Figure 4 is a two-stage protocol. Multi-stage protocols make it easier to pack trailers
tightly, because workers in shipping can pick from among several pallets in shipping queues,
while still allowing value-added processing by other criteria. The disadvantage is that pallets
are handled multiple times. Furthermore, the crossdock must be wider to accommodate the
additional queues, which increases both fixed costs and labor cost due to travel. (In Section 4
we consider the throughput implications of having multiple staging queues.)