## 2 Materials and Methods: Use of Cargo Bikes in City Logistics Systems
### Existing City Logistics Systems with Cargo Bikes  
Based on studies, nowadays, in most European cities, every second motorized travel in freight transport could be handled by bikes instead of passenger cars and lorries [16]. In the case of home deliveries, every fourth package could be delivered by two-wheeled utility bikes [16]. Accordingly, such systems are operating in a large number of European cities. For example, DHL works in several cities with cargo bikes. We would like to highlight their cubicycle system, a four-wheeled construction [17], which is used in several cities in the Netherlands (e.g., in Utrecht), and additionally in Gent, Frankfurt, and Taipei. In these systems, EUR-pallet-sized (EUR-pallet: 800 mm \(\times\) 1200 mm) intermodal units are delivered by lorries to transshipment points where they are passed over by a special equipment to the cargo bikes (Armadillo cubicycles), and they solve the LTL (less thank truck load) last-mile deliveries of the delivery locations of their zone. In the geometrical model-based new approach, which is presented in this paper, the deliveries are organized in a similar way, with more stages and transshipment points, but the routes will be selected based on the geometrical structure of the network. Another city logistics system that should be highlighted is Eadesopedela from Rome, Italy. In this system, from a so-called \"mobile storage\" the goods are loaded to cargo bikes at a higher point of the city, and they go to the delivery locations by using the advantages of the terrain [18]. This mobile storage-based concept is dynamic, so the performances and the emissions can be minimized. A similar system is operated by UPS in Hamburg, Dublin, and Leuven [19], and TNT had a similar pilot project in Brussels [20]. In both cases, an intermodal unit functioned as mobile storage, and the cargo bikes were loaded from them. Additionally, several city logistics solutions can be mentioned: At Vanapedal, in Barcelona, two- and three-wheeled vehicles are used; at Zolle in Rome, only fruits and vegetables are delivered; and the logistics system of Outspoken in Cambridge handles last-mile deliveries and postal mails. In the KoMoDo pilot project in Berlin [21], Hermes operated with cubicycles with special trailers, so it became possible to handle two EUR-pallet-sized intermodal units in their last-mile deliveries [22]. It may also be interesting to examine projects where cargo bikes are combined with other green transportation modes. In Paris, in the Vert Chez Vous system [23], barges deliver cargo trikes on the Seine, and the trikes are loaded with small packets on the boat during the delivery. As a result of this solution, 15 trucks can be replaced each day [24]. DHL has a combined solution in Amsterdam with small cargo boats and cargo bikes, and in Frankfurt, in the LogistikTram pilot project, cargo bikes were combined with cargo trams [25]. In this solution, special logistics units were loaded to the bikes from the trams at transshipment points. Based on the analysis of 50 city logistics projects, a study concluded that cargo bike-based city logistics solutions could lead to high profit. The authors of this paper highlighted that their result is coherent, and other studies proved the same advantages, not only from an economic point of view but also in terms of the environment and the quality of life [26]. As in our former project, from where the graph theory-based idea comes, primarily Budapest was examined, so the existing cargo bike solutions of the city are important as well. In the city, the length of the bike path-network was 187 km before the pandemic in 2020 [27], a bike-sharing system is available, and there are approximately ten logistics provider companies that use utility bikes for their deliveries. Only some of the active providers are operating cargo bikes or cargo trikes, and significant development potentials can be expected in this field.