LOGISTICS OF FREQUENT SERVICES - A VEHICLE ROUTING PROBLEM WITH TIME WINDOWS

A vehicle routing problem with time windows, to which this paper is devoted, refers to a situation when a supplier is to prepare a schedule of deliveries to the number of customers with a fleet of vehicles. This issue seems to be a significant problem in the field of logistics, especially when we consider a supplier who has to conduct numerous deliveries to trading points or service outlets located in a limited area and all the consignments have to be delivered to the designated customers during a working day. The supplier is also supposed to provide the customers with the highest quality of service which means that every supply is supposed to arrive at the customer's within the previously defined time window. Obviously, the supplier is interested in assigning the smallest possible subset of his fleet to fulfilling deliveries, therefore there is a strong need for generating a delivery schedule which guarantees fulfillment of the supplier's and customers' requirements. In this paper a vehicle routing problem with time windows is presented as a theoretical problem based on a real example of a Polish medium-sized enterprise. We describe the problem and present a mix integer linear programming model developed for this particular case. An approach to the vehicle routing problem with time windows was based on mathematical models dedicated to transportation and manufacturing problems. The model was employed for solving a small-sized delivery scheduling problem. In the paper results of computational experiment are reported and directions for further research are suggested.