Future research will focus on testing hybridisations of the two proposed algorithms, to obtain better solutions. Another interesting study could be to consider the two levels in a hierarchical way in an iterative process (i.e. solving one stage, the other one being fixed) until convergence. Another important perspective is to test the robustness of the solutions found when confronted with disturbances such as, for example, variable quantity of carts, variable travel times and variable delivery/pickup times. The best tool for evaluating the robustness of the solutions seems to be discrete event simulation. This method has already been implemented , and the first results of the simulation have confirmed the good quality of the results presented in this paper.