A heuristic approach to the overnight security service problem

Abstract

This paper introduces the overnight security service problem. The model obtained is a single-objective mixed integer programming problem. It is NP -hard in the strong sense, and exact approaches are not practicable when solving real-life instances. Thus, the model is solved heuristically, through a decomposition in two subproblem. The former is a capacitated clustering problem, the latter is a multiple travelling salesman problem with time windows. Both have a radius constraint which is unusual. The computational results prove the robustness of the approach used. Moreover, a detailed discussion of the results shows that the management objectives are satisfied, providing lower costs, a strong guarantee on the level of service and several different solutions. Scope and purpose This paper addresses the management of an overnight security service. Its model includes a number of informal objectives and operational constraints due to practical management requests. Once formalized, it combines a clustering problem and a routing problem, both challenging to solve exactly. Therefore, this paper proposes a heuristic approach to generate good solutions in a reasonable amount of time. The approach achieves a strong improvement both in the quality of service and in the cost. As well, it generates a wide variety of solutions, as required for security reasons. The results prove fairly robust with respect to modelling approximations and to unexpected events.