Time slot management in road freight transport

Initial situation and problem definition

Time window management systems (TWMS) have led to increasing efficiency at the loading dock in recent years. Primarily industrial and trading companies benefit from this development by increasing transparency, planning reliability, and equal workload in arrivals. For forwarding companies, however, the strict allocation of time slots is becoming a challenge. Due to time window restrictions, they are confronted with increased expenditure and increasing complexity in route planning.

Furthermore, the use of TWMS often has financial consequences, for example, caused by booking fees, waiting times, and inefficiencies in route planning. This problem is highly relevant due to the high-cost pressure on the transport market and the apparent shortage of skilled workers among dispatchers, especially for small and medium-sized forwarding companies.

Objective

The aim of the industrial joint research project “Delivery Time window management in road freight traffic” was to investigate the effects of TWMS in a simulation-based way, considering the strategies of individual actors with a focus on freight forwarders and warehouse operators. Following on from this, coordination mechanisms for the improved use of TWMSs were to be developed in a cross-actor consideration, and their effectiveness was evaluated based on simulation. With a focus on the dispatchers, available assistance systems for decision-making support in route planning with time window specifications should also be sounded out and their limits and potentials investigated. The results of the simulation study and a practical guideline for the documentation of central project results are available to forwarding companies to use the findings and recommendations for action from the project to improve planning and dispatching processes.

Main results

The project was processed in seven work packages. Work package 1 included the problem description and delimitation. In work package 2, a basic simulation model was developed at an early stage of the project. This model was adapted and further developed based on a comprehensive data collection in work package 3. In work package 4 realistic and representative scenarios were defined. Based on these scenarios, work package 5 investigated the effects of selected behavioral patterns of warehouse operators and coordination mechanisms for the improved use of time slot management systems (TWMS). A concentration on the dispatchers and their behaviors took place in work package 6, before the documentation of the results in the form of a guideline was carried out in work package 7.

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.

In the simulation study, it was shown that the waiting time at the loading dock depends on the strategy of the warehouse operator. Overall, the application of TWMS can contribute to a reduction of the average waiting time per delivery, with greater reductions in inflexible application than in strict application. The advantage of flexible use of TWMS is that during free time slots (e.g. if the booked truck is delayed) unloading is continued according to the FIFO principle and trucks arriving late are still cleared. However, the coordinating effect of TSMS only unfolds when the capacity utilization in the transport network is accordingly high. Against this background, the use of TWMS to reduce waiting times, especially in the popular morning delivery period, proves to be beneficial.

The effect of six selected coordination mechanisms was tested in the simulation study. A reduction of the average waiting time compared to no coordination as a basic scenario was realized by an accelerated release of time slots in case of emerging delays and higher pricing of popular time slots in the morning. The two bilateral coordination mechanisms thus proved to be effective measures in the simulation study. Comparable waiting times, as in the case of omitted coordination, were found with a double-booking option, block-by-block time window release, and a prioritized booking sequence. The highest average waiting times occurred with locally limited order allocations, which therefore proved to be ineffective in the simulation study.

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.

Key Data:

Duration: January 2016 to December 2017

Sponsor: The IGF project (18499) of the Research Association of the German Logistics Association (BVL), Schlachte 31, 28195 Bremen was funded by the AiF within the framework of the program for the promotion of joint industrial research (IGF) by the Federal Ministry of Economics and Energy based on a resolution of the German Bundestag.