For agile layouts, we need models t

For agile layouts, we need models that account for different routing and dispatching policies of the material-handling system. These models could then be used to study the effects of different policies on layout performance. Furthermore, we could use the queueing model to evaluate and compare the performance of classical layout configurations under varying conditions. We might identify new configurations that are more effective in achieving small WIP levels. In particular, identifying configurations that reduce distance variance without affecting average distance can be valuable. Such configurations might include the star layout, where departments are equidistant from each other, or the hub-and-spoke layout, in which each hub consists of several equidistant departments and is served by a dedicated transporter. In many applications，differentiating between WIP at different departments or different stages of the production process is useful. WIP tends to appreciate in value as it progresses through the production process. We should favor layouts that reduce the most expensive WIP first, for example, those in which departments that carry out the last production steps are centrally located. Another important avenue of research is to integrate layout design with the design of the material-handling system. For example， we could simultaneously decide on material-handling capacity(number of transporters or transporter carrying capacity ) and department placement, with the objective of minimizing both WIP-holding cost and capital investment costs. We could then examine the trade-offs between capacity and WIP.