A hybrid algorithm for the Vehicle Routing Problem with Time Windows

The Vehicle Routing Problem with Time Windows is a particular case of the classical Vehicle Routing Problem in which the demands of each customer should be met within an established time window. Due to the combinatorial complexity of the problem its resolution by pure exact methods is, in many cases, computationally impractical. This fact motivates the development of heuristic algorithms, which are usually faster but do not guarantee the best solution for the problem. This work proposes a hybrid algorithm that combines the metaheuristic Iterated Local Search, the Variable Neighborhood Descent procedure and an exact Set Partitioning model. The latter mathematical procedure is periodically activated in order to find the best combination of the routes generated along the execution of the algorithm. The computational results demonstrate that the proposed hybrid approach is quite competitive, since out of the 56 test problems considered, the algorithm was found capable to improve the best known heuristic/hybrid solution in 12 cases and to equal the result of another 27.