Time slot management in road freight transport

Within the scope of work package 1, comprehensive research in the scientific literature as well as in the German-language practical literature was carried out. As the main result, it could be pointed out that in the practice-oriented literature the perspectives of warehouse operators and forwarding companies are equally addressed and TWMS are often treated in the context of operational problems at the loading dock. In the scientific literature, on the other hand, the perspective of the warehouse operator is in the foreground. TWMS are mostly considered in the context of the supply control of infrastructural nodes like ports. Time windows are also increasingly considered as restrictions in mathematical optimization problems in route and process planning. Consequences for the dispatching process of forwarders and violations of time window restrictions are hardly investigated. This insufficient consideration of the perspective of the forwarding company or the dispatcher could be identified as a research gap and could be selected as a starting point for the project work.

Based on the results of the literature analysis, an agent-based simulation model was developed to illustrate the processes involved in scheduling with time window specifications and the carrying out of routes. The goal was to develop a model with several forwarding companies and warehouses, in which the processes of route planning, time window booking, and time window-controlled delivery can be represented. To achieve the goal, an agent-based approach was chosen and the interactions between dispatchers, truck drivers, warehouse operators were modeled in a generic transport network. In doing so, assumptions for the fields highlighted in pink in the figure were made as realistic as possible. The designed model was transferred into a computer model with the software AnyLogic 8.0.5. The simulation model was verified and validated. Additionally, the possibilities for the interpretation of the simulation results were implemented. The interpretation focused on the driving and waiting times of the trucks as well as the current status of the available time windows and order processing.

To further develop the simulation model, planning and implementation tasks as well as characteristic behavioral patterns of the actors were recorded in detail and practice-oriented in workshops, interviews, and case studies. Thus, three behaviors of warehouse operators, four typical procedures for the implementation of time slots, and three main problem areas at the loading dock were identified. Also, 19 coordination mechanisms were developed to improve the use of TWMS.

The 19 identified coordination mechanisms were categorized according to two criteria. First, the scope of the concepts was investigated. Isolated concepts primarily concern a single actor and thus only the warehouse operator or forwarding companies. Bilateral concepts are to be understood as cross-actor coordination mechanisms, which are located between two actors. They require additional coordination and communication between the warehouse operator and forwarding companies. Network-based concepts are comprehensive concepts for the coordination of the entire transport network. These concerns thus several forwarding companies and/or several warehouses.

The data basis from work package 3 was used to derive realistic scenarios for the simulation study. Six of the 19 identified coordination mechanisms were integrated into the model. In the simulation study, these were each combined with a scenario for the implementation of time windows (strict, flexible, or no implementation) and a scenario for the scheduling of time windows (shortest route, fastest route). Furthermore, a systematic variation of the utilization in the transport network could be carried out.

To deal with the increasing demands on the dispatcher in a differentiated manner, the process of dispatching and time window booking was examined in detail. For this purpose, the dispatching process was recorded during on-site visits and an evaluation of available assistance systems to support the dispatcher was conducted. The focus of the investigation was especially on small and medium-sized forwarding companies, which are confronted with specific requirements due to a low order volume and a changing customer base.

40 selected software solutions were examined based on their web presence for six functionalities to support route planning with time slot specifications, rescheduling of routes, and the announcement of delays (see Figure 4). It became apparent that booked time window can be considered in route planning for more than half of the analyzed software solutions. To support ETA calculation and control (event management, live tracking, transport information) it was shown that live tracking functions are most likely to be realized in software solutions. A consideration of the current traffic situation as well as an event management function could only be detected in about one-third of the assistance systems. Concerning the functional range, it was found out that this varies greatly with existing solutions. Besides, a trend towards increasing the adaptability and individualization of software solutions became apparent.

Based on the simulation study as well as on data collection in workshops, interviews, and through case studies, ten of the 19 developed coordination mechanisms were identified as particularly useful for small and medium-sized forwarding companies. These are highlighted in grey in the table. It is shown that mechanisms such as the successive release of time slots or the extension of time slots to popular opening hours can contribute to an increase in flexibility in the booking. Other mechanisms, such as making the planning of incoming goods more flexible and the improved use of ETA data, are aimed at improving the time-slot controlled delivery. Common to these measures is that they require an increase in communication and the exchange of real-time data between warehouse operators and forwarding companies.