An Application of the Ant Colony System Metaheuristic to the Vehicle Routing Problem with Pickup and Delivery and Time Windows

In this paper, it is presented a methodology for solving the Vehicle Routing Problem with Pickup and Delivery and Time Windows (VRPPDTW). The proposed methodology can be divided in two phases, i.e, the construction phase and the refinement phase. In the construction phase, the generation of an initial solution is made through Ant Colony Optimization (ACO) meta-heuristic with the elitism concept. Only the best ant can lay down pheromone, trying to improve the generated solutions by the ants at each iteration. The generated solutions go to the refinement phase through local search with First Improvement Descent Method and three neighborhood structures. After the solution is refined, the pheromone is layered over the covered arcs, helping to guide the next ants. The process is auto catalytic, i.e., the subsequent iterations use the information generated from the previous results, assisting in the convergence and accuracy. The developed methodology was evaluated using a set of standard instances from literature to test its efficiency, generating some better results than those found in literature.