A Bi-Objective Study of the Weekly Stability of Household Waste Collection in the City of Conakry, with the Number of Single-Frequency Collection Points Is Greater than That of Double-Collection Points

This article examines the weekly optimization of household waste collection in Conakry, Guinea. Faced with increasing waste volumes, the study proposes an organization into two sets of routes: at the beginning ($S_{deb}$ ) and end of the week ($S_{fin}$ ). The objective is twofold: to minimize the total cost (distance traveled) and to maximize stability between these two sets, i.e., to reduce their differences. The methodology is based on a mathematical model of the Vehicle Routing Problem with Time Windows (VRPTW) type, adapted to account for collection frequency (once or twice a week). The central hypothesis is that the number of single-frequency collection points is greater than that of double-collection points. For this scenario, two heuristic methods are designed and tested on modified Solomon instances. The results indicate a trade-off between the objectives. Method 1, which first builds tours for the $Z_{c_2}$ nodes and then inserts the $Z_{c_1}$ nodes, generally yields better results in terms of cost reduction. Method 2, which iteratively completes each existing tour, favors better overall stability between the beginning- and end-of-week routes. Thus, the choice of method depends on the priority set by the decision-maker: cost minimization or pursuit of operational stability.