Richard Hornstra presents an innovative view on route scheduling, taking into account the handling operations at a customer.
Traditionally, many routing problems have the objective of designing the shortest routes so as to service all customers, and handling operations are assumed to take a fixed (constant) amount of time, regardless of the sequence or amounts of drops. I state that this assumption is untrue: the time needed for handling operations depends on the sequence of the truck load, and needs to be taken into account when designing the optimal routes. In many cases, detouring or visiting customers in a different sequence to decrease handling operations will be highly beneficial. Handling operations are defined as the actions corresponding to the unloading and reloading of one item from the truck.
Let’s look at an example, consider the following simplified situation: the trucks contain one single stack which obeys the Last-In-First-Out policy, meaning that only the most recently loaded item is accessible. The figure illustrates what handling operations might look like for a customer visit. Here, the two pickup items obstructing the delivery require additional operations at the current stop, and for the next customer the three pickup items obstruct the delivery.
In settings in which routing- and handling costs are of similar magnitude, the optimal routes display a clear trade-off between these two costs. If transport companies are naïve and design their routes purely based on routing distance, they may face the nasty surprise of extremely high handling times, whereas detouring and visiting customers in a different sequence would have prevented a lot of unexpected hassle.
My conclusions are the following. First, if a limited amount of vehicles is available and relatively many customers are visited by a single vehicle, significant detouring is highly beneficial. Second, investing in additional vehicles to decrease the number of customers per route, and thus handling operations, results in only slightly increased overall routing cost whereas handing cost diminish greatly.
This article is based on a master’s thesis by Richard Hornstra. Richard graduated at the RijksUniversiteit Groningen in Aug 2017. Even though the thesis was of a theoretical nature, many practical settings have similarities. Using the insights obtained from the thesis, it may be worthwhile to re-examine existing operations keeping in mind these handling operations in order to become even more efficient.