3.2. The expected travel distance
There are two factors that determine the travel distance of a
picker in a pick-and-pass system. One is the location of starting
bin of each order. The distribution of this variable can be described
by Eq. (8). Another factor is the picking locations in an order.
The travel distance is zero if and only if a picker’s starting
location is equal to the final picking location in the order. When
the picker starts to process order from bin m and the terminal position
is bin i, for i – m, the picker either goes to bin i while no
items need to be picked except those between bin i and bin m,
or to bin a where a is the farthest position in the opposite direction
of bin i. Thus,