An ant system algorithm for the mixed vehicle routing problem with backhauls

Ant system algorithms have been used successfully to solve many hard combinatorial problems. In this paper we introduce an ant system method to solve the mixed vehicle routing problem with backhauls. Some enhancements to the general characteristics of ant system algorithms are proposed. We concentrate on the way the candidate list is constructed, a look ahead scheme to incorporate into the visibility function and efficient rules to deal with local as well as global updating. Computational results on test problems are reported and compared to known results.