Vol. 2 (2012) No. 5 ISSN: 2088-5334 A Review on Quantitative Approaches for Dock Door Assignment in Cross-Docking Adibah Shuib, Wan Nor Ashikin Wan Ahmad Fatthi Faculty of Computer and Mathematical Sciences, Universiti Teknologi MARA (UiTM), Shah Alam, Selangor, Malaysia Email : adibah@tmsk.uitm.edu.my, wannorashikin@ymail.com Abstract - Cross docking is a relatively new technique in supply chain operations. It offers limited storage time to maximize the efficiency of goods transshipment. Efficient operation of a cross docking system requires an appropriate coordination of inbound and outbound flows, accurate planning and dynamic scheduling. The planning strategies at cross docking terminals, which are receiving growing attention today, are the truck-to-door assignment and destination to door assignment problems. This paper provides a comprehensive literature review of quantitative approaches in dock door assignment problems of cross docking planning. The contributions of this paper are to identify the gap of knowledge in operational levels mainly in dock door assignment and to point out the future research direction in cross docking. Keywords - cross-docking; dock door assignment; quantitative approaches; mathematical model; optimization I. INTRODUCTION In contrast to traditional warehouse, a cross docking terminal is a distribution center which carries no or at least a reduced amount of stock. The idea of cross docking is to transfer shipments directly from incoming to outgoing trucks without storage in between. Usually shipments will spend less than 24 hours in cross docks or sometimes less than one hour. In a traditional model, warehouse maintains stock until they received the orders from customers, then the goods is picked, packed and shipped to them. When replenishment arrives at the warehouse, they are stored until the demand is identified. In a cross docking model, customer is known before the goods get to the warehouse and there is no need for storage. Besides, it also supports the shipments of full truck load (FTL) rather than Less Than Truck Load (LTL) [1]. As there is no or less inventory in storage due to direct transshipment, cross docking has been a potential logistic technique in order to reduce the inventory holding cost, order picking cost, transportation cost and delivery time [2]. Cross docking center serves as a consolidation platform of inbound products which offers short cycle times. The material arrived from supplier to cross docking terminal will be unloaded, sorted, consolidated and finally loaded onto the outgoing trucks which forward the shipments to the respective locations. As cross docking allows a consolidation of differently sized shipments for the same destination with full truck loads, the transportation cost will be more economical [2]. In general, the operation in cross docking terminal is divided into three main phases, which are unloading, sorting and loading processes. Once the goods arrive at the arrival docks, they are scanned and verified to determine their specified destination. In some cross docking centers, the products are also weighted, sized and labeled at the shipping dock. Then, goods are taken by some material handling equipments, such as forklift operated by worker or some kind of automated conveyer belt, to the staging area. Here, the inbound goods are sorted, consolidated, and temporarily stored until the outbound shipment is completed. Then, the goods are forwarded to the shipping door for the next process, which is loading them into the outbound truck. Once an outbound truck has been completely loaded, the truck will move away from the terminal to allow another truck to dock for loading. Cross docking can be applied for various purposes. For manufacturing, cross docking can be a potential platform for consolidating inbound supplies by respecting the Just in Time policy. For distribution, cross docking can be used to consolidate inbound goods from different suppliers which can be then delivered when the last inbound shipment is received. For transportation, it involves the consolidation of shipments from different suppliers which is normally in LTL batches in order to obtain economies of scale. Aside from that, for retail, cross docking is concerned with receiving goods from multiple suppliers, sorting them and shipping them to different stores. In fact, cross docking system has been successfully applied in many industries and several famous companies such as Wal-Mart, Home Depot, Costco, Canadian Tire, FedEx Freight, Toyota, Goodyear GB Ltd and Kodak Co. ([3], [4], [5]). 30