## 4 Results and Discussion
### Loop 4 Congestion and Loop 5 Demand Trigger  
The Loop 4 \"Congestion brake\" (Figure 5) is a balancing loop that activates in response to an increase in the variable \"Traffic and congestion\". When the number of vehicles attempting to access a specific urban area exceeds the optimal capacity, congestion inevitably increases. Recognizing this situation, the \"Dynamic access closing\" system intervenes to reduce the vehicular entry capacity. This dynamic management can manifest through various concrete strategies, such as temporarily reducing the duration of green lights at inbound traffic signals, temporarily closing certain access lanes, or even creating temporary LTZs that restrict access to certain categories of vehicles or all unauthorized vehicles. The direct consequence of this dynamic closure is a decrease in the variable \"Number of accesses\" which is the number of vehicles that can effectively access the congested area per unit of time. A lower inflow of vehicles leads to a reduction in the \"Road infrastructure utilization\" at that specific point. With fewer vehicles in motion, the result is a decrease in the variable \"Traffic and congestion\" completing the negative feedback loop that tends to bring the system back towards an equilibrium with less congestion.  
The Loop 5 \"Demand trigger\" is a reinforcing loop triggered in the presence of low levels of \"Traffic and congestion\". In these fluid conditions, the \"Dynamic access opening\" system can react by easing entry restrictions. This can occur by increasing the duration of green lights at inbound traffic signals, reopening previously closed lanes, or suspending access limitations such as LTZs. The increased access capacity leads to an improved \"Perceived ease of access/travel time\" by road users. This positive perception incentivizes an increase in the \"Demand for access\" to the area: more people are willing to use their vehicles to reach the destination, knowing that traffic is smooth and access is facilitated. The increase in demand translates into a greater \"Number of accesses\" of vehicles entering. A larger number of accessing vehicles leads to increased \"Road infrastructure utilization\". If this utilization approaches or exceeds the optimal capacity of the infrastructure, an  
Figure 5: Loop 4 Congestion brake (Balancing Loop) and Loop 5 Demand trigger.  
increase in the variable \"Traffic and congestion\" occurs, closing the positive feedback loop that amplifies the initial trend, in this case potentially towards greater congestion in the long term.  
The synergistic yet opposing interaction of these two loops is fundamental to urban traffic dynamics. The effectiveness of dynamic access management critically depends on the precise calibration of activation thresholds for closing and opening measures, the intensity with which these measures are implemented, and the intrinsic delays within the system. Poorly defined thresholds, disproportionate responses, and significant delays can compromise the goal of optimizing traffic flow. Prudent management aims to leverage the stabilizing capacity of Loop 4 to contain congestion, while preventing Loop 5 from triggering an uncontrolled increase in demand and traffic, seeking a dynamic equilibrium that promotes sustainable urban mobility.  
The analysis of the conceptual model reveals two primary dynamics influencing urban logistics efficiency: a negative reinforcing loop, the Escalation of congestion from restrictions (Loop 6), and a balancing loop, the Balancing of dynamic access (Loop 7) (Figure 6).