## 2 Materials and Methods: Use of Cargo Bikes in City Logistics Systems
### Summary of Research on Cargo Bikes
It is also worthwhile to highlight that a graph-based approach to the cargo bikes-based city logistics systems would also be new, even though such an approach is used in transport and logistics research, for example, in the case of transport networks [44; 45], inverse logistics aspects [46] or maintenance aspects [47]. Next, we would like to present the cargo bike-related results of our data collection, and we would like to summarize the results of the simulation project which motivated this paper. Possible Use of Cargo Bikes in the City Logistics System of Concentrated Sets of Delivery Locations in Budapest  
In the first phase of the research, 5 CSDLs in Budapest were examined, and we received data from about 540 stores by use of our own questionnaire [4], so the main logistics properties of 4 shopping malls and the properties of the stores of the biggest shopping area of the city are known. As in the case of the fourth shopping mall, not every cargo bike delivery-related question was included; only the data of 490 stores (327 stores from 3 shopping malls and 163 stores from a shopping area) are examined in this section. First, we would like to highlight data about the delivery units. This question was answered by 475 stores of the 490. Of these, 417 (87.8% of the responders) are using (mostly small) boxes, and their quantity, size, weight, and volume are various--these are the most non-standard units in these systems. In one delivery transaction, an average of 16.6 boxes are arriving (standard deviation, 25.8), 5% of them are under 1 kg, 49.8% are between 1 and 5 kg, and 45.2% are more than 5 kg. This means a sum of 6 kg of goods in boxes every day per store (st. dev., 19.7 kg; yearly sum, 2.19 tons of goods in boxes/store). Most of these could be handled by cargo bikes, as the amount and their weight are mostly small. Of the responding stores, 12.8% are using pallet unit loads (there are stores that are using more delivery unit types); in one delivery, an average of 4.6 pallet unit loads are arriving (st. dev., 5.6). Of these, 42.9% are under 100 kg, and another 50% are under 500 kg, so most of these units could be handled by the three- or more-wheeled cargo bikes with a bigger capacity. Additionally, other, mostly small delivery units were mentioned by the stores, as can be seen in Figure 2.  
The next important question was about the delivery vehicles currently being used. Most of the 474 responder stores are usinglorries (277 stores, 58.4%) and their own passenger cars (171 stores, 36.1%) for the deliveries. These smaller vehicles could be easily replaced by the different types of cargo bikes in most cases, as most of the delivery units are small. Despite all of this, currently, only 5.1% of the stores (24 stores) are using bike or motorbike couriers for their deliveries. It was examined what share of stores assumes that a given cargo bike (BULLITT two-wheeled bike, with a 50 \(\times\) 50 \(\times\) 70 cm delivery box) would be appropriate for their logistics transactions. Of the 375 responder stores, 29.3% answered that based on the size of their logistics units, the cargo bike could be used. Of these, 50% (55 stores) answered that the cargo bikes could be used for their incoming deliveries, and in the case of 20% (22 stores), they responded that the bikes could be used for home deliveries. A figure of 41.8% (46 stores) suggested that cargo bikes could serve the deliveries between their stores (see Figure 3). In the case of the incoming deliveries, an average of 3.91 daily deliveries by this cargo bike type would be necessary (st. dev., 5.29), and a maximum of 25 deliveries would be enough. In the case of 76.1%, a daily maximum of 3, and if 91.3%, a maximum of 10 daily deliveries would be enough. Based on their answers, 180 deliveries each day would be necessary to handle the demands of the 46 responding stores.