Sustainable Warehouse Logistics: a NIP Model for non-road vehicles and storage configuration selection

In modern competitive market, logistics plays a key role in creating competitive advantage and profitability. In recent years, many firms adopted green supply chain practices (GSCP) in order to improve their environmental performances while also achieving economic goals (Wu et al. 2015). According to European Logistics Association (ELA/AT Kearney 2004), the warehousing activity contributes to about 20% of the total logistics costs. The adoption of sustainable warehouse logistic strategies could lead to achieve a significant reduction of time and costs required to perform internal logistics activities and to increase the environmental performances of logistics systems. Order picking is the most labour-intensive, costly, and energy-consuming activity for almost every warehouse. Depending on the particular application, the process can be designed and managed in order to minimize the throughput time for an order, or maximize the use of the space, or maximize the accessibility to all items, etc. Many different order picking system types are adopted in warehouses. In most cases workers are employed for these activities, in particular in the picker-to-parts systems (De Koster 2004), where the operator (order picker) drives a forklift along the aisles to retrieve items. The aim of this study is to develop a non-linear integer model allowing identifying a strategy, based on picker-to-parts system, with the goal of optimizing the environmental performance of the internal logistic activities in the warehouse. Suitable storage strategies are identified on the basis of the type of the forklifts adopted (internal combustion or electric engine equipped) and the type of storage configuration adopted (storage racks or stackable units).