During a decision-making process the traditional methods of modelling, which are used for urban logistics, as well as statistical and probabilistic methods may be not enough effective due to their inability sufficiently consider heterogeneity, complexity and unpre-dictability of the stakeholders. These methods are not capable to provide knowledge in the whole logistics process and to include dynamics in the system. Consequently, Multi-Agent System (MAS) is used to describe the interconnections between stakeholders and measure the effect of their actions on the urban logistics politics analysis. The technique consists of three stages: specification, validation and analysis. During the first step, the information which relates to the decision structure is collected. Then validation of the cre-ated model in respect to base models is performed, after which the analysis, based on the considering different scenarios and results of the evaluation of the model, is realized in or-der to choose the most suitable solution [11]. As it was mentioned above MAS modelling techniques allows investigating the complex freight transport systems, in which some multiple stakeholders are involved [9]. The MAS consider every stakeholder’s group as an independent organization, that is interested in some specific aspects of the solution by creating special objects - “Agents”. Since usually two or more “Agents” participate in the decision-making process, MAS joins the possibilities, knowledge, goals and points of view of different agents and helps them to achieve their common goal through coopera-tion and coordinacoopera-tion. The system doesn’t limit the number of “Agents” thus it is very flexible in terms of the stakeholder’s participation [11].
For the urban areas Taniguchi in [21] classified stakeholders into four groups: shippers, freight carriers, residents and administrators, based on their objectives and different types of behaviour. Shippers focus on the minimization of the costs in the supply chains. Freight carries try to perform the shippers requires which are based on the collection and deliv-ering of goods within strict time frameworks. Residents just wish to live in a noiseless place with clean air and administrators, in their turn, want to keep the sustainability of the transport system to maintain the vitality of the city. The VRPTW-D model, which is pre-sented in the paper, increased profits for freight carriers and decreased costs for shippers due to dynamic correction of the route plan for vehicles to current travel times. Tamagawa in [22] proposed the model, in which five stakeholders were involved: shippers, freight carriers, residents, administrators and motorway operators. They used Q-learning [23] in the decision-making process for the “Agents” considering the outcomes of previous
ac-tions. The model was applied for testing road network with the implementation of several city logistics measures. Finally, the appropriate network for all stakeholders was created, despite some small disadvantages. Boussier in [24] used MAS to model the distribution of goods in big and small cities with electric vehicles. The paper describes the simulator which considers different scenarios and pays significant attention to the sharing of parking places between freight vehicles and passengers cars.
3 FORMULATION OF THE PROBLEM
This paper demonstrates the application of simulation methods to transport logistics based on the example of the construction of simulation systems presenting the processes of the work of the company as well as the calibration of system’s parameters in order to produce optimization of the operations that have some disadvantages. The corporation under con-sideration occupies the major place within the local waste-processing activity. The main components of the work system are the net of seven areas and their interconnections with the major company. Each region is represented by the organization which is responsible for the collection of the waste from the whole region area and its transportation to the major company, where it will be burned, reprocessed or handled in some other way in de-pendence on the kind of garbage. The research is mostly concentrated on the considering the process of the garbage transit.
The first key term here is common service schedule for the regions. Each area may have several cars which in a specified order come to the corporation, where they are served and finally come back to the point of departure. The first problem may arise in this case due to the assumption that the drivers may not strictly follow the established schedule because of unforeseen circumstances and human factors. The possibility of being late, early or not being able to come at all, may affect the appearance of the queue in which drivers will be forced to spend some time before being served. Moreover, in the case of the big queue length, some vehicles may not even enter the company due to the end of the working time. Thus, as a solution of the problem, it is supposed to study the features of arrival process, define the factors cause the emergence of the queue and influence its characteristics as well as to find the optimal conditions under which the deterioration of the company performance will be minimal. Further, this task will be called as the problem of traffic simulation.
Another important term in the traffic system is the annual plan for the implementation of garbage transportation in the amount determined for each company. Despite the existing formal schedules and plans of the realization of the work performance, the real situation does not always correspond to the assumed. Consequently, it is important to study how big is the difference between required supplies and reality. This problem can be charac-terized as the study of dynamics of the system of loads, where the loads are the amount of garbage.
4 PROBLEM OF TRAFFIC SIMULATION
4.1 Methodology for solving the problem of traffic simulation
Considering problem-related to the traffic simulation it is logical to assume that the first step of the solution is to determine the empirical model of the traffic system. The model considers the information about the current work system but concentrates on the descrip-tion of processes affecting the appearance of the queue and its influence on the perfor-mance within one working day. The formulated model can be further used for the collec-tion of statistical data and testing, required on the stage of the verifying of the candidates for optimal parameters. The next stage after the model formulation is the quantitative simulations that allow getting a big amount of output data required for analysis of system efficiency. The number of the samples depends on the task conditions. For the current problem, the statistics were collected during one year of work simulation is assumed enough. Then the statistical analysis is used to define the problems and their sources.
If the reasons of the inefficiency and problems in the work of the company can not be uniquely determined, then the hypotheses can be formulated and verified by analyzing the results of the simulation of the model with presumably eliminated sources of problems.
Based on the conclusions about the problems the next step related to the optimization processes is realized.
The implication of the algorithm described above to the problem of traffic simulation is described in further sections.