A City Logistics Optimization Model Integrating Passengers And Perishable Products

Lusaka is the capital city of Zambia.The city has experienced massive growth in the past years which has led to several logistic challenges especially in the central business district.As in any case,management of a system becomes difficult when the number of system components increase,and it even becomes more difficult and expensive for the government to monitor compliance.This has been evidenced by the increased number of accidents,opening up of stations in undesignated places,congestion in central business districts and non-compliance to other regulations like taxes and speed limits even as the unemployment level remains high.Moreover,this confirms the complexity with which city logistics comes with.Building on the work of Pimentel et al^[1]and Masson et al^[2],the current study seeks to develop a city logistics optimization model by considering the nature of products（perishability）,distribution centers and type of vehicle used.The objectives were to build a city logistics transport system optimization model and to propose a sustainable city logistics management system.The study employed a quantitative research method because it is aimed at building mathematical models.A two-echelon optimization model was built based on the Mixed Urban Transportation Problem and the Vehicle Routing Problem.Numerical analysis of the proposed models was done in using IBM ILOG CPLEX Optimization Studio 12.9.0.0,Python（Jupyter notebook）and Docplex on IBM Decision Optimization cloud.The optimal minimized cost of serving ten customers in different locations was found to be 982.2,three buses and six city freighters were used to satisfy the demand.The model is an operational level model and is able to help transport operators with real time capacity planning by use of indicator constraints,buses with dedicated capacity and small freight facilities at bus stops deal with the synchronization problem.The proposed co-modality system reduces underutilization of public transport even in off peak periods.It assures shippers of timely deliveries,lower transport costs and the use of less vehicles.Unlike the investment in expensive infrastructure projects which has been used as the conventional way of eliminating congestion,the study proposes coordination of transport and logistics services in the city to achieve desired results at a minimal cost.