Hybrid MIP method for a Pickup and Delivery Problem with Time Windows and Dock Service Constraints

 We consider a pickup and delivery vehicle routing problem (PDP) commonly find in real-world logistics operations. The problem includes a set of practical complications that have received little attention in the vehicle routing literature. In this problem, there are multiple vehicle types available to cover a set of transportation orders, each of which has pickup time windows and delivery time windows. Transportation orders and vehicle types must satisfy a set of compatibility constraints that specify which orders can or cannot be covered by which vehicle types. In addition we include some dock service capacity constraints as is required on common real world operations when there is a large quantity of vehicles to schedule. This problem requires to be attended on large scale instances (transportation orders ≥ 500), (single-haul vehicles ≥ 100). As a generalization of the traveling salesman problem, clearly this problem is NP-hard. The exact algorithms are too slow for large scale instances. The PDP-TWDS is both a packing problem (assign order to vehicles), and a routing problem (find the best route for each vehicle) with several side constraints. We propose a model to solve the problem in three stages. The first stage constructs initial solutions at aggregated level relaxing time windows and dock service constraints on the original problem. The other two stages imposes time windows and dock service constraints within a cut generation scheme. Our results are favorable in finding good quality solutions in relatively short computational times. KeywordsOptimization, vehicle routing, logistics & distribution planning, scheduling, time windows.