The Impact of Combining Inbound and Outbound Demand in City Logistics Systems

City logistics seeks to optimize the distribution of goods in urban areas by developing new business models. Such models are not only centered on cost reduction, but also account for reducing the negative impact resulting from city logistics activities. Therefore, environmental aspects or congestion are important factors as well. Through consolidation of goods of different shipper-consignee pairs, the utilization of urban vehicles is improved and the total kilometers traveled within the city can be reduced. In the literature, inbound and outbound traffic are treated separately. This, however, results in empty urban vehicle traffic and reduces utilization of the system. Therefore, we consider a city logistics system that simultaneously accounts for both inbound and outbound demand. We consider a two-tier system, where the inbound goods are transported from external zones to satellites from where the final distribution is performed. The outbound demands are shipped via satellites to the external zones. To analyze the impact of considering both flows, we define and compare key performance indicators, like the urban vehicle utilization and number of vehicles. Numerical analyses are performed on different network structures and demand patterns. The results show the importance of combining both flows within one system. Moreover, we give insights on how different key performance indicators vary depending on the network and demand scenario.