Adding to the aforementioned discussions, we see many other opportunities for future research. Overall, Table 2 shows that little work has been carried out on integrating asset management in SND problems , while in multimodal transportation, especially in containerized shipment, more than one type of loading units are involved, and repositioning their empties is costly. Furthermore, these assets require simultaneous allocation planning.
As an example, creew scheduling is usually studied independently, but it also depends on the service schedules, and embedding it in SND problems is expected to provide higher performance efficiency. In recent literature, zhu et al. (2011) extend the conventional SND and include car classification and blocking, and train make-up in a railway system. Their space-time modeling includes three layers for service, block, and car. They design a hybrid metaheuristic algorithm combining slope scaling, long-term memory-base perturbation strategies, and ellipsoidal search method, which can solve problems with up to 10 yards, 60 tracks and 3050 services, In solving small sized instances, in case their model cannot find the optimal solution in 10 hours, it reaches an optimality gap of 0.13%
Moreover, in solving bigger sizes, it outperforms a commercial solving both in time and solution quality.