase the domination number to 3. Figure 10: Average travel time; Section 3—all variants. It means that the topological vulnerability of this network, described by parameter bc(G), equals 1. Therefore, the network presented in Figure 11 is vulnerable to disturbances. Now, let us consider an edge-dominating set and edge-domination number for the network presented in Figure 12. Arcs can constitute the minimal edge-dominating set: [\"City Center\"; \"Tri-City Bypass--Wielki Kack\"], [\"Morska-Estakada\"; \"Tri-City Bypass--Estakada Kwiatkowskiego\"], and [\"Port Area\"; \"Gdynia Oksyvie\"]. The minimum edge-domination number equals 3. The edge-dominating set describes three arcs, which are critical for the Gdynia urban road network. Consequently, blocking one of these connections will result in the necessity to transfer all traffic generated in the port to the \"City Centre\" and \"Gdynia Chylonia\" nodes. However, for a long time, there have been plans to connect the port directly with the Tri-City bypass at the Chylonia junction by \"Red Road\" for a long time. Figure 12 shows the completed model of the road network in Gdynia after completing the plans. In this case, the dominating set can still be the same. However, the bondage-connected number goes up to two. It means that the network's resilience to disruptions of individual routes, especially those departing from the port, is improved. In other words, the flow of heavy vehicles from the port could be spread over many alternative routes in the event of adverse events. Thus, there is a chance to improve the parameters assessed during the simulation.