The paper presents the problem of the optimization of the length of the series and production batch, and thus the optimal frequency of production changeovers, taking into account the total cost approach and the use of the simulation method. The author has developed a model which, with the given parameters (costs and time of production changeover, costs of maintaining stocks of finished products and storage, value of manufactured products, sales variability and predictability), allows to calculate the economic effects of determining the length of a series and a production batch. In the author's opinion, the simulation method (at least in some cases) may be more appropriate in solving the problem of determining the optimal length of a series or production batch than the use of mathematical formulas. The calculations also took into account the impact of series and batch optimization on the company's profitability in order to assess the significance of this problem for financial results. The calculations were performed for two sample products and for two probability distributions — Gauss and Gamma. The results of the research show that the optimization of the production series may be important from the point of view of economic efficiency, that mathematical formulas may be less suitable for calculating the optimal production series than computer simulation, and that, in the case of significant variability of the sales level, in addition to the costs of changing production and maintaining inventories, lost sales costs should also be taken into account.

The main purpose of the article is to estimate the possibility of reducing the external costs of transport by increasing the efficiency of transport processes in freight transport. Analyzes carried out by the author based on available statistical data and literature on the subject as well as research conducted by the author in the transport industry. The author also postulates verification of both the level of external costs of transport and the methods used for their estimation.