## 2 Materials and Methods: Use of Cargo Bikes in City Logistics Systems
### Summary of Research on Cargo Bikes  
Naturally, as cargo bikes are becoming more widespread, several research projects have examined cargo bike-based city logistics systems. Most of these studies deal with their application possibilities and with the possible environmental and financial effects of the application. Based on a study from 2014, most of the available publications and documents are examining cargo bikes in Europe, and they are looking for the potential application fields of them; but it is generally argued that cargo bike solutions are a viable alternative for the future [29]. It is also interesting that cargo bikes can be considered as an alternative to walking in the case of the last section of urban deliveries between the loading area and the customer, similarly to drones [30]. A study from 2014 concluded that if the costs, payloads, and range are examined, (electric) cargo bikes are between simple bikes and passenger cars [31], which also have an important role in urban transportation and in urban logistics. Most of the studies concluded that motorized delivery transactions should be replaced by new solutions, which is why cargo bikes are getting more attention. Based on a paper from 2012, it was primarily the smaller companies that were working with cargo bikes in the CEP-sector (Courier, Express, and Parcel), and their application was motivated mostly by the problems of urban transport and by green aspects [32]. Nowadays, most of the bigger city logistics providers (like DHL or GLS) are expanding their roles in cargo bike deliveries. Based on a paper from 2017, approximately 10% of lorries and trucks could be replaced nowadays by cargo bikes (without decreasing efficiency) in urban areas where there is a maximum of 2 km linear distances. This could reduce CO2 emissions significantly, and the external costs could be reduced by 25%. Based on these, cargo bikes could be real alternatives for the transport situation of overcrowded and severely polluted city centers [33]. In another paper from 2019, cargo bikes with electric power assistance can be more cost-effective than lorries, in the case of small amounts, in densely populated urban areas [34]. In this paper, parking issues were highlighted as well, with cargo bikes having a huge advantage in this field over lorries. As modeling is the primary focus of this paper, the most significant studies are those where the development and application of models for cargo bike-based city logistics systems are in focus. These models can have several different purposes, and they use several different objective functions. Some models can compare given scenarios, while in some others, they are trying to find the best solution to a problem by optimization. A study shows that the growth of the shares of CEP deliveries and home deliveries gives an extra reason to examine this field. In this paper, the situation of Munich was discussed, the optimal position of the centers was sought out with a view to optimal cargo bike routes, and the necessary delivery times and the effects of the new system were examined. In this paper, not only the mathematically optimal position for the depo was highlighted, but the greenest and most sustainable position, too. It was concluded that the sum distance could be reduced by integrating cargo bikes into the system, while the delivery times could still be met [35]. In a paper from 2011, the application of cargo bikes and micro consolidation centers in Manhattan (New York) was examined. In the investigated area, there are more than 100,000 delivery transactions each day, and based on their results, a significant part of them could be handled by electric cargo trikes--their integration for last mile deliveries would not cause an increase in costs, while the external effects could be reduced [36]. In a paper from 2017, the application of consolidation centers and cargo bikes in Sao Paulo was examined.