## 1 Introduction
heuristics and found that blocking has a stronger negative impact on simple heuristics, particularly the work of [7,10], who analyzed the effect of picker blocking on routing heuristics. The authors of Ref. [7] combined routing strategies between three pickers. The most common combination in practice, the S-shape heuristic, yielded a 10.2% longer throughput time than the best combination while the throughput time for return routing was 31.83% longer as it led to a higher number of blockings. Likewise, Ref. [10] found that the S-shape led to the longest mean throughput times for most of the combinations investigated because of its lack of flexibility. The midpoint heuristic, in combination with random storage assignment, outperforms the S-shape and return policies. The authors argued that the reason is likely because midpoint policy divides the storage area into two halves and in a random storage assignment, the stock keeping units (SKUs) are almost evenly distributed over the whole storage area. Blocking can be mostly avoided in warehouses with large aisles, but route deviation always remains a challenge. In practice, route deviation by the order picker is very common. Deviation may occur in two ways, either by skipping an aisle containing items from the picklist or by skipping items in an aisle, or both [12]. In either case, deviation is a behavioral issue that is detrimental to the efficiency of routing policies. In fact, the literature has shown that deviation leads to underperformed policies and that its negative effects are stronger on certain policies than on others. For instance, Ref. [12] investigated the effect of deviations from given routes on the efficiency of routing heuristics. The design experiment revealed that the midpoint without deviations outperformed the S-shape and return (without deviations) for orders containing a small number of picks. For a large number of picks, the S-shape outperformed the return and midpoint, assuming no deviations. To eliminate pickers' deviations and thus decrease operating cost, Ref. [12] proposed that training be held and handheld guiding devices be provided to the order pickers to help them adhere to the optimal routing or the predetermined route. However, integrating technologies into the pickingsystem does not guarantee a decrease in operating cost due to picking errors. The authors of Ref. [13] demonstrated that the introduction of modern technological solutions alone in the warehouse does not successfully eliminate errors. They devised a strategic framework that centers around three aspects of the warehouse: organizational, human, and technological. Unless the warehouse has a clear logistic strategy, well-trained order pickers, and adequate technologies, minimizing the number of errors will be limited. In order words, identical warehouses with the same technologies may differ in picking accuracy. Picking errors are therefore still existent in picker-to-parts order picking systems and may cause additional time to fulfill an order depending on the handheld or paperless technology. In both practical and laboratory experiments, it has been shown that pickers' probability to make picking errors also depends on the type of device used and the warehouse configuration. For instance, Ref. [14] made a comparison of voice, handheld, and paper technologies and found that the use of handheld technologies was associated with lower errors than voice technologies. They concluded that handheld technologies could detect upstream errors, such as receiving, replenishment, or inventory control, better than the voice technology, since voice technologies require selectors to query the computer for additional information, which does not easily happen. The authors of Ref. [15], on the other hand, found that a low-level picking warehouse favors voice technologies comparative to handheld technologies based on the cost efficiency when they control for error occurrence, while Ref. [16] rank voice and handheld technologies equally in terms of errors' interception.