The Collection Depots Location Problem on Networks Oded Berman, 1 Zvi Drezner, 2 and George O. Wesolowsky 3 1 Joseph L. Rotman School of Management, University of Toronto, Toronto, Ontario M5S 3E6, Canada 2 Department of Management Science/Information System, California State University-Fullerton, Fullerton, California 92834 3 Faculty of Business, McMaster University, Hamilton, Ontario L8S 4M4, Canada Received January 1999; revised May 2001; accepted 16 July 2001 Abstract: In this paper we investigate the collection depots location problem on a network. A facility needs to be located to serve a set of customers. Each service consists of a trip to the customer, collecting materials, dropping the materials at one of the available collection depots and returning to the facility to wait for the next call. Two objectives are considered: minimizing the weighted sum of distances and minimizing the maximum distance. The properties of the solutions to these problems are described. c  2002 John Wiley & Sons, Inc. Naval Research Logistics 49: 15–24, 2002; DOI 10.1002/nav.10000 1. INTRODUCTION The collection depots location problem was introduced in Drezner and Wesolowsky [2]. A set of demand points is located at some of the nodes of the network. A given set of collection depots is also located at some nodes of the network. A service trip can take one of two equivalent forms. 1. The server travels from the facility to the customer, picks up materials to be disposed of, travels to one of the available collection depots (the collection depot which provides the shortest way back to the facility), deposits the materials, and returns to the facility. 2. The server travels to an available collection depot to pick up materials, then travels to the customer, deposits the materials, and returns to the facility. In this case too the collection depot is selected such that the total distance of the trip is minimized. Note that these two forms of a trip are mirror images of one another and result in the same expression for the objective function. Many applications are described in Drezner and Wesolowsky [2]. As examples we mention a septic tank cleaning service, garbage collection or tree pruning service, a delivery service that Correspondence to: O. Berman c  2002 John Wiley & Sons, Inc.