Scheduling periodic customer visits for a Travelling Salesperson

Michael Polacek, Karl F. Doerner, Richard F. Hartl, Günter Kiechle, Marc Reimann (2007): Scheduling periodic customer visits for a Travelling Salesperson In: European Journal of Operational Research, vol. 179 (3). - pp. 823-837.

The problem considered in this paper deals with determining daily routes for a traveling salesperson who provides customers in Upper Austria with product range information of a large, global food wholesaler. Each customer has to be visited at least once a year, with some customers requiring up to 1 visit per month. Further, some customers may not be visited each day of the week. Our decision support system uses a commercial GIS software to extract customer data for input into the optimization procedure and to visualize the results obtained by the algorithm.

The optimization approach is based on the Variable Neighborhood Search algorithm which assigns customers to days and determines routes for the salesperson for each day with the primary objective to minimize the total travel time of the salesperson. Another objective studied is to minimize the number of days needed by the salesperson to visit all customers in a given month. Further we analyze the effects of changes in the business environment like increases in the amount or flexibility of the salesperson’s working time and variations in the possible days for customer visits. Finally, we enrich the objective function by considering periodicity requirements for customer visits. Specifically, we penalize irregular schedules, where the time between two successive customer visits varies.