## 4 Results and Discussion  
The proposed model, which explores the interrelations among key factors of Smart Urban Logistics and urban access management, aims to offer a useful basis for reflection on potential implications and policy actions. While still at an early stage, it contributes an analytical framework to support understanding of how urban access strategies may affect fleet composition and the broader dynamics of urban logistics in an integrated perspective. Entering into the detail of the CLD, a crucial variable in the model is the Portion of alternative vehicles, defined as the percentage ratio between the capacity of alternative vehicles used (such as electric vehicles and HP vehicles) compared to the total capacity of the fleet vehicles. The Portion of alternative vehicles is directly influenced by three out of four measures studied (UVAR and incentives for alternative vehicles) and is fundamental for analyzing modal shift phenomena. The availability of vehicles and their potential capacities also affects the Portion of alternative vehicles, influenced by both market factors and company constraints. Understanding how these factors interact is essential for optimizing the Portion of alternative vehicles and promoting the adoption of alternative and sustainable transportation options. The Portion of alternative vehicles is linked to the cost of the alternative vehicles and to the level of use of traditional vehicles. Additionally, it can be observed that the availability of vehicles with higher capacity in the market may accelerate modal shift, leading to a further increase in the presence of alternative vehicles compared to the total, but over time, this will result in a slowdown in the Portion of alternative vehicles according to a limit which is the total fleet.  
The presence of UVAR measures affects the fleet composition, and so the Portion of alternative vehicles, by reducing the use of traditional vehicles, thereby encouraging the use of alternative vehicles that could be acquired, outsourced for delivery services, or replaced with alternative vehicles. The literature identifies several types of UVAR, including emission-based regulations, vehicle type and dimension regulations, trip purpose regulations, scheme timescales, permit regulations, and other regulations. However, these various measures can be broadly categorized into two main perspectives: spatial and temporal. Spatial regulations limit access to specific areas, while temporal regulations restrict access during certain time periods, or a combination of both. In either case, the overall fleet capacity (the capacity of traditional vehicles plus the capacity of alternative vehicles) is impacted. Restrictions on spatial access diminish the capacity available for conventional vehicles, making it necessary to increase the use of alternative modes to sustain the same overall logistical performance. On the other hand, temporal access limitations reduce capacity to zero during the restricted periods. The presence of incentives for acquiring alternative vehicles is positively correlated with Portion of alternative vehicles, potentially acting as a \"multiplier\" for the capacity of alternative vehicles. This is because, thanks to the incentives, a new capacity can be acquired at a lower cost, or even halved, depending on the value of the incentives themselves. It is advisable to keep the two types of incentives separate because the distinct types of vehicles (whether electric or HP) impact the variables of interest in different ways. For example, electric vehicles have an impact on emissions but not on traffic.