Exploring fairness and centralisation in insular waste collection systems

This paper studies a household waste collection problem to serve a set of rural islands. The problem is modelled as an Insular Travelling Salesman Problem (InTSP), which simultaneously optimises port selection decisions for a set of islands or isolated regions to be served, along with the optimal maritime visit sequence for the selected ports. The problem considers two types of costs, the Maritime Transportation Cost incurred by a vehicle for visiting all the selected ports, and the Ground Transportation Cost incurred by island inhabitants to move the freight from (to) the selected ports. Based on an existing Extended Stakeholder Network Structure, this research aims to simultaneously balance fairness and efficiency among the islands, in addition to control the centralisation level in decision making process by contrasting the central level (i.e., maritime operations), and the regional or island level (i.e., ground operations). This research enhances the literature by proposing a baseline formulation of an Extended Goal Programming Model along with three distinct variants of normalisation. Results of a real-world application of insular routing in Southern Chile are presented, discussing the advantages and shortcomings of each formulation. The results show the advantages of employing the proposed modelling approach when addressing the studied problem from managerial and political perspectives. Choosing the appropriate normalization significantly affects the number and diversity of obtained solutions, which may finally enhance the decision-making process. The results denote how increasing efficiency may lead to “unfair” solutions in terms of perceived ground transportation cost by inhabitants of different islands.