## 2 Materials and Methods: Use of Cargo Bikes in City Logistics Systems
### Summary of Research on Cargo Bikes
In this city, TNT is currently operating cargo trikes for city logistics, while on most of the routes, there are problems with the use of lorries because of congestion, so the advantage of cargo bikes could be taken here, too [37]. Examining the case of London, the benefits of the application of cargo bikes are the reduction of vehicle purchase, delivery and parking costs, faster deliveries in congested city centers, and the reduction of emission. As a disadvantage, safety aspects and limited capacity were highlighted [32]. The expected benefits can be confirmed by the results of the pilot project from London in 2010. In this project, 7 fuel oil-powered lorries were replaced by 6 cargo trikes, 3 electric lorries, and 1 fuel oil-powered truck, adding a consolidation center to the system. In this project, in the urban areas, the mileage was reduced by 20%, and CO2 emission was decreased by 54% [38]. In a study from 2019, the case of Seoul was examined, and similarly to our project, a city logistics system with cargo bikes and lorries was modeled. In this model, the share of cargo bikes and lorries was handled as an important strategic decision, and they analyzed scenarios by use of VRP algorithms (Vehicle Routing Problem) for the whole city. In their model, simulated annealing was used, and in the scenarios, more and more lorries were replaced by cargo bikes. Based on their results, the sum costs can be significantly reduced by adding cargo bikes; but it is also a significant result that not every lorry should be replaced by bikes because of their capacity. They concluded that CO2 emission could be reduced approximately by 10% [39]. In a study from 2016, the combined application of cargo bikes and lorries was examined in Vienna. In this project, a two-stage model was developed, in which the different delivery vehicles are synchronized. They concluded, too, that emissions can be reduced by integrating cargo bikes. However, they say that the delivery costs can be increased [40]. A paper from 2018 focused mainly on restaurant deliveries by cargo bikes, examining them by simulation. In this research, lorries were added to the examined logistics system, which delivered the goods to urban consolidation points, and the last-mile delivery tasks were handled by cargo bikes. In this model, there is a new objective next to the minimization of the sum mileage: the minimization of the sum delays [41], which is very important in the case of delivering foods. The authors of this study published a simulation-based decision support system, too, and their results draw attention to the fact that, in these kinds of systems, it is essential to appropriate the number of available cargo bikes [42]. In another paper from 2017, a discrete-event-simulation-based (DES-based) solution was developed for the examination of the use of cargo bikes in multi-layer logistics networks, and the model was adapted for Grenoble. This model provides results about the daily time needs, demands, and the number of deliveries. Based on the results, it was concluded that CO\({}_{2}\) emissions could be reduced in this concept as well, and urban traffic jams will also be reduced [43]. The results of former research projects show that the city logistics use of cargo bikes can be various, and, from the modeling point of view, this area can be approached in many ways. Comparing the results of several projects, it can be concluded that in the case of the integration of cargo bikes, emissions and congestions could be reduced. However, mixed results can be seen for the different cost components: some of them can be reduced, but others are increasing in the new concepts. Based on the results of the literature review, it can be concluded that the geometrical model and the graph theory-based approach will be a completely new research direction, but several items from the results of previous research can be used, especially from models which examine lorries and cargo bikes together.