Typical decision problems in design and control of order picking processes concern optimal layout design,
storage assignment, zoning, order batching, routing and order accumulation and sorting (see de Koster et al (2007)).
Routing methods are of particular importance as they influence directly the time needed for an order picking batch.
Splitting up the total picker’s time, about half of the time is spent during travel (see Tompkins et al (2003)). This
means that an optimum routing for an order picking batch is crucial for minimising the total time of a batch. A given
constant time for the other activities of a picker, the routing with the minimum travel time will be achieved if the
sequence of the lines within the order picking batch is optimum. An excellent overview of routing methods and the
research work done so far can be found in de Koster et al. (2007) who report that „In practice, the problem of
routing order pickers in a warehouse is mainly solved by using heuristics.“